Printer Friendly

Optimal Supply of Water and Nitrogen Improves Grain Yield, Water Use Efficiency and Crop Nitrogen Recovery in Wheat.

Byline: Sadia Bibi, Anwar-ul-Hassan, Ghulam Murtaza and Ehsanullah

Abstract

Little information is available on the role of optimized application of irrigation and N on crop N recovery and NO3-N build up and movement in soil profile. A field experiment was carried out to evaluate the effects of irrigation and N management practices on wheat yield, water and fertilizer use efficiency and NO3-N distribution in soil. The treatments included were three levels of irrigation; 0.7, 1.0 and 1.3% of the estimated evapo-transpiration (ETc) and four levels of N; 0, 110, 160 and 210 kg N ha-1 in split plot design. The N was applied either in two splits (50% at sowing + 50% at maximum tillering) or three splits (50% at sowing + 25% at maximum tillering + 25% at spike initiation). Nitrogen applied at 110 kg ha-1 in three splits produced higher wheat yield, N recovery and water use efficiency (WUE) than two splits. Further, application of N in three splits had considerably lesser accumulation of NO3-N in soil as compared to two splits.

A significant irrigation effect was observed on grain yield, N recovery and WUE. The highest levels were achieved with water application according to crop water requirement (1.0 ETc). The deficit irrigation produced significantly lower grain yield (3.15 t ha-1) than full (3.80 t ha-1) and excessive (3.80 t ha-1) irrigations. Response of WUE to irrigation levels was in the order, 1.0 ETc (11.03 kg ha-1 mm-1)>0.7 ETc (10.63 kg ha-1 mm-1)>1.7 ETc (9.84 kg ha-1 mm-1). Deficit irrigation resulted in higher build up of NO3-N in surface soil. In contrast, excessive irrigation resulted in greater concentration of NO3-N in lower depths of soil. The results from this research show that there is great potential for decreasing N leaching and increasing wheat crop yield and N use efficiency thorugh controlled irrigation and N application according to crop demand.

Keywords: Deficit irrigation; Photosynthesis; Estimated evapotranspiration; Drainage losses; Nitrate leaching

Introduction

Nitrogen being major essential nutrient plays an important role for growth and development of plants. Plants can absorb N both in the form NO3-N and NH4-N. Mobility of positively charged NH4 ion in soil is low especially in soils of the temperate regions including Pakistan with alkaline pH. The NO3-N is highly mobile in soil and can easily leach down the soil profile (Sahrawat, 1982). Sepaskhah and Hosseini (2008) indicated that there was substantial increase in yields of crops including wheat with the application of N. Contrary to this, it has been reported that the yield response to N fertilizer application was not linear (Cossey et al., 2002), resulting in very low nitrogen use efficiency (NUE). Low NUE is a major problem associated with many conventional farming systems in the world and results in higher production costs, leading to lower net returns for farmers (Wang et al., 2010).

There are number of factors that can affect the build up and movement of residual NO3-N in soil. Among these, fertilizer and irrigation practices are the most important to consider in order to decrease leaching losses and improve economic yield and environmental sustainability. Research indicates a positive relationship between amounts of N versus leaching of NO3 away from active root zone (Jalali, 2005). Fan et al. (2010) reported very low leaching losses of NO3-N when application rate was below 150 kg N ha-1, but leaching of NO3 increased when N rate increased to 225-300 kg ha-1. Therefore, N applied at optimum rate can help minimize leaching losses of NO3.

A common practice for N application in cereals by farmers in Pakistan is to apply one half (1/2) at sowing and remaining half in two or three equal splits at critical growth stages (FAO, 2004). However, there is no systematic study on the effect of N split application on NO3 leaching losses. It has been observed that the presence of high N concentration in soil when there is no crop or with low crop's demand viz. before emergence and/or at harvesting, results in low NUE and high leaching losses (Bhardwaj et al., 2010; Shi et al., 2012). Therefore, the timing and method of fertilizer N application is another important factor affecting NO3 leaching losses, which can be decreased by providing N at the time of maximum uptake (Oberle and Keeney, 1990). Split application of N could improve NUE and reduce NO3-N leaching losses (Jia et al., 2014).

In arid to semi-arid regions, farmers normally apply water more than the crop needs to get optimal yields and to maintain salinity at acceptable levels (Sepaskhah and Hosseini, 2012). However, irrigation water applied at levels exceeding crop needs through conventional irrigation methods is among the major reasons for enhanced N leaching losses (Meisinger and Delgado, 2002). Mirjat et al. (2008) conducted field experiments in Sindh, Pakistan to assess the impact of four irrigation methods on NO3-N movement in soils. The four irrigation methods investigated were two traditional flooding (basin and furrow) and two micro irrigation (trickle and sprinklers) methods. The studies showed that basin and furrow irrigation resulted in leaching of NO3-N to deeper soil depths than with trickle and sprinkler methods.

It was further concluded that concentration of NO3-N at 1.2 m soil depth as a result of traditional flooding method of irrigation was above the established by National Standards for Drinking Water Quality (NSDWQ, 2008).

Farmers in Pakistan normally apply higher than optimum levels of N and irrigation water, which could result in environmental problems. In the past, little attention has been paid to NO3-N leaching. Although these regions have less total rainfall all the year round but about 60-70% of the annual precipitation is usually concentrated in monsoon season (July-September). Heavy rainfall in monsoon season transports surface NO3 deep into the soil profile. This phenomenon is more prevalent in areas where summer fallow procedure is practiced. In addition to heavy rains, the usual flood irrigation which is common farming practice could also cause NO3 transport to deeper soil layers. In some parts of the country underground waters contained NO3 at levels exceeding the maximum permissible concentration suggested by WHO (Imtiaz et al., 2004; Kazmi and Khan, 2005; Tahir and Rasheed, 2008).

These reports has begun the debate if intensive agricultural activities like high rates of N fertilizers especially at sowing, repeated application of organic manures and/or high levels of irrigation are responsible for high levels of NO3 in water. Recent literature shows that NO3 leaching is a global issue. This may or may not be true about Pakistan particularly in Punjab because of the shortage of systematic studies on NO3-N dynamics in soil-plant system in this region. Therefore, it is need of time to carry out field studies to identify the water saving irrigation practices along with proper rate and time of N application to improve the yield as well as decrease leaching losses of N. This experiment was, therefore, carried out with the objectives to monitor the individual and combined effects of irrigation levels and nitrogen rates and application timing on yield of wheat crop, crop N recovery and NO3-N distribution in soil.

Materials and Methods

Experimental Site and Climate

A field experiment was conducted at research farm, Institute of Soil and Environmental Sciences, University of Agriculture Faisalabad (Latitude 310-26' N, Longitude 730-06' E and Altitude 184.4 m) during 2011-2013. The climate of the region is subtropical, semi-arid with severe summers and winters (Table 1). Soil of the experimental area is well drained, poor in N and P contents and calcareous comprising of alluvial deposits mixed with loess (Table 2). It belongs to Hafizabad soil series (aridisoil-loam, mixed, semi-active, isohyperthermic Typic Calciargids) in USDA classification.

Treatments and Experimental Design

The experimental site had been following wheat-maize rotation for almost past six years. The experimental lay out was split plot in randomized complete block with three replications. The irrigation regimes and N treatments were randomly allocated to main plots and subplots, respectivley. The plot area was 63 m2 (7.38 m x 8.53 m). Three rates of N (110, 160 and 210 kg ha-1) were applied as urea (46% N) in either two or three splits. For two equal splits (N50 + N50), fertilizer was applied at sowing and tillering stages of wheat. For three split (N50 + N25 + N25), N was applied at sowing, tillering and spike initiation. Including control (no N application), this constitute seven treatments of N (Table 3).

The crop was exposed to three irrigation regimes: (1) I0.7 (deficit irrigation) in which crop was watered to compensate 30% less than its evapotranspiration water loss (ETc) during the previous days after last irrigation, (2) I1.0 (full irrigation) in which crop was irrigated to compensate the full evapotranspiration water loss (ETc) during the previous days after the last irrigation and (3) I1.3 (excessive irrigation) in which crop was watered, i.e. 30% more than evapotranspiration water loss during the previous days after the last irrigation. Irrigation levels were chosen to simulate deficit irrigation commonly due to water scarcity situation/unavailability of water to farmers, full irrigation to produce optimum yield, and excessive irrigation to simulate monsoon situations or to study leaching behavior of nitrate. A weather station, which is 300 m far from the experimental site provided input into the ET model (CROPWAT 8.0).

The total depth of irrigation water applied to wheat for the above three irrigation treatments was 156.6, 223.7 and 290.8 mm for deficit, full and excessive irrigation, respectively. In case of rainfall received more than the designed irrigation treatments, the scheduled irrigation was skipped.

Crop Management

Seeds of wheat cultivar Sahar-2006 were collected from Wheat Research Institute, Ayub Agricultural Research Institute, Faisalabad, Pakistan. Initial moisture and germination percentages were 10 and 93%, respectively.

Crop was supplied with phosphorus at 85 and 140 kg P2O5 ha-1 and potassium at 62 and 110 kg K2O ha-1. Single super phosphate (SSP) and sulfate of potash (SOP) were used as sources of phosphorus and potassium, respectively. Crop was sown with a seed rate of 150 kg ha-1on December 10, 2011 and was harvested on April 21, 2012. Flat sowing of crop was achieved by planting with hand drill at 22 cm row interval. Recommended agricultural practices were carried out during the study period. The plots were ensured weed free manually and/or by application of weedicides (Atrazine-38SC). Likewise, crop was kept free from insect and pathogen attack by pesticide application.

Irrigation Scheduling According to Estimated Evapotranspiration

The ET0 (reference crop evapotranspiration) was calculated by computer softawre CROPWAT 8.0 that calculates the ET0 using Penman-Monteith FAO-56 Equation (Allen et al., 1998).

(EQUATION)

Where, Rn stands for net radiation at the crop surface [MJ m-2 day-1], G stands for soil heat flux density (MJ m-2 day-1), Tmean stands for the mean daily air temperature at 2 m height (C); u2 is wind speed at 2 m height [m s-1]; es and ea are saturation vapour pressure (kPa) and actual vapour pressure (kPa), respectively, es - ea, the saturation vapour pressure deficit (kPa); D, the slope of vapour pressure curve (kPa C-1) and g is psychrometric constant (kPa C-1). The ET0 was multiplied with crop coefficient (Kc) to calculate estimated crop evapotranspiration (ETc; mm day-1).

ETc = Kcx ET0

The Kc is defined as the ratio of crop ET rate to the reference ET rate and Kc values for wheat were taken from FAO Manual 56 (Allen et al., 1998).

Actual evapotranspiration (ETa) was calculated by the following relation;

ETa = Ks ETc

Where Ks is the stress factor and ETc is the crop potential evapotranspiration under standards or no stress conditions. Stress factor (Ks) or evapotranspiration reduction factor (ETred.) was calculated by relationship between the relative evapotranspiration reduction [1- (ETa/ETm)] and the relative yield reduction [1-(Ya /Ym)] using the method given by Doorenbos and Kassam (1979).

The measured amount of irrigation water was applied with the help of cutthroat flumes. The time required to irrigate the field plots to desired irrigation depth was calculated as follows:

Qt = Ad

Where Q is discharge (m3 min-1), t is time (min), A is area of plot (m2) and d is the depth of irrigation (m) which was either 0.7ETc, 1.0ETc or 1.3ETc.

Measurements and Calculations

Gas exchange attributes: A portable infra-red gas analyzer (IRGA) (model LCi-SD; ADC Bioscientific Ltd., England) was used to measure the photosynthetic rate (A) on a sunny day in the morning between (9: 00-11: 00 am) at photosynthetic photon flux density of 1200-1400 uM m-2 s-1 (Ben-Asher et al., 2006). Starting from one month after sowing, five measurements were taken at 7-day interval. Measurements were performed in triplicate from each treatment plot on fully expanded youngest leaves of selected plants.

Harvesting and plant analysis: Plant height was recorded in 10 replicates when the crop attained its maximum height. At maturity, after leaving the border rows of 1 m from all the four sides of the plot, net plot (63 m2) was harvested manually. Crop was threshed to record straw and grain yields and 1000-grain weight. Representative plant samples were collected, oven dried at 700C for 72 h and ground in stainless steel mill. Ground plant material was digested in H2SO4-H2O2 mixture and N was determined using Kjeldahl distillation apparatus.

Water use efficiency: Water use efficiency was calculated in response to evapotranspiration of a specific crop. Crop water use efficiency was calculated as (Howell et al., 1990):

WUEET= GY/ETa

Where WUEET is the water use efficiency based on evapotranspiration (kg ha-1 mm-1), GY is the grain yield (kg ha-1) and ETa (mm) is actual evapotranspiration.

Estimation of crop N recovery: The dired plant samples were digested using wet oxidation method described by Moore and Chapman (1986). Total N concentration was determined using the Kjeldahl distillation and titration method (Bremner and Mulvaney, 1982). Using the grain or straw dry matter yield and concentrations of N, uptake of the N by grain or straw was calculated. These data were utilized to compute crop N recovery as follows (Motavalli et al., 1989):

Crop N recovery (%) = [(Nf -Nc)/F] x 100

Where Nf = N uptake from fertilized plot (kg ha-1), Nc = N uptake from control (kg ha-1) and F = total amount of N applied (kg ha-1).

Soil sampling and analyses: Before sowing and after harvesting of crop, soil samples were collected randomly from each treatment plot. Composite soil samples were characterized for various physical (bulk density, percent porosity, saturated hydraulic conductivity, infiltration rate, penetration resistance and particle size distribution) and chemical properties (total organic carbon, electrical conductivity, pH and total N, available P and available K content). Soil organic carbon was measured by potassium dichromate method suggested by Ryan et al. (2001). Saturated soil paste was prepared and characterized for pHs and ECe following the methods described by Richards (1954). For total N in soil method of Bremner and Mulvaney (1982) was adopted. Availabe P was determined by using spectrophotometer (Olsen and Sommers, 1982) and available K was determined by using flame photometer following the method given by (Richards, 1954).

Soil texture was determined following the Bouyoucos hydrometer method given by Moodie et al. (1959). Soil bulk density was determined by the core method as described by Grossman and Reinsch (2002). Infiltration rate was measured with the help of double ring infiltrometer (Klute, 1986). Soil saturated hydraulic conductivity was measured by Guelph Permeameter (Model 2800 KI), taking three steady-state readings. Soil strength was measured with Eijkelkamp cone penetrometer.

Table 1: Monthly average weather data druing the study period

Month###Sunshine (h/day)###Reference ET (mm)###Max. temp (C)###Min. temp (C)###Relative humidity (%)###Rainfall (mm)

December###7###1.7###20.9###4.2###59.1###0

January###7###1.4###17.3###3.2###69.6###3.8

February###7###2.4###18.4###4.6###62.1###8.0

March###8###2.9###25.9###11.7###58.2###1.5

April###9###3.8###32.7###18.0###59.1###7.8

May###10###6.5###38.9###23.3###43.3###0

Total###----###----###----###----###----###21.1

Table 2: Physico-chemical properties of the profile of experiment soil

Property###Depth (cm)###Value

pHs###-------###7.56

ECe (dS m-1)###-------###1.45

Clay (%)###-------###30

Silt (%)###-------###28

Sand (%)###-------###42

Texture###-------###sandy clay loam

Bulk density (Mg m-3)###0-15###1.42

###15-30###1.38

Penetration resistance (kPa)###-------###1011

Total porosity (%)###0-15###46.0

###15-30###48.0

Infiltration rate (mm h-1)###-------###25.49

Saturated hydraulic conductivity (Kfs) (mm h-1) -------###53.2

Available P (Olsen) (mg kg-1)###0-15###7.5

###15-30###6.2

Available K (mg kg-1)###0-15###111

###15-30###104

Total N (mg kg-1)###0-15###0.54

###15-30###0.40

Organic carbon (g kg-1)###0-10###4.75

###10-20###2.66

###20-30###1.46

NO3-N (mg kg-1)###0-30###6.3

###30-60###8.1

###60-90###8.7

###90-120###5.2

Table 3: Rate and time of N fertilizer application to wheat

Rate of N applied (kg ha-1)###Time of N application

0###No nitrogen

110###50% at sowing + 50% at tillering*

###50% at sowing + 25% at tillering + 25%

###at spike initiation

160###50% at sowing + 50% at tillering

###50% at sowing + 25% at tillering + 25%

###at spike initiation

220###50% at sowing + 50% at tillering

###50% at sowing + 25% at tillering + 25%

###at spike initiation

Monitoring of NO3-N status in soil: The regular monitoring for NO3-N status of soil was carried out approximately after every month during the growing season for wheat. The soil for NO3-N analyses was collected at four depths (0-30, 30-60, 60-90 and 90-120 cm) and stored in an ice box till shifting to lab. The well prepared (dried, ground and sieved) soil samples were stored in refrigerator at 0C until analysis was done. Soil NO3-N was extracted with 0.02 N copper sulfate, and measured spectrophotometrically (UV-2550, Shimadzu, Japan) using chromotropic acid as color developing reagent (Sims and Jackson, 1971).

Residual NO3-N (kg N ha-1) in soil was calculated according to the modified equation by Xue and Hao (2011):

Total residual NO3-N = Ti x BDi x [NO3]i x 0.1

Where Ti is the thickness of soil layer in cm; BDi is the bulk density in g cm-3; [NO3]i is the soil NO3-N concentration in mg kg-1, 0.1 is the conversion factor.

Statistical Analysis

The data collected were statistically analysed using Analysis of Variance (ANOVA) technique following randomized complete block design with split plot arrangement (Gomez and Gomez, 1984). Significance was determined for all the analyses at 0.05 probability level. Contrast analysis was done for pairwise comparison among treatments. The software package R was used to analyse the data as well as prepare the graphics.

Resutls

Agronomic Yield and Photosynthetic Rate

The plant height, photosynthetic rate, 1000 grain weight and grain yield of wheat as affected by different treatment combinations (Table 4) showed that the effect of irrigation, N and irrigation by N interaction on plant height was statistically significant (Table 5). The data regarding plant height averaged over N treatments reveal that the full (I1.0) and higher irrigation (I1.3) resulted in significantly taller plants than deficit irrigation (I0.7), and height of plants was similar at I1.0 and I1.3 irrigation levels. Plant height increased with increasing rate of N. The tallest plants were recorded in I1.3 x N2S3 treatment combination. Plant height of wheat showed statistically non-significant differences between and among two or three splits at all the levels of N and irrigation.

Table 4: Effect of irrigation and nitrogen treatments on crop growth and yield parameters of wheat

Nitrogen###Plant height (cm)###Photosynthetic rate (umol m-2s-1)###1000-grain weight (g)###Grain yield (t ha-1)

###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean

N0###72.6###82.5###82.9###79.3###8.28###9.45###9.96###9.23###30.9###35.1###35.4###33.8###2.17###2.48###2.36###2.34

N1S2###88.7###94.7###95.4###92.2###10.91###13.27###13.06###12.41###38.7###41.1###42.7###40.8###3.12###3.64###3.66###3.47

N1S3###88.9###96.1###95.9###93.7###11.68###16.00###16.73###14.81###39.8###42.7###44.3###42.8###3.24###3.85###3.88###3.66

N2S2###94.4###98.1###97.8###96.8###12.03###18.58###17.62###16.07###41.5###44.1###45.2###43.6###3.40###4.11###4.25###3.92

N2S3###94.9###97.7###99.6###97.4###11.69###19.36###18.31###16.45###42.5###45.3###45.6###44.5###3.51###4.46###4.47###4.15

N3S2###94.0###99.0###99.3###97.4###11.16###16.43###15.97###14.52###42.1###44.2###44.1###43.4###3.36###4.01###4.23###3.87

N3S3###95.1###99.0###98.7###97.6###11.42###16.32###16.22###14.65###42.2###44.3###44.1###43.6###3.24###4.04###4.23###3.84

Mean###89.8###95.3###95.7###11.02###15.63###15.41###39.7###42.4###43.1###3.15###3.80###3.87

Table 5: Analysis of variance and contrasts for plant height, photosynthetic rate, 1000 grain weight, straw and grain yield of wheat in response to irrigation and nitrogen treatments

SOV###Df###Plant height###Photosynthetic rate###1000 grain weight###Grain yield

###Mean squares###Mean squares###Mean squares###Mean squares

Block###2###4.48###0.299###1.899###9384.6

Irrigation (I)###2###225.63**###141.77**###66.53**###3329011.7***

Error###4###7.43###0.56###0.078###2764.2

Nitrogen (N)###6###388.91**###55.46**###120.85***###3221242.3***

IxN###12###6.19*###4.42**###1.09###68905.4***

Contrasts

Among treatments at

I=0.7###6###93.35***###3.56***###23.49***###345413.0***

I=1.0###6###35.13***###10.96***###10.06***###422116.1***

I=1.3###6###31.85***###8.50***###8.44***###623807.4***

Control vs N at

I=0.7###1###259.49***###3.06**###42.56***###514211.0***

I=1.0###1###5.32NS###32.02***###2.11*###717465.7***

I=1.3###1###5.05NS###21.69***###3.46**###1237137.4***

Among N at

I=0.7###5###4.72NS###0.63NS###0.46NS###11707.8NS

I=1.0###5###4.35NS###3.69***###0.21 NS###32317.6 NS

I=1.3###5###3.95NS###3.27***###0.69 NS###55649.7 NS

2 splits vs 3 splits at

I=0.7###1###4.14NS###4.13NS###1.15 NS###10562.8 NS

I=1.0###1###2.97NS###1.55NS###1.27 NS###77326.7 NS

I=1.3###1###1.99NS###3.20**###0.46 NS###44790.8 NS

Among 3 splits at

I=0.7###2###22.05**###0.44NS###0.11 NS###20508.2 NS

I=1.0###2###5.54NS###3.66**###0.02 NS###1692.9 NS

I=1.3###2###3.74NS###2.49**###0.41 NS###3570.1 NS

Among 3 splits at

I=0.7###2###0.07NS###0.32NS###0.15 NS###2041.3 NS

I=1.0###2###4.39NS###3.77**###0.05 NS###18313.8 NS

I=1.3###2###2.69NS###1.59*###0.67 NS###29993.4 NS

Error###36###2.882###0.48###0.41###14217.9

Regarding photosynthetic rate (Table 5) data showed that individual as well as interactive effects of irrigation and N were statistically significant (pless than 0.001). The photosynthetic rate varied from 8.28 umol m-2 s-1 in N0I0.7 to 19.36 umol m-2 s-1 in N2S3I1.0. It increased up to 160 kg N ha-1 and slightly decreased above this N rate. Contrast analysis (Table 5) showed that photosynthetic rate for the control plots (0 kg N ha-1) was less than N treated plots and there were significant differences among all the N treatd plants. Further, there were non-significant differences in photosynthetic rate in response to N application in two and three splits at deficit and full irrigation regimes, however, split applications displayed significant results at high irrigation level (I1.3).

Averaged across irrigation levels, the photosynthetic rate remained higher with N application in three splits compared to N application in two splits and these differences were much higher at lower level of N (110 kg N ha-1) than at higher levels of N (160 kg N ha-1 and 210 kg N ha-1). The mean photosynthetic rate was only 11.02 in I0.7, which increased to 15.63 umol m-2 s-1 with I1.0 (higher by 42% than I0.7) and to 15.41 umol m-2 s-1 with I1.3 (higher by 40% than I0.7).

Table 6: Effect of irrigation and nitrogen on ET (mm), D (mm), WUE (mm kg ha-1) and CNR (%) of wheat

Treatments###Seasonal ET###Drainage losses###Crop water use efficiency (WUE)###Crop N recovery (CNR)

###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean###I0.7###I1.0###I1.3###Mean

N0###267.0###315.1###362.4###314.9###7.72###16.58###20.58###14.96###8.12###7.87###6.51###7.50###-###-###-

N1S2###282.5###332.4###373.6###329.5###5.23###13.22###17.30###11.92###11.03###10.95###9.79###10.59###35###47###50###44

N1S3###294.0###343.9###385.4###341.1###3.86###11.10###14.37###9.78###11.03###11.20###10.08###10.77###45###56###58###53

N2S2###311.1###354.6###401.1###355.6###2.82###8.92###12.09###9.94###10.92###11.60###10.60###11.04###36###49###51###46

N2S3###323.6###367.3###411.6###367.5###1.92###7.54###9.54###6.33###10.86###12.13###10.87###11.29###39###58###58###51

N3S2###312.0###360.3###403.8###358.7###1.96###7.23###9.39###6.19###11.19###11.87###10.48###11.18###27###36###39###34

N3S3###311.9###361.2###404.4###359.1###2.08###7.49###9.13###6.23###11.24###11.56###10.54###11.12###25###36###38###33

Mean###300.3###347.8###391.7###3.66###10.30###13.20###10.63###11.03###9.84###35###47###49

Table 7: Analysis of variance and contrasts for seasonal ET, Drainage losses, WUE and CNR

SOV###df###Seasonal ET###Drainage###WUEET###CNR

###Mean squares###Mean squares###Mean squares###Mean squares

Block###2###3.54###0.50###0.029###36.70

Irrigation (I)###2###43929.64***###502.86***###7.657***###951.19***

Error-1###4###0.41###0.07###0.112###16.69

Nitrogen (N)###6###3229.17***###102.62***###16.252***###3552.96***

IxN###12###9.09***###4.21***###0.298 NS###34.98***

Contrasts

Among treatments at

I=0.7###6###182.70***###3.86***###2.891***###714.95***

I=1.0###6###138.90***###9.25***###2.729***###631.69***

I=1.3###6###103.23***###16.47***###2.931***###692.01***

Control vs N at

I=0.7###1###258.53***###4.42***###6.455***###774.54***

I=1.0###1###59.10***###17.39***###4.998***###862.19***

I=1.3###1###9.66 NS###32.28***###6.145***###1009.36***

Among N at

I=0.7###5###40.28***###0.67**###0.036 NS###47.41***

I=1.0###5###38.11***###2.73***###0.215 NS###21.40***

I=1.3###5###33.12***###7.49***###0.206 NS###20.38***

2 splits vs 3 splits at

I=0.7###1###40.89***###0.40 NS###0.084 NS###105.02***

I=1.0###1###24.04***###0.84*###0.000 NS###89.37***

I=1.3###1###15.72**###4.13***###0.006 NS###57.36***

Among 3 splits at

I=0.7###2###0.58 NS###0.04 NS###0.011 NS###26.19***

I=1.0###2###6.54 NS###1.46***###0.092 NS###12.25 NS

I=1.3###2###0.08 NS###4.15***###0.114 NS###15.98 NS

Among 3 splits at

I=0.7###2###1.11 NS###0.05 NS###0.154 NS###8.18 NS

I=1.0###2###5.03 NS###0.73 NS###0.636 NS###6.99 NS

I=1.3###2###2.17 NS###2.50***###0.504 NS###1.95NS

Error###36###1.54###0.15###0.118###2.981

Both individual as well as interactive effects of irrigation and N was significant (p= 0.012) on 1000-grain weight (TGW). The TGW ranged from 30.9 g in N0I0.7 to 45.6 g in N2S3I1.3. The grain weight increased up to 160 kg N ha-1 and above these levels, a slight decrease in grain weight was observed. Contrast analysis (Table 5) showed that crop treated with N irrespective of rate and timing produced significantly heavier grains than control (0 kg N ha-1) at all levels of irrigation. The TGW was higher with N application in three splits compared to N application in two splits, however, difference between three and two splits was much higher at lower rate of N (110 kg N ha-1) than at higher rates (160 kg N ha-1 and 210 kg N ha-1). Averaged across N treatments for the three irrigation levels, TGW was only 39.7 g with I0.7, which increased to 42.4 g with I1.0, 7% higher than I0.7 and then to 43.1 g with I1.3, higher by 8% than I0.7.

Table 8: Analysis of variance for NO3-N kg ha-1 in soil profile at various growth stages of wheat

SOV###Df###Mean squares

Block###2###0.26

Irrigation (I)###2###4556.21***

Error-1###4###3.47

Nitrogen (N)###6###19081.74***

IxN###12###78.03***

Error###36###1.37

Depth (D)###3###9790.92***

Error###6###2.37

IxD###6###149.73***

Error###12###1.05

NxD###18###211.84***

Error###36###1.38

IxNxD###36###5.72***

Error###72###2.15

Sampling date (SD)###3###1114.39***

Error###6###1.19

IxSD###6###40.81***

Error###12###0.73

NxSD###18###191.83***

Error###36###1.02

IxNxSD###36###8.14***

Error###72###1.83

DxSD###9###229.99***

Error###18###0.983

IxDxSD###18###16.89***

Error###36###1.27

NxDxSD###54###16.00***

Error###108###1.07

IxNxDxSD###108###5.38***

Error###216###1.39

There was significant effect of irrigation, N and their interaction on grain yield of wheat. It varied from 2.17 in N0I0.7 to 4.47 in N2S3I1.3 (Table 4). Contrast analysis (Table 5) showed that grain yield was significantly (pless than 0.001) affected by treatments at all levels of irrigations. The difference between the yield from N treated and those of control plots was significant only at deficit (I0.7) and full irrigation (I1.0). However, statistically similar yield was recorded for treated and non-treated plots at higher irrigation (I1.7). Greater differences in GY occured across N treatments as compared with irrigation levels. It is noteworthy that N rate of 160 was sufficient to maximize the grain yield at all levels of irrigation. In the current study, regardless of timing of N application, yield did not improve (even decreased slightly) above the 160 kg N ha-1 rate.

Averaged over irrigation levels, the grain yield was higher with N application in three splits compared to two splits at all the rates of N except 210 kg N ha-1, where almost similar or even less yield was obtained with three splits of N.

Crop N Recovery

Recovery of N ranged from 25% in N3S3I0.7 to 58% in N2S3I1.0 and was at par with N2S3I1.0. Contrast analysis for crop N recovery showed significant variations among the N treatments at all levels of irrigation. Significant differences were observed between two splits and three splits of N at various levels of irrigation. Application of N at 110 and 160 kg ha-1 in three splits resulted in 20% and 11% more N recovery compared to the same rates of N applied in two splits. Therefore, if N is applied in three splits, it would be possible to save 50 kg N ha-1 without compromising yield and crop N utilization. In order to further clarify the effect of irrigation on N recovery, data were averaged across N treatments. The N recovery was only 35% in deficit irrigation (I0.7), which increased to 47% in full irrigation (I1.0) (higher by 34% than I0.7) and then to 49% in higher irrigation (I1.3).

Crop Water Use and Drainage

A significant effect of irrigation, N and their interaction on ET and D of wheat crop was found (Table 7). Plots treated with N irrespective of rate and timing registered significantly greater ET than of plots without N (0 kg N ha-1) at all irrigation levels. When N rate surpassed a certain threshold (160 kg N ha-1), the total ET greatly decreased, indicating that ET could not increase further if too much N was applied. The seasonal ET ranged from 267.0 mm (N0I0.7) to 411.6 mm (N2S3I1.3). The seasonal ET values were higher in three splits of N compared to the two splits of N. The total crop ET increased linearly with an increase in irrigation levels. The mean ET was 300.3 mm in I0.7, which increased to 347.8 mm with I1.0 (higher by 16% than I0.7) and then to 391.7 mm with I1.3 (higher by 30 and 21% than I0.7 and 11.0, respectively).

With an increase in level of fertilization, the D values decreased since increase in level of fertilization increased the crop water use (ET). At similar level, N application in three splits resulted in considerably lower values of D as compared to two splits of N. For instance, at same level of N (110 kg N ha-1), the D loss was 11.92 mm with two splits of N, which decreased to 9.78 mm with three splits of N (lower by 22 % than two splits). The difference between two and three splits of N was observed only up to N application of 160 kg ha-1. Irrigation had significant impact on drainage losses of water and D increased linearly with increasing irrigation level. The data revealed that D loss was only 3.5% in deficit irrigation (I0.7), which increased to 10.3 % in full irrigation (I1.0) and then to 49% in higher irrigation (I1.3).

Water Use Efficiency

Results (Table 7) indicated statistically significant effect of irrigation, N and interactive effect of irrigation and N on WUEET of wheat crop. Contrast analysis (Table 7) showed that ET based WUE was significantly (pless than 0.001) affected by N treatments at all levels of irrigations. Likewise, plots treated with N irrespective of rate and timing registered significantly greater WUEET than the WUEET without N (0 kg N ha-1) at all irrigations. Statistically non-significant differences were observed between two splits (average of N1S2, N2S2 and N3S2: whole of N in two equal splits, i.e. 50% + 50%) and three splits (average of N1S3, N2S3 and N3S3: whole of N in three unequal splits, i.e. 50% + 25% + 25%) at various levels of irrigation. The results further showed that both with the increase in water as well as N supply, the WUEET tended to increase, however, the increase ceased when the water and N supply reached a certain level (Table 6).

It is noteworthy that full irrigation (I1.0) and N rate of 160 kg N ha-1 was sufficient to maximize the WUEET. In the present study, both the deficit as well as the excessive irrigation registered lesser WUEET than the full irrigation.

Temporal Variation of NO3-N

The temporal vriation of soil NO3-from initiation to completion of the experiment has been shown in Fig. 1. The data analysis of NO3-over growth stages of wheat (Table 8) show significant effects of irrigation, nitrogen, soil depth, sampling date and all possible interactions.

Regardless of irrigation levels, three splits of N resulted in lower levels of residual NO - in soil as compared to two splits of N. Further, the effect of split application on NO3-N in soil could not be found until 60 days after sowing (DAS). This could be due to the fact that until 60 DAS, all the treatment plots (irrespective of two or three splits) received equal amount of N (50% of the total N applied). Irrespective of irrigation and split application: soil NO3 - was found to be greater under the highest levels of N (N3: 210) followed by N2 (160 kg N ha-1), N1 (110 kg N ha-1) and N0 (control) throughout the study period. Irrigation showed significant effect on NO3-N content in soil (120 cm) throughout the growth period of wheat. There was much higher build up of residual NO3-N in 1.2 m soil profile with I0.7, as compared to I1.0 and I1.3.

For example, at 60 DAS, residual NO3-was only 63.51 kg ha-1 with I1.3, which increased to 74.59 kg ha-1 with I1.0 (higher by 17% than I1.0) and then to 83.37 kg ha-1 with I0.7 (higher by 11% and 31 % than I1.0 and I1.3). Similar effects of irrigation levels on accumulation of NO3-in soil profile were found for all the sampling dates during the growing season of wheat.

Distribution of NO3-N in Soil Profile

Concentration of NO3-N in the subsurface layers was considerably lesser than surface layers in all the treatments (Fig. 2). Irrespective of splits and irrigation levels, the NO3- N concentration increased with increasing rate of N and treatment N3 (210 kg N ha-1) had a significant higher NO3- N concentration than other N treatments in the 0-120 cm depth soil profile. Such accumulation of NO3- in the soil profile may result in excessive N leaching into deeper soil layers during monsoon or high irrigation levels. The data also depicted that the three splits of N resulted in considerably lower soil NO3-N than the two splits of N however; the considerable differences were noted up to 0-90 cm soil depth. Below 0-90 cm soil depth, the differences between two and three splits decreased. Moreover, the differences between two and three splits were true for only lower levels of N (N1 and N2).

At highest levels of N application (210 kg ha-1), there was no considerable difference between the soil NO3-N in two and three splits at all levels of irrigation.

The soil NO3-N contents were substantially higher for deficit irrigation than full and higher irrigation levels at all soil depths. Higher irrigation levels lead to more NO3-N leaching from root zone, resulting lower soil NO3-N concentrations in surface layers of soil at harvest. The similar fashion for depth distribution of NO3-N was found in all the the treatments. Regarding depth distribution of NO3- N in deficit and full irrigation, there was no differences in concentration upto 0-60 cm soil depth, however, below this depth concentration decreased sharply.

Discussion

The results from current experiment showed that full and higher irrigation along with 160 kg N ha-1 increased the height of wheat plants compared to other treatments. One plausible explanation for these results is that high and optimum irrigation levels resulted in better availability of applied N, leading to more cell division and enlargement and consequently the taller plants (Kirda et al., 2005). Gheysari et al. (2009) reported increase in plant height with the increasing levels of irrigation and N. Our results showed non-sginficant impact of split applications on plant height. However, these results are contrary to the findings of Niaz et al. (2014) who reported increase in plant height with increasing number of nitrogen splits. These contradictory results might be due to variation in rate and timing of N application, climatic conditions and the species and cultivars employed for experimentation.

An increase in photosynthetic rate with N could be attributed to beneficial impact of N on photosynthetic apparatus. Sugiharto et al. (1990) reported a significant positive correlation between leaf N concentration and their photosynthetic capacity suggesting critical role of N in synthesis of components of the photosynthetic apparatus. Shangguan et al. (2000) reported an increase in mean photosynthetic rate in wheat and maize with increasing rate of N application. Further, the current study added important evidence in the interactive effects of N addition and soil water on the photosynthetic rate of wheat. Cabrera-Bosquet et al. (2007) also reported significant positive interaction of N and soil water on the photosynthetic rate in durum wheat.

In our experiment, grain weight increased with increasing rate of N, but the positive impact of N on grain weight was accelerated by high water availability and decreased by water shortage. This could be attributed to increased availability and uptake of N under optimum water availability (Di Tomaso, 1995). Fertilizer-N improved grains weight but excessive use was not beneficial as reported by Brown and Petrie (2006) who showed that plants supplied with excessive N produced more vegetative growth and acquired less kernel weight. Considerable increase in grain weight with the application of N in three splits may be attributed to enhanced availability of N for a longer period in soil due to less leaching and volatilization losses of N. These factors enable the plants to synthesize more photosynthates at later stage, which in turn, were translocated to produce large sized gains (Lopez-Bellido et al., 2006).

Results reveled that grain yield increased with N application and the amount of water supplied influenced the response to N, i.e. at the same level of N application, grain yield was more for full and higher irrigation than grain yield at deficit irrigation. Al-Kaisi et al. (2005) reported that the optimum N rate for maximum crop yield was the same under different irrigation conditions. The same optimum N rate for maximum yield under different irrigation conditions could be due to the decrease in NUE as soil water content decreased. In the current experiment, regardless of crop season and timing, yield did not improve (even decreased slightly) above N application of 160 kg ha-1. The decrease in grain yield with higher rates particularly at sowing could be attributed to increaseed straw yield, and this might have depleted moisture contents and contributed to yield decrease (Kalra et al., 2007).

Split application of N is more beneficial in terms of grain yield at lower level of N than splitting the higher levels of N fertilization (Binder et al., 2000). Nitrogen availability throughout the growing period of a crop is necessary to attain good crop productivity. Delayed or early application of N does not allow sufficient time for plant activities related to physiological, phenological, agronomic and N uptake traits thus leading to lower crop production. Moreover, application of N during earlier growth stages can result in range of possible losses due to its greater immobilization, leaching, and clay fixation. The increase in grain yield of wheat with the three splits of N fertilizer may also be related to improved photosynthesis and grain weight (Table 4) resulting from enhanced availability for uptake (Table 6) throughout the growing season (Hooper et al., 2015) and also less losses of N from leaching.

The utilization of applied N by wheat was evaluated in terms of CNR. The N recovery values recorded in the present investigation is within the range reported by Fischer et al. (1993) and Moser (2004). A reduction in CNR with increase in fertilizer dose has been reported by other workers. Lenka et al. (2013) reported reduction of apparent fertilizer N recovery in wheat and maize crops with increase in fertilizer dose. The reduction in CNR with increasing dose may be attributed to more leaching and volatilization losses of N with the application of N more than crop needs. The increase in CNR with three splits of N could be readily explained by more uptake and less leaching losses of N (Lopez-Bellido et al., 2006).

Application of N irrespective of rate and timing registered significantly greater ET than the ET of control at all irrigation levels. The response of ET to N fertilization was almost similar to the response of grain yield to N fertilization, i.e. when N rate surpassed a certain threshold (160 kg N ha-1), the total ET greatly decreased, indicating that ET could not increase further if too much N was applied. This could be attributed to the fact that N promotes both shoot and root growth and enabling more soil water to be absorbed (Gajri et al., 1989). Another explanation could be that N fertilization increases the leaf area index and transpiration rates of wheat. However, N applied at level above than recommended makes soil environments stressful by increasing N concentration in soil solution, thus preventing roots from absorbing water. The ET values noted in this study are well close to reported by other researchers (Lenka et al., 2009; Zhong and Shungguan, 2014).

However, these values are higher than reported by Behera and Panda (2009). The greater ET with three splits of N may be related with the much higher shoot biomass and root growth that resulted in higher ET. Similarly greater availability of soil water with full and higher irrigations than with deficit irrigation increased plant growth and thereby resulted in higher amount of evapotranspiration. These observations are in agreement with the findings of Ram et al. (2013) who reported that ET of wheat increased from 289 mm with two irrigations to 512 mm with five irrigations in Indian Punjab.

The lesser drainage losses in three splits of N as compared with two splits of N may be due to the fact that application of N in three splits resulted in better crop growth and hence better utilization of applied water with former. Irrigation had significant impact on drainage losses and D increased linearly with increasing irrigation level. Similarly, an increase in D losses with increase in irrigation water has also been reported in wheat and maize crops (Behera and Panda, 2009).

Our results showed increase in WUEET with N fertilization. Similar to our reults, the increase in WUEET with N fertilization has been reported by Albrizio et al. (2010). The decrease in WUEET with the highest levels of N (210 kg N ha-1) at all levels of irrigation could be ascribed to the decrease in grain yield with excessive levels of N fertilization. Unexpected reduction in WUEET with deficit irrigation may be related to grain yield decline with water stress that resulted in lower WUEET. Oweis et al. (2011) reported severe decline in WUEET under water stress. The authors postulated that at lower irrigation levels, plants remaining under water stress used less water and produced low grain yield with low WUEET indices. The decline in WUEET with excessive irrigation compared with deficit and full irrigation may be due to relatively greater evapotranspiration (ET) than the corresponding increase in grain yield.

Zwart and Bastiaansen (2004) reported a decrease in WUEET with water supply at levels more than the crop evapotranspiration demands.

The residual soil NO3-under highest level of N (irrespective of splits) also led to a lower crop N recovery. A discernable build up of residual NO3-N in soil in response to overdose of N application has been reported in other parts of the world (Andraski et al., 2000; Wang et al., 2010; Gholamhoseini et al., 2013b). The build up of residual soil nitrate to the extent of 213 kg N ha-1 in 120 cm soil depth was reported from two years wheat-maize cropping system in India (Lenka et al., 2013). Likewise, Cui et al. (2010) reported build up of residual NO3-N in soil profile in response to continuous application of excessive N in North China Plain. Similarly, lower levels of residual NO3- were reported in high irrigation treatment than in low irrigation treatment at 120 cm (Lenka et al., 2013) and 200 cm (Wang et al., 2010) soil profile.

In contrast, higher NO - accumulation was observed under irrigation (135 kg N ha-1 yr-1) as compared to dry land conditions (82.5 kg N ha-1 yr-1 in the 0-400 cm soil profile (Fan et al., 2010). These discrepancies may be related to the differences in sampling depth in these experiments. In our experiment, sampling depth was restricted to 120 cm soil depth and thus it may be possible that irrigation helped leaching of some NO3- below the 120 cm soil depth.

This situation warrants the judicious use of N fertilizer both under deficit and excessive irrigation conditions. Excessive application of N in water scarce conditions may result in lower crop yield and N recovery and thus leading to soil NO3- build up. However, excessive application of N in over irrigation situations, may lead to leaching of N with water passing the soil profile and polluting the upper groundwater.

Conclusion

Our results showed the potential of optimizing of N the rate, application timings and irrigation in an effort to reduce N losses without decreasing yield, or in a best scenario with an increase in yield. The promising results regarding the effects of three splits of N along with water application according to crop water requirement (ETc) necessitates the evaluation of these factors under various agro-ecological and soil conditions in Pakistan. The potential of NO3 leaching in response to high levles of N and irrigation water under different cropping systems has not been evaluated. Long term field studies under different agricultural practices to monitor the build up and leaching of NO3 should be conducted.

Acknowledgements

The support from Soil and Water Chemistry Laboratory, Institute of Soil and Environmental Sciences, Univerity of Agriculture, Faisalabad is gratefully acknoweleged.

References

Albrizio, R., M. Todorovic, T. Matic and A.M. Stellacci, 2010. Comparing the interactive effects of water and nitrogen on durum wheat and barley grown in a Mediterranean environment. Field Crop Res., 115: 179-190

Al-Kaisi, M.M., X. Yin and M.A. Licht. 2005. Soil carbon and nitrogen changes as influenced by tillage and cropping systems in some Iowa soils. Agric. Ecosyst. Environ., 105: 635-647

Allen, R.G., L.S. Pereira, D. Raes and M. Smith, 1998. Crop Evapotranspiration: Guidelines for Computing Crop Water Requirements. FAO Irrigation and Drainage Paper 56. Food and Agriculture Organization, Rome, Italy

Andraski, T., L. Bundy and K. Brye, 2000. Crop management and corn nitrogen rate effects on nitrate leaching. J. Environ. Qual., 29: 1095-1103

Behera, S. and R. Panda, 2009. Effect of fertilization and irrigation schedule on water and fertilizer solute transport for wheat crop in a sub-humid sub-tropical region. Agric. Ecosyst. Environ., 130: 141-155

Ben-Asher, J., I. Tsuyuki, B.A. Bravdo and M. Sagih, 2006. Irrigation of grapevines with saline water, I. leaf area index, stomatal conductance, transpiration and photosynthesis. Agric. Water Manage., 83: 13-21

Bhardwaj, V., V. Yadav and B.S. Chauhan, 2010. Effect of nitrogen application timings and varieties on growth and yield of wheat grown on raised beds. Arch. Agron. Soil Sci., 56: 211-222

Binder, D.L., D.H. Sander and D.T. Walters, 2000. Maize response to time of nitrogen application as affected by level of nitrogen deficiency. Agron. J., 92: 1228-1236

Bremner, J.M and C.S. Mulvaney, 1982. Nitrogen-Total. In: Methods of Soil Analysis, Part 2. 2nd edition, pp: 595-624. A.L. Page and R.H. Miller (eds.). Agron. Monogr. 9. ASA and SSSA, Madison, WI

Brown, B.D. and S. Petrie, 2006. Irrigated hard winter wheat response to fall, spring, and late season applied nitrogen. Field Crop Res., 96: 260-268

Cabrera-Bosquet L., G. Molero, J. Bort, S. Nogues and J.L. Araus, 2007. The combined effect of constantwater deficit and nitrogen supply on WUE, NUE and Delta C-13 in durum wheat potted plants. Ann. Appl. Biol., 151: 277-289

Cossey, D.A., W.E. Thomason, R.W. Mullen, K.J. Wynn, C.W. Woolfolk, G.V. Johnson and W.R. Raun, 2002. Relationship between ammonium and nitrate in wheat plant tissue and estimated nitrogen loss. J. Plant Nutr., 25: 1429-1442

Cui, Z., X. Chen and F. Zhang, 2010. Current nitrogen management status and measures to improve the intensive wheat-maize system in China. Ambio, 39: 376-384

Di Tomaso, J.M., 1995. Approaches for improving crop competitiveness through the manipulation of fertilization strategies. Weed Sci., 43: 491-497

Doorenbos, J. and A.H. Kassam, 1979. Yield Response to Water, p: 193. FAO Irrigation and Drainage Paper No. 24. Food and Agriculture Organization of the United Nations, Rome, Italy

Fan, J., M. Hao and S.S. Malhi, 2010. Accumulation of nitrate N in the soil profile and its implications for the environment under dryland agriculture in northern China: A review. Can. J. Soil. Sci., 90: 429-440

FAO. Fertilizer Use by Crop in Pakistan. FAO, Rome. 2004. Online available at http: //www.fao.org/docrep/007/y5460e/y5460e0 8.htm#bm08

Fischer, R., 1993. Irrigated spring wheat and timing and amount of nitrogen fertilizer. II. Physiology of grain yield response. Field Crop Res., 33: 57-80

Gajri, P., S. Prihar and V. Arora, 1989. Effects of nitrogen and early irrigation on root development and water use by wheat on two soils. Field Crop Res., 21: 103-114

Gheysari, M., S.M. Mirlatifi, M. Homaee, M.E. Asadi and G. Hoogenboom, 2009. Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates. Agric. Water Manage., 96: 946-954

Gholamhoseini, M., A. Ghalavand, A. Dolatabadian, E. Jamshidi and A. Khodaei-Joghan, 2013b. Effects of arbuscular mycorrhizal inoculation on growth, yield, nutrient uptake and irrigation water productivity of sunflowers grown under drought stress. Agric. Water Manage., 117: 106-114

Gomez, K.A. and A.A. Gomez, 1984. Statistical Procedures for Agricultural Research, 2nd edition. John Wiley and sons, Inc. London, UK

Grossman, R.B. and T.G. Reinsch, 2002. Bulk density and linear extensibility. In: Methods of Soil Analysis, Part 4, pp: 201-228. J.H. Dane and G.C. Topp (eds.). SSSA Book Ser. 5. SSSA, Madison, WI

Hooper, P., Y. Zhou, D.R. Coventry and G.K. McDonald, 2015. Use of nitrogen fertilizer in a targeted way to improve grain yield, quality, and nitrogen use efficiency. Agron. J., doi: 10.2134/agronj14.0363

Howell, T.A., R.H. Cuenca and K.H. Solomon, 1990. Crop yield response. In: Management of Farm Irrigation System. Hoffman, G.J., T.A. Howell and K.H. Solomon (Eds.),, pp: 93-122. The American Society of Agricultural Engineers (ASAE).

Imtiaz, N., T. Aftab, Z. Iqbal, M. Rasi and A. Hussain, 2004. Nitrate burden in drinking water of Northern Punjab, Pakistan. J. Chem. Soc. Pak., 26: 450-452

Jalali, M., 2005. Nitrates leaching from agricultural land in Hamadan, Western Iran. Agric. Ecosyst. Environ., 110: 210-218

Jia, X., L. Shao, P. Liu, B. Zhao, L. Gu, S. Dong and B. Zhao, 2014. Effect of different nitrogen and irrigation treatments on yield and nitrate leaching of summer maize (Zea mays L.) under lysimeter conditions. Agric. Water Manage., 137: 92-103

Kalra, N., D. Chakraborty, P.R. Kumar, M. Jolly and P. Sharma, 2007. An approach to bridging yield gaps, combining response to water and other resource inputs for wheat in northern India, using research trials and farmers' fields data. Agric.Water Manage., 93: 54-64

Kazmi, S.S. and S.A. Khan, 2005. Level of nitrate and nitrite contents in drinking water of selected samples received at AFPGMI, Rawalpindi. Pak. J. Physiol., 1: 1-2

Kirda, C., S. Topcu, H. Kaman, A. Ulger, A. Yazici, M. Cetin and M. Derici, 2005. Grain yield response and N-fertiliser recovery of maize under deficit irrigation. Field Crop Res., 93: 132-141

Klute, A., 1986. Methods of Soil Analysis. Part 1 - Physical and Mineralogical Methods 2nd edition. SSSA Book Series No. 5. SSSA and ASA, Madison, WI

Lenka, S., A.K. Singh and N.K. Lenka, 2009. Water and nitrogen interaction on soil profile water extraction and ET in maize- wheat cropping system. Agric. Water Manage., 96: 195-207

Lenka, S., A.K. Singh and N.K. Lenka. 2013. Soil water and nitrogen interaction effect on residual soil nitrate and crop nitrogen recovery under maize-wheat cropping system in the semi-arid region of northern India. Agric. Ecosys. Environ., 179: 108-115

Lopez-Bellido, L., R.J. Lopez-Bellido and F.J. Lopez-Bellido. 2006. Fertilizer nitrogen efficiency in durum wheat under rainfed Mediterranean conditions: effect of split application. Agron. J., 98: 55-62

Maharjan, B. and R.T. Venterea, 2013. Nitrite intensity explains N management effects on N2O emissions in maize. Soil Biol. Biochem., 66: 229-238

Meisinger, J.J. and J.A. Delgado, 2002. Principles for managing nitrogen leaching. J. Soil Water Conserv., 57: 485-498

Mirjat, M.S., A.S. Chandio, S.A. Memon and M.U. Mirjat, 2008. Nitrate Movement in the Soil Profile under Irrigated Agriculture: A Case Study. Agric. Engg. Int. The CIGR, E-J., Manuscript LW 07 024

Moodie, R.E., R.W. Smith and R.A. MacGreery, 1959. Laboratory Manual of Soil Fertility, p: 175. State College Washington, Mimeograph, Pullman, Washington, USA

Moore, P.D. and S.B. Chapman, 1986. Methods in Plant Ecology, 2nd edition. Blackwell Scientific Publications, Oxford, UK

Moser, S.B., 2004. Effects of pre-anthesis drought stress and nitrogen on yield, nitrogen use efficiency and grain minerals of tropical maize varieties. A Ph.D. Dissertation submitted to the Swiss Federal Institute of Technology, Zurich, Diss., ETH No. 15527

Motavalli, P.P., K.A. Kelling and J.C. Converse, 1989. First-year nutrient availability from injected dairy manure application. Soil Sci. Soc. Amer. J., 48: 896-900

Niaz, A., M. Yaseen, M. Arshad and R. Ahmad, 2014. Variable nitrogen rates and timing effect on yield, nitrogen uptake and economic feasibility of maize production. J. Agric. Res., 52: 1-10

Oberle, S.L. and D.R. Keeney, 1990. Factors influencing corn fertilizer N requirements in the Northern U.S. Corn Belt. J. Prod. Agric., 3: 527- 534

Olsen, S.R. and L.E. Sommers, 1982. Phosphorous. In: Page, A.L. (ed.), Methods of Soil Analysis, Agronomy No. 9, Part 2: Chemical and Microbiological Properties, 2nd edition, pp: 403-430. American Society Agronomy, Madison, Wisconsin, USA

Oweis, T., H. Farahani and A. Hachum, 2011. Evapotranspiration and water use of full and deficit irrigated cotton in the Mediterranean environment in northern Syria. Agric. Water Manage., 98: 1239-1248

Ram, H., V. Dadhwal, K.K. Vashist and H. Kaur, 2013. Grain yield and water use efficiency of wheat (Triticum aestivum L.) in relation to irrigation levels and rice straw mulching in North West India. Agric. Water Manage., 128: 92-101

Richards, L.A., 1954. Diagnosis and Improvement of Saline and Alkali Soils. USDA Handbook 60. Washington DC, USA

Ryan, J., G. Estefan and A. Rashid, 2001. Soil and Plant Analysis Laboratory Manual, 2nd edition. Aleppo, Syrian Arab Republic ICARDA, Syria

Sahrawat, K.L., 1982. Nitrification in some tropical soils. Plant Soil, 65: 281-286

Sepaskhah, A.R. and S.N. Hosseini, 2008. Effects of alternate furrow irrigation and nitrogen application rates on yield and water- and nitrogen-use efficiency of winter wheat (Triticum aestivum L.). Plant Prod. Sci., 11: 250-259

Shangguan, Z., M. Shao and J. Dyckmans, 2000. Effects of nitrogen nutrition and water deficit on net photosynthetic rate and chlorophyll fluorescence in winter wheat. J. Plant Physiol., 156: 46-51

Shi, Z., D. Lia, Q. Jing, J. Kia, D. Jianga, W. Cao and T. Dai, 2012. Effects of nitrogen applications on soil nitrogen balance and nitrogen utilization of winter wheat in a rice-wheat rotation. Field Crop Res., 127: 241-247

Sims, J.R. and G.D. Jackson, 1971. Rapid analysis of soil nitrate with chromotropic acid. Soil Sci. Soc. Amer. Proc., 35: 603-606

Sugiharto, B., K. Miyata, H. Nakamoto, H. Sasakawa and T. Sugiyama, 1990. Regulation of expression of carbon-assimilating enzymes by nitrogen in maize leaf. Plant Physiol., 92: 963-969

Tahir, M.A. and H. Rasheed, 2008. Distribution of nitrate in the water resources of Pakistan. Afr. J. Environ. Sci. Technol., 11: 397-403

Wang, Q., F. Li, L. Zhao, E. Zhang, S. Shi, W. Zhao, W. Song and M.M. Vance, 2010. Effects of irrigation and nitrogen application rates on nitrate nitrogen distribution and fertilizer nitrogen loss, wheat yield and nitrogen uptake on a recently reclaimed sandy farmland. Plant Soil, 337: 325-339

Xue, X. and M. Hao, 2011. Nitrate leaching on loess soils in north-west China: Appropriate fertilizer rates for winter wheat. Acta Agric. Scand. Sec. B-Soil Plant Sci., 61: 253-263

Zhong, Y. and Z. Shangguan, 2014. Water consumption characteristics and water use efficiency of winter wheat under long-term nitrogen fertilization regimes in northwest china. PLoS ONE., 6: e98850

Zwart, S.J. and W.G. Bastiaanssen, 2004. Review of measured crop water productivity values for irrigated wheat, rice, cotton and maize. Agric. Water Manage., 69: 115-133
COPYRIGHT 2016 Asianet-Pakistan
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2016 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Bibi, Sadia; Hassan, Anwar-ul-; Murtaza, Ghulam; Ehsanullah
Publication:International Journal of Agriculture and Biology
Article Type:Report
Geographic Code:9PAKI
Date:Apr 30, 2016
Words:10841
Previous Article:Short-day Photoperiod Effects on Plant Growth, Flower Bud Differentiation, and Yield Formation in Adzuki Bean (Vigna angularis).
Next Article:First Report of the Molecular Characterization of the Endosymbiont Candidatus portiera aleyrodidarum from Cotton Whiteflies Collected from Pakistan.
Topics:

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters