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Effects of municipal solid waste compost, rice-straw compost and mineral fertilisers on biological and chemical properties of a saline soil and yields in a mustard-pearl millet cropping system.

Introduction

Improving and maintaining fertility of saline soil is vital to meeting the demands of food grain production for an increasing population in many parts of the world. In India, soils covering 6.73 Mha are salt-affected, with sodic soils comprising 3.77 Mha and saline soils 2.96 Mha (Tripathi 2011); another 16.2 Mha of land is predicted to become salt-affected by 2050 (Central Soil Salinity Research Institute 2014). Salinity has severely restricted global agriculture in arid and semi-arid regions. This stress is becoming more prevalent as land-use intensity increases throughout the world (Dong et al. 2009).

Salinity inhibits plant growth through low osmotic potential of the soil solution, ion toxicity and ion imbalance, which further reduce nutrient uptake (Marschner 2012). However, inappropriate irrigation and drainage systems have resulted in rising groundwater levels, which have the potential to trigger salt accumulation in the soil profile and have a negative effect on crop production (Sharma and Minhas 2005; Qadir et al. 2009). In addition, limited precipitation, high evaporation and inadequate soil and water management have contributed to an increase in salinity. It is well known that saline soil has low fertility and biological activity. Saline soils are deficient in soil organic carbon (SOC), nitrogen (N), phosphorus (P) and potassium (K.) (Lakhdar et a!. 2008). In saline soil antagonism of sodium, which leads deficiency of K and calcium (Marschner 2012).

Effective techniques for managing soil salinity and increasing crop productivity need to be developed. The restoration of microbial activity is a basic step in reclamation of saline soil. Application of organic amendments improves soil physical, chemical and biological properties of saline soil, and this is connected with an increase in the organic C content (Crecchio et al. 2004). The biomass of organic amendments plays an important role in nutrient cycling through increased microbial population (Christcnen and Johnston 1997). Organic amendments in association with microflora enhance mineralisation, with a concomitant increase in C02 release and, consequently, soil aeration (Muhammad et al. 2007), presumably due to stimulation of enzymatic activities. Such an increase in mineralisation helps to improve soil fertility and crop productivity in saline soil.

An important source of organic amendment is municipal solid waste (MSW), which is gaining importance for increasing microbial and chemical properties of saline soil. In India, per capita waste generation is 0.2-0.6 kg [day.sup.-1], amounting to ~42 Mt annually (Asnani 2004). The amount of MSW is expected to increase significantly in the near future as the country strives to attain the status of industrialised nation by 2020 (Central Pollution Control Board 2004; Sharma and Shah 2005). Poor collection and inadequate management are responsible for the accumulation of MSW in India. Sustainable management of MSW is needed for environmental protection and economic development. Several strategies have been applied for efficient management of MSW in developing countries, but their performance has not been critically investigated (Aliu et al. 2014). Attention has focused on composting of MSW in order to reduce the volume to be disposed in landfill and to provide a new organic amendment for saline and non-saline soils as a possible alternative for costly chemical fertilisers.

Another source of organic amendment is rice straw. About 250 Mt of straw residue is produced annually in rice-wheat cropping systems in the Indo-Gangetic Plains of India (Gupta et al. 2004). Wheat residue after grain harvest is valued for animal feed, and there is no difficulty in its removal from the field and subsequent management. On the other hand, rice residues are generally not used for animal feed in northern India, although they are used as cattle feed in eastern and southern parts of the country. Consequently, rice residues are usually burnt on a large scale, polluting the environment and decreasing soil biota and C in the top layer of soil. Direct incorporation of the rice straw into the soil is limited because of agronomic problems such as temporary immobilisation of nutrients and associated crop yield reduction (Singh et al. 2005). Thus, the lack of alternative uses and lack of appropriate mechanisms to handle increasing quantities of rice residues have driven most farmers to bum them as a method of disposal (Singh et al. 2005). An alternative means of utilising these large quantities of residues and recycling them back to the field is to convert them into a value-added product--compost (Meena and Biswas 2014). MSW compost (MSWC) and rice-straw compost (RSC) may enhance biological activity and rebuild fertility of saline soils.

The application of MSWC with mineral fertilisers has been shown to increase soil microbial properties and crop production (Oucdraogo et al. 2006). Organic amendments not only influence soil fertility directly, but can also affect the composition and activity of soil microorganisms (Crecchio et al. 2004). The literature shows that organic amendments can remediate salinity as well as improve microbial biomass and activity. Most studies have consistently shown enhancement of microbial biomass C (MBC), basal respiration and enzyme activities on application of organic amendments (Perucci 1992; Crecchio et al. 2004; Garcia-Gil et al. 2004; Ros et ai 2006). Soil microorganisms arc essential to agricultural ecosystems, playing a paramount role in C cycling and nutrient mineralisation, therefore affecting soil fertility (Nannipieri et al. 2002). Several studies have examined biological activities and biomass in saline soil; however, little information is available about such effects of MSWC and RSC in saline soil. The objective of this study was to determine the effects of organic amendments and mineral fertilisers on soil microbial activities and fertility of saline soils. We hypothesised that application of organic amendments would increase microbial activity and crops yield by alleviating the negative effect of salinity.

Methods and materials

Compost preparation

The MSWC was collected from Municipal Corporation of Delhi, New Delhi. It originated from fruit and vegetable peels, waste from the paper industry, food waste, sweepings, cardboard and waste paper. RSC was prepared with Trichoderma viride inoculation. For composting, chopped rice straw (length 5-6 cm), soaked in water for 24 h, was mixed thoroughly on a polyethylene sheet. A uniform dose of urea solution at 0.25 kg N 100 [kg.sup.-1] rice straw (air-dry weight basis, 30 [+ or -] 1[degrees]C) was added to reduce the C : N ratio. Fresh cow dung at 10 kg 100 [kg.sup.-1] rice straw was made into slurry and added to the compost mass to acts as a natural inoculant. A uniform dose of T. viride at 50 g fresh mycclia 100 [kg.sup.-1] rice straw was added to the compost mass to hasten the composting rate. The entire composting mass was mixed thoroughly and put in cement pits, each of 100 L capacity. Manual turning was performed after 30, 60 and 90 days of composting to provide adequate aeration. Moisture was maintained at 60% of water-holding capacity throughout the composting period (120 days).

Chemical analysis of MSWC and RSC

At maturity (after 120 days), representative samples were drawn from each pit in triplicate. Compost samples were first air-dried (30 [+ or -] 1[degrees]C) and then oven-dried (65 [+ or -] 1[degrees]C) for 24 h, crushed to pass through a 2-mm sieve, thoroughly mixed, and used for analysis of total nutrient content. Total N was determined by digesting the sample with [H.sub.2]S[O.sub.4] by using a digestion mixture ([K.sub.2]S[O.sub.4] : CuS[O.sub.4], 10:1) according to a micro-Kjeldahl method (Bremncr and Mulvaneyl982). Total P content in the acid digest was determined by spectrophotometer after developing vanadomolybdo-phosphatc yellow colour complex as described by Jackson (1973). Potassium content in the acid digest was determined by a flame photometer (Jackson 1973). Total C content was determined by ignition method (Jackson 1973). Concentrations of micronutrient cations iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) and heavy metals nickel (Ni), lead (Pb) and cadmium (Cd) were determined by atomic absorption spectroscopy (Karaca 2004). Cation exchange capacity (CEC) was determined as per the procedure of Jackson (1973). Chemical properties of MSWC and RSC are shown in Table 1.

Experimental site and soil

The field experiment on a cropping system of mustard (Brassica juncea)-pearl millet (Pennisetum glaucum) was conducted from October 2012 to March 2014 at the research farm in Nain village, Panipat district, of ICAR-Central Soil Salinity Research Institute (CSSRI), Kamal, India. The soil at the experimental site is a sandy loam and the climate is semi-arid subtropical with hot summers (May-Junc) and cold winters (Dccember-January). Initial soil samples were collected in surface soil (0-15 cm depth). The main physico-chemical and biological properties of the pre-experimental soil were: texture, sandy loam with sand 56.4%, silt 25% and clay 18.6% (Bouyoucos 1962); [pH.sub.w] (1:2, soil : water) 8.4; electrical conductivity ([EC.sub.w]; 1:2, soil:water) 7.2dS [m.sup.-1]; CEC 11.68cmol(+) [kg.sup.-1] soil (Jackson 1973); organic C 1.9 g [kg.sup.-1] (Walkley and Black 1934); available N 108 kg [ha.sup.-1] (Subbiah and Asija 1956); 0.5 M NaHC[O.sub.3]-extractable P 18.1 kg [ha.sup.-1] (Olsen et al. 1954); neutral 1N N[H.sub.4]OAc-extractable K 203 kg [ha.sup.-1] (Hanway and Heidel 1952); MBC 176.1 mg [kg.sup.-1] (Jenkinson and Powlson 1976); dehydrogenase activity (DHA) 43.2 [micro]g triphenylformazan (TPF) [g.sup.-1] soil 24 [h.sup.-1] (Klein et al. 1971); alkaline phosphatase activity (ALPA) 79.2[micro]g para-nitrophenol phosphate (PNP) [g.sup.-1] soil 24 [h.sup.-1] (Tabatabai and Bremner 1969); and urease activity (UA) 64 N[H.sub.4] mg [kg.sup.-1] soil 24 [h.sup.-1] (Nannipieri et al. 1980).

Field experiment

Performances of MSWC,RSC and mineral fertilisers were evaluated in the mustard-pearl millet cropping system. Six treatments were used: (i) untreated control; (ii) 100% recommended dose of mineral fertilisers (RDF); (iii) RSC at 141 [ha.sup.-1]; (iv) MSWC 161 [ha.sup.-1]; (v) RSC 71 [ha.sup.-1] + 50% RDF; (vi) MSWC 8t [ha.sup.-1] + 50% RDF. The experiments were laid out in a randomised block design with three replications of plot size 5.0 m by 5.0 m.

Mustard was grown as the first crop in October and harvested in March, whereas pearl millet was grown in July and harvested in early October. The cropping system was continued for 2 years (2012-14) and harvested for total biomass, straw and grain yield. Row-to-row spacing was 45 cm for both crops. Mustard variety CS-52 was salt-tolerant, whereas pearl millet variety Proagro 9444 was not. Groundwater of the site was highly saline (EC ~ 16-20 dS [m.sup.-1]) and not suitable for irrigation. A rain gauge and evaporimeter were established 10m from the experimental site, in August 2013. Total rainfall received was 322 mm during 2013 and 562mm during 2014 (Fig. 1a, b). Mustard was irrigated with pond water that was harvested during rainy season (July-Scptcmber). Pearl millet was totally dependent on monsoon rain. Other agronomic practices were carried out as and when required. The recommended dose of NPK fertilisers applied to mustard and pearl millet was60:30:30. Fertilisers used were urea, di-ammonium phosphate (DAP) and muriate of potash (MOP). Half of the dose of N and full doses of composts, P and K were applied as basal in each crop by broadcasting followed by manually mixing before sowing. The remaining half of the N was applied at 35M0 days after sowing of mustard and 20-25 days after sowing of pearl millet.

Soil analyses

Plot-wise soil samples were collected from surface soil (0-15 cm) after the harvest of each crop. Immediately after collection, ~100 g of each of the moist soil samples from field was placed at 4[degrees]C in a refrigerator for subsequent determination of microbial parameters (MBC and enzyme activities).

Biological analyses

Soil MBC was determined by the fumigation-extraction method (Jenkinson and Powlson 1976). The amount of the MBC in soil was calculated as follows:

MBC = ([OC.sub.F] - [OC.sub.UF])/[K.sub.EC]

where [OC.sub.F] and [OC.sub.UF] are the organic C extracted from fumigated and unfumigated soil, respectively (expressed on oven dry basis); and [K.sub.EC] is the efficiency of extraction, where a value of 0.45 is considered appropriate for microbial extraction efficiency and used for the calculation.

The DHA in soil was determined by the method of Klein et al. (1971). ALPA was determined colourimetrically by using modified universal buffer at pH 11 as outlined by Tabatabai and Bremner (1969). UA was determined by measuring the rate of [NH.sub.4.sup.+] released during soil incubation with urea for 90 min at 30[degrees]C (Nannipieri et al. 1980).

Chemical analyses

Soil samples (0-15 cm depth) were collected from each plot at monthly intervals during the growing season for analysis of EC only (Jackson 1973). Post-harvest soil samples were collected from each plot after harvest of each crop, air-dried, ground to pass through a 2-mm sieve by using a wooden pestle and mortar, and analysed for organic C (Walkley and Black 1934), available N (Subbiah and Asija 1956), available P (Olsen et al 1954) and available K (Hanway and Heidel 1952).

Statistical analyses

Data generated from the field experiments were subjected to the statistical analyses of variance appropriate to the experimental design. Data were assessed by Duncan's multiple range tests with a probability P = 0.05 (Duncan 1955). Least significant difference (l.s.d.) between means was calculated using the SPSS program (SPSS version 16.0; SPSS Inc., Chicago).

Results and discussion

Microbial biomass carbon

The MBC was significantly (P< 0.05) increased with integrated use of MSWC + 50% RDF (254 and 259 mg [kg.sup.-1] soil) after mustard and pearl millet harvest, respectively, relative to the unfertilised control during first growing season (2012-13), and was statistically similar (P > 0.05) between MSWC + 50% RDF and RSC + 50% RDF. MBC was significantly (P < 0.05) increased with 100% RDF relative to the control. MBC increased by 27% and 38% with MSWC and by 25% and 32% with RSC relative to the control after mustard and pearl millet harvests, respectively (Fig. 2a). The experimental soil was low in MBC content, which is a limiting factor for biomass C and crop productivity in saline soil. Thus, it is important to increase its amount through application of organic amendments (Tripathi et al. 2006).

In 2013-14, MBC was increased by 24% and 32% after mustard and pearl millet, respectively, with application of 100% RDF (Fig. 2b). Integrated use of MSWC + 50% RDF increased MBC by 29% and 30% over use of 100% RDF alone after mustard and pearl millet, respectively. MBC increased significantly (P<0.05) with MSWC alone or in combination with 50% RDF, compared with the control. MBC was higher with MSWC at 161 [ha.sup.-1] (242 and 253 mg [kg.sup.-1]) than RSC at 14t [ha.sup.-1] (235 and 244 mg [kg.sup.-1]) after mustard and pearl millet, respectively. MSWC has previously been shown to result in higher microbial biomass (Christencn and Johnston 1997). The increase in MBC with MSWC + 50% RDF may be attributed to integrated use of organic and mineral fertilisers in intensive cropping systems such as mustard-pearl millet. Application of organic amendments for a longer period has been found to stimulate microbial growth (Garcia-Gil et al. 2000; Chakraborty et al. 2011). Soil treated with either MSWC or RSC was found have a higher concentration of MBC than soil treated with mineral fertilisers. This might be due to the high quantities of readily utilisable energy sources incorporated through composts (Shen et al. 1997). MBC contributes to maintenance of soil fertility and soil quality in both nonsaline and saline soils.

Dehydrogenase activity

Not only is DH A considered an important indicator of soil health and quality, it also reflects overall soil microbial activity (Nannipicri et al. 1980; Bolton et al. 1985). In the present study. Dl IA increased with use organic amendments and mineral fertiliser in the first growing season (2012-13), relative to the control. Treatments receiving organic amendments cither alone or in combination with 50% RDF showed significantly increased DHA after mustard and pearl millet harvests (Fig. 3a). However, use of MSWC alone increased DHA by 26% and 24% over 100% RDF after mustard and pearl millet, respectively. Therefore, DHA might be less influenced by mineral fertilisation (Kautz et al. 2004).

In 2013-14, the organic amendments resulted in higher DHA than in the first growing season. Combined use of RSC + 50% RDF resulted in DHA of 79 and 86 [micro]g TPF [g.sup.-1] soil 24 [h.sup.-1] after mustard and pearl millet harvests, respectively, which was significantly higher than for 100% RDF (Fig. 3b). Soil treated with MSWC + 50% RDF had 43% and 45% higher DHA than soil treated with 100% RDF, after mustard and pearl millet, respectively, whereas plots treated with 100% RDF had 69% and 100% higher DHA than the control. DHA was more influenced by organic amendments than by mineral fertiliser throughout the experiment, possibly because incorporation of organic amendments into soil stimulates its activity (Rao and Pathak 1996; Liang et al. 2005).

Alkaline phosphatase activity

Alkaline phosphatase plays an important role in the transformation of organic P to inorganic forms more appropriate for plants. Phosphorus is an essential nutrient for plants, and the greater part of soil P occurs in the organic form (Tabatabai 1994). Our study clearly indicates that in the control treatment, ALPA declined with the intensive mustard-pearl millet cropping system. Combined incorporation of organic amendments along with 50% RDF significantly (P<0.05) increased ALPA over that of the control after mustard and pearl millet in first growing season (2012-13). The lowest ALPA values were 82 and 80 [micro]g PNP [g.sup.-1] soil 24 [h.sup.-1] in the control plots after mustard and pearl millet, respectively (Fig. 4a). The remarkable increase in ALPA to 154 and 161 [micro]g PNP [g.sup.-1] soil 24 [h.sup.-1] with MSWC + 50% RDF after mustard and pearl millet, respectively, might be due to organic amendment stimulating phosphatase activity in saline media (Juma and Tabatabai 1988).

In 2013-14, application of MSWC or RSC either alone or in combination with 50% RDF significantly increased ALPA relative to the control after mustard and pearl millet harvests (Fig. 4b). RSC significantly increased ALPA in soil by 12% and 10% after mustard and pearl millet, respectively. Integrated use of MSWC + 50% RDF significantly increased ALPA by 58% and 55% compared with use of 100% RDF, after mustard and pearl millet, respectively. However, the combined application of 50% RDF and compost accelerated the decrease in the organic P fractions, possibly through promotion of microbial activity in the plough layer, even though a large amount of organic P was input by compost (Lee et al. 2004).

Urease activity

Urease is predominately involved in the N-cyclc of the soil, where it catalyses the hydrolysis of urea into ammonia or the ammonium ion (Tabatabai and Bremner 1972; Cookson 1999). In the first growing season, UA in the plots with MSWC + 50% RDF (81 and 92 N[H.sub.4] mg [kg.sup.-1] soil 24 [h.sup.-1]) was significantly higher than in the control, but was statistically similar to RSC + 50% RDF, after mustard and pearl millet, respectively (Fig. 5a). UA was increased by 8% and 23% in plots with 100% RDF compared with the control after mustard and pearl millet, respectively. RSC alone resulted in 10% and 28% higher UA than the control after mustard and pearl millet, respectively. However, treatments did not significantly change with respect to UA except in the control after harvest of pearl millet in the first year of the crop cycle. It might be because activity of urease is stimulated by application of organic amendments over a longer rather than a shorter period (Chakraborty et ul. 2011).

During 2013-14, UA increased significantly with application of either MSWC or RSC along with 50% RDF (Fig. 5b) after mustard and pearl millet. Compared with the control, all treatments significantly increased UA. Maximum UA was observed with MSWC+ 50% RDF, followed by RSC+ 50% RDF. The UA increased 40% and 49% with use of RSC alone, and by 47% and 59% with MSWC alone, over the control after mustard and pearl millet, respectively. UA was significantly higher with organic amendments and with mineral fertilisers after second year than first year of cropping. This might be because N mineralisation was enhanced later in the experiment, with early adverse effect of pH on nitrites relieved by the remedial influence of organic matter decomposition (Pathak and Rao 1998).

Soil organic carbon

Results clearly indicated that combined addition of cither RSC or MSWC with 50% RDF significantly (P< 0.05) increased SOC concentration over the control during 2012-13 (Fig. 6a). Integrated use of MSWC+ 50% RDF maintained 3.9 and 4.1 g [kg.sup.-1] of SOC after mustard and pearl millet, which was significantly more than the control in first year of cropping.

In second year (2013-14), MSWC maintained a greater concentration of SOC (4.4 and 4.5 g [kg.sup.-1]) than RSC (4.0 and 4.1 g [kg.sup.-1]) after mustard and pearl millet, respectively (Fig. 6b). Soil treated with either MSWC or RSC had a higher concentration of SOC than the control (Bhattacharyya et al. 2009).

There was little change in SOC in all treatments after first year of the crop cycle, although it did gradually increased over time. It may be because only a fraction of the organic material is initially degraded and made available to plants and soil microorganisms (Hadas et al. 1996). Effect of organic amendments on SOC depends on the chemical nature of the amendments (Tejada et al. 2006). The chemical nature of the organic amendment is likely to affect the rate at which it is decomposed by the microbial community (Hahn and Quideau 2013). Repeated use of MSWC consistently increased soil organic matter content and soil C : N ratio to levels above those of unfertilised soil (Crecchio et al. 2004; Montemurro et al. 2006). Chemical fertilisers are expected to keep the soil organic matter pool at 60t [ha.sup.-1] in 2050; however, compost addition may enhance this pool to be more than double that of the conventional tillage system at 0-15 cm soil depth without fertiliser (Ginting et al. 2003).

Available nutrients

Soil available N, P and K increased in all treated plots during first year (2012-13). Integrated use of MSWC+ 50% RDF resulted significant build-up in available N, P and K, by 28%, 140% and 30%, respectively, over the control after the mustard harvest (Table 2). Available N, P and K. were 141, 36 and 265 kg [ha.sup.-1]. respectively, with MSWC+ 50% RDF after the pearl millet harvest, also significantly higher than in the control. Available N, P and K were 45%, 122% and 34% higher with 100% RDF than the control (Table 2). Application of 100% RDF resulted in greater amounts of available N, P and K than RSC alone after first growing season. This is because mineral fertilisers have higher concentrations of water-soluble N, P and K. Later, however, available nutrients in RSC plots increased with continuous release of nutrients in the compost; this demonstrates a slow release of nutrients, with the effect being long term (Hooda et al. 2001; Park et al. 2004).

Available N, P and K. improved significantly (P<0.05) in all plots receiving mineral fertiliser alone or in combination organic amendments than control (Table 2), after the second year of mustard and pearl millet (2013-14). Soil treated with 100% RDF had 61%, 183% and 42% more available N, P and K., respectively, than control soil after mustard harvest. Application of RSC +50% RDF resulted in significantly more available N, P and K than the control. Integrated use of MSWC + 50% RDF resulted in significantly more N, P and K after mustard (163, 38 and 280 kg [ha.sup.-1]) and pearl millet (169, 42 and 286 kg [ha.sup.-1]) harvests than use of 100% RDF alone. Organic amendments in saline soil may enrich the rhizosphere with micro- and macronutrient elements, counteracting nutrient depletion (Lakhdar et al. 2008). Muhammad et al. (2007) reported an increase of NaHC[O.sub.3]-tractable P in saline soil following 1% compost amendment. Decomposition of organic matter releases humic acid, which in turn converts unavailable soil phosphates into available forms. Under saline soil, mineralisation of compost increases the plant-available K fraction through increases in CEC (Walker and Bernal 2008).

Dynamics of soil salinity

Salt concentrations (i.e. EC) during 2012-13 as influenced by organic amendments, alone or in combination with 50% RDF, arc presented in Fig. 7. No significant differences were observed among the treatments throughout the mustard growing season (Fig. 7a).Treatments with organic amendments had lower EC at 90 and 120 days of pearl millet growth than the treatment with 100% RDF (Fig. 7b). Treatment with MSWC + 50% RDF decreased salt content by 16% compared with the control at 120 days. At the start of the season, soil salinity was high (EC 7.2 dS [m.sup.-1]) and on par with treatments during the mustard growing season. In August 2013, during monsoon season, 297mm of rainfall was received (Fig. 1a), which leached down the soluble salts. The leaching of salts was more effective with organic amendments along with 50% RDF than with other treatments because organic amendments improve soil physical condition, helping to leach down the salts from the root-zone. However, combined use of RSC + 50% RDF resulted in 12% lower salt concentration than the control at 120 days of growing pearl millet. It may be that organic amendments decrease bulk density, and enhance soil porosity and aeration, because of improvement in leaching (Khaleel et al. 1981).

In 2013-14, salt concentration was significantly reduced with the integrated use of MSWC + 50% RDF relative to use of 100% RDF alone at 150 days of mustard growth (Fig. 8a). The smallest decrease in salinity was observed with use of 100% RDF alone and the largest with MSWC + 50% RDF, followed by RSC+ 50% RDF throughout the growing period of mustard. Salinity was significantly decreased by 37% with MSWC + 50% RDF at 150 days of mustard growth. In the second year of mustard, irrigation (140 mm) and rainfall (75 mm) further leached the soluble salts from the soil profile.

The level of salinity during growth of pearl millet in 2013-14 was decreased considerably under organic amendments with 50% RDF (Fig. 8b). During the pearl millet growing season, 330 mm of rainfall was received from July to September (Fig. 1 b). In the treatment receiving RSC + 50% RDF, salt concentration significantly decreased by 43% relative to use of 100% RDF alone at 120 days of pearl millet growth, and the decrease was even greater in the treatment receiving MSWC+ 50% RDF. This is because of the greater mass of organic matter added through MSWC and the C[O.sub.2] evolved from the decomposition of compost and respiration, which improves of soil structure and permeability, thus enhancing salt leaching, reducing surface evaporation and inhibiting salt accumulation in surface soils (Raychev et al. 2001).

Soil pH

There was no significant difference among the treatments for soil pH after mustard and pearl millet harvest during first growing season (2012-13) (Tabic 3) However, slightly lower values of pH (8.1 and 7.9) were observed with integrated use of MSWC+ 50% RDF after mustard and pearl millet harvest, respectively. During 2013-14, soil pH was significantly reduced with MSWC +50% RDF relative to the control after mustard and pearl millet harvests. Comparing use of organic amendments alone, MSWC had lower values of soil pH than RSC after the harvest of mustard and pearl millet crops. This may be attributed to the compost application creating a favourable environment for microbial activity. Furthermore, microbial activities increase the partial pressure of C[O.sub.2], which lowers the soil pH. The C[O.sub.2] evolved from the decomposition of compost and respiration of live roots forms carbonic acid and sulfuric acid after reacting with water and S[O.sub.4] in the soil, which lowers soil pH over time (Singh et al. 2012).

Yield of mustard and pearl millet

Results indicated that higher grain and straw yield of both crops were observed with integrated use of organic amendments and 50% RDF rather than use of 100% RDF alone (Table 4). Grain yields of crops were significantly affected by application of RSC and MSWC along with 50% RDF. Application of 100% RDF increased grain yields of mustard and pearl millet by 6% each over the control during 2012-13. MSWC + 50% RDF recorded the highest grain and straw production of both crops. Treatment receiving RSC+ 50% RDF increased grain yield by 10% and 28% for mustard and pearl millet, respectively, relative to 100% RDF alone. The higher yield of crops with organic amendments plus 50% RDF was possibly due to beneficial effects on microbial activities and better supply of balanced plant nutrients, which arc not supplied by inorganic fertilisers alone (Yadav et al. 2000).

After the second year of the cropping cycle (2013-14), integrated use of MSWC + 50% RDF showed significantly higher grain yield (2.50 and 2.70tha~') of mustard and pearl millet, respectively, than use of 100% RDF alone (Table 4). The treatment RSC+ 50% RDF recorded grain yield increases of 31% and 23% for mustard and pearl millet, respectively over the control. The greatest increase in grain yield was observed with MSWC+ 50% RDF over the control. This might be due to integration of organic amendments plus mineral fertilisers, which could be attributed to better synchrony of nutrient supply (Singh et al. 2004). The improved soil physical properties in the compost-amended plots might also have contributed to the improvement in crop yields. Similar results of improved soil physical properties from addition of organic amendments were reported by Hati et al. (2006) and Gopinath et al. (2008). Our findings demonstrated that highest grain and straw yield of both crops occurred with integrated use of organic amendments with mineral fertilisers.

Conclusion

Application of organic amendments at 7-8t [ha.sup.-1] along with mineral fertilisers under a mustard-pearl millet cropping system in saline soil resulted in higher MBC, enzyme activities, SOC and available N, P and K., which improved crop yields. The results demonstrated that MSWC at 8t [ha.sup.-1] +50% RDF gave significant improvement in DHA, ALPA and UA as well as soil fertility in terms of available nutrients over use of 100% RDF alone after the second year of mustard and pearl millet. MSWC at 8t [ha.sup.-1] + 50% RDF resulted in the highest grain and straw yield for both crops throughout the 2-ycar cropping cycle. Our findings demonstrate that integration of organic amendments and mineral fertilisers maintained lower salinity during each growing season of mustard and pearl millet than the unfertilised control.

Organic amendments do not completely overcome the adverse effects of salinity. However, continuous use of composts improves biological and chemical properties of saline soil. Therefore, compost can provide better soil conditioning for crop production in saline soils. Investigations of heavy metal build-up in soil and the economics of the compost technology are also considered worthwhile for future studies.

http://dx.doi.org/10.1071/SRI5342

Acknowledgements

The authors thank the Director, ICAR-Central Soil Salinity Research Institute, Kamal, Haryana, India, for financing this work and Head, Division of Soil and Crop Management, ICAR-Central Soil Salinity Research Institute, Kamal, Haryana, India, for excellent technical assistance.

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M. D. Meena (A,B), P. K. Joshi (A), B. Narjary (A), P. Sheoran (A), H. S. Jat (A), A. R. Chinchmalatpure (A), R. K. Yadav (A), and D. K. Sharma (A)

(A) ICAR-Central Soil Salinity Research Institute (CSSSRI), Karnal- 132001, Haryana, India.

(B) Corresponding author. Email: murliiari@gmail.com

Table 1. Characteristics of rice-straw compost (RSC) and municipal
solid waste (MSWC)

Values are mean [+ or -] standard deviation

Parameters                          RSC                   MSWC

Moisture (%)                 9.46 [+ or -] 0.24    8.45 [+ or -] 0.20
p[H.sub.w] (1:5)             8.16 [+ or -] 0.39    8.21 [+ or -] 0.29
[EC.sub.w] (dS[m.sup.-1])    2.80 [+ or -] 0.24    3.40 [+ or -] 0.26
CEC (cmol(+) [kg.sup.-1]      170 [+ or -] 12       200 [+ or -] 11.0
  compost)
Total C (%)                  32.4 [+ or -] 0.47    30.1 [+ or -] 0.56
Total N (%)                  1.15 [+ or -] 0.1     0.86 [+ or -] 0.1
C:N                          28.3 [+ or -] 0.2     35.1 [+ or -] 0.4
Total P (%)                  0.38 [+ or -] 0.05    0.37 [+ or -] 0.12
Total K (%)                  1.27 [+ or -] 0.04    0.90 [+ or -] 0.02
Total Fe (%)                  0.3 [+ or -] 0.08    0.75 [+ or -] 0.28
Total Mn (mg [kg.sup.-1])   170.5 [+ or -] 26.0   303.5 [+ or -] 119.2
Total Zn (mg [kg.sup.-1])   186.1 [+ or -] 38.2   514.5 [+ or -] 88.1
Total Cu (mg [kg.sup.-1])    49.1 [+ or -] 10.6   348.8 [+ or -] 138.5

Heavy metals

Total Ni (mg [kg.sup.-1])     4.3 [+ or -] 1.1     37.8 [+ or -] 8.1
Total Pb (mg [kg.sup.-1])          Trace           57.2 [+ or -] 5.0
Total Cd (mg [kg.sup.-1])          Trace                 Trace

Table 2. Effects of organic amendments and mineral fertilisers on
nutrient availability (kg [ha.sup.-1]) after harvest of mustard and
pearl millet crops

T1, Control; T2, 100% recommended dose of fertiliser (RDF); T3,
rice-straw compost (RSC) at 14 t [ha.sup.-1]; T4, municipal solid
waste compost (MSWC) at 16 t [ha.sup.-1]; T5, RSC at 7 t [ha.sup.-1]
+50% RDF; T6, MSWC at 8 t [ha.sup.-1] + 50% RDF. Within columns,
means followed by the same letter are not significantly different at
P < 0.05 according to Duncan's multiple range test for separation of
means

Treatment                             2012-13

                       After mustard        After pearl millet
                          harvest                harvest

                      N      P       K       N      P       K

T1                  104b    14b    198b     88b    12c    184b
T2                  124ab   26a    230ab   128a    27b    247ab
T3                  116a    24a    226ab   123a    25b    230a
T4                  125a    27a    234ab   127a    28b    241a
T5                  126a    28a    240ab   137a    30ab   250a
T6                  133a    34a    257ab   141a    36a    265a
1.s.d. (P = 0.05)   15.1    9.5    51.0    17.2    6.1    51.5

Treatment                             2013-14

                       After mustard        After pearl millet
                          harvest                harvest

                      N      P       K       N      P       K

T1                   84d    lid    176f     85c    11d    171d
T2                  136c    32c    251e    145b    33c    255c
T3                  138c    31c    255cd   152ab   37b    258c
T4                  146bc   33bc   266bc   161ab   38b    269b
T5                  155ab   36ab   273ab   165ab   39b    277ab
T6                  163a    38a    280a    169a    42a    286a
1.s.d. (P = 0.05)   15.0    3.0    12.3    19.9    2.5    10.2

Table 3. Soil [pH.sub.w] (1 :2) as affected by organic amendments
vis-a-vis and mineral fertilisers after harvest of mustard and pearl
millet

T1, Control; T2, 100% recommended dose of fertiliser (RDF); T3,
rice-straw compost (RSC) at 14 t [ha.sup.-1]; T4, municipal solid
waste compost (MSWC) at 16 t [ha.sup.-1]; T5, RSC at 7 t [ha.sup.-1]
+50% RDF; T6, MSWC at 8 t [ha.sup.-1] +50% RDF. Within columns,
means followed by the same letter are not significantly different at
P = 0.05 according to Duncan's multiple range test for separation of
means

Treatments               2012-13                  2013-14

                  Mustard   Pearl millet   Mustard   Pearl millet

T1                 8.2a         8.2a        8.2b        8.1d
T2                 8.2a         8.1a        8.2b        8.0cd
T3                 8.2a         8.0a        8.1ab       8.0cd
T4                 8.2a         8.0a        8.0ab       7.9bc
T5                 8.2a         8.0a        7.9a        7.8ab
T6                 8.1a         7.9a        7.8a        7.7a
l.s.d. (P=0.05)    0.1          0.4         0.3         0.4

Table 4. Yield (t [ha.sup.-1]) of mustard and pearl millet as
influenced by MSWC, RSC and mineral fertilisers

T1, Control; T2, 100% recommended dose of fertiliser (RDF); T3,
rice-straw compost (RSC) at 14 t [ha.sup.-1]; T4, municipal solid
waste compost (MSWC) at 16 t [ha.sup.-1]; T5, RSC at 7 t [ha.sup.-1]
+50% RDF; T6, MSWC at 8 t [ha.sup.-1] +50% RDF. Within columns,
means followed by the same letter are not significantly different at
P = 0.05 according to Duncan's multiple range test for separation of
means

Treatment                          2012-13

                         Mustard          Pearl millet

                    Grain     Straw     Grain     Straw

T1                  1.89c     3.10c     1,63c     7.37a
T2                  2.01be    3.44bc    l.72bc    7.62a
T3                  2.05bc    3.98bc    1.89abc   7.69a
T4                  2.10b     4.21b     2.10abc   7.61a
T5                  2.21ab    5.35a     2.2lab    7.91a
T6                  2.37a     5.58a     2.31a     7.97a
1.s.d. (P = 0.05)   0.23      0.34      1.48      0.59

Treatment                          2013-14

                         Mustard          Pearl millet

                    Grain     Straw     Grain     Straw

T1                  1.73c     4.83d     2.11b     7.17a
T2                  2.10b     5.60cd    2.34ab    7.67a
T3                  2,l7ab    5.77bc    2.35ab    7.73a
T4                  2.20ab    6.37abc   2.53a     7.90a
T5                  2.27ab    6.54ab    2.59a     8.07a
T6                  2.50a     6.89a     2.70a     8.23a
1.s.d. (P = 0.05)   0.34      0.83      0.35      1.33

Fig. 1.  Meteorological data during the field experiment
(a) August-December 2013, (b) January-Decemeber 2014.

(a)

        Evaporation   Rain

Aug.    90.4          297.4
Sep.    120.7         12.8
Oct.    92.9          4.3
Nov.    91.8          3.3
Dec.    60.2          4.0
Total   455.9         321.8

(b)

        Evaporation   Rain

Jan.    29.5          40.0
Feb.    39.7          1.3
Mar.    90.0          30.1
Apr.    219.9         3.4
May     240.6         114.2
June    369.5         32.0
July    221.5         75.6
Aug.    187.9         120
Sep.    88.0          135
Oct.    91.5          0
Nov.    98.4          0
Dec.    47.7          10

Note: Table made from bar graph.


----------

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Author:Meena, M.D.; Joshi, P.K.; Narjary, B.; Sheoran, P.; Jat, H.S.; Chinchmalatpure, A.R.; Yadav, R.K.; S
Publication:Soil Research
Article Type:Report
Geographic Code:9INDI
Date:Nov 1, 2016
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