Effects of Biochar, Phosphorus Fertilizer and Poultry Manure on Cowpea (Vigna unguiculata) Growth, YIELD and Selected Soil Properties.

The application of biochar in combination with organic and inorganic fertilizers as a means of improving soil quality and nutrient cycling may help alleviate the problem of low fertility in highly weathered soils of tropical and subtropical regions. The objective of this study was to determine the effects of biochar, phosphorus fertilizer and poultry manure applied either alone or in combination on growth and yield of cowpea (Vigna unguiculata cv blackeye) and selected soil properties. The study was conducted over two growing seasons, 2013/14 and 2014/15 on an oxisol. Treatments consisted of (i) control (ii) biochar (20 tons ha^-1) (iii) fertilizer (80 kg P ha^-1) (iv) poultry manure (10 t ha^-1) (v) biochar + fertilizer, (vi) biochar + poultry manure, arranged in a randomized complete block design and replicated three times, with cowpea as the test crop. The amendments were applied once at the beginning of the first season. At harvest, dry matter (DM), grain yield and selected soil properties (pH, aggregate stability and bulk density) were determined and subjected to analysis of variance. In 2013/14 season, grain yield ranged from 5.34 t ha^-1 (control) to 11.97 t ha^-1 (biochar + manure). Biochar, fertilizer and manure produced 14, 32 and 32% more grain yield, respectively, than the control. A combination of biochar and fertilizer produced 2.5 t ha^-1 more grain than fertilizer alone, while a combination of biochar and manure produced 4.2 t ha^-1 more grain than manure alone. In 2014/15, grain yield ranged from 0.28 t ha^-1 (control) to 1.44 t ha^-1 (biochar + manure). Biochar, fertilizer and manure produced 43, 59 and 75% more grain yield, respectively, than the control. Biochar + fertilizer and produced 0.5 t ha^-1 more grain than fertilizer alone, while biochar + manure produced 0.3 t ha^-1 more grain than manure alone. A similar trend in DM yield was observed in both seasons. There were no differences observed in the measured soil properties in the first season. The results obtained from this study clearly demonstrate that application of biochar in combination with either inorganic or organic fertilizers increased both grain and DM yield significantly than either the inorganic or organic fertilizer alone.