PHOSPHORUS DYNAMICS IN RASULPUR SOIL SERIES (TYPIC CAMBORTHID) UNDER RICE BASED CROPPING SYSTEM

O. U. Rehman, S. M. Mehdi *, M. Sarfraz* M. A. Shakir*, and G. Shabir*

*Soil and Water Conservation Research Station Fatehjang, Attock
**Soil Salinity Research Institute, Pindi Bhattian
Corresponding Author E-mail: drobaidtmn@yahoo.com

ABSTRACT

Phosphorus (P) nutrition of the rice cropping system is very important due to alternate wetting and drying cycles. A field experiment was conducted on a sandy loam soil (Typic Camborthid) to observe residual effect of P on succeeding crops and rate of P depletion after one crop rotation (wheat- sorghum fodder-rice). Rice was raised as second crop on the residual P after sorghum fodder, grown after wheat.  Analysis of variance (ANOVA) technique under RCBD was used and Duncan’s multiple range test (DMR) was applied to see the significance of difference among treatment means. Maximum residual P after sorghum fodder was 13.10 mg kg-1, considered quite sufficient for rice crop.  The significantly higher yield of paddy (2.83 Mg ha-1) and straw (2.96 Mg ha-1) was found where residual P was 10.65 mg kg-1 soil. Maximum P concentration (0.15 %) in paddy was found at highest residual P level while in straw it was maximum (0.10 %) where residual P was 10.65 mg kg-1 soil. Similar trend was found in case of P uptake i.e. it was significantly higher in paddy (4.22 Kg ha-1) at highest residual P level and straw (3.05 Kg ha-1) where residual P was 10.65 mg kg-1 while total P uptake was maximum (7.20 kg ha-1) at highest residual P level. Maximum Olsen- P (8.70 mg kg-1) was found after harvest of rice crop where maximum P was applied to wheat. Level of P depletion at the end of three crops was found to be 0.004 mg kg-1 annum-1 where P was applied at 13.76 mg kg-1 soil and this depletion was promoted where no NPK was applied and further deterioration was noticed where only NK was applied without P. However at the higher rates of P application, there was no net P depletion It may be concluded from this study that phosphatic fertilizers be recommended and applied to the crops by taking P adsorption capacities into the account and P application should be soil and crop specific as the solution P and Olsen P vary with varying soils and crops. The residual P upto 13.1 mg Kg-1 can support 2 to 3 succeeding crops in loose textured soils and soils are being mined annum-1 @ 0.138 mg P kg-1 if no fertilizers are applied @ 0.149 mg P kg-1 if only NK are applied in light textured soils under rice cropping system.
Key words: P decline rate, phosphorus, residual effect, rice, Typic Camborthid.