Land and water are the two most vital natural resources of the world and these are under tremendous stress due to the ever increasing biotic pressure. Accelerated land degradation caused by soil erosion, waterlogging, salinization, alkalization, acidification, fertility depletion, physical and biological deterioration affecting about fifty percent of the land area, adds to the dimensions of unsustainability issues of agriculture, employment and environment. The optimal management of these resources with minimal adverse impact is, therefore, essential for development and human survival (Anon. 2000).
Coastal soils are mostly saline in nature and is caused during the process of their formation under marine influence and subsequently due to periodical inundation with tidal water, and, in case of low lands having proximity to the sea, due to the high water table with high concentration of salts in it (Rai, 2004).
A general symptom of salt injury to plants in coastal areas may be due to osmotic stress, specific ion effects, ion antagonisms, toxicities caused by ions released through cation exchange, and effects of ionic activities. In flooded soils, salt displaces K+ , Ca+, Mg+ from the exchange sites into soil solution. In wet acid sulphate soils excess water soluble iron, aluminium, hydrogen sulphide and organic substance, especially fatty acids, are common examples to affect the rice crop (Rai, 2004).
Out of about 42.1 million hectare of total rice in India, rice is the predominantly grown crop in coastal areas and West Bengal, having the largest share of coastal area, has about 90 percent of the total area under 30-90 cm depth of water and this huge rice needs endeavour to increase in productivity of this crop. In the predominantly monocropped coastal rice tract the cropping intensity in Indian East coast plain is about 134 percent. Mono or multiple rice cultivation, in vogue in several areas, impairs soil fertility greatly, declining the productivity. Small size of average operational holdings, as found in Kerala (0.36 ha) and West Bengal (0.92 ha), suggests change in the cropping system. Research focus, thus, needs to be reoriented towards an integrated planning for rice-based multiple crop planning which should be compatible with the available land and water resources for sustainable productivity (Rai, 2004).
Most of the coastal saline soils are deficient in nitrogen. Besides lesser utilization of nitrogenous fertilizer, especially in coastal areas, the mineralization of soil organic nitrogen,, and thus the release of native nitrogen to the plant available form, is also slowed down in the salt affected soils due to decrease in the population as well as activity of microbes with increase in soil salinity. The level of phosphorus in the coastal saline soils is highly variable, and depends largely on the nature and degree of salinity. Very little work has been done on the transformation and availability of P to crops in coastal saline soils. The availability of potassium largely depends on the parent material, clay minerals and weathering conditions. It also depends on the nature and amount of salts in the soil. Work done so far on the role of micronutrients in coastal saline soils is meager (Rai, 2004).
Motschenbacher et al (2011) has reported that rice production is associated with frequent cycling between anaerobic and aerobic conditions, which can lead to a greater rate of soil organic matter (SOM) decomposition, thus potentially increasing soil bulk density (BD) over time which ultimately leads to hardening of paddy soil. This problem may also be solved through impregnation of roots of legume plants in soil as it will be followed in this future research programme.
Considering such crucial soil physico-chemical conditions in coastal saline areas, natural cycling of plant nutrients through various crop rotations in rice-based cropping sequence will be carried out in the future research programme.
Review of Literature
The crop rotations with grasses and legumes cause better aggregation than cereals alone due to increased root density and increased organic carbon content in soil (Singh and Singh, 1970; Yadav and Gupta, 1977). The legumes improve aggregation not due to increase in organic matter but owing to the cementing materials produced during crop growth by association of micro-organisms with them (Rangaswamy and Ramalingam, 1961; Gupta and Sen, 1962; Ghildyal, 1969). The green manuring of clay loam with dhaincha and sunhemp and sandy loam with guar increase the percentage of water-stable aggregates (Darra et al., 1968; Havanagi and Mann, 1970; Singh et al., 1981). These cementing materials produced during growth of leguminous plants have the capacity to adsorb ions responsible for salinity of soil.
A good vegetative cover usually influences on resisting soil erosion(Weaver, 1937) and, thus, can help in restoring soil fertility. As classified by Chhabra (2002) ravine tolerant crops and grasses have greater scope in crop rotation in this proposed research programme.
•To study the physico-chemical effects of legume crop cultivation on paddy soil in a coastal saline area.
•To study the role of legume crops in rice-based cropping sequence to contain soil salinity problem in coastal area.
•To study the residual effect of enriched soil fertility status observed, if any, after legume crop on productivity of aman rice.
•To study the efficacy of numbers of leguminous plants (e.g. rabi and summer pulses, and green manure) on aman rice in a crop-rotation with regard to soil fertility and rice productivity.
Plan of Work:
Role of legume crop rotation in rice-based cropping sequence in managing soil salinity problem and in maintaining soil fertility and rice productivity in coastal alluvial soil of Gosaba in West Bengal
Fertiliser Dose for Rabi and Summer Pulses: Nil
Fertiliser Dose for Aman Rice: Nil
Four crop rotations:
T0: Aman rice followed by no leguminous crop.
T1: Rabi pulse (Khesari as paira crop) – Aman rice.
T2: Rabi pulse (Khesari as paira crop) – Summer moong – Aman rice.
T3: Rabi pulse (Khesari as paira crop) –Summer moong – Dhaincha as green manure- Aman rice.
The experiment will be repeated in the 2nd and 3rd years following the same treatments in same land.
Plot Size: 5m X 5m
1. Before 1st crop, initial soil samples will be analysed for available N, P, K, Ca, Mg, S, and DTPA – extractable Fe, Cu, Zn & Mn; and physico-chemical properties of soil like pH, ECe, CEC, ESP.
2. After harvesting of each crop soil samples will be analysed for available N, P, K, Ca, Mg, S, and DTPA – extractable Fe, Cu, Zn & Mn; and physico-chemical properties of soil like pH, ECe, CEC, ESP. ESP; and chemical analysis of harvested seeds of aman rice, Khesari and Summer moong for N, P, K, Ca, Mg, S, Fe, Cu, Zn & Mn.
3. Yield data of aman rice, Khesari and Summer moong will be recorded after harvest of each crop.
4. After each crop rotation statistical interpretation of data will be done.
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