Pravin N. Gajbhiye

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.

Categorisation of soils based on potassium reserves and production systems: implications in K management

Crop fertilisation with potassium in rainfed agriculture in India is not practised, merely on the assumption that Indian soils are rich in potassium and crops do not need external K supply. However, under continuous cropping in rainfed regions, huge crop K removals are reported, up to 150-200 kg/ha annually, depending upon amount and distribution of rainfall and biomass production. Thus, most of the crops essentially deplete soil K reserves. The present study evaluates the soil K reserves under diverse rainfed production systems and categorises rainfed soils based on different soil K fractions. Depth-wise sampling was done from 21 locations across different soil types under 8 production systems, and various fractions of soil K were determined. Total K was highest in Inceptisols (1.60-2.28%), followed by Aridisols (1.45-1.84%), Vertisols and Vertic sub-groups (0.24-1.72%), and Alfisols and Oxisols (0.30-1.86%), showing a wide variation within each group. Nonexchangeable K reserves were found in a proportionate manner to total K in most of the soil profile. Unlike nonexchangeable K reserves, Vertisols had higher exchangeable K than Inceptisols and Alfisols/Oxisols. Nonexchageable K showed significant positive correlation with total K in Inceptisols and Vertisols, whereas it was non-significant in Alfisols/Oxisosls. However, significant positive correlations were recorded with exchangeable K and nonexchangeable K in all soil types, indicating the dynamic equilibrium between 2 soil K fractions. Nonexchangeable K reserves were included along with exchangeable K in categorising soils into 9 groups for evolving better strategies to manage soil K fertility in rainfed agriculture in India. Finger millet and groundnut crops at Bangalore and Anantapur regions (category I) need immediate attention on K nutrition, as these soils are low in both exchangeable and nonexchangeable K. Similarly, crops grown on soils of S.K. Nagar, Ballowal-Saunkri, and Rakh-Dhiansar, with low exchangeable K and medium nonexchangeable K, would need K fertilisation as these crops (maize and pearlmillet) are K-exhaustive (category II). Pearl millet and upland rice in category III and cotton in category IV need K additions at critical stages. Upland rice in category V needs a maintenance dose of K. In category VI, cereal crops may not need K additions immediately as they have medium exchangeable K and high nonexchangeable K. Long-term sorghum cropping may need K supply after few years (category VII). Soils in category VIII are adequate in nonexchangeable K and medium exchangeable K and the crops, groundnut, cotton, sorghum, and soybean, may not need external K immediately. For soils in category IX, K fertilisation is not required to the crops (sorghum and soybean) as these soils have high exchangeable and nonexchangeable K.

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.

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.

Evaluation of Sweet Orange (Citrus sinensis L. Osbeck) cv. Sathgudi Budded on Five Rootstocks for Differential Behavior in Relation to Nutrient Utilization in Alfisol

The experiment was conducted to evaluate the nutrient utilization ability of sweet orange (Citrus sinensis L. Osbeck) budded on five rootstocks (viz., Sathgudi, Rangpur lime, Cleopatra mandarin, Troyer citrange, and Trifoliate orange) in Alfisols at the experimental farm of the Citrus Improvement Project, S. V. Agricultural College Farm, Tirupati, Andhra Pradesh, India. Results of the study revealed that all the five rootstocks showed differential behaviors in terms of nutrient absorption from the soil. Rootstocks exhibited significant variation in the leaf content of potassium (K), copper (Cu), manganese (Mn), and boron (B) at all the three stages of sampling. Concentrations of the following key nutrient elements significantly varied: phosphorus (P), calcium (Ca), magnesium (Mg), zinc (Zn), and Cu at stage 1; K, Ca, Mg, Zn, iron (Fe), and Mn at stage 2; and nitrogen (N), P, Zn, Fe, and B at stage 3. The performances of rootstocks in terms of relative nutrient accumulation indices (RNAIs) were in the order of Sathgudi (1.00) > Rangpur lime (0.98) > Cleopatra mandarin (0.96) > Trifoliate orange (0.76) > Troyer citrange (0.69). The present study clearly demonstrated that citrus rootstocks employed had differential nutritional behavior and different abilities to utilize plant nutrient elements. Thus, the findings of the present study and the methodology adopted can help the horticultural breeders and nutritionists choose the best rootstock/scion combination having the desirable traits of nutrient utilization ability and also to plan effective fertilizer schedule programs for achieving greater yields.

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.

Improvement and Assessment of Soil Quality under Long-Term Conservation Agricultural Practices in Hot, Arid Tropical Aridisol

Soils in the hot, arid topical regions are low in organic matter and fertility and are structurally poor. Consequently, these soils suffer on account of poor physical, chemical, and biological soil quality traits, leading to miserably low crop yields. Long-term use of conjunctive nutrient management and conservation tillage practices may have a profound effect on improving the quality of these soils. Therefore, the objective of this study was to identify the key soil quality indicators, indices, and the best soil- and nutrient-management practices that can improve soil quality on long-term basis for enhanced productivity under a pearl millet–based system. The studies were conducted for the Hissar Centre of All-India Coordinated Research Project at the Central Research Institute for Dryland Agriculture, Hyderabad. Conjunctive nutrient-use treatments and conservation tillage significantly influenced the majority of the soil quality parameters in both the experiments. In experiment 1, the key soil quality indicators that significantly contributed to soil quality in a rainfed pearl millet–mung bean system were available nitrogen (N, 35%), available zinc (Zn; 35%), available copper (Cu; 10%), pH (10%), available potassium (K; 5%), and dehydrogenase assay (5%). The three best conjunctive nutrient-use treatments in terms of soil quality indices (SQI) were T3, 25 kg N (compost) (1.52) > T6, 15 kg N (compost) + 10 kg N (inorganic) + biofertilizer (1.49) > T5, 15 kg N (compost) + 10 kg N (green leaf manure) (1.47). In experiment 2, under a rainfed pearl millet system, the key indicators and their percentage contributions were electrical conductivity (15%), available N (19%), exchangeable magnesium (Mg; 18%), available manganese (Mn; 13%), dehydrogenase assay (19%), microbial biomass carbon (C; 5%), and bulk density (11%). The three best tillage + nutrient treatments identified from the viewpoint of soil quality were T1, conventional tillage (CT) + two intercultures (IC) + 100% N (organic source/compost) (1.74) > T3, CT + two IC + 100% N (inorganic source) (1.74) > T4, low tillage + two IC + 100% N (organic source/compost) (1.70). The findings of the present study as well as the state-of-the-art methodology adopted could be of much interest and use to the future researchers including students, land managers, state agricultural officers, growers/farmers, and all other associated stakeholders. The prediction function developed between long-term pearl millet crop yields (y) and soil quality indices (x) in this study could be of much use in predicting the crop yields with a given change in soil quality index under similar situations.

Soil Quality Assessment under Restorative Soil Management Practices in Soybean (Glycine Max) after Six Years in Semi-Arid Tropical Black Lands of Central India

ABSTRACT Vertisol soils of central India are heavy in texture, with high clay content and low organic matter. These soils are prone to degradation and the soil loss is due to poor management practices including excessive tillage. Based on a long-term study conducted for improving the quality of these soils, it was found that management practice such as low tillage (LT) + 4 t ha−1 compost + herbicide (Hb) recorded significantly higher organic carbon (OC) (6.22 g kg−1) and available N (188.5 kg ha−1) compared to conventional tillage (CT) + recommended fertilizer (RF) + off-season tillage (OT) + hand weeding (HW) (OC: 4.71 g kg−1, available nitrogen (N) (159.3 kg ha−1). Among the physical soil quality parameters, mean weight diameter (MWD) was significantly higher under LT + 4 t ha−1 straw + Hb (0.59 mm). The practice of LT + 4 t ha−1 straw + HW recorded significantly higher microbial biomass carbon (MBC) (388.8 μg g−1). The order of key indicators and their contribution towards soil quality was as follows: OC (29%) >, MBC (27%) > available zinc (Zn) (22%) > MWD (9%) > available boron (B) (8%), > dehydrogenase activity (DHA) (5%). The order of the best treatment which maintained soil quality index (SQI) values reasonably good (>1.5) was as follows: LT + 4t ha−1 compost + HW (1.65) > LT + 4 t ha−1 compost +Hb (1.60) > LT + 4t ha−1 straw + HW (1.50). Hence, these treatments could be recommended to the farmers for maintaining higher soil quality in Vertisols under soybean system. Correlation studies revealed stronger relationship between key indicators like OC (R2 = 0.627), MBC (R2 = 0.884), available Zn (R2 = 0.739) and DHA (R2 = 0.604) with Relative Soil Quality Index (RSQI). The results of the present study would be highly useful to the researchers, farmers and land managers.