K. Srinivas

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.

Soil fertility and quality assessment under tree-, crop-, and pasture-based land-use systems in a rainfed environment.

A study was conducted to assess the long‐term impact of land‐use systems on soil physicochemical properties and chemical properties (exchangeable and total nutrients) and overall chemical soil quality in a rainfed Alfisol (Typic Haplustalf) representing the semi‐arid tropical region at Hayathnagar Research Farm of the Central Research Institute for Dryland Agriculture, Hyderabad, India, situated at 17° 18′ N latitude, 78° 36′ E longitude with an elevation of 515 m above mean sea level. Four, 10‐year‐old land‐use systems were adopted for this study. Soil samples were collected from 12 soil profiles (4 systems × 3 replications) from depths of 0–0.05, 0.05–0.15, 0.15–0.30, and 0.30–0.60 m. Study revealed that physicochemical properties such as pH, electrical conductivity (EC), cation exchange capacity (CEC), and organic carbon (OC) were significantly influenced by the land‐use systems. Among the land‐use systems, agroforestry system resulted in the highest pH (7.5), CEC (13.6 cmol kg−1), and organic carbon (C) content (9.6 g kg−1). Exchangeable nutrient cations [calcium (Ca), magnesium (Mg), and sodium (Na)] and total nutrients [nitrogen (N), phosphorus (P), potassium (K), Ca, Mg, copper (Cu), manganese (Mn), zinc (Zn), and iron (Fe)] were also significantly influenced by land‐use systems. The greatest Ca content was found (7.4 c mol kg−1) in arable land system, whereas greatest Mg content (4.7 c mol kg−1) was found in the agroforestry system. Total N content was greatest (607.5 mg kg−1) in the pastoral system and decreased with soil depth. Total P content varied from 473.5 mg kg−1 in arable land to 880.0 mg kg−1 in the pastoral system and decreased with depth. The effect of land‐use systems on total hydrolyzable‐N pool was significant only up to the 0‐ to 0.15‐m soil depth. Despite being statistically nonsignificant, the agroforestry system recorded greater humic acid (12.8%) and fulvic acid (7.9%) contents than the agrihorticultural system. Chemical soil quality index (CSQI) varied from 0.76 in arable land to 0.92 in the agroforestry system. From the viewpoint of aggradation of soil chemical quality, the agroforestry system (CSQI: 0.92) was most superior, followed by the agrihorticultural system (CSQI: 0.86) and pastoral system (CSQI: 0.80).

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.

Effect of Combined Use of Organic and Inorganic Sources of Nutrients on Sunflower Yield, Soil Fertility, and Overall Soil Quality in Rainfed Alfisol

Abstract To study the response of inorganic and organic nitrogen (N) sources both alone and in conjunction and their influence on soil quality, a field experiment was conducted during kharif and rabi seasons using sunflower (MSFH‐8) as test crop. The experimental site soil was Typic Haplustalf situated at Hayatnagar Research Farm of Central Research Institute of Dryland Agriculture, Hyderabad, India, at 17° 18′ N latitude, 78° 36′ E longitude. The experiment design was a simple randomized block design with 11 treatments replicated four times. Among all the treatments, vermicompost (VC)+Fert at 25+25 kg N ha−1 recorded the highest grain yields of 1878 and 2160 kg ha−1 during both kharif and rabi seasons, respectively, which were 43.9 and 85.1% higher than their respective control plots. Apparent N recovery varied from as little as 38.30% (FYM at 50 kg N ha−1) to 62.16 (25 kg N ha−1) during kharif and 49.65 (75 kg ha−1) to 83.28% (VC+Fert at 25+25 kg N ha−1) during rabi season. Conjunctive nutrient treatments proved quite superior to other set of treatments in improving the uptake of N, phosphorus (P), potassium (K), sulfur (S), and micronutrients in sunflower and their buildup in the soil. Highest relative soil quality indexes (RSQI) were observed under VC+Fert at 25+25 kg N ha−1 (1.00) followed by VC+Gly at 25+25 kg N ha−1 (0.87). Considering the yield and relative soil quality indices (RSQI), conjunctive applications of VC with either inorganic fertilizer, FYM, or Gly at 25+25 kg N ha−1 could be a successful and sustainable soil nutrient management practice in semi‐arid tropical Alfisols. Besides this, the fertilizer N demand could be reduced up to 50%.

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.

Kinetics of Decomposition of Un‐conventional Farm‐Based Crop Residues and Their Composting and Quality Monitoring

Abstract Castor and sunflower, drought‐tolerant crops, are cultivated in the semi‐arid tropics of the world. The nutrient‐rich residues of these crops are mostly burnt because of their high C/N (C/N)‐ratios. These high C/N‐ratio residues can be composted and recycled successfully, if they are supplemented with other low C/N‐ratio farm‐based organics and some chemical additives. To study the rate kinetics and half‐life of decomposition of castor (C/N ratio: 75∶90) and sunflower (C/N ratio 57∶47) residue mixtures and the manure value of the compost thus prepared, two on‐farm experiments were conducted at Hayathnagar Research Farm (17° 18′ N latitude, 78° 36′ E longitude, and an elevation of 515 m above sea level) of Central Research Institute for Dryland Agriculture, Hyderabad, India. The decay rate constants obtained on the basis of the exponential functions using the data on weight loss, C concentration, and C/N ratios indicated that among the four combinations of treatments, castor stalks+gliricidia loppings+cattle dung had the fastest rate of decomposition with an average rate constant value of 0.0043 day−1. To achieve 50% decomposition (half‐life), the time periods computed for castor stalks+gliricidia loppings+cattle dung and sunflower stalks+gliricidia loppings+cattle were 197 and 278 days, respectively. On an average basis, sunflower‐based manure contained a significantly higher amount of total N (14.6 gm kg−1) than castor‐based manures (12.2 gm kg−1). The corresponding total hydrolyzable N values were 8.2 and 8.15 gm kg−1, respectively. Amino acid N was found to be the predominant constituent of the total acid hydrolyzable N in the manure. Use of earthworms in composting enriched the manure in terms of mineral [nitrate (NO3)+ammonium (NH4)‐N] and hexosamine‐N fractions. The full article deals with the decomposition patterns (periodical changes in weight loss, C concentration and C/N ratios), decay‐prediction functions, composting, and manure quality of the castor‐ and sunflower‐based residue mixtures.

DETERMINATION OF OPTIMUM PHOSPHORUS LEVEL FOR GRAIN SORGHUM USING EXTERNAL AND INTERNAL RESPONSE INDICATORS IN RAINFED SEMI-ARID TROPICAL ALFISOL

The productivity of sorghum, an important staple food crops in semi-arid tropics of the world, is low due to scarcity of moisture and poor soil fertility. Response of crops to phosphorus (P) application in these soils is erratic and tricky, which depends upon the available P status in soils, distribution of rainfall, adsorption and desorption capacity of soil, and overall P sink created by crop depending upon its vigor. Delineation of optimum P level for higher productivity and to avoid wastage of precious P fertilizer thus becomes inevitable. Hence, an experiment was conducted at Hayathnagar Research Farm of Central Research Institute for Dryland Agriculture, Hyderabad to i) study the external (relative grain yields, agronomic efficiency, harvest index) and internal response (fertilizer P use efficiency, P uptake harvest index) indicators of sorghum to various levels of P application, ii) development of prediction functions to arrive at optimum P dose and iii) P use - removal balance for grain sorghum for these rainfed semi-arid tropical Alfisols. Results of the study indicated that P application to sorghum in these Alfisol soils beyond 23 kg ha−1 might not be much economical and desirable. It was observed that the maximum grain yield of 87% could be achieved at a leaf P concentration of 0.39% at boot leaf or flag leaf stage and 0.30% at 50% flowering stage. The prediction functions were developed to understand the quantitative relationship between external and internal response indicators. The zero P balance (neither depletion nor excessive build up) obtained at 20 kg ha−1 level (per se near 23 kg P ha−1) indicates that this level is sufficient for sorghum crop to perform with an agronomic efficiency of 19.42 kg grain kg−1 P. The findings of this study would help in efficient use of P fertilizer for achieving desirable yield levels and will in turn reduce the expenditure on P fertilizers that are mostly imported by India and majority of other developing countries.