Ch. Srinivasarao

Release Kinetics of Nonexchangeable Potassium by Different Extractants from Soils of Varying Mineralogy and Depth

Abstract Nonexchangeable potassium (K) release kinetics of six major benchmark soil series of India as affected by mineralogy of clay and silt fractions, soil depth and extraction media was investigated. The cumulative release of nonexchangeable K was greater in smectitic soils (353 mg K kg−1 at 0‐ to 15‐cm depth and 296 mg K kg−1 at 15‐ to 30‐cm depth, averaged for 2 soils and 3 extractants) than in illitic (151 mg K kg−1 at 0‐ to 15‐cm depth and 112 mg K kg−1 at 15‐ to 30‐cm depth) and kaolinitic (194 mg K kg−1 at 0‐ to 15‐cm depth and 167 mg K kg−1 at 15‐ to 30‐cm depth) soils. Surface soils exhibited larger cumulative K release in smectitic and illitic soils, whereas subsurface soils had larger K release in kaolinitic soils. Among the extractants, 0.01 M citric acid extracted a larger amount of nonexchangeable K followed by 0.01 M CaCl2 and 0.01 M HCl. The efficiency of citric acid extractant was greater in illitic soils than in smectitic and kaolinitic soils. Release kinetics of nonexchangeable K conformed fairly well to parabolic and first‐order kinetic models. The curve pattern of parabolic diffusion model suggested diffusion controlled kinetics in all the soils, with a characteristic initial fast rate up to 7 h followed by a slower rate. Greater nonexchangeable K release rates in smectitic soils, calculated from the first‐order equation (b=91.13×10−4 h−1), suggested that the layer edge and wedge zones and swelling nature of clay facilitated the easier exchange. In contrast to smectitic soils, higher release rate constants obtained from parabolic diffusion equation (b=39.23×10−3 h−1) in illitic soils revealed that the low amount of exchangeable K on clay surface and larger amount of interlayer K allowed greater diffusion gradients, thus justifying the better fit of first‐order kinetic equation in smectitic soils and parabolic diffusion equation in illitic soils.

Phosphorus and Micronutrient Nutrition of Chickpea Genotypes in a Multi-Nutrient-Deficient Typic Ustochrept

ABSTRACT The chickpea breeding program in India has not yet considered the genotypic variation in phosphorus (P) efficiency, despite the fact that the largest proportion of chickpea-growing soils are P deficient. Since general P application to chickpea is at sub-optimum levels, efficient P-utilizing genotypes will perform better than others under P-deficient conditions. High levels of P application may induce zinc (Zn) deficiency in plants grown on Zn-deficient soils. Twenty chickpea genotypes were evaluated for their P efficiency at varied levels of added P, and the effect of P levels on Zn, iron (Fe), copper (Cu), and manganese (Mn) nutrition was studied in pot-culture experiments. Three criteria were used for evaluating P efficiency; shoot dry-matter yield without P, P-uptake efficiency (PUPE), and P-utilization efficiency (PUSE). Under P-deficiency conditions (control), the genotypes BG-256, HK-94-134, Phule-G-5, and Vikash produced the highest shoot biomass. However, genotypes that were found to be superior in the absence of P did not perform in a similar way under optimum P supply. Root dry weight showed a highly significant correlation with P uptake at all P levels. In the case of PUPE, genotypes KPG-59 and Pusa-209 were found to be superior to others. With increasing P levels, PUSE declined in all the genotypes. Increasing P up to 13.5 mg kg−1 soil increased Zn concentration, while further increase led to decreased concentration. Genotypes KPG-59, BG-256, RSG-888, and JG-315 showed Zn concentrations below the critical limit of 20 μg Zn g−1 dry weight (DW) at the high level of P application (27.0 mg kg−1). Iron concentration decreased with increasing P levels. Up to 13.5 mg kg−1 P application, Cu concentration increased and thereafter decreased. Manganese concentration gradually increased with the increasing P levels studied. Based on three criteria, BG-256 can be recommended for use in P-deficient conditions and can be good germplasm source material for chickpea-breeding programs for evolving P-efficient genotypes. Results also suggest that when selecting P-efficient genotypes of chickpea, it is essential to apply deficient micronutrients.

Soil carbon sequestration in rainfed production systems in the semiarid tropics of India

Severe soil organic carbon (SOC) depletion is a major constraint in rainfed agroecosystems in India because it directly influences soil quality, crop productivity and sustainability. The magnitude of soil organic, inorganic and total carbon stocks in the semi-arid bioclimate is estimated at 2.9, 1.9 and 4.8 Pg respectively. Sorghum, finger millet, pearl millet, maize, rice, groundnut, soybean, cotton, food legumes etc. are predominant crop production systems with a little, if any, recycling of organic matter. Data from the long term experiments on major rainfed production systems in India show that higher amount of crop residue C input (Mg/ha/y) return back to soil in soybean-safflower (3.37) system practiced in Vertisol region of central India. Long term addition of chemical fertilizer and organic amendments improved the SOC stock. For every Mg/ha increase in SOC stock in the root zone, there occurs an increase in grain yield (kg/ha) of 13, 101, 90, 170, 145, 18 and 160 for groundnut, finger millet, sorghum, pearl millet, soybean and rice, respectively. Long-term cropping without using any organic amendment and/or mineral fertilizers can severely deplete the SOC stock which is the highest in groundnut-finger millet system (0.92 Mg C/ha/y) in Alfisols. Some agroforestry systems also have a huge potential of C sequestration to the extent of 10Mg/ha/y in short rotation eucalyptus and Leucaena plantations. The critical level of C input requirements for maintaining SOC at the antecedent level ranges from 1.1 to 3.5 Mg C/ha/y and differs among soil type and production systems. National level policy interventions needed to promote sustainable use of soil and water resources include prohibiting residue burning, reducing deforestation, promoting integrated farming systems and facilitating payments for ecosystem services. A wide spread adoption of these measures can improve soil quality through increase in SOC sequestration and improvement in agronomic productivity of rainfed agroecosystems.

Conservation Agriculture and Soil Carbon Sequestration

Changes to agricultural practices in response to climate change and widespread soil degradation are being investigated to improve food security, enhance environmental conservation, and achieve sustainability. Since soil organic carbon (SOC) concentration is a strong determinant of soil physicochemical and biological activities, carbon (C) sequestration in agricultural soils requires changes to management practices. Conservation agriculture (CA)—based on minimum soil disturbance, adequate surface cover, and complex crop rotations—has been proposed as an alternative system to conventional agriculture. This chapter reviews potential impacts of CA mainly on C sequestration, collates information on the influence of tillage, integrated nutrient management (INM), fertilizers, residue management and cover crops on SOC stocks, and deliberates on the mitigation of greenhouse gas (GHG) emissions, economics, etc. by CA from existing case studies. Whether conversion to a CA system can increase C sequestration is not yet clear. More research is needed, particularly long-term research, to delineate ecological conditions suitable for adaptation in a CA system. Harshness of arid and semiarid climate exacerbates the risk of soil degradation by depleting SOC stock and increasing risks of erosion and salinization. Widespread adoption of CA can reduce the cost of farm operations including fuel consumption, while conserving soil water, improving soil functions, controlling erosion, and sustaining productivity.

Continuous Cropping, Fertilization, and Organic Manure Application Effects on Potassium in an Alfisol under Arid Conditions

Effects of continuous cropping and addition of organic manures (farmyard manure, FYM, and groundnut shells, GNS) along with inorganic fertilizers on nonexchangeable potassium (K) release kinetics in a K-deficient Alfisol were studied in a 20-year manurial experiment under arid conditions. There was a depletion in available K under continuous cropping without K input (control) as compared to other treatments such as 100% nitrogen–phosphorus–potassium (NPK), 50% NPK + 4 metric tons (MT) groundnut shells ha−1, 50% NPK + 4 MT FYM ha−1, and 100% organic (i.e., 5 MT FYM ha−1). Over 20 years of cropping without K input, available K was reduced from 155 kg ha−1 (in 1985) to 82 kg ha−1 (in 2005), showing a negative balance of 73 kg ha−1. Soil in control plots showed available K in the deficient range (<50 mg kg−1), whereas four other fertilizer and manurial treatments were greater than the critical limit. Considerable improvements in nonexchangeable K-release parameters such as step K and cumulative K release were observed in manured plots over control. Parabolic diffusion and first-order kinetic equations explained K release from soils. Potassium-release rates were drastically reduced in control plots, and there were increased release rates with continuous addition of manures. Results suggest that soils with groundnut shells or FYM (4 MT ha−1) along with 50% inorganic fertilizer additions could maintain greater K release rates after 20 years of cropping as compared to cropping without K input.

Effect of modification of tree density and geometry on intercrop yields and economic returns in leucaena-based agro-forestry systems for wood production in Andhra Pradesh, Southern India.

SUMMARY Leucaena leucocephala is cultivated at close spacings that do not permit intercropping. This has been a discouraging factor for small landholders who need regular income to establish leucaena plantations and benefit from the rapidly expanding market for wood. Therefore, on-farm experiments were conducted near Bhadrachalam, Khammam district, Andhra Pradesh, India, from August 2001 to January 2006, to study the effect of reducing tree density and modifying tree geometry on the growth of leucaena and productivity of intercrops. The inter-row spacing of 1.3 m in farmers’ practice was increased up to 13 m to examine whether wide-row planting and grouping of certain rows would facilitate extended intercropping without sacrificing wood yield. Tree density treatments tried were 1.3 × 1.3 m, 3 × 0.75 m, 3 × 1m , 5× 0.8 m and 3 × 2 m which gives densities of 5919, 4444, 3333, 2500 and 1666 trees ha −1 , respectively. Tree geometry treatments tested were 7 × 1 m paired row spacing (7 × 1 PR), 10 × 1m triple row spacing (10 × 1 TR), and 13 × 1mf our rows (13× 1 FR) with a constant tree population of 2500 trees ha −1 .C owpea (Vigna unguiculata) was the intercrop. While changes in tree density affected diameter at breast height (DBH) significantly, modification of tree geometry did not affect tree height and DBH. Marketable wood and dry biomass productivity was highest with 3 × 0.75 m spacing, and reducing tree density and alteration of tree geometry reduced the biomass considerably. In 2001, 2002 and 2003 seasons, respectively, tree spacing at 3 m produced mean yields of 97, 23 and 11% of the sole crop cowpea yield whereas modified tree geometry treatments produced mean yields of 97, 61 and 20% of sole crop yield. The widest spacing (13 × 1 FR) recorded 95, 73 and 30% of the sole crop yields during 2001, 2002 and 2003, respectively. Net returns from intercropping of leucaena in 3 × 0.75 m spacing was 36% higher than that of the farmers’ practice. Although wider tree geometry treatments recorded lower net returns, they provided higher intercrop yields and returns in the first two years of plantation establishment. Therefore, it can be concluded that in regions where annual rainfall is around 1000 mm, leucaena can be planted at a spacing of 3 × 0.75 m for improving intercrop performance, higher tree productivity and returns.

Phosphorous and Mung Bean Residue Incorporation Improve Soil Fertility and Crop Productivity in Sorghum and Mungbean-Lentil Cropping System

ABSTRACT In sorghum and mungbean – lentil cropping system, field experiments were conducted for three successive years to assess the effect of mung bean residue incorporation on sorghum and succeeding lentil productivity along with different doses of phosphorus (P; 0, 30, 60 kg ha− 1) applied to these crops. The level of soil fertility was also tested with or without incorporation of mung bean residue. The interaction of phosphorus to mungbean residue incorporation was thus studied in relation to improve crop productivity with balancing fertilizer requirements through an eco-friendly approach. Sorghum grain yield increased significantly when 60 kg P2O5 ha− 1 was applied and mungbean residue incorporated. The response was reduced to 30 kg P2O5 ha− 1 when mungbean residue was not incorporated. The succeeding lentil crop responded up to 60 kg P2O5 ha− 1 only when preceding sorghum crop received 0 or 30 kg P2O5 ha− 1. Response to applied P2O5 to lentil reduced to 30 kg ha− 1 when preceding sorghum crop received 60 kg P2O5 ha− 1 and mungbean residue incorporated. Available soil nitrogen, phosphorus, and organic carbon content increased when mungbean residue was incorporated; however, available potassium (K) of the soil decreased from its initial value.

Chlorophyll fluorescence induction kinetics and yield responses in rainfed crops with variable potassium nutrition in K deficient semi-arid alfisols.

Optimum potassium (K) nutrition in semi-arid regions may help crop plants to overcome constraints in their growth and development such as moisture stress, leading to higher productivity of rainfed crops, thus judicious K management is essential. A study was conducted to evaluate the importance of K nutrition on physiological processes like photosynthesis through chlorophyll a fluorescence and chlorophyll fluorescence induction kinetics (OJIP) of rainfed crops viz., maize (Zea mays L.), pearl millet (Pennisetum glaucum), groundnut (Arachis hypogaea), sunflower (Helianthus annuus), castor (Ricinus communis L.) and cotton (Gossypium hirsutum) under water stress conditions by studying their growth attributes, water relations, yield, K uptake and use efficiency under varied K levels. Highest chlorophyll content was observed under K60 in maize and pearl millet. Narrow and wide Chl a:b ratio was observed in castor and groundnut respectively. The fluorescence yield decreased in the crops as K dosage increased, evidenced by increasing of all points (O, J, I and P) of the OJIP curves. The fluorescence transient curve for K60 was lower than K0 and K40 for all the crops. Potassium levels altered the fluorescence induction and impaired photosynthetic systems in all the crops studied. There was no distinct trend observed in leaf water potential of crops under study. Uptake of K was high in sunflower with increased rate of K application. Quantitatively, K uptake by castor crop was lesser compared to all other crops. Our results indicate that the yield reduction under low K was due to the low capacity of the crops to translocate K from non-photosynthetic organs such as stems and petioles to upper leaves and harvested organs and this in turn influenced the capacity of the crops to produce a high economic yield per unit of K taken up thus reducing utilization efficiency of K.

Effect of Predominant Integrated Nutrient Management Practices on Soil Quality Indicators and Soil Quality Indices under Post Monsoon (Rabi) Sorghum (Sorghum Bicolor) in Rainfed Black Soils (Vertisols) of Western India

ABSTRACT A long-term study was conducted to study the impact of integrated nutrient management on soil quality in post-monsoon sorghum (Sorghum bicolor) at Solapur in Maharashtra State in Western India under All India Coordinated Research Project for Dryland Agriculture. The experiment was laid out with ten Integrated Nutrient Management Treatments in a randomized block design with three replications. The results of the study indicated that among all the integrated nutrient management treatments practiced, the application of 25 kg nitrogen (N) ha−1 through crop residue (CR) + 25 kg N ha−1 (urea) showed the highest soil quality index of 2.36, which was at par with other treatments receiving farmyard manure (FYM) and crop residues along with urea. The relative order of performance of the integrated nutrient management treatments in influencing soil quality was: T6: 25 kg N ha−1 (CR) + 25 kg N ha−1 (urea) (2.36) >T5: 25 kg N ha−1 (FYM) (2.31) > T7: 25 kg N ha−1 (FYM) +25 kg N ha−1 (urea) (2.30) = T8: 25 kg N ha−1 (CR) +25 kg N ha−1 (Leucaena loppings) (2.30) > T10: 25 kg N ha−1 (Leucaena loppings) +25 kg N ha−1 (urea) (2.17) > T4: 25 kg N ha−1 (CR:crop residues) (2.16) > T9: 25 kg N ha−1 (Leucaena loppings) (2.15) > T3: 50 kg N ha−1 (urea) (2.10) > T2: 25 kg N ha−1 (urea) (1.99) > T1: 0 kg N ha−1 (control) (1.77). The results of the study also indicated that average percent contribution of each soil key indicator towards soil quality indices was: pH (3.97%), EC (1.94%), organic carbon (18.6%), available P (2.80%), available K (6.57%), exchangeable Ca (7.02%), available S (3.45%), Available Zn (17.9%), dehydrogenase (DHA) (16.2%), microbial biomass carbon (MBC) (18.5%) and mean weight diameter (MWD) (3.14%). Thus, the results of the present study will be highly useful to the land managers in planning effective management of soil quality.

Developments in Management of Abiotic Stresses in Dryland Agriculture

Abiotic stress is one of the important consequences of climate change that will have a telling effect on crop growth and productivity in the near future. The impact of abiotic stress on crop production has emerged as a major research priority during the past decade. Several forecasts for the coming decades project increase in atmospheric CO2 and temperature and changes in precipitation, resulting in more frequent droughts and floods, cold and heat waves and other extreme events. The key aspect of sustainable development in agriculture involves resource conservation-based strategies, cropping system-based strategies and exploitation of genetic resources. Soil degradation should be prevented by practices and techniques, such as no-till sowing of crops, drip irrigation, crop rotation and leaving land fallow. Suitable farming systems that have potential to increase food production and promote soil conservation for each agroecological zones should be identified. Holistic land management and soil health restoration are also one of the key aspects of suitable development towards managing food security. In addition, maintenance of soil life and soil quality through practices such as organic fertilizer supplementation and judicious use of chemical fertilizers and pesticides should be a priority. Judicious management of water on a watershed basis should be undertaken to make maximum use of available water. Biotechnological improvement of crops and evolution of crop varieties suitable for climate change also form the key for sustainable development. Tapping of genetic resources to identify varieties and new crops that can adapt and cope with climate risk also forms a key approach in sustainable development to tackle the problem of food security. Adaptation to climate change requires long-term investments in strategic research and new policy initiatives that put climate change adaptation in planning. A comprehensive understanding of abiotic stress, especially the mechanism and tolerance aspects for adaptation strategies, across the full range of warming scenarios and regions is essential for preparing for climate change. Therefore, a judicious mixture of basic and applied research outlooks has been presented on developments in management of abiotic stresses in dryland agriculture.