Department: Agricultural And Bio-resources Engineering
Nwachukwu, C. P.
Extreme climatic factors (temperature, precipitation etc) which at times lead to drought and flooding affect crop yield negatively, apart from the climatic factors, poor soil quality as a result of vehicular movement leads to compaction, compaction leads to poor root growth and this affects crop yield. There is need to evaluate the soil structure by using different soil treatments to obtain the soil physico-chemical properties.
In this study, a PVC drip irrigation was designed to investigate the effect of different soil treatments on crop yield, soil temperature and soil moisture content using maize variety, Oba super 13 as test crop. The plot was divided into 3 major plots (each plot representing different tillage method) and 27 subplots. The soil treatments involved three levels of irrigation deficit, three levels of tillage method and three levels of NPK application rate. The irrigation treatments comprised of three levels of irrigation (50% management allowable depletion, 30% management allowable depletion and 10% management allowable depletion). The tillage treatments (conventional tillage, conservative tillage and no tillage), while the NPK application treatments were (400Kg/Ha, 500Kg/Ha and 600Kg/Ha). Different irrigation parameters were evaluated for different crop growth stages, different soil treatments and different soil depths (0-25cm, 25-50, 50-75 and 75-100cm depths). Soil moisture content at seven matric potentials (-0.01MPa, -0.03MPa, -0.07MPa, -0.1MPa,, -0.2MPa, -0.5MPa and -1.5MPa) were determined for different soil levels at different tillage methods using the pressure plate apparatus. The field capacity was determined at -0.01MPa, while the permanent wilting point was determined at -1.5MPa. The least limiting water range (LLWR) was also determined for the different tillage practices using the moisture contents at; field capacity, permanent wilting, 10% air filled porosity and penetration resistance at 2MPa. For conventional tillage, the LLWR obtained for 0-25cm, 25-50cm, 50-75cm and 75-100cm depths were; 0.044, 0.062, 0.068 and 0.051cm3/cm3 respectively, for conservative tillage at 0-25cm, 25-50cm, 50-75cm and 75-100cm, 0.051, 0.055, 0.063, and 0.051cm3/cm3 respectively, while for no tillage at the four soil depths, 0.074, 0.073, 0.06 and 0.06cm3/cm3 were obtained. The crop yield for all the subplots were determined, maximum crop yield of 2540Kg/Ha was obtained at conservative tillage with 10%MAD, and 600Kg/Ha NPK application rate, while minimum tillage of 1234.67Kg/Ha was obtained at no tillage, 50%MAD and 400kg/ha NPK application rate. Controllable variables were optimised using response surface methodology (RSM) with crop yield for all the subplots, average soil moisture content for the subplots throughout the growing period and average soil temperature for the subplots throughout the growing period as the responses. The optimum values based on the run gave irrigation deficit as 11.594%, NPK application rate as 596.406Kg/Ha, best tillage method as conservative tillage, crop yield of 2543.589Kg/Ha, soil moisture content of 10.396% and soil temperature of 23.74°C. The evaluation of the optimal parameters and observed parameters gave the values of 0.86, 0.92, 0.74 and 0.26 for coefficient of determination (R2), root mean square error (RMSE), index of agreement (d) and coefficient of performance (CP1A) respectively.
The highest maize yield was obtained in conservative tillage despite the poor values of the least limiting water range. This shows that it is possible to obtain high yield in soil with poor structure by not allowing the available moisture to go beyond the upper and lower ranges of the LLWR.
It is recommended to continue with the research for more years to observe the outcome. It is also recommended to replicate the work with other test crops and different environment.