GROWTH AND CORM YIELD RESPONSE OF UPLAND COCOYAM (Xanthosoma sagittifolium L) TO SAWDUST MULCH AND N P K 20 : 10 : 10 FERTILIZER RATES IN THE HUMID FOREST ZONE OF NIGERIA

Cocoyam(Xanthosoma sagittifolium (L) is the third ranking carbohydrate in Nigeria and is intensively cultivated and consumed by resource-poor farm families in Southeastern and Southwestern parts of the Country. The crop has high potential as a food security crop but yields are very low and adequate research attention is yet to be accorded the crop for increased productivity. This trial was aimed at developing a sustainable technology for increased productivity of the crop. A field trial was conducted in 2000/2001 and 2001/2002 cropping seasons at the Crop Research Farm of the University of Calabar in the humid rain forest zone of Southeastern Nigeria. The eight treatments studied were control (zero inputs), 20t/ha sawdust mulch, 200, 300 and 400 kg/ha of N P K 20:10:10 fertilizer rates applied sole and in combination with 20 t/ha sawdust mulch. A randomized complete block design (R C B) was used in three replications. The experiment showed that application of sawdust mulch and fertilizer consistently increased cocoyam yield with increasing rates of fertilizer applied. Sawdust mulch applied sole raise cocoyam yields above the control by 36% in 2000/2001 and 52% in 2001/2002. Combining sawdust mulch with any fertilizer rate resulted in significantly (p = 0.05) higher yield than when the fertilizer rate was applied sole. A combination of sawdust mulch and fertilizer applied at 200, 300 and 400 kg/ha produced higher yields by 3.4 t/ha (34%), 3.7 t/ha (29%), and 3.7 t/ha (19%) than the corresponding sole fertilizer rate in 2000/2001. Yield increases in 2001/2002 cropping were 5.7 t/ha (50%), 3.6 t/ha (26%) and 2.4 t/ha (13%) in the corresponding treatments. The highest cocoyam yields of 4.57 t/ha and 4.71 t/ha in 2000/2001 and 2001/2002 respectively were obtained by combining sawdust mulch with 400 kg/ha of N P K fertilizer. It could therefore be concluded that joint application of sawdust mulch and fertilizer is beneficial to cocoyam and farmers should combine 20 t/ha sawdust mulch with 400 kg/ha N P K fertilizer for high and sustainable productivity of cocoyam in the rain forest zone of Southeastern Nigeria.