Direct and residual effect of nitrophosphates of varying water solubility on crop yield and olsen-P in a typic haplustept

In a long-term experiment (in progress at PAU research farm since 1994) on a Typic Haplustept involving potato-sunflower-pearl millet sequence; three differentially water-soluble P carriers [DAP (18:46:0), ANP (20:20:0) and Suphala (15:15:15)] were applied at five rates (0, 30, 60, 90 & 120 kg P2O5 ha⁻¹) to potato crop and the succeeding crops (sunflower & pearl millet) were raised on residual P. Surface (0–15 cm) and the sub-surface (15–30, 30–45, 45–60, 60–90 & 90–120 cm) soil samples were collected after the harvest of each crop from 60 and 120 kg P2O5 ha⁻¹ treatment plots, to study Olsen-P distribution and accumulation in soil profile. Potato tuber yield increased significantly up to 60 kg P2O5 ha⁻¹. Olsen-P content generally decreased with depth but the decrease was nonsignificant beyond 45 cm depth. The highest values of Olsen-P in the profile were observed with Suphala followed by ANP and the least with DAP. The three fertilizers used, however, did not differ significantly as far as yield, P uptake and P accumulation were concerned. Less than one-third (33%) of added P to potato crop was accumulated as Olsen-P in the surface (0–15 cm) layer and the accumulation decreased with depth. Nearly 61% of the total Olsen-P in the profile accumulated in the upper 30 cm layer with 60 kg P₂O₅ ha⁻¹ application rate while for 120 kg P₂O₅ ha⁻¹ rate, 58% was accumulated in the upper 45 cm. This indicates that translocation of Olsen-P increased with increase in rate of P application.