Balance sheet of soil nitrogen and phosphorus vis-a-vis soybean productivity under different levels and sources of phosphorus and plant growth regulators in sub-humid Rajasthan

Abstract

An experiment was conducted at Udaipur during kharif seasons of 2009 and 2010 on soybean crop involving 27 treatments i. e. three levels (20, 30 and 40 kg P2O5/ ha) and three sources (single super phosphate or SSP, phosphorus rich organic manure or PROM and di-ammonium phosphate or DAP) of phosphorus in main plots and three plant growth regulators or PGRs (water spray, benzyl adenine 50 ppm and NAA 100 ppm) in sub-plots of a split plot design having three replications. Results revealed that 40 kg P2O5/ha, SSP and NAA recorded a pooled grain and stover yields of 25.95 and 37.37, 25.12 and 36.23, and 24.23 and 35.73 q/ha, respectively, which were not only maximum but also significantly superior to their respective counter treatments. Higher soybean productivity recorded in 40 kg P2O5/ha, SSP and NAA treatments linked with considerably higher mean uptake of nitrogen and P2O5 which were 243.96 and 24.79; 228.10 and 24.52 and 229.90 and 23.44 kg/ha, respectively. Data on actual soil nitrogen status after crop harvest or E values (kg/ha) showed that among different levels of phosphorus, mean N ranged from 269.52 at 20 kg P2O5 to 298.24 at 40 kg P2O5/ha, while mean P2O5 varied between 23.41 at 20 kg P2O5 and 25.99 at 40 kg P2O5/ha. Among different phosphorus sources, the order of mean E values (kg/ha) for N were PROM (294.93)>DAP (281.69)>SSP (275.98) but order for mean E P2O5 values was SSP (26.09)>PROM (24.33)>DAP (24.31). Among PGRs, the order for mean E values of N and P2O5 (kg/ha) was NAA (286.47 and 25.00)>benzyl adenine (284.64 and 24.79)>water spray (281.48 and 24.39). Data on actual mean gain or loss (G=E–initial soil nutrient status) of N showed that different levels and sources of phosphorus as well as PGRs recorded a negative balance ranging from -2.94 kg/ha at 40 kg P2O5/ha to -31.67 kg/ha at 20 kg P2O5/ha. Contrary to N, different levels and sources of phosphorus as well as PGRs recorded a positive balance in mean G values (kg/ha) that for various P2O5 levels ranged from 0.25 at 20 kg P2O5/ha to 2.83 at 40 kg P2O5/ha; for different phosphorus sources between 0.99 in DAP to 2.56 in SSP and between 1.63 in benzyl adenine to 1.84 in NAA among PGRs evaluated in this study.