Long-term in situ moisture conservation in horti-pasture system improves biological health of degraded land.

In situ moisture conservation practices can conserve fertile topsoil and enhance available water in soil profile. We hypothesised that reclaiming degraded land ecologically through tree + pasture + in situ moisture conservation practices would significantly improve soil organic carbon (SOC) and health. Hence, the objectives were a) to identify changes in nutrient cycling enzymes and SOC status due to different in situ soil moisture conservation options in surface and subsurface soil layers, and b) to test the potentiality of soil enzymes to determine long-term nutrient availability. We conducted a long-term experiment involving aonla (Emblica officinalis) trees + pasture (Cenchrus ciliaris + Stylosanthes seabrana) + in situ soil moisture conservation measures viz. staggered contour trenches (T1), continuous contour trenches (T2), stone mulch (T3), vegetative barriers (T4), control (T5) and fallow land (T6) since 2007. Recommended dose of nitrogen (N), phosphorus (P) and potassium (K) were added to all treatments, except T6. SOC concentration increased by ~51 and 31% in T1 and T2, respectively, over T5 in surface (0-15 cm) soil. Culturable bacterial and fungal populations increased by ~20 and 95% in T1 over T5 in surface soil. Activities of all soil enzymes increased in T1 and T2 (ranging from 42 to 289%) over T5 and T6 in both surface and sub-surface (15-30 cm) layers. However, specific activity of phenol oxidase was ~25% lower for T1 than T6, suggesting more efficient SOC sequestration in T1. Moreover, geometric mean enzyme activity of T1 was ~65 and 33% higher than T5 and T3, respectively, in surface soil. Treated soil quality index (T-SQI) of T1 was ~184% higher than T5. Soil functional diversity was also ~1.24 and 1.22 times higher in T1 and T2 than T5, respectively. Peroxidase was the major C degrading enzyme in this ecosystem. Protease, urease and phosphatase significantly influenced N and P availability along with fruit and pasture yields. Importantly, ~96, 62 and 82% variability of SOC, N and P concentrations, respectively, could be attributed to their corresponding enzyme activities. Principal components analysis (PCA) revealed one-way operational role of soil enzymes. Thus, enzymes are potentially important for recycling nutrients from litters, root biomass of fruit trees and grasses to boost their availability in the long run. Adoption of horti-pasture system combined with moisture conservation practices and staggered contour trenches or continuous contour trenches ensured higher above ground biomass yield, SOC, nutrient availability and soil quality. Thus, long-term use of these practices could be recommended for reclamation and improving soil health and crop productivity of degraded lands of central India.

Nitrogen-enriched biochar co-compost for the amelioration of degraded tropical soil.

Tropical soils are often deeply weathered and vulnerable to degradation having low pH and unfavorable Al/Fe levels, which can constrain crop production. This study aims to examine nitrogen-enriched novel biochar co-composts prepared from rice straw, maize stover, and gram residue in various mixing ratios of the biochar and their feedstock materials for the amelioration of acidic tropical soil. Three pristine biochar and six co-composts were prepared, characterized, and evaluated for improving the chemical and biological quality of the soil against a conventional lime treatment. The pH, cation exchange capacity (CEC), calcium carbonate equivalence (CCE) and nitrogen content of co-composts varied between 7.78-8.86, 25.3-30.5 cmol (p+) kg-1, 25.5-30.5%, and 0.81-1.05%, respectively. The co-compost prepared from gram residue biochar mixed with maize stover at a 1:7 dry-weight ratio showed the highest rise in soil pH and CEC, giving an identical performance with the lime treatment and significantly better effect (p < .05) than the unamended control. Agglomerates of calcite and dolomite in biochar co-composts, and surface functional groups contributed to pH neutralization and increased CEC of the amended soil. The co-composts also significantly (p < .05) increased the dehydrogenase (1.87 µg TPF g-1 soil h-1), ß-glucosidase (90 µg PNP g-1 soil h-1), and leucine amino peptidase (3.22 µmol MUC g-1 soil h-1) enzyme activities in the soil, thereby improving the soil's biological quality. The results of this study are encouraging for small-scale farmers in tropical developing countries to sustainably reutilize crop residues via biochar-based co-composting technology.

Kinetics of phosphorus and potassium release from rock phosphate and waste mica enriched compost and their effect on yield and nutrient uptake by wheat (Triticum aestivum).

An attempt was made to study the efficient use of rice straw and indigenous source of phosphorus and potassium in crop production through composting technology. Various enriched composts were prepared using rice straw, rock phosphate (RP), waste mica and bioinoculant (Aspergillus awamori) and kinetics of release of phosphorus and potassium from enriched composts and their effect on yield and nutrient uptake by wheat (Triticum aestivum) were carried out. Results showed sharp increases in release in water-soluble P and K from all the composts at 8th to 12th day of leaching, thereafter, it decreased gradually. Maximum release of water-soluble P and K were obtained in ordinary compost than enriched composts during the initial stages of leaching, but their differences narrowed down at latter stages. Data in pot experiments revealed that enriched composts performed poorly than diammonium phosphate during initial stages of crop growth, but they out yielded at the latter stages, particularly at maturity stage, as evident from their higher yield, uptake, nutrient recoveries and fertility status of P and K in soils. Moreover, enriched composts prepared with RP and waste mica along with A. awamori resulted in significantly higher biomass yield, uptake and recoveries of P and K as well as available P and K in soils than composts prepared without inoculant. Results indicated that enriched compost could be an alternate technology for the efficient management of rice straw, low-grade RP and waste mica in crop production, which could help to reduce the reliance on costly chemical fertilizers.

Rock phosphate enriched compost: an approach to improve low-grade Indian rock phosphate.

In this study, rock phosphate enriched composts (RP-compost) were prepared by mixing four low-grade Indian rock phosphates with rice straw with and without Aspergillus awamori. RP-compost had higher total P, citrate soluble P (CSP), organic P (Org.P), acid and alkaline phosphatase activities, and lower water soluble P (WSP) and microbial biomass C (MBC) than normal compost. Inoculation with A. awamori increased total P, WSP, CSP, Org.P, MBC and acid phosphatase activity. RP-compost recorded lower Olsen P at the initial period of incubation study than diammonium phosphate (DAP), but improved significantly with the progress of time. RP-compost prepared at 4% charged rate resulted in higher Olsen P throughout the incubation period compared to 2% charged rate. Similar trend were obtained with those RP-composts prepared with A. awamori. Data on pot experiment revealed higher yield and P uptake by mungbean (Vigna radiata) due to addition of RP-composts over control. The effectiveness of RP-compost ranged from 61.4% (MussoorieRP-compost) to 94.1% (PuruliaRP-compost) as that of DAP on dry matter yield and 48.8% (JhabuaRP-compost) to 83.7% (PuruliaRP-compost) on total P uptake. Enriched compost prepared at 4% charged rate recorded 15.8% and 10.6% extra yield and P uptake, respectively by mungbean over 2% charged compost. Also RP-compost inoculated with A. awamori resulted in 13.0 and 21.5% extra yield and P uptake than without A. awamori treated group. Thus, RP enriched compost could be an alternative and viable technology to utilize both low-grade RPs and rice straw efficiently.

Assessment of maturity indices of rock phosphate enriched composts using variable crop residues.

This study aimed to asses maturity indices of rock phosphate enriched composts using crop residues having variable C/N ratios. There were distinct differences in concentration of NH4+-N, NO3--N, Olsen-P and NH4OAc-K for composts generated from different crop residues, the highest being in rice straw. Water soluble P varied from 3.47-4.45% of total P, while citrate soluble P varied from 32.7-54.0% of total P. Rice straw composts showed lower C/N, WSC/Org-N and E4/E6 ratio and higher germination index indicating that they are well-matured and stabilized compost. The relative order of performance of crop residues in aggrading compost quality was chickpea stover>rice straw>mustard stover>wheat straw>tree leaves. The results demonstrated that all the enriched composts had higher contents of available nutrients and quality indices, indicating that enriched composts could be used to substitute costly chemical fertilizers for crop production.