Demand-Driven Technologies for Sustainable Maize ... - IITA

200At 8 WAP, fi ve plants were randomly harvested from the two middlerows for measurements of VAM infection and total tissue N and P. Atphysiological maturity, 7 m 2 (in 2002) and 4 m 2 (in 2003) portions ofthe two middle rows were sampled for grain yield and measurementsof total N and P exported in the grain.Statistical analysisData collected on soybean genotypes were combined over 2 years foreach location and analyzed using the mixed model ANOVA procedureof SAS (Littel et al. 1996). In this model, P treatment and genotypewere considered as fi xed effects and replications as random effects.Data collected for maize in rotation were analyzed separately for eachyear, since treatments for the years were not the same. Differences inmeans were declared signifi cant at P ≤ 0.05 using the standard errorof the mean (Snedecor and Cochran 1980).ResultsPlant growth characteristicsGrain yield of soybean genotypes under low P conditions ranged from249 to 688 kg ha -1 at Shika, from 537 to 1004 kg ha -1 at Fashola, andfrom 205 to 624 kg ha -1 at Davié (Table 2). These are low, relative toaverage yield potentials previously reported (IITA 1981). Application ofTSP improved soybean growth at all locations with the highest responsesbeing recorded at Shika while the responses at Davié were smaller.Responses to RP application were, however, less pronounced and grainyields of many genotypes were not increased, especially at Fashola andDavié. Within the TSP treatments, increases in grain yield ranged from80 to 308% at Shika, from 21 to 57% at Fashola, and from 3 to 63%at Davié. Responses to RP application ranged from 9 to 152% at Shika,from –16 to 22% at Fashola, and from –13 to 28% at Davié. Overthe three sites, TGm1566 was among the soybean genotypes with thehighest yields without added P. TGm1360, TGm1215, and TGm1540were among the lowest yielding without P. TGm1566, TGm1196, andTGm1419 were in the highest yielding group when TSP was added. Thelowest yielding lines at 0P generally had the highest relative response toTSP. This inverse relationship was particularly marked at Shika, wherethe average responses to applied P was nearly 200% compared to 40%at the other sites. At Shika, TGm1293, TGm1360, and TGm1540 werethe lowest yielding at 0P and showed the largest relative response toTSP. Grain yield at 0P was a predictor of yield with TSP addition (R 2 =59.0%, P ≤ 0.002) for the yields averaged over the three sites. Figure1a shows the relationship between response to TSP and yield at 0P andwhich was highly signifi cant (R 2 = 0.63; P ≤ 0.001) but with lower, nonsignificant regression coeffi cient (R 2 = 0.028; P = 0.58) were obtained