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

207P uptake in grainPhosphorus exported in grain of soybean genotypes under lowP conditions ranged from 0.88 to 2.39 kg ha -1 at Shika, from 3.12to 5.23 kg ha -1 at Fashola, and from 1.03 to 3.68 kg ha -1 at Davié(Table 5). These values increased in response to TSP application butthe increase was less pronounced with RP application. At Shika, theincrease ranged from 16 to 181% for RP, and from 92 to 327%for TSP. The response to RP application was also lower at Davié andthe pattern of response was similar to that reported for grain yield.TGm1566 had signifi cantly more P exported in grain at both low andhigh P conditions at Shika. The response to RP across genotypes wasgenerally negligible at the other two locations, even though TGm1566gave the highest response of 24% at Fashola.VAM colonization of soybean rootsColonization of soybean roots by indigenous VAM fungi propaguleswere generally low and ranged from 19 to 25% at Shika, from 17 to28% at Fashola, and from 10 to 17% at Davié, under low P conditions.These generally low levels of colonization were further depressed byTSP but not by RP application. Variation among genotypes in VAMcolonization of roots was wide but not statistically signifi cant at any ofthe P levels and location (data not shown).Soil Olsen P contents, P fractions and pH at maize plantingIn 2002, available P (Olsen P) content (mg P kg -1 ) of soil from theprevious (2001) P treatment plots across soybean genotypes atFashola was signifi cantly higher in the TSP plots (5.27) than the RP(4.16) and 0P plots (3.57). At Davié, the mean Olsen P was highestin the previous TSP (4.65) and RP (4.18) plots, and these resultswere signifi cantly higher than in the 0P plots (3.39). Similar trendswere observed for the previous (2002) soybean plots in 2003 whereOlsen P content (mg P kg -1 soil) in TSP plots (8.96) at Shika wassignifi cant and higher than those of previous 0P (3.69) and RP plots(4.59). At Fashola, unlike in 2002, the highest mean Olsen P valuewas obtained from previous RP plots (3.98) across soybean genotypesand was signifi cant over contents in the previous 0P (3.18) and TSPplots (3.32). At Davié, the highest mean Olsen P content of 7.90 mg Pkg -1 soil from TSP plots was signifi cantly higher than the mean OlsenP contents of the 0P (4.05) and RP plots (5.11). Within a given Ptreatment, the Olsen P contents were not affected by the cultivation ofthe previous crop (maize or soybean genotypes). Similarly, comparedto maize cultivation, previous cultivation of soybean did not result insignifi cant changes in the mean soil pH and P fractions at the threelocations, irrespective of previous P source.