Effects of Conservation Tillage, Phosphorus and Variety on Selected Soil Physical Properties and Cowpea Productivity at Minna in Nigeria’s Southern Guinea Savanna

This study was conducted to evaluate the influence of conservation tillage, inorganic phosphorus fertilizer and variety on soil physical properties and cowpea productivity at Minna in the Southern Guinea Savanna of Nigeria. Three tillage practices (zero, reduced and ridged), three phosphorus rates (0, 30 and 60 kg P2O5 ha-1) and three cowpea varieties (IT93K-452-1, IT99K-573-1-1 and IT90K-277-2) were factorially combined and laid out in randomized complete block design with three replications. Two crops of cowpea were cultivated sequentially. Soil and crop indices used for the evaluation were soil bulk density, soil organic carbon content, mean weight diameter, soil moisture content, haulm yield and grain yield. Conservation tillage significantly affected the four soil indices while phosphorus rates significantly affected soil organic carbon content, mean weight diameter and soil moisture content. There was a varietal effect on soil organic carbon content and soil moisture content. Conservation tillage methods influenced haulm yield significantly but had no significant effect on grain yield. Phosphorus application and variety, on the other hand, significantly affected both haulm and grain yields. Notably, in the early harvest, the application of 60 kg P2O5 ha-1 raised haulm yield from 2,489 kg ha-1 (untreated control) to 5,482 kg ha-1, and grain yield from 614 kg ha-1 (untreated control) to 1,440 kg ha-1, representing 120% and 135% increments for haulm and grain yields respectively. Farmers are advised to combine either zero or reduced tillage with 60 kg P2O5 ha-1 and IT99K-573-1-1 for maximum haulm and grain yields.