Direct and Residual Effect of Phosphorous Sources and Manures on Yield and Nutrient Uptake by Rice in Alfisol

Field experiments were conducted to study direct and residual effect of P-sources and organic manures on rice. Green leaf manuring increased the yield and nutrient uptake by rice. The increase in grain yield with the addition of GLM + URP @ 60 kg P 2 O 5 ha -1 over URP @ 60 kg P 2 O 5 ha -1 were 31 per cent in the fertilized plots and 27.9 per cent in the residual plots. Combined application of GLM and P @ 60 kg P 2 O 5 ha -1 irrespective of the P source increased the nutrient uptake by rice. A drastic reduction of value : cost ratio at higher level of fertilizer P application, irrespective of the P sources was recorded. The additional expenditure on incorporation of poultry manure was the highest which dropped the value : cost ratio considerably.


Materials and Methods
Field experiments were conducted to evaluate the direct and residual efficiency of P sources along with organic manures with rice as test crop.(Kharif season-I crop; Rabi season-II crop -residual crop).As per the treatment schedule, P at three levels viz.,0,30 and 60 kg P2O5 ha -1 was added through two P sources viz., single super phosphate (SSP) and Udaipur rock phosphate (URP) with or without organic manures viz., FYM, poultry manure and green leaf manure (GLM) @ 12.5 t ha -1 .Treatment combinations were triplicated and the design of the experiment was factorial RBD.The experiment was conducted in Madukkur soil series (Alfisol).The grain and straw yields were recorded.To study the residual effect, original layout was maintained without disturbance and second crop of rice was raised as residual crop in rabi season.In the triacid digest of plant samples, N, P and K were determined by microkjeldhal method (Bremner, 1965), Vanadomolybdate yellow colour method (Jackson, 1973) and flame photometric method (Stanford and English, 1949) respectively.The value-cost ratio (VCR) worked out from the value of increased yield due to the incorporation of organic manures and the additional expenditure on incorporation of organic manures.

Results and Discussion
The initial soil was sandy clay loam in texture (clay 23%, silt 9% and sand 67%), neutral in soil reaction(pH 7.3),non-saline(EC : 0.24 dSm -1 ) and had a CEC of 22.2 c mol (p+) kg -1 soil.The organic carbon content of the soil was 0.48% with initial available N of 146 kg ha -1 , available P of 9.50 kg ha -1 and K of 250 kg ha -1 .
Among the organic manures studied, green leaf manuring increased the grain yield (Table 2).The decomposing green leaf manuring release organic acids and CO2, both tending to lower the soil pH and raise solubility of calcium phosphate (Singh, 1984).This increased P availability which in turn increased the dry matter production, P uptake and thus grain yield.These findings corroborates with the results of Hundal et al. (1992).
Application of SSP has recorded the highest grain yield compared to URP.The grain yield (5.51t ha -1 ) recorded in the treatment that received SSP @ 60 kg ha -1 was significantly higher than the yield *Corresponding author email: kaleeswari@tnau.ac.in  (4.90 t ha -1 ) recorded due to the application of SSP @ 30 kg ha -1 (Table 1).This could be due to the fact that the readily available P in SSP has favoured better absorption of P as evidenced by higher P uptake by grain and straw as compared to slowly available P sources like URP.This is in accordance with the findings of Rani Perumal et al. (1994).
In the residual plots, increase in grain yield due to the incorporation of GLM over no manured plots was 31.1 per cent.This indicates that the incorporation of GLM alone resulted in higher yield and supplementation of P fertilizers either in the form of URP or SSP exhibited an additive effect.The residual effect of organic manures on rice grain yield in rice-rice cropping sequence was reported by Ladha et al., 2000.Green leaf manuring increased the N, P and K uptake by grain.Application of P through SSP   (Chutia et al. 1998 ;Yadvinder singh et al, 2004).Irrespective of the P sources, the highest nutrient uptake was registered at 60 kg P2O5 ha -1 as compared with that of 30 kg P2O5 ha -1 .
A drastic reduction in VCR was observed at higher level of fertilizer P application.The additional expenditure on incorporation of poultry manure was the highest which dropped the VCR considerably.(Table .3)Combined application of organic manure + SSP / URP @ 60 kg P2O5 ha -1 although increased the grain yield higher than the application of organic manure + SSP / URP @ 30 kg P2O5 ha -1 it was not an economic increase.Hence, combined application of GLM @ 12.5 t ha -1 + SSP /URP@ 30 kg P2O5 ha -1 can be applied for rice monoculture under wetland ecosystem to save the fertilizer P bill.

Table 3 . Calculated value :cost ratio (VCR) and additional return per hectare to the incorporation of organic manures
SSP: Single Super Phosphate; URP: Udaipur Rock Phosphate favoured higher nutrient uptake by grain (Table.1).