Combined Use of Organic and Inorganic Nutrient Sources for Soil Fertility Maintenance and Replenishment

A green manure (GM) is a crop used primarily as a soil amendment and a nutrient source for subsequent crops. Green manure approaches to crop production may improve economic viability, while reducing the environmental impacts of agriculture. However, such approaches are complex because they depend on interactions between the GM, the environment, and management. We suggest that the research and management techniques developed for synthetic inputs are not adequate for effective GM use. This review provides a conceptual framework to more critically evaluate GM use, and we discuss a limited number of key examples involving GM adaptation and growth, effects on soil organic matter, N release and availability for future crops, and pest control. We explore the deficiencies in our current understanding of GM approaches and argue that economic justification of GM requires provision of multiple services (such as nutrient supply, pest and weed control, and increase of soil organic matter). We propose that future research efforts make improved use of whole systems and participatory strategies to better address both the complexity of GMbased cropping systems and the obstacles preventing farmer adoption of GM approaches. D

http://www.dzumenvis.nic.in/GM%20Crops/pdf/Green%20Manure%20Approaches%20to%20Crop.pdf

Green Manure Approaches to Crop Production: A Synthesis

Soil is a potential C sink and could offset rising atmospheric CO 2 . The capacity of soils to store and sequester C will depend on the rate of C inputs from plant productivity relative to C exports controlled by microbial decomposition. Management practices, such as no-tillage and high intensity cropping sequences, have the potential to enhance C and N sequestration in agricultural soils. An investigation was carried out to study the influence of long-term applications of fertilizers and manures on different organic C fractions in a Typic Haplustept under intensive sequence of cropping with maize–wheat–cowpea in a semi-arid sub-tropic of India. In 0–15 cm, the bulk density was lowest (1.52 Mg m −3 ) in plots treated with 100% NPK + FYM, while the control treatment showed the highest value (1.67 Mg m −3 ). Balanced application of NPK (100% NPK) showed significantly lower bulk density (1.56 Mg m −3 ) over either 100% N (1.67 Mg m −3 ) or 100% NP (1.61 Mg m −3 ) in surface soils. The application of super-optimal dose of NPK (150% NPK) showed higher total organic C (TOC) (12.9 g C kg −1 ) over either 50% NPK (9.3 g C kg −1 ) or 100% NPK (10.0 g C kg −1 ) in 0–15 cm soil layer. There was an improvement in TOC in 100% NPK or 100% NP (9.3 g C kg −1 ) over 100% N (8.7 g C kg −1 ) in the same depth. The application of FYM with 100% NPK showed 15.2, 9.9 and 5.2 g C kg −1 in 0–15, 15–30 and 30–45 cm, respectively. Application of graded doses of NPK from 50 to 150% of recommendation NPK significantly enhanced other organic C fractions like, microbial biomass C (MBC), particulate organic C (POC) and KMnO 4 oxidizable C (KMnO 4 –C) in all the three soil depths. The TOC in 0–45 cm soil depth in 150% NPK (63.5 Mg C ha −1 ) was increased by 39% over that in 50% NPK treatment (51.5 Mg C ha −1 ) and 29% over that in 100% NPK treatment (54.1 Mg C ha −1 ). Integrated use of farmyard manure with 100% NPK (100% NPK + FYM) emerged as the most efficient management system in accumulating largest amount of organic C (72.1 Mg C ha −1 ) in soil. Nevertheless, this treatment also sequestered highest amount of organic C (731 kg C ha −1  year −1 ). Particulate organic carbon, a physically protected carbon pool in soil, could well be protected in sub-surface soil layers than in surface soil layer as a means of carbon aggradations. Microbial metabolic quotient (qCO 2 ) was significantly lower in 100% NPK + FYM over other treatments to indicate this to be the most efficient manuring practice to preserve organic carbon in soil where it facilitates aggradations of more recalcitrant organic C in soil. As compared to POC, total TOC proved to be a better predictor of MBC as it strongly correlated with total carbon mineralized from soil.

Long-term manuring and fertilization effects on soil organic carbon pools in a Typic Haplustept of semi-arid sub-tropical India

Reducing emissions of greenhouse gases (GHG) from agriculture is related to increasing and protecting soil organic matter (SOM) concentration. Agricultural soils can be a significant sink for atmospheric carbon (C) through increase of the SOM concentration. The natural ecosystems such as forests or prairies, where C gains are in equilibrium with losses, lose a large fraction of the antecedent C pool upon conversion to agricultural ecosystems. Adoption of recommended management practices (RMPs) can enhance the soil organic carbon (SOC) pool to fill the large C sink capacity on the world's agricultural soils. This article collates, reviews, and synthesizes the available information on SOC sequestration by RMPs, with specific references to crop rotations and tillage practices, cover crops, ley farming and agroforestry, use of manure and biosolids, N fertilization, and precision farming and irrigation. There is a strong interaction among RMPs with regards to their effect on SOC concentration and soil quality....

http://tinread.usarb.md:8888/tinread/fulltext/lal/crop_man.pdf

Crop Management for Soil Carbon Sequestration

Soil organic matter level, mineralizable C and N, microbial biomass C and dehydrogenase, urease and alkaline phosphatase activities were studied in soils from a field experiment under a pearl millet-wheat cropping sequence receiving inorganic fertilizers and a combination of inorganic fertilizers and organic amendments for the last 11 years. The amounts of soil organic matter and mineralizable C and N increased with the application of inorganic fertilizers. However, there were greater increases of these parameters when farmyard manure, wheat straw or Sesbania bispinosa green manure was applied along with inorganic fertilizers. Microbial biomass C increased from 147 mg kg–1 soil in unfertilized soil to 423 mg kg–1 soil in soil amended with wheat straw and inorganic fertilizers. The urease and alkaline phosphatase activities of soils increased significantly with a combination of inorganic fertilizers and organic amendments. The results indicate that soil organic matter level and soil microbial activities, vital for the nutrient turnover and long-term productivity of the soil, are enhanced by use of organic amendments along with inorganic fertilizers.

Influence of inorganic fertilizers and organic amendments on soil organic matter and soil microbial properties under tropical conditions

The analysis of continuous fertilizer and manurial experiments in tropical conditions of India have shown that soil microbial biomass C and N increased with balanced fertilization. The additions of organic amendments increased microbial biomass even when the organic C content of the soil did not increase. The increase in microbial biomass was attributed to better plant growth resulting in higher rhizodeposition. The crop yields and N uptake were higher with the addition of farm yard manure or Sesbania green manure.

Organic matter-microbial biomass relationships in field experiments under tropical conditions: Effects of inorganic fertilization and organic amendments

Raghubir Singh

Papers

Organic matter-microbial biomass relationships in field experiments under tropical conditions: Effects of inorganic fertilization and organic amendments