Categorisation of soils based on potassium reserves and production systems: implications in K management
Ch. Srinivasarao A D , K. P. R. Vittal B , K. N. Tiwari C , P. N. Gajbhiye B and Sumanta Kundu AA Global Theme Agroecosystems, International Crops Research Institute for Semi Arid Tropics (ICRISAT), Patancheru 502 324, Andhra Pradesh, India.
B Central Research Institute for Dryland Agriculture, Santoshnagar, Hyderabad 500059, Andhra Pradesh, India.
C Potash and Phosphate Institute of Canada, India Programme, Gurgaon 122017, Haryana, India.
D Corresponding author. Email: s.cherukumalli@cgiar.org
Australian Journal of Soil Research 45(6) 438-447 https://doi.org/10.1071/SR07024
Submitted: 8 February 2007 Accepted: 20 August 2007 Published: 20 September 2007
Abstract
Crop fertilisation with potassium in rainfed agriculture in India is not practised, merely on the assumption that Indian soils are rich in potassium and crops do not need external K supply. However, under continuous cropping in rainfed regions, huge crop K removals are reported, up to 150–200 kg/ha annually, depending upon amount and distribution of rainfall and biomass production. Thus, most of the crops essentially deplete soil K reserves. The present study evaluates the soil K reserves under diverse rainfed production systems and categorises rainfed soils based on different soil K fractions. Depth-wise sampling was done from 21 locations across different soil types under 8 production systems, and various fractions of soil K were determined. Total K was highest in Inceptisols (1.60–2.28%), followed by Aridisols (1.45–1.84%), Vertisols and Vertic sub-groups (0.24–1.72%), and Alfisols and Oxisols (0.30–1.86%), showing a wide variation within each group. Nonexchangeable K reserves were found in a proportionate manner to total K in most of the soil profile. Unlike nonexchangeable K reserves, Vertisols had higher exchangeable K than Inceptisols and Alfisols/Oxisols. Nonexchageable K showed significant positive correlation with total K in Inceptisols and Vertisols, whereas it was non-significant in Alfisols/Oxisosls. However, significant positive correlations were recorded with exchangeable K and nonexchangeable K in all soil types, indicating the dynamic equilibrium between 2 soil K fractions.
Nonexchangeable K reserves were included along with exchangeable K in categorising soils into 9 groups for evolving better strategies to manage soil K fertility in rainfed agriculture in India. Finger millet and groundnut crops at Bangalore and Anantapur regions (category I) need immediate attention on K nutrition, as these soils are low in both exchangeable and nonexchangeable K. Similarly, crops grown on soils of S.K. Nagar, Ballowal-Saunkri, and Rakh-Dhiansar, with low exchangeable K and medium nonexchangeable K, would need K fertilisation as these crops (maize and pearlmillet) are K-exhaustive (category II). Pearl millet and upland rice in category III and cotton in category IV need K additions at critical stages. Upland rice in category V needs a maintenance dose of K. In category VI, cereal crops may not need K additions immediately as they have medium exchangeable K and high nonexchangeable K. Long-term sorghum cropping may need K supply after few years (category VII). Soils in category VIII are adequate in nonexchangeable K and medium exchangeable K and the crops, groundnut, cotton, sorghum, and soybean, may not need external K immediately. For soils in category IX, K fertilisation is not required to the crops (sorghum and soybean) as these soils have high exchangeable and nonexchangeable K.
Additional keywords: soil potassium reserves, nonexchangeable K, rainfed regions, soil categorisation.
Acknowledgments
The authors are thankful to chief scientists of various All India Coordinated Research Project on Dryland Agriculture centres for helping in soil sampling and Potash and Phosphate Institute of Canada – India Programme for supporting this research. Authors are thankful to Mr Rama Mohan for helping in preparing Fig. 1.
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