干旱区生态环境知识资源中心

The status of available macronutrients [phosphorus (P) and potassium (K)] and soil organic carbon (SOC) of the surface soil under a rice-wheat cropping system was studied in 40 districts of the Indo-Gangetic Plains (IGP) of India. The soil samples were collected from the farmers’ fields in four transects (Trans-, Upper, Middle, and Lower Gangetic Plains) of the IGP. The selection of farmers, villages, blocks, and districts within an agro-climatic zone (ACZ) was done on the basis of a multistage statistical approach. The available macronutrients were characterized as low, medium, and high. In Trans-Gangetic Plains, SOC, available P, and available K were in the ranges of 0.06-0.86%, 6.7-85.1 kg ha(-1), and 50-347 kg ha(-1), respectively. In Upper Gangetic Plains, the respective values were in the ranges of 0.05-2.55%, 4.5-155.0 kg ha(-1), and 45 to 560 kg ha(-1). Similarly, in Middle Gangetic Plains, these values were in the ranges of 0.04-2.01%, 4.7-183.7 kg ha(-1), and 72-554 kg ha(-1), respectively. In Lower Gangetic Plains, respective values were 0.12-1.78%, 2.2-112.0 kg ha(-1), and 83-553 kg ha(-1). In Trans-Gangetic plains, the majority of the soils in the midplains ACZ representing intensively cultivated rice-wheat system area were low to medium in SOC and available P, whereas available K status was medium to high. Irrespective of the agroclimatic variations, more than 90% of the soils were low to medium in SOC and available P with a marginal deficiency of K. The majority of the coarse-textured soils in Shiwaliks were found to have low to medium SOC and available P, whereas less intensively cultivated arid zone soils were high in SOC, available P, and available K. In Upper and Middle Gangetic Plains, the majority of the soils tested medium for SOC and medium to high in available P and K. The dominance of medium status of available P in these soils could be due to mining of soil P by the rice-wheat cropping system practiced in these regions for more than 300 years. In Lower Gangetic Plains, the SOC was medium to high in most of the soils, whereas available P and K were high. Recent introduction of the rice-wheat system on intensive scale in these traditionally rice-growing areas resulted in less mining of SOC, P, and K.