There are several strategies to improve soil organic carbon through which soil health can be improved. Better management practices (BMPs) that enhance soil health and allow sustained agricultural productivity need to be promoted in dryland areas. Activities that promote the accumulation and supply of organic matter, such as the use of cover crops, refraining from burning, and those that reduce decomposition rates such as reduced and zero tillage, lead to an increase in the organic matter content in the soil (Sampson and Scholes, 2000).
Growing cover crops is one of the best practices for improving organic matter levels and, hence, soil quality. The term green manure is often used to indicate the same plant species that are used as cover crops. However, green manure refers specifically to a crop in the rotation grown for incorporation of the non-decomposed vegetative matter in the soil (Venkateswarlu et al. 2007). Though horse gram which is a cover crop is not an assured crop for grain production in rabi season in deficit rainfall year, it is an assured crop for biomass production (Srinivasarao et al. 2011).
Gliricidia green leaf manuring
For seed propagation, Gliricidia seeds are soaked in water for 8-10 h, preferably overnight. The soaked seeds are sown in small polythene bags filled with a mixture of red soil, sand, and farmyard manure (1:1:1) and watered regularly. Generally, 3 to 4 month-old seedlings can be planted on bunds in the rainy season. Seed propagation method is more convenient for establishing a large number of plants.
Nutrient additions through Gliricidia
Amount of Gliricidia leaf manure application depends upon the growth of boundary plantations. Usually, about 1 to 2 t ha-1 leaf manures can be applied. Application of 1 t ha-1 gliricidia leaf manure provides 21 kg N, 2.5 kg P, 18 kg K, 85 g Zn, 164 g Mn, 365 g Cu, 728 g Fe besides considerable quantities of S, Ca, Mg, B, Mo etc. The amounts of nutrients added through 2 t gliricidia ha-1 are N (42 kg), P (5 kg), K (36 kg), Zn (170 g), Mn (328g), Cu (730 g) and Fe (1456 g)
Soil health improvement using Gliricidia
Gliricidia leaf manuring improves organic matter content in the soil. Use of Gliricidia as green manure minimizes the usage of chemical fertilizers that are very expensive and also environmentally unfriendly. Gliricidia roots stabilize lands with high slopes. Gliricidia root rhizosphere soil samples showed improved organic carbon content in different depths of soil profiles. Similarly, the biological health of soil improved considerably in terms of the population of fungi, bacteria, actinomycetes, total microbial count, microbial biomass carbon and nitrogen. Improvement of soil environment in the gliricidia rhizosphere in the field bund soil could be due to the improvement of organic carbon and root activity and rhizodeposition (Srinivasarao et al.
Cover crops as green manuring (Horsegram and Dhaincha)
On-farm generation of horse gram biomass or dhaincha (Fig. 5) by using off-season rainfall showed the production of 3.03-4.28 t ha-1 yr -1 for soil incorporation (Srinivasarao et al. 2011b). Horsegram is a legume crop with a low requirement for water that quickly produces N-rich foliage. It is as a cover crop was introduced in the rainfed dryland district of Nalgonda to improve soil health and water retention. Horsegram incorporation in rainfed sorghum-sunflower and sunflower-sorghum rotations during rainy season demonstrated the restoration of degraded soils and improved crop yields. In general, mean monthly rainfall distribution at the experimental site during 1994-2003 was as follows: total annual rainfall (738mm); crop season (516mm); off season (144mm); fallow period (78mm).
Tank silt possesses high water retention capacity and acts as good source of nutrients. Analysis conducted in several tanks in Nalgonda district of Andhra Pradesh showed the potential of tank silt in supplying organic carbon and several nutrients.
As tank silt provides all of the nutrients in adequate quantities, and also improves soil health and water holding capacity essential for drought proofing in rainfed areas, it can be considered as an alternative for fertilizers, thereby contributing towards climate change mitigation. Tank silt amended at the rate of 30 t ha-1 in alternate year improved water retention capacity, carbon and nutrient status, and protected rainfed crops during intermittent droughts
Cereal-legume intercropping facilitates to maintain and improve soil fertility (Andrew, 1979). mIn this context, re- the introduction of long-term rotations intercrops and grain legumes play an important role (Karlen 1994). Cereal-legume intercropping is practised in tropical regions (Hauggaard-Nielsen et al. 2001) and rain-fed tracts of the globe (Dhima et al. 2007). Intercropping is advocated due to its benefits for yield increase, conserving soil, control of weeds, control legume root parasite infections and high-quality fodder.
Interventions like zero till maize improved yields by 13% over conventional method besides savings on water and labour (Fig. 7). The zero till maize introduced during rabi 2007 was upscaled within the cluster and outscored beyond the cluster during the year. This was systematically attempted through well-designed training and exposure visits for the farmers of the cluster. Rabi 2008 saw the zero till maize spreading to 20 farmers in Dupahad cluster.
FYM compost pits promotion
Farm Yard Manure (FYM) can be prepared by cow dung, cow urine, and waste straw and dairy waste. Cow manure is rich in humus, the bulky and fibrous material that comes from undigested plant matter. Cow manure is composted by putting it into a bin or pile and letting it decompose. It contains about 2.0% nitrogen, 0.5% phosphorous, and 1.5% potassium (Table 2). FYM compost pits were introduced in Dupahad cluster of Nalgonda district. A pit was dug (4×6×10 ft) near cattle shed above the level of the soil. The excavated soil was spread on the surface. The pit was then filled with grass and soil up to 10-15cm. Cow dung manure was then spread up to 15-20 cm and left for one to two month
Crop residues recycling
As part of integrated nutrient management, raising of glyricidia on the bunds, vermicomposting, composting, and incorporation of crop residue in soil were promoted in this cluster. Rice, sorghum, groundnut shells, pigeon pea residue were available in Dupahad cluster. In Dupahad cluster, on adding crop residues soil health parameters like organic carbon, microbial biomass carbon and particulate organic carbon were improved.
The soil organic carbon increased from 0.31 to almost 0.50 per cent after rice-wheat crop cycles, where the residue was either retained or incorporated. In addition to organic carbon, crop residues also cover a large part of nutrient requirements of crop plants. Finally, in order to refurbish soil productivity and increase the efficiency of inorganic fertilizer efficient crop residue management plays a vital role.
- Centrial institue of dryland agriculture