Rice residue promotes mobilisation and plant acquisition of soil phosphorus under wheat (Triticum aestivum)-rice (Oryza sativa) cropping sequence in a semi-arid Inceptisol.

Disposal of significant tonnages of rice straw is expensive, but using it to mobilise phosphorus (P) from inorganically fixed pools in the soil may add value. This study was carried out to determine whether the use of rice straw mixed with phosphorus-solubilizing microbes could solubilize a sizable portion fixed soil P and affect P transformation, silicon (Si) concentration, organic acid concentrations, and enzyme activity to increase plant growth. Depending on the soil temperature, the application of rice straw at 12 Mg ha-1 with phosphorus-solubilizing microbes could solubilize 3.4-3.6% of inorganic P, and minimised the hysteresis impact by 6-8%. At plant maturity, application of rice straw at 12 Mg ha-1 with phosphorus-solubilizing microbes and 75% of recommended P application raised the activity of dehydrogenase, alkaline phosphatase activity, cellulase, and peroxidase by 77, 65, 87, and 82% in soil, respectively. It also boosted Si concentration in the soil by 58%. Wheat grain yield was 40% and 18% higher under rice straw at 12 Mg ha-1 with phosphorus-solubilizing microbes with 75% of recommended P application than under no and 100% P application, respectively. Rice grain yield also increased significantly with the same treatment. Additionally, it increased root volume, length, and P uptake by 2.38, 1.74 and 1.62-times above control for wheat and 1.98, 1.67, and 2.06-times above control for rice, respectively. According to path analysis, P solubilisation by Si and organic acids considerably increased (18-32%) P availability in the rhizosphere. Therefore, cultivators could be advised to use rice straw at 12 Mg ha-1 with phosphorus-solubilizing microbes with 75% P of mineral P fertiliser to save 25% P fertiliser without reducing wheat and rice yield.

Enhancing cation and anion exchange capacity of rice straw biochar by chemical modification for increased plant nutrient retention.

Biochar, a potential alternative of infield crop residue burning, can prevent nutrient leaching from soil and augment soil fertility. However, pristine biochar contains low cation (CEC) and anion (AEC) exchange capacity. This study developed fourteen engineered biochar by treating a rice straw biochar (RBC-W) first separately with different CEC and AEC enhancing chemicals, and then with their combined treatments to increase CEC and AEC in the novel biochar composites. Following a screening experiment, promising engineered biochar, namely RBC-W treated with O3-HCl-FeCl3 (RBC-O-Cl), H2SO4-HNO3-HCl-FeCl3 (RBC-A-Cl), and NaOH-Fe(NO3)3(RBC-OH-Fe), underwent physicochemical characterization and soil leaching-cum nutrient retention studies. RBC-O-Cl, RBC-A-Cl, and RBC-OH-Fe recorded a spectacular rise in CEC and AEC over RBC-W. All the engineered biochar remarkably reduced the leaching of NH4+-N, NO3- -N, PO43--P and K+ from a sandy loam soil and increased retention of these nutrients. RBC-O-Cl at 4.46 g kg-1 dosage emerged as the most effective soil amendment increasing the retention of above ions by 33.7, 27.8, 15.0, and 5.74 % over a comparable dose of RBC-W. The engineered biochar could thus enhance plants' nutrient use efficiency and reduce the use of costly chemical fertilizers that are harmful to environmental quality.

Accumulation of Metals in Soils, Groundwater and Edible Parts of Crops Grown Under Long-Term Irrigation with Sewage Mixed Industrial Effluents.

Farmers in developing countries irrigate crops using raw urban and industrial effluents with consequent risks from metal contamination. Therefore, soils, crops and groundwater from an effluent irrigation use site were assessed for Cd, Cr, Ni and Pb. Total and available contents of metals in soil followed the order Pb>Ni>Cr>Cd. Crops accumulated more Pb, followed by Cd, Ni and Cr. Pb exceeded the permissible limit with wastewater irrigation only, but Cd exceeded the limit even with combined irrigations of wastewater and groundwater. Among crops, sugar beet assimilated highest Cd (3.14 µg g(-1)) and Pb (6.42 µg g(-1)) concentrations. Legumes accumulated more metals than cereals. Long-term use of wastewater and its conjunctive use with groundwater led to toxic accumulations of Cd, Pb, Ni and Cr. Cd with higher availability and mobility indices and lower toxicity limit, posed the maximum risk of food-chain contamination.

Remote sensing and geographic information system for appraisal of salt-affected soils in India.

Quantification of the nature, extent, and spatial distribution of salt-affected soils (SAS) for India and the world is essential for planning and implementing reclamation programs in a timely and cost-effective manner for sustained crop production. The national extent of SAS for India over the last four decades was assessed by conventional and remote sensing approaches using diverse methodologies and class definitions and ranged from 6.0 to 26.1 million hectares (Mha) and 1.2 to 10.1 Mha, respectively. In 1966, an area of 6 Mha under SAS was first reported using the former approach. Three national estimates, obtained using remote sensing, were reconciled using a geographic information system, resulting in an acceptable extent of 6.73 Mha. Moderately and severely salt-encrusted lands having large contiguous area have been correctly mapped, but slightly salt-encrusted land having smaller affected areas within croplands has not been accurately mapped. Recent satellite sensors (e.g., Resourcesat-1, Cartosat-2, IKONOS-II, and RISAT-2), along with improved image processing techniques integrated with terrain and other spatial data using a geographic information system, are enabling mapping at large scale. Significant variations in salt encrustation at the surface caused by soil moisture, waterlogging conditions, salt-tolerant crops, and dynamics of subsurface salts present constraints in appraisal, delineation, and mapping efforts. The article provides an overview of development, identification, characterization, and delineation of SAS, past and current national scenarios of SAS using conventional and remote sensing approaches, reconciliation of national estimates, issues of SAS mapping, and future scope.

Extraction of cadmium and tolerance of three annual cut flowers on Cd-contaminated soils.

To evaluate the production potential and Cd removal by three flower crops, viz.: marigold (Tagetes erecta), chrysanthemum (Chrysanthemum indicum) and gladiolus (Gladiolus grandiflorus), an experiment was conducted on differentially contaminated soils (DTPA-Cd 0.6-68.4 mg kg(-1)). Biotoxicity of Cd lead to reductions in growth and flower yield of marigold at DTPA-Cd >or= 7.9 mg kg(-1) soil, while the productivity of chrysanthemum and gladiolus was sustained up to 21.2 mg kg(-1). DTPA-Cd for 50% yield reduction (C(50)) was 85, 106 and 215 mg kg(-1) soil for marigold, chrysanthemum and gladiolus, respectively, that indicates a better Cd-tolerance in gladiolus. The uptake of Cd increased with contents in soils and the maximum accumulation occurred in leaves. Among the economic parts, gladiolus spikes accumulated the highest Cd (7.2) followed by flowers of marigold (6.5) and chrysanthemum (4.0 mg kg(-1)). But, because of higher biomass, the total Cd removal was the maximum with chrysanthemum (8.3) followed by gladiolus (6.0) and the minimum (2.6 mg m(-2)) with marigold. Gladiolus with highest tolerance and Cd-content in saleable part holds potential to clean up the moderately contaminated soils.