Abstract
Knowledge of different potassium fractions in soils is essential for potassium management to determine long term sustainability of a cropping system. It is generally believed that our soils are not deficient in available potassium due to dominance of illitic clay mineral, therefore farmers usually skip the application of potassium in many crops. But increased cropping intensity and introduction of hybrid varieties are resulting in a considerable drain of potassium reserves and crops are becoming responsive to potassium fertilizer application. This study was conducted to monitor the changes in different fractions of soil potassium viz. water soluble, exchangeable, non exchangeable and total potassium. For this study two sites were selected from research area of Institute of Soil Chemistry and Environmental Sciences, Ayub Agricultural Research Institute, Faisalabad. In 1st long term study (since 1978) seven combinations of organic and inorganic sources were used. In 2nd study (since 1986) two sources of potassium were tested. Soil samples from these two studies were collected from 0-60 cm depth with interval of 15 cm. Results indicated that both soluble and exchangeable potassium concentration in soil decreased with depth at both sites. At 1st site range of soluble and exchangeable K was 2.5 to 10.5 mg kg-1 and 57 to 273 mg kg-1 , respectively, while in 2nd study water soluble and exchangeable K varied from 1.35 to 6.0 and 63 to 83 mg kg-1 . It is interesting to note that application of nitrogen through farm manure (FM) improved the soluble and exchangeable potassium in soil profile. Data revealed that in 1 st long term study FM showed 209% and 127% increase in soluble K, while 43% and 33% increase in exchangeable K over NP and control at 0-15 cm depth. In case of 2nd long term study muriate of potash caused 18% and 5% increase in water soluble and exchangeable K over sulphate of potash, respectively, at 0-15 cm depth. There was no consistent trend of non-exchangeable and total potassium in soil profile and among various fertilizer application sources and combinations. The study concludes that no appreciable changes were observed in potassium pools of sandy clay loam and clay loam soils under long term fertilizer application. FM application improved potassium fraction as compared to inorganic sources.
Fareeha Habib, Shahid Javid, Ifra Saleem, Shabana Ehsan, Zahid Ashfaq Ahmad. (2014) Potassium dynamics in soil under long term regimes of organic and inorganic fertilizer application, The Journal Soil & Environment , Volume 33, Issue 2.
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