Categorisation of soils based on potassium reserves and production systems: implications in K management

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.

Spatial variability of potassium in agricultural soils of the canton of Fribourg, Switzerland

“…). Other studies (Rezapour et al, 2010;Srinivasarao et al, 2007;Zhang et al, 2009) have also reported significant differences of total K content among different soil types, mainly due to soil texture and soil mineralogy.…”

Assessing Soil Quality in a Semiarid Tropical Watershed Using a Geographic Information System

“…The available K in the watershed varied between 84 and 611 kg ha" . The general mind set of the region's farmers is that these soils are rich in available K; consequently, they do not apply K fertilizer (Srinivasarao et al, 2007). Long-term cultivation without any K fertilizer as well as the strong leaching process (Sun et al, 2000) might have caused deficiencies in available K (52% of samples were <280kgha"), causing a strong spatial variation within the watershed.…”

Kinetics of potassium release in sweet potato cropped soils: a case study in the highlands of Papua New Guinea

“…The NH 4 OAc-K content varied widely and ranged from 2.3 mg kg −1 to as high as 369 mg kg −1 . Non-exchangeable K in most of the samples ranged from low to medium (Srinivasarao et al, 2007;Walter et al, 2011). About 76 % of the samples were "low" (non-exchangeable K contents <300 mg kg −1 ) in the non-exchangeable K supply, while 20 % of samples were "medium" (300-600 mg kg −1 ) and only 4 % of samples were in the "high" (> 600 mg kg −1 ) category.…”

“…About 76 % of the samples were "low" (non-exchangeable K contents <300 mg kg −1 ) in the non-exchangeable K supply, while 20 % of samples were "medium" (300-600 mg kg −1 ) and only 4 % of samples were in the "high" (> 600 mg kg −1 ) category. About 40 % of samples were "low" in plant-available K (exchangeable K content below 50 mg kg −1 ), 40 % of samples were "medium" (K content of 50-125 mg kg −1 ) and only 20 % of samples were "high" (K content > 125 mg kg −1 ) in exchangeable K content (Srinivasarao et al, 2007;Walter et al, 2011).…”