G. R. Korwar

Evaluation of long-term soil management practices using key indicators and soil quality indices in a semi-arid tropical Alfisol

Alfisol soils of rainfed semi-arid tropics (SAT) are degrading due to several physical, chemical, and biological constraints. Appropriate soil-nutrient management practices may help to check further soil degradation. A long-term experiment comprising tillage and conjunctive nutrient use treatments under a sorghum (Sorghum bicolor (L.) Moench)–mung bean (Vigna radiata (L.) Wilkzec) system was conducted during 1998–05 on SAT Alfisols (Typic Haplustalf) at the Central Research Institute for Dryland Agriculture, Hyderabad. The study evaluated soil and nutrient management treatments for their long-term influence on soil quality using key indicators and soil quality indices (SQI). Of the 21 soil quality parameters considered for study, easily oxidisable N (KMnO4 oxidisable-N), DTPA extractable Zn and Cu, microbial biomass carbon (MBC), mean weight diameter (MWD) of soil aggregates, and hydraulic conductivity (HC) played a major role in influencing the soil quality and were designated as the key indicators of ‘soil quality’ for this system. The SQI obtained by the integration of key indicators varied from 0.66 (unamended control) to 0.83 (4 Mg compost + 20 kg N as urea) under conventional tillage (CT), and from 0.66 (control) to 0.89 (4 Mg compost + 2 Mg gliricidia loppings) under reduced tillage (RT). Tillage did not influence the SQI, whereas the conjunctive nutrient-use treatments had a significant effect. On an average, under both CT and RT, the sole organic treatment improved the soil quality by 31.8% over the control. The conjunctive nutrient-use treatments improved soil quality by 24.2–27.2%, and the sole inorganic treatment by 18.2% over the control. Statistically, the treatments improved soil quality in the following order: 4 Mg compost + 2 Mg gliricidia loppings > 2 Mg Gliricidia loppings + 20 kg N as urea = 4 Mg compost + 20 kg N as urea > 40 kg N as urea. The percentage contribution of the key indicators towards the SQI was: MBC (28.5%), available N (28.6%), DTPA-Zn (25.3%), DTPA-Cu (8.6%), HC (6.1%), and MWD (2.9%). The functions predicting the changes in yield and sustainability yield index with a given change in SQI were also determined.

Influence of Tillage and Nutrient Sources on Yield Sustainability and Soil Quality under Sorghum–Mung Bean System in Rainfed Semi‐arid Tropics

The crop production in rainfed semi‐arid tropical (SAT) Alfisols is constrained by low soil organic matter, poor soil fertility, soil structural infirmities, and scarce moisture availability. To offset some of these constraints, a long‐term study of tillage [conventional (CT) and reduced (RT)] and conjunctive nutrient‐use treatments was conducted in SAT Alfisol at Hyderabad, India, under sorghum–mung bean system. The order of performance of the treatments in increasing the sorghum yield was 2 Mg gliricidia loppings + 20 kg nitrogen (N) through urea (T4) (93.2%) > 4 Mg compost + 20 kg N through urea (T3) (88.7%) > 40 kg N through urea (T2) (88.5%) > 4 Mg compost + 2 Mg gliricidia loppings (T5) (82.2%). In the case of mung bean, where half as much N was applied as was to the sorghum, the order of performance of the treatments in increasing the grain yields was T3 (63.6%) >T5 (60.3%) >T4 (58.0%) >T2 (49.6%). Tillage significantly influenced the hydraulic conductivity only, whereas the conjunctive nutrient‐use treatments significantly influenced the predominant physical, chemical, and biological soil‐quality parameters. Among the conjunctive nutrient‐use treatments, T5 was found to be superior in influencing the majority of the soil‐quality parameters and increased the organic carbon by 21.6%, available N by 24.5%, dehydrogenase activity by 56.1%, microbial biomass carbon by 38.8%, labile carbon by 20.3%, and microbial biomass nitrogen by 38.8% over the unamended control and proved superior most in improving soil quality.

Effect of Soil and Nutrient-Management Treatments on Soil Quality Indices under Cotton-Based Production System in Rainfed Semi-arid Tropical Vertisol

Rainfed semi-arid tropical Vertisols of the Indian subcontinent encounter many problems on account of the physical, chemical, and biological soil qualities and consequently have poor crop yields. To ensure sustainable crop production, there is a need to improve and periodically assess the quality of these soils by adopting suitable soil and nutrient-management practices on a long-term basis. Hence, soil quality assessment studies were conducted at the Central Research Institute for Dryland Agriculture, Hyderabad, India, by adopting an ongoing long-term experiment from Akola Centre (Maharashtra) of All-India Coordinated Research Project for Dryland Agriculture (AICRPDA) for the rainfed Vertisol. This long-term experiment was initiated in 1987 with six soil and nutrient management treatments: T1, control; T2, 50 kg nitrogen (N) + 25 kg phosphorus pentoxide (P2O5) ha−1; T3, 25 kg N ha−1 through leuceana; T4, 25 kg N ha−1 through farmyard manure (FYM); T5, 25 kg N + 25 kg P2O5 + 25 kg N ha−1 through FYM; and T6, 25 kg P2O5 ha−1 + 50 kg N ha−1 through leuceana under cotton + greengram intercropping (1:1). Out of the 19 soil quality parameters studied, significant influence of the soil and nutrient-management treatments was observed on almost all the parameters except exchangeable calcium (Ca), available iron (Fe), labile carbon (LC), and bulk density (BD). A standard methodology using principal component analysis (PCA) and linear scoring technique (LST) was adopted to identify the key indicators and for computation of soil quality indices. The various key soil quality indicators identified for these Vertisols under cotton + green gram system were pH, electrical conductivity (EC), organic carbon (OC), available K, exchangeable magnesium (Mg), dehydrogenase assay (DHA), and microbial biomass carbon (MBC). The soil quality indices as influenced by different long-term soil and nutrient-management treatments varied from 1.46 to 2.10. Among the treatments, the conjunctive use of 25 kg P2O5 ha−1 + 50 kg N ha−1 through leuceana green biomass (T6) maintained significantly higher soil quality index with a value of 2.10 followed by use of 25 kg N + 25 kg P2O5 + 25 kg N ha−1 through FYM (T5) (2.01). The order of percent contribution of these identified indicators to soil quality indices was OC (28%) > MBC (25%) > available K (24%) > EC (7%) > pH (6%) = DHA (6%) > exchangeable Mg (4%). Thus, the findings of the present study could be of immense use to the researchers, land managers, farmers, nongovernment organizations (NGOs) and other stakeholders for making periodical assessment of key indicators of soil quality, identifying the best soil and nutrient-management treatments and practices, and planning for improving soil quality to achieve higher productivity goals on a sustainable basis in rainfed semi-arid tropical Vertisol regions. The methodology of the study could also be useful for other rainfed semi-arid tropical Vertisol regions of the world.

Influence of fly ash mixtures on early tree growth and physicochemical properties of soil in semi-arid tropical Alfisols

The beneficial effects of planting mixtures comprising of fly ash at the rate of 66%, 33% and 17% by soil volume were assessed for the early growth of two economic tree species, teak (Tectona grandis) and leucaena (Leucaena leucocephala) in rainfed Semi-Arid Tropical (SAT) Alfisols in India. Measurements of tree growth were made at six monthly intervals over a 3-year period. Fly ash at 66% by soil volume of the planting pit significantly increased the diameter of teak at breast height (dbh). In leucaena, application of fly ash at 17% by soil volume was found to be effective in increasing dbh during most of the study period. Changes in soil physicochemical properties (bulk density, water retention at 0.033 and 1.5 MPa, profile moisture content, pH, soluble salt content and organic carbon) were simultaneously studied. Among these soil properties, plant available water (PAW) and organic carbon (OC) contents explained variations in diameter at breast height (dbh) in teak during most of the sampling period, while none of the soil properties significantly explained dbh in leucaena. The highest dose of fly ash applied (66% by volume) decreased bulk density (BD) and increased PAW in teak and to an extent in leucaena during the first 2 years of tree growth. Higher profile moisture content was noted in pits treated with 66% fly ash during the dry period of November (after the end of seasonal rainfall which occurred from June to October) during the first and second year after application.

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.

Strategies for Improving the Productivity of Rainfed Farms in India with Special Emphasis on Soil Quality Improvement

Rainfed agriculture encounters several constraints on account of climatic, edaphic, and social factors. Out of the 97 million farm holdings, about 76% come under marginal and small categories. The productivity levels of these areas have remained lower across years because of frequent droughts occurring due to high variability in the quantum and distribution of rainfall, poor soil health, low fertilizer use, imbalanced fertilization, small farm size and poor mechanization, poor socio-economic conditions and low risk-bearing capacity, low credit availability and infrastructure constraints. Consequently, farmers are distracted from agriculture and tend to migrate to cities to look for alternative jobs. Hence, there is a great need to increase the productivity of rainfed crops and overall net returns to keep the farmers in agriculture. A paradigm shift in rainfed agriculture can be expected through technological thrusts and policy changes. The strategies that need to be emphasized include: (i) land care and soil-quality improvement through conservation agricultural practices, balanced fertilization, harnessing the potential of biofertilizers and microorganisms, and carbon sequestration; (ii) efficient crops, cropping systems, and best plant types; (iii) management of land and water on watershed basis; (iv) adoption of a farming-systems approach by diversifying enterprises with high-income modules; (v) mechanization for timely agricultural operations and precision agricultural approach; (vi) post-harvest, cold-storage, value-addition modules; (vii) assured employment and wage system; (viii) organic farming; (ix) rehabilitation of rainfed wastelands; (x) policy changes and other support system; and (xi) human-resource development, training and consultancy. This paper deals in depth with some of these issues and strategies.

Response of Sunflower to Sources and Levels of Sulfur under Rainfed Semi‐arid Tropical Conditions

Sulfur (S) is one of the severely limited nutrients in rainfed semi‐arid tropical Alfisols. Its application plays an important role in improving the yield and quality of oilseed crops. To identify the optimum level of sulfur for greater yield and oil content in the sunflower crop (MSFH‐8) through suitable sources, a field experiment involving varying levels of S through two sources (gypsum and elemental S) in combination with standard levels of nitrogen (N) and phosphorus (P) was conducted on a sandy loam soil (Typic Haplustalf) at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad, situated at an altitude of 515 m above mean sea level and on 78° 36′ E longitude and 17° 18′ N latitude. The response to S application in sunflower crop in terms of growth parameters, yield components, nutrient uptake, and seed oil content was conspicuous. The application of graded levels of sulfur at rates of 20, 40, and 60 kg ha−1 applied through elemental S significantly increased the seed yield of the sunflower crop over the control by 5.4, 10.7, and 18.1% respectively, whereas the corresponding increases in case of gypsum (CaSO4·2H2O) were 25.1, 28.8, and 33.9% respectively. The greatest seed yield of sunflower (1175 kg ha−1) and percentage oil content (39.7%) was obtained with 60 kg S ha−1 through gypsum under rainfed conditions. Our study clearly indicated that the application of S at relatively high levels significantly increased the uptake of N, P, and S. The percentage oil content in seed recorded a positive and highly significant relationship with the uptake of N (r = 0.958**), P (r = 0.967**), and S (r = 0.951**), signifying the importance of balanced nutrition in influencing the oil content of seed in sunflower. The application of S through gypsum at rate of 60 kg S ha−1 along with 40 kg N and 30 kg P2O5 ha−1 was most superior in enhancing the seed yield and percentage oil content in seed.

Effects of Soil Management Practices on Key Soil Quality Indicators and Indices in Pearl Millet (Pennisetum americanum (L.) Leeke)–Based System in Hot Semi-arid Inceptisols

Rainfed Inceptisol soils, despite their agricultural potential, pose serious problems, including soil erosion, low fertility, nutrient imbalance, and low soil organic matter, and ultimately lead to poor soil quality. To address these constraints, two long-term experiments were initiated to study conservation agricultural practices, comprising conventional and low tillage as well as conjunctive use of organic and inorganic sources of nutrients in Inceptisol soils of Agra center of the All-India Coordinated Research Project for Dryland Agriculture (AICRPDA). The first experiment included tillage and nutrient-management practices, whereas the second studied only conjunctive nutrient-management practices. Both used pearl millet (Pennisetum americanum (L.) Linn) as test crop. These experiments were adopted for soil quality assessment studies at 4 and 8 years after their completion, respectively, at the Central Research Institute for Dryland Agriculture (CRIDA), Hyderabad, India. Soil quality assessment was done by identifying the key indicators using principal component analysis (PCA), linear scoring technique (LST), soil quality indices (SQI), and relative soil quality indices (RSQI). Results revealed that most of the soil quality parameters were significantly influenced by the management treatments in both the experiments. In experiment 1, soil quality indices varied from 0.86 to 1.08 across the treatments. Tillage as well as the nutrient-management treatments played a significant role in influencing the SQI. Among the tillage practices, low tillage with one interculture + weedicide application resulted in a greater soil quality index (0.98) followed by conventional tillage + one interculture (0.94), which was at par with low tillage + one interculture (0.93). Among the nutrient-management treatments, application of 100% organic sources of nutrients gave the greatest SQI of 1.05, whereas the other two practices of 50% nitrogen (N) (organic) + 50% (inorganic source) (0.92) and 100% N (inorganic source) (0.88) were statistically at par with each other. The various parameters that emerged as key soil quality indicators along with their percentage contributions toward SQI were organic carbon (17%), exchangeable calcium (Ca) (10%), available zinc (Zn) (9%), available copper (Cu) (6%), dehydrogenase assay (6%), microbial biomass carbon (25%) and mean weight diameter of soil aggregates (27%). In experiment 2, SQI varied from 2.33 to 3.47, and 50% urea + 50% farmyard manure (FYM) showed the greatest SQI of 3.47, which was at par with 100% RDF + 25 kg zinc sulfate (ZnSO4) (3.20). Under this set of treatments, the key soil quality indicators and their contributions to SQI were organic carbon (19%), available N (20%), exchangeable Ca (3%), available Zn (4%) and Cu (17%), labile carbon (20%), and mean weight diameter of soil aggregates (17%). The quantitative relationship established in this study between mean pearl millet yields (Y) and RSQI irrespective of the management treatments for both the experiments together could be quite useful to predict the yield quantitatively with respect to a given change in soil quality for these rainfed Inceptisols. The methodology used in this study is not only useful to these Inceptisols but can also be used for varying soil types, climate, and associated conditions elsewhere in the world.

Effects of Conjunctive Use of Organic and Inorganic Sources of Nutrients on Soil Quality Indicators and Soil Quality Index in Sole Maize, Maize + Soybean, and Sole Soybean Cropping Systems in Hot Semi-arid Tropical Vertisol

The soils in the hot semi-arid tropical (SAT) regions generally have low organic matter and nutrient reserves. Soil-management problems in these soils primarily occur because of poor physical conditions and inadequate drainage through excess runoff, finally resulting in poor crop growth. Hence, the present investigation was conducted to study the long-term impact of conjunctive nutrient use treatments on soil quality indicators and soil quality indices under three cropping systems: (i) sole soybean, (ii) soybean + maize, and (iii) sole maize cropping systems at the Indore Centre of the All-India Coordinated Research Project for Dryland Agriculture (AICRPDA) using Navjot and JS-335 as cultivars of maize and soybean, respectively. In 2005, the soil quality assessment study under this experiment was undertaken after 8 years of experimentation. Soil quality assessment was done by identifying the key indicators using principal component analysis (PCA) and linear scoring technique (LST). Soil quality indices (SQI) and relative soil quality indices (RSQI) were also computed. Results revealed that most of the soil quality parameters were significantly influenced by the conjunctive nutrient management treatments. The common key indicators that emerged in all the treatments were pH, organic carbon (OC), exchangeable magnesium (Mg), available zinc (Zn), copper (Cu), manganese (Mn), and boron (B). The soil quality indices across the management treatments under sole maize system varied from 1.70 to 2.40 and application of 20 kg nitrogen (N) (compost) + 20 kg N through urea as top dressing emerged as a one of the most superior treatments with SQI value of 2.40. The soil quality indices in maize + soybean system varied from 1.12 to 1.47 and application of 20 kg N (compost) + 20 kg N through urea + azotobacter at 2 kg ha−1 proved to be significant with the greatest SQI value of 1.47. In the case of the sole soybean system, the SQI varied from 1.21 to 1.61. After considering all the systems together, the average best performance SQI score (ABP-SQI score) was computed, which varied from 1.14 to 1.56. The greatest value was recorded in the treatment with 20 kg N (compost) + 20 kg N (gliricidia) + 10 kg N (urea). The quantitative relationship developed in this study between mean soybean and maize yields (Y) and RSQI values (X), irrespective of the management treatments, could be quite useful to predict the yield quantitatively with respect to a given change in key indicators for these rainfed Vertisols.

EFFECT OF LONG-TERM USE OF TILLAGE, RESIDUES AND N LEVELS IN SORGHUM ( SORGHUM VULGARE (L)) – CASTOR ( RICINUS COMMUNIS ) CROPPING SYSTEM UNDER RAINFED CONDITIONS – CROP RESPONSES AND ECONOMIC PERFORMANCE – PART I

This experiment was conducted to study the long-term effect of soil management treatments on crop yields, sustainability yield indices (SYI) and soil fertility in rainfed semi-arid tropical Alfisol at Hayathnagar Research Farm, Hyderabad, India, during the period 1995 to 2009. The experiment was conducted in a split–split plot design with conventional tillage (CT) and minimum tillage (MT) as main factors, surface application of sorghum stover @ 2 t ha −1 (SS), fresh Gliricidia loppings @ 2 t ha −1 (GL) and ‘no’ residue (NR) as sub-factors and levels of N viz. 0 (N 0 ), 30 (N 30 ), 60 (N 60 ) and 90 (N 90 ) kg N ha −1 as sub–sub factors in a castor–sorghum two-year rotation. On an average, CT maintained 30.4 and 57.0% higher grain yields of sorghum and castor, respectively, over MT. Between two residues, GL performed well in both the crops. The highest yields of sorghum (1425 kg ha −1 ) and castor (876 kg ha −1 ) were recorded at 90 kg N ha −1 . CT maintained higher SYI of 0.44 compared to MT (0.38) and higher agronomic efficiency (AE) of 13.5 and 6.76 kg grain kg −1 N for sorghum and castor crop, respectively. Use of crop residue as mulch had an advantage in increasing the yield of both the crops with increase in rainfall under CT even without N application (control), probably by making the soil more receptive to water infiltration, better moisture storage and by reducing the evaporative losses. Using response functions, the optimum fertilizer N requirement was also computed for a given set of tillage and residue combinations. The revised optimum fertilizer N doses for sorghum and castor varied from 45 to 56 kg ha −1 and 46 to 74 kg ha −1 , respectively, under different tillage and residue combinations and could be recommended depending upon the soil management practices.