Response of maize grain and stover yields to tillage and different soil fertility management practices in the Semi-Deciduous Forest Zone of Ghana

A thesis presented to the Department of Crop and Soil Sciences, Faculty of Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfilment of the requirements for the award of the degree of Doctor of Philosophy in Soil Science

A study was carried out using runoff plots and Decision Support System for Agrotechnology Transfer (DSSAT) Crop Simulation Model to identify appropriate site-specific soil management practices which best conserve soil, nutrients and water for increased and sustainable maize production. The 4-season experiment (2012 major, 2013 major and minor and 2014 major seasons) was a factorial in Randomized Complete Block Design (RCBD) arranged in a split plot with 3 replications. The tillage treatments (main plot) comprised no-till (NT), hoe tillage (HT), plough-plant (PP) and plough-harrow-plant (PHP) whilst that of the soil amendments (sub-plot) were control (no amendment), 100 % NPK fertilizer (15-15-15) at recommended rate, 3 t/ha poultry manure (PM) and 50 % rate of PM + 50 % rate of NPK fertilizer. The annual rainfall erosivity over a 10-year period which was calculated using the Modified Fournier Index (MFI) revealed a high erosion risk (559.24 MJ. mm/(ha.h.y)) in the study area. The erodibility of PP plots was found to be significantly lower (P<0.05) (0.018 Mg.ha.h/(ha.MJ.mm)) than that of NT (0.024 Mg.ha.h/(ha.MJ.mm)). Runoff ranged from 12.57 to 23.95 mm for NT and Bare, respectively. Predicted and measured soil loss was least under NT (0.14 and 1.14 Mg/ha) and highest on Bare plots (4.00 and 20.88 Mg/ha). NT with the greatest erodibility values, resulted in low soil loss due to effective cover management practices. Reduction in soil depth and water holding capacity followed the similar trend as soil loss. Bulk density decreased immediately after land preparation but increased by the end of the cropping season under PP, PHP and HT whilst under NT it decreased. Total porosity under the different tillage practices were sensitive to increases in bulk density in the order of HT>PP>PHP>NT. NT recorded higher cumulative infiltration amount (2358 mm), sorptivity (103.38 mm/s ½ ) and steady state infiltrability (0.7 mm/sec) and the least cumulative infiltration amount (834 mm), sorptivity (25.88 mm/s ½ ) and steady state infiltrability (0.3 mm/sec) under HT. Ks ranged from 4.93 to 12.75 cm/h in the order of PHP > HT > NT > PP but the highest (17.04 cm/h) was obtained under adjacent fallow field. Ks was highest under 100 % PM (9.75 cm/h) and least under 100 % NPK (4.32 cm/h) in the order of 100% PM >50 % rate of PM + 50 % rate of NPK fertilizer> 100% NPK. The enhanced Ks under the iv combined 50 % rates of NPK and PM (i.e. [2.16 + 4.88 = 7.04] cm/h) was considered an additive effect (7.32 cm/h). The highest soil moisture storage was recorded under NT and PP. Over the three seasons of experimentation, stover and grain yield, differed among the various tillage and soil fertility amendments and their combinations. Stover yield under the tillage practices ranged from 4.19 to 5.39 Mg/ha for HT and NT whilst that of the soil fertility amendments ranged from 4.22 to 5.22 Mg/ha for control and 100 % NPK, respectively. Maize grain yield under the tillage practices ranged from 1.25 to 1.55 Mg/ha in the decreasing order of HT>NT>PP>PHP and that of the soil fertility amendments ranged from 1.19 to 1.52 Mg/ha in a decreasing order of 100 % NPK>50 % rate of PM + 50 % rate of NPK fertilizer>100 % PM>Control. The low grain yield observed during the study was due to the incidence of long dry spells and moisture stress during critical stages of crop growth. The response of grain yield to different soil managements was best when the different tillage systems especially NT and PP were amended with combination of 50 % rate of PM + 50 % rate of NPK fertilizer. WUE followed the same trend observed for above-ground dry matter and grain yield. N, P and K uptake was better under PP and NT for maize biomass and HT for maize grain than the other tillage treatments. Uptake was better under 100 % PM and 100 % NPK for maize biomass and 50 % rate of PM + 50 % rate of NPK fertilizer and 100 % NPK for maize grain. The recommended choice of tillage practices coupled with the combination of NPK and poultry manure amendments for sustainable maize production in smallholder farms was in a decreasing order of NT>PP>PHP>HT. NT with proper residue management and plough-plant amended with combination of NPK and poultry manure, enhanced soil physical properties and reduced soil loss. The DSSAT-CSM can satisfactorily be used to predict maize yield under changing climatic conditions and has provided a menu of sustainable climate–smart soil management options in the study area.

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