ASSESSMENT OF SOIL BIOLOGICAL AND PHYSICO-CHEMICAL BENEFITS OF LEGUME-CEREAL ROTATION SYSTEMS IN DERIVED SAVANNA ZONE OF NIGERIA
Green house and field experiments were undertaken in this study. The green house study was done in International Institute of Tropical Agriculture (IITA), Ibadan, green house, while the field experiments were conducted in the Department of Soil Science, University of Nigeria, Teaching and Research Farm and Dominican Centre for Human Resources Development, Moniya-Ibadan Farm in 2008 and 2009 crop years. The green house study was a 2 x 3 x 2 factorial in completely randomized design (CRD), comprising of two crop rotations, three nitrogen levels and two residue management options as factors, replicated thrice to give 36 pots. In the field experiment, the design was a 4 x 2 x 2 factorial in randomized complete block design (RCBD) with four crop rotations, two nitrogen levels and two residue management options as factors and replicated three times making 48 plots. Each year involved two growing periods comprising initial growth of velvet-bean, cowpea, soybean and maize and subsequent residual growth of maize in all the plots. Soil samples at a depth of 0 to 15cm were collected at onset of the experiment and at the end of each rotation cropping for 2 years for determination of soil properties. Green house experiment had 37 samples while field experiment had 97 samples in each location. In addition, maize dry matter and grain yields were collected at the end of each rotation cropping. The difference between the grain yields of legume/cereal and maize/maize rrotations divided by the grain yield of maize/maize rotation was used to calculate rotation benefit. The soil properties and maize yields were subjected to analysis of variance (ANOVA) and stepwise regression, significantly different means were separated using Fischer’s least significant difference (f-LSD 0.05). At the end of the green house experiment, velvet-bean/maize rotation significantly (p < 0.05) increased maize yield over continuous maize by 13.59 %, nitrogen (N) benefit accounted for 4.56 % while non-N benefit accounted for 9.03 %. In 2008, in the UNN soil, the values of N (0.107 %), Ca (0.83 cmol/kg), Mg (0.59 cmol/kg), ECEC (2.86 cmol/kg) and SMBP (0.0024 %) were significantly (p < 0.05) higher in the legume rotation systems while pH (4.7) was significantly (p <0.05) higher in continuous maize. In 2009, the values for N (0.07 %), P (15.64 mg/kg), Mg (0.26 cmol/kg), SMBP (0.0007 %), Ksat (27.5 cm/hr) and AS (21.97 %) were significantly (p < 0.05) higher in legume rotations than in continuous maize. Moreso, in 2008, Moniya soils had ECEC (3.22 cmol/kg) and SMBP (0.0016 %) significantly (p < 0.05) higher in legume rotations while in 2009, SMBC (0.026 %), Pt (44.48 %) and Ksat (25.76 cm/hr) were significantly higher (p < 0.05) in legume rotations. Regression analyses showed that in Moniya, N and TVS contributed 44 % changes in dry matter while N, P and TVS contributed 74 % of the changes in grain yield in 2008. In 2009, SMBC and N contributed 62 % of the changes in dry matter and SMBC, EA and Ksat contributed 61 % of the changes in grain yield. In 2008, N and Mg UNN soil contributed 51 % of the changes in dry matter and 44 % of the changes in grain yield while in 2009, EA, MBC and Ksat contributed 57 % of the changes in dry matter and SMBC, SMBN and Ksat contributed 69 % in grain yield. Comparatively, velvet-bean/maize rotation had highest percentage rotation benefits (255 %) relative to cowpea/maize (25 %) and soybean/maize (43 %) rotations. Non-N benefits had increase in exchangeable K, Mg, available P, MBC and Ksat.
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