Sustainable Management of Soils of Dryland Ecosystems of India for Enhancing Agronomic Productivity and Sequestering Carbon

Soil organic carbon (SOC) is a strong determinant of soil quality and crop productivity, especially in the arid and semiarid environments of the tropics. Drought stress, high temperatures reaching up to 45°C for 8–10 weeks in a year, coupled with low biomass productivity are common features of dry agroecosystems. India, with only 2.5% of the world’s geographical area, is a home to 17% of the global population. Population increased from 361 million in 1951 to 1140 million in 2011, more than threefold increase over 50 years. Productivity levels of rainfed dryland crops are far below those of global average. Thus, increasing productivity of rainfed cropping systems is an urgent task to meet the food demand of an ever-increasing population because 57% of the total arable land area of 141Mha is under rainfed farming. Yields of important rainfed production systems in long-term manurial experiments under different climate and soil types show declining trends even with adoption of some recommended management practices (RMPs). Some RMPs include diverse crop rotations with legumes, and integrated nutrient management (INM) involving addition of farmyard manure (FYM), use of groundnut shells (GNS) and other crop residues (CRs), green leaf manuring (GLM), etc. These RMPs have been tested in seven long-term experiments of 13–27 years duration established in diverse soils and agroecoregions. These studies, under the auspices of the All India Coordinated Research Project on Dryland Agriculture (AICRPDA), were conducted under diverse soil and climatic conditions, viz., Anantapur and Bengaluru (Alfisol), Solapur and Indore (Vertisol), Sardar Krushinagar (Entisol), and Varanasi (Inceptisol). Seven rainfed cropping system experiments involved major crops of the region including groundnut (Arachis hypogaea), finger millet (Eleusine coracana), winter sorghum (Sorghum bicolor), pearl millet (Pennisetum glaucum), cluster bean (Cyamopsis tetragonoloba), castor (Ricinus communis), soybean (Glycine max), safflower (Carthamus tinctorius), lentil (Lens esculenta), and upland rice (Oryza sativa). Diverse nutrient management treatments assessed included cattle manure, green leaf manure, crop residues, and chemical fertilizers. Common soil fertility management treatments across seven experiments were control (no fertilizer or organics), 100% recommended dose of fertilizers (RDFs), 50% RDF+50% organics, and 100% organics. Maintaining or improving SOC concentration in rainfed dryland agroecosystems is a major agronomic challenge. Yet, the data from long-term experiments show that increasing SOC concentration by C sequestration and stabilization positively affects yields of several crops. Agronomic efficiency of added nutrients and partial factor productivity of crops are maintained or enhanced with INM practices including application of organics in conjunction with chemical fertilizers, but decline with application of only chemical fertilizers because of declining SOC concentration and soil quality with continuous cropping. In comparison with the control, grain yield of all crops are increased significantly with the adoption of INM practices using locally available organic resources. The magnitude of increase in yield (Mgha⁻¹) in respect to control is from: (1)0.78 to 1.03 in groundnut with 50% RDF+FYM4Mgha⁻¹, (2) 0.40 to 1.34 and 0.82 to 3.96 in groundnut and finger millet, respectively, through FYM10Mgha⁻¹+100% NPK in groundnut–finger millet rotation, (3) 0.84 to 3.28 in finger millet through FYM10Mgha⁻¹+100% NPK, (4) 0.61 to 1.19 in winter sorghum through 25kgNha⁻¹ (Leucaena clippings)+25kgNha⁻¹ (urea), (5) 0.43 to 0.81, 0.32 to 0.58 and 0.44 to 0.83 in pear millet, cluster bean, and castor, respectively, through 50% RDN (fertilizer)+50% RDN (FYM), (6) 1.04 to 2.10 and 0.63 to 1.49 in soybean and safflower, respectively, through FYM6Mgha⁻¹+20kgN+13kgPha⁻¹, and (7) 1.08 to 1.95 and 0.48 to 1.04 in rice and lentil, respectively, through 50% N (FYM)+50% RDF treatment. Treatments receiving INM practices also exhibited higher sustainable yield index (SYI) over unfertilized control and sole application of either chemical fertilizers or organic manures. For every Mgha⁻¹ increase in SOC stock in the root zone, there was an increase in grain yield (kgha⁻¹) of 13 for groundnut, 101 for finger millet, 90 for sorghum, 170 for pearl millet, 145 for soybean, 18 for lentil, and 160 for rice. Improved nutrient management practices were identified on the basis of the mean rate of SOC sequestration. The average SOC sequestration rate (kgCha⁻¹year⁻¹) measured with different management treatments were: (1) 570 for 50% RDF+4Mgha⁻¹ GNS, (2) 570–720 for FYM 10Mgha⁻¹+100% NPK, (3) 650 for 25kgNha⁻¹ (sorghum residue)+25kgN (Leucaena clippings), (4) 240 for 50% RDN (fertilizer)+50% RDN (FYM), (5) 790 for FYM6Mgha⁻¹+20kgN+13kg P, and (6) 320 for 100% organic (FYM). The critical level of C input requirements for maintaining SOC at the antecedent level ranged from 1 to 3.5MgCha⁻¹ year⁻¹ and differed among soil type and production system. The critical level of C input was higher in soybean system and lower in winter sorghum system and increased with increase in mean annual temperature from humid to semiarid to arid ecosystems. Thus, RMPs based on locally available organic resources are a win–win situation for improving productivity and SOC sequestration, thus advancing food security and improving the environment.