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

216maize-after-soybean plots over those of the corresponding maize-aftermaizeplots ranged from –29 to 141% across the P treatments in threelocations. However, only the total P in grain of maize-after-soybeangenotype TGm0944 (7.94 kg ha -1 ) within the 15P plot, and maizeafter-soybeangenotypes TGm1251 (6.40 kg ha -1 ) and TGm1540(6.24 kg ha -1 ) within previous TSP plots at Shika were signifi cantlyhigher than that of maize-after-maize plots. This was also the case fordifferences between maize-after-soybean genotype TGm1540 (18.50kg ha -1 ) within 15P plots, maize-after-soybean TGm1420 (17.19 kgha -1 ) within the previous RP plots at Davié, and their correspondingmaize-after-maize plots.DiscussionThe results of this study have revealed that the promiscuous soybeangenotypes used differ considerably in P nutrition under low and highP conditions and responses to P application could be large, dependingon the location and soil biophysical conditions. In a varietal screeningstudy at Fashola, AbdelGadir (1998) observed variations amongpromiscuous soybean genotypes in selected growth parameters inresponse to P application. The high grain yields and the correspondinghigh P uptake of the genotype TG×1456-2E may suggest animprovement in agronomic traits over most of the TGm accessions.Also, previous analysis of the genotypes for P use, and P responseeffi ciency revealed that, unlike the other genotypes, TG×1456-2E andTGm1566 demonstrated a high low-P use and P response effi ciencyunder low and high conditions, which was consistent across thelocations (Table 2). This may suggest that an unconscious selectionfor P effi ciency (low or applied P) had occurred during breeding andselection for increased grain yield.Vanlauwe et al. (2000) reported a site-specifi c response to RP intwo herbaceous legumes in the northern Guinea savanna of Nigeriabut the application of RP in our study had limited effects on growthand grain yield enhancement on the soybean genotypes. This maysuggest poor use of RP as a P source by the soybean genotypes dueto low Ca requirements and uptake (Bekele et al. 1983), or limitedsoybean rhizosphere-induced dissolution of RP (Kamh et al. 2002).However, certain genotypes demonstrated the capacity to use RPbetter than the others (Table 2) and this may be related to variations inroot morphology among soybean genotypes and architecture (Ohwakiand Hirata 1992) or other mechanisms (Bekele et al. 1983; Kamh etal. 2002) and needs to be further examined.In West Africa, farmers’ adoption of technology is linked to foodand cash for the household and the dissemination of grain legumes is