Evaluation of soil properties and okra performance under methods of seedbed preparation at Owo, Southwest Nigeria.
Okra (Abelmoschus esculentus L. Moench) is one of the important vegetables grown not only in Nigeria but also in the temperate and sub-tropical region of the world. According to Majanbu et al. (1985), the fresh immature fruits and young leaves are used in preparing soups while the mature pods contain a mucilaginous substance that can be used as plasma replacement or blood volume expander and manufacture of paper. The mature stems of some varieties contain crude fibre which is beneficial in increasing intestinal peristalsis (Oyolu, 1980). Okra seeds also contain a high content of edible oil and quality protein due to its high lysine content (Savello et al., 1980; Tindall, 1983). Al-Wandawi (1983) reported that the crop can serve as a supplement to cereal based diets.
In Nigeria, most small farmers grow crops such as okra in multiple cropping systems and planting of seeds may be done at any position of manually constructed mounds or ridges or in untilled manually cleared soil. Although studies were conducted on response of okra to tillage methods (Ojeniyi, 1991 ; Ojeniyi and Ogbonaya, 1994; Adeyemi et al., 2005), it is necessary to evaluate soil physical and chemical properties and okra nutrient status and yield in seedbeds located at different positions of mound and ridge systems. This will enable recommendation of suitable placement position for okra. The evaluation may also advance understanding of soil factors affecting nutrient availability and yield in okra production.
The present work carried out in the forest-savanna transition zone of southwest Nigeria studied the response of okra yield components and nutrient contents to the physical and chemical soil conditions at the top, side, base positions of mounds and ridges, in furrows and untilled zero tillage and manually cleared soils.
Materials and methods
Seedbed Preparation and Planting:
The field experiments were conducted in the early and late cropping seasons of 2007 at the Rufus Giwa Polytechnic, Owo (Latitude 7012'N, Longitude 5035'E) in the forest-savanna transition zone of southwest Nigeria. The rainfall of Owo ranges between 1100 mm to 1500 mm per annum and mean monthly temperature of 24-32[degrees]C. The soil of the experimental site belongs to the broad group Alfisol (USDA, 1975) of the basement complex, though, locally classified as Okemesi Series (Smyth and Montgomery, 1962). The site has been an arable crop field, cultivated to a variety of arable crops, such as cassava, maize, yam, sorghum, groundnut, melon. The ten seedbeds evaluated for okra were zero tillage in which paraquat (1,1 dimethyl 4,4 bipyridilium dichloride) was sprayed before planting, untilled manually cleared soil, mound top, mound side, mound base, mound furrow, ridge top, ridge side, ridge base and ridge furrow. Mound and ridge were manually constructed with hoe after land clearing. The treatments were laid out in a randomized complete block design with three replicates. For each trial, okra seeds (Var. NHAE-47-4) obtained from National Horticultural Research Institute, Ibadan were planted at 3 seeds per stand, 2 cm deep at a spacing of 60 cm x 50 cm on 3 April and 5 August for the early season and late season, respectively. Each plot size measured 7 m x 7 m. The missing stands were supplied immediately after seedling emergence and thinned to one vigorous seedling per stand. Weeds were manually controlled by hoeing at 3, 5 and 7 weeks after planting. Insect pests were controlled by spraying cypermethrin fortnightly at the rate of 30 ml per 10 L of water starting from two weeks after seedling emergence.
Soil Physical Properties:
Selected soil physical properties were determined 80 days after planting. Five steel core samples collected from 0-10 cm depth in each plot were used for evaluation of bulk density and gravimetric water content after oven-dried at 105[degrees]C for 24 hours. Soil temperature was determined at 15.00 hr. with a soil thermometer inserted to 10 cm depth. The mean values were computed.
Soil Chemical Analysis:
Prior to planting, 10 core soil samples, randomly taken from 0-15 cm top soil were thoroughly mixed inside a plastic bucket to form a composite which was later analyzed for physical and chemical properties. Post-planting soil samples (0-15 cm depth) were collected from each treatment plot 80 days after planting. Soil samples were air-dried and sieved using 2 mm sieve. The samples were subjected to routine chemical analysis as described by Tel and Hagarty (1984). The soil organic carbon (SOC) was determined using dichromate oxidation method. Total N was determined by the micro-Kjeldahl method. Available P was determined colorimetrically after Bray-P1 extraction. Exchangeable K, Ca and Mg were extracted with 1 N ammonium acetate, K was determined using flame photometer and Ca and Mg by atomic absorption spectrophotometer.
At beginning of flowering, leaf samples were collected randomly from each plot, oven dried at 800C for 24 hours and ground in a Willey-mill. Leaf N was determined by micro-Kjeldahl approach. Ground samples were digested with nitric-perchloric acid mixture (AOAC, 1990). Phosphorus was determined colorimetrically by vanado-molybdate method, K by flame photometer and Ca and Mg by atomic absorption spectrophotometer.
Determination of Growth and Yield Components:
Ten plants were randomly selected per plot for determination of plant height and leaf area at 7 weeks after planting. Pods were harvested at 4 days interval and weighed. Pod weight was evaluated based on the cumulative number of pods at eight harvests.
All the data collected were analyzed using the analysis of variance (ANOVA) and the significance of treatment means were determined using either Duncan's multiple range test (DMRT) or least significant difference (LSD) at 5% level of probability (Gomez and Gomez, 1984).
Results and discussion
The results of the physical and chemical analysis of soil of the experimental site before cropping are presented in Table 1. The soil is sandy loam in texture, with a pH of 6.5, a level suitable for okra production and many tropical crops. The organic carbon of 2.89 g kg-1 and total nitrogen of 0.22 g kg-1 were low. The soil available P of 11 .3 mg kg-1 was adequate. The exchangeable bases (K, Ca and Mg) were also adequate (Akinrinde and Obigbesan, 2000).
The data presented in Table 2 show the values of soil bulk density, gravimetric water content and temperature recorded for seedbeds in case of early and late okra crops. Mound and ridge furrows had the highest value of bulk density and this was significantly higher (p=0.05) than untilled zero tillage and manually cleared soils and those at different positions of mound or ridge. This could be attributed to the removal of loose top soil with higher content of organic matter during mounding and ridging operations that led to exposure of the more compact subsoil with its attendant raised density. Bulk density of untilled zero tillage and manually cleared soils were significantly higher (p=0.05) than those for mound and ridge positions. This could be attributed to non-tillage and compaction. Mounding and ridging as forms of tillage led to reduced soil bulk density compared with untilled soils and compacted furrow soils. This could be adduced to the loosening effects of tillage (Agbede, 2006).
The zero tillage had the highest soil water content and lowest soil temperature followed by manually clearing, mound furrow, ridge furrow, mound base, ridge base, mound side, ridge side, mound top and ridge top in that order (Table 2). However, soil temperature decreased in the reverse order. There were reduced temperature in zero tillage and manual clearing. These results confirm findings of Adekiya and Ojeniyi (2002) and Ojeniyi et al. (2006) that temperatures are usually higher on soils located at top, side and base of a mound or ridge than zero tilled and manually cleared soils. The higher soil water status and lower soil temperature observed in untilled zero tillage and manually cleared soils compared with soils located at different positions of mound or ridge could be adduced to organic matter in soil surface which acted as mulch to reduce temperature and evaporation loss of water (Ojeniyi et al., 2006). The higher soil water status produced by mound and ridge furrows compared with soils located at different positions of mound and ridge could be related to higher clay content of mound and ridge furrow soils due to scraping of top soil. Another possible reason for higher water status of furrow soils was the movement of rain water from the mound and ridge positions during intense rain and its subsequent deposition in the furrows. The lower soil water status and higher temperature observed with soils located at the top, side and base positions of mound and ridge compared with zero tillage, manual clearing and compacted mound and ridge furrow soils could be related to increase in porosity of tilled soil which raises soil temperature during the day by reducing conduction of heat into soil (Ojeniyi and Dexter, 1979). Mounding or ridging was also found to expose soil to radiation and increases evaporation loss of soil water (Lal, 1986; Ojeniyi et al., 1999).
Table 3 shows the effect of seedbeds on soil chemical properties. Seedbeds had no significant effect (P=0.05) on soil organic C, Ca and Mg contents for the early and late okra crops but there was a significant effect of seedbeds on soil N, P and K status for the early and late okra crops. Zero tillage had the highest values of soil organic C (SOC), total N, available P and exchangeable K and Ca contents compared with other seedbeds. Mound and ridge furrows had the least fertility as indicated by the lowest values of soil organic C, N, P, K, Ca and Mg contents compared with other seedbeds. The highest values of SOC, N, P, K and Ca observed in zero tillage could be attributed to presence of vegetative mulch and accumulation of organic matter (Agbede, 2007). Similar observations were reported by Ojeniyi (1991) and Ojeniyi and Ogbonaya (1994). There were no significant differences between the nutrient content of soils located at the top, side and base of a mo und or ridge and these were significantly higher than compacted mound and ridge furrows in most cases. This was attributable to possible increase in oxidation and mineralization of incorporated organic matter (Allison, 1973; Ojeniyi, 1993). The least values of SOC, N, P, K, Ca and Mg contents recorded for compacted furrows was attributable to removal of organic matter from surface soil during mounding or ridging which left less fertile subsoil on the surface in addition to erosion and leaching.
The data on response of leaf nutrient status of okra to different types of seedbeds are shown in Table 4. Although seedbeds did not have significant effect (p = 0.05) on leaf N, P, K, Ca and Mg status, okra planted in zero tilled and manually cleared soils gave relatively higher leaf N, P and K status compared with crops planted at top, side and base positions of mound and ridge and furrow soils. The mound and ridge furrows with highest bulk density had least N, P, K, Ca and Mg status.
In the early season okra crop, growth and yield parameters of okra such as plant height, leaf area, number of pods per plant and pod weight were higher at different positions of mound or ridge compared with other seedbeds. This could be due to lower bulk density and higher P and K values. However, significant differences were not observed between different positions of mound or ridge and zero tillage and manual clearing. The yield of zero tillage and manual clearing compared favourably well with mound top, ridge side, mound base, ridge top, ridge side and ridge base probably because of reduced soil bulk density, highest SOC, N, P, K and Ca and higher Mg status. In the late season of okra crop, zero tillage produced significantly higher okra pod yield than any seedbed treatment. This might be due to highest values of SOC, N, P, K and Ca status and leaf N, P and K and soil water content recorded for zero tillage. Therefore, mounding or ridging degraded soil nutrient faster compared with untilled zero tillage and manually cleared soils. The more compact soils of the mo und and ridge furrows gave least growth and okra pod yield in the early and late seasons. This could be attributed to high bulk density and lower soil and leaf nutrient contents produced by the compacted furrows relative to zero tillage and manual clearing soils and mound or ridge positions. Field experiments have shown that availability of P and K in the soil improved growth and pod yield of okra (Adeyemi et al., 2005). The mean soil bulk density for mound furrow and ridge furrow was 1.58 Mg [m.sup.-3]. Therefore, bulk density above 1.2 8 Mg [m.sup.-3] would adversely affect growth and yield of okra on an Alfisol of southwest Nigeria. Trouse (1979) indicated that soil compressed just above 0.1 5 Mg [m.sup.-3] could reduce root growth to about half of its capability, and that such reductions in root growth could prevent plants from achieving potential yields. Also, the mean bulk density of 1 .58 Mg [m.sup.-3] recorded for the compacted furrow soils was clearly above the optimum required for the growth and development of a number of important crops in the tropics (Obi and Nnabude, 1988). Similar findings were reported by Ojeniyi and Ogbonaya (1994) that zero tillage produced significantly higher yield than hoeing, ridging and heaping in the late season, while ridge ranked best in the early season. However, these results are contradictory to that of Asoegwu (1987) who worked on soil with high bulk density in eastern Nigeria and found that (ridging only the seedbed) of okra and melon fields were significantly superior to minimum tillage and no-tillage. He attributed better growth and yield differences to the degree of soil pulverization and the ease of root penetration and development. These differences might have been due to variation in soil type, fertility status and climatic conditions. In this present study, planting in mound and ridge furrows reduced yield by 66% and 59%, respectively compared with untilled soils and those at different positions of mound or ridge. Therefore, soil bulk density and nutrient content dictated okra performance and nutrient status.
Okra can be grown sustainably in the forest-savanna transition zone of southwest Nigeria in zero tilled and manually cleared soils and any position on mound or ridge without a significant loss in soil fertility and yield of okra. Planting should not be done in the mound or ridge furrow due to its high bulk density and lower fertility that led to reduced nutrient uptake, growth and yield of okra.
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(1) Agbede, T.M. and (2) Ologunagba, I.B.
(1) Department of Agricultural Engineering Technology, Rufus Giwa Polytechnic, P. M. B. 1019, Owo, Ondo State.
(2) Department of Civil Engineering Technology, Rufus Giwa Polytechnic, P. M. B. 1019, Owo, Ondo State.
Corresponding Author: Agbede, T.M., Department of Agricultural Engineering Technology, Rufus Giwa Polytechnic, P.M.B. 1019, Owo, Ondo State.
Tel: +234 8038171300; E-mail: email@example.com
Table 1: Physical and chemical properties of soil of the experimental site before cropping Soil property 0-1 5 cm depth Sand (g [kg.sup.-1]) 741 Silt (g [kg.sup.-1]) 133 Clay (g [kg.sup.-1]) 126 Textural class sandy loam pH 6.5 Bulk density (Mg [m.sup.-3]) 1.41 Organic carbon (g [kg.sup.-1]) 2.89 Total N (g [kg.sup.-1]) 0.22 Available P (mg [kg.sup.-1]) 11.3 Exchangeable K (cmol [kg.sup.-1]) 0.64 Exchangeable Ca (cmol [kg.sup.-1]) 5.91 Exchangeable Mg (cmol [kg.sup.-1]) 0.82 Table 2: Effect of seedbeds on soil bulk density, water content and temperature Bulk density Seedbed (Mg [m.sup.-3]) E (a) L (b) Zero tillage 1.25b 1.26b Manual clearing 1.26b 1.28b Mound top 1.08c 1.09c Mound side 1.11c 1.13c Mound base 1.13c 1.14c Mound furrow 1.56a 1.58a Ridge top 1.08c 1.12c Ridge side 1.12c 1.13c Ridge base 1.13c 1.15c Ridge furrow 1.55a 1.58a Water content Seedbed (g [kg.sup.-1]) E L Zero tillage 102a 91a Manual clearing 100a 88a Mound top 84b 71b Mound side 85b 71b Mound base 90b 72b Mound furrow 98a 86a Ridge top 83b 68b Ridge side 85b 68b Ridge base 89b 72b Ridge furrow 98a 85a Temperature Seedbed ([degrees]C) E L Zero tillage 30.1b 31.6b Manual clearing 30.5b 32.0b Mound top 34.0a 35.5a Mound side 33.7a 35.2a Mound base 32.1ab 33.6ab Mound furrow 30.8b 32.3b Ridge top 34.2a 35.7a Ridge side 33.9a 35.4a Ridge base 33.9ab 34.4ab Ridge furrow 31.6b 33.1b * Means carrying the same letters are not significantly different (P = 0.05) according to Duncan's Multiple Range Test. (a) Early okra crop (b) Late okra crop Table 3: Effect of seedbeds on soil chemical properties (0-15 cm depth) SOC (g [kg.sup.-1]) Seedbed E (a) L (b) Zero tillage 2.74 (NS) 2.65 (NS) Manual clearing 2.71 2.58 Mound top 2.42 2.33 Mound side 2.44 2.34 Mound base 2.48 2.36 Mound furrow 1.92 1.75 Ridge top 2.43 2.34 Ridge side 2.43 2.35 Ridge base 2.46 2.36 Ridge furrow 1.88 1.73 Total N (g [kg.sup.-1]) Seedbed E L Zero tillage 0.21a 0.20a Manual clearing 0.19b 0.18b Mound top 0.17c 0.15c Mound side 0.17c 0.16c Mound base 0.17c 0.16c Mound furrow 0.15d 0.12d Ridge top 0.17c 0.16c Ridge side 0.17c 0.16c Ridge base 0.17c 0.16c Ridge furrow 0.14d 0.12d P (mg [kg.sup.-1]) Seedbed E L Zero tillage 9.1a 9.5a Manual clearing 9.0a 9.0a Mound top 9.8a 8.0b Mound side 9.5a 8.0b Mound base 9.4a 8.1b Mound furrow 7.9b 7.3c Ridge top 9.6a 8.0b Ridge side 9.6a 8.1b Ridge base 9.4a 8.1b Ridge furrow 7.8b 7.1c K (cmol [kg.sup.-1]) Seedbed E L Zero tillage 0.59a 0.55a Manual clearing 0.48b 0.41b Mound top 0.46b 0.31c Mound side 0.47b 0.33c Mound base 0.47b 0.33c Mound furrow 0.35c 0.29d Ridge top 0.47b 0.32c Ridge side 0.47b 0.33c Ridge base 0.48b 0.32c Ridge furrow 0.34c 0.28d Ca (cmol [kg.sup.-1]) Seedbed E L Zero tillage 5.13 (NS) 5.09 (NS) Manual clearing 4.86 4.57 Mound top 4.66 4.93 Mound side 4.71 4.65 Mound base 4.53 4.44 Mound furrow 3.11 3.10 Ridge top 4.72 4.69 Ridge side 4.68 4.55 Ridge base 4.77 4.65 Ridge furrow 3.20 3.18 Mg (cmol [kg.sup.-1]) Seedbed E L Zero tillage 0.67 (NS) 0.53 (NS) Manual clearing 0.71 0.57 Mound top 0.78 0.65 Mound side 0.76 0.65 Mound base 0.77 0.68 Mound furrow 0.51 0.45 Ridge top 0.76 0.65 Ridge side 0.79 0.67 Ridge base 0.80 0.69 Ridge furrow 0.49 0.39 * Means carrying the same letters are not significantly different (P = 0.05) according to Duncan's Multiple Range Test. (a) Early crop (b) Late crop Table 4: Effect of seedbeds on leaf composition of okra Seedbed N (%) P (%) E (a) L (b) E L Zero tillage 2.25 2.21 0.58 0.45 M anual clearing 2.10 2.06 0.56 0.41 M ou nd to p 1.89 1.81 0.49 0.41 Mound side 1.92 1.85 0.50 0.43 Mound base 1.95 1.87 0.49 0.42 M ound furrow 1.46 1.38 0.32 0.26 Ridge top 1.93 1.86 0.49 0.40 Ridge side 1.91 1.84 0.51 0.42 Ridge base 1.93 1.86 0.51 0.43 Ridge furrow 1.48 1.32 0.30 0.29 LSD (0.05) NS NS NS NS Seedbed K (%) Ca (%) E L E L Zero tillage 3.4 3.2 0.51 0.47 M anual clearing 3.1 2.9 0.49 0.46 M ou nd to p 2.9 2.5 0.52 0.49 Mound side 2.8 2.6 0.46 0.46 Mound base 2.9 2.8 0.49 0.47 M ound furrow 2.2 1.8 0.41 0.39 Ridge top 3.0 2.9 0.51 0.47 Ridge side 2.8 2.8 0.47 0.45 Ridge base 2.8 2.7 0.49 0.46 Ridge furrow 2.0 1.8 0.42 0.40 LSD (0.05) NS NS NS NS Seedbed Mg (%) E L Zero tillage 0.15 0.13 M anual clearing 0.15 0.12 M ou nd to p 0.15 0.13 Mound side 0.14 0.13 Mound base 0.15 0.12 M ound furrow 0.11 0.07 Ridge top 0.14 0.12 Ridge side 0.15 0.13 Ridge base 0.14 0.13 Ridge furrow 0.11 0.08 LSD (0.05) NS NS (a) Early crop (b) Late crop Table 5: Effect of seedbeds on growth and yield of okra Seedbed Plant height (cm) E (a) L (b) Zero tillage 51.44ab 60.03a Manual clearing 50.99ab 58.15a Mound to p 55.42a 48.95b Mound side 53.33a 48.57b Mound base 53.33a 46.86b Mound furrow 40.89c 35.14c Ridge top 55.46a 48.95b Ridge side 53.31a 48.66b Ridge base 53.29a 47.03b Ridge furrow 41.60c 35.12c Seedbed Leaf area ([cm.sup.2]) E L Zero tillage 134.01ab 145.68a Manual clearing 132.92ab 150.52a Mound to p 143.60a 128.43b Mound side 138.56a 128.43b Mound base 136.84a 130.59b Mound furrow 118.57c 112.33c Ridge top 143.21a 128.60b Ridge side 138.66a 126.98b Ridge base 136.38a 131.03b Ridge furrow 116.69c 114.05c Seedbed No of pods per plant E L Zero tillage 7.1NS 10.4a Manual clearing 6.8 8.8b Mound to p 7.5 8.0b Mound side 7.3 8.4b Mound base 7.4 8.6b Mound furrow 5.2 5.0c Ridge top 7.6 8.5b Ridge side 7.4 8.5b Ridge base 7.2 8.7b Ridge furrow 5.3 5.1c Seedbed Pod weight ([tha.sup.-1]) E L Zero tillage 3.38a 3.92a Manual clearing 3.35a 3.46b Mound to p 3.44a 3.33b Mound side 3.42a 3.36b Mound base 3.42a 3.34b Mound furrow 2.16b 2.09c Ridge top 3.39a 3.36b Ridge side 3.43a 3.35b Ridge base 3.40a 3.34b Ridge furrow 2.18b 2.06c * Means carrying the same letters are not significantly different (P = 0.05) according to Duncan's Multiple Range Test. (a) Early crop (b) Late crop
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|Title Annotation:||Original Article|
|Author:||Agbede, T.M.; Ologunagba, I.B.|
|Publication:||American-Eurasian Journal of Sustainable Agriculture|
|Date:||Sep 1, 2009|
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