By – Priyanka Irungbam, Dinesh Kumar, A.S. Mailappa, Arunkumar Phurailatpam and P. Debnath
Introduction
Sustainable agriculture aims to increase productivity while minimizing environmental impacts and conserving natural resources. One of the major challenges is improving nutrient use efficiency (NUE)—the ability of crops to effectively utilize available nutrients. NUE not only depends on the ability to efficiently take up the nutrient from the soil, but also on the transport, storage, mobilization, usage within the plant, and even on the environment. Nutrient use efficiency is defined as the extent to which the nutrients and management practices interact to give a specified yield level.
Legume intercropping has emerged as an eco-friendly and efficient strategy to enhance NUE by optimizing nutrient availability and utilization.Intercropping with legumes provides many benefits such as stable yields, efficient use of resources, fix atmospheric N in soil, improve soil quality, reduce crop yield variability and fortify family diets with protein and micronutrients (Layeket al., 2018)
Concept of Legume Intercropping
Legume intercropping involves growing legumes (e.g., cowpea, soybean, pigeon pea, groundnut) alongside non-legume crops such as cereals or oilseeds or in Agri-horticulture or agroforestry systems.
Common systems:
* Maize + cowpea/groundnut
* Sorghum + pigeon pea/green gram
* Wheat + chickpea/pea
* Citrus orchard + legumes
Mechanisms Enhancing Nutrient Use Efficiency
Biological Nitrogen Fixation
Legumes form symbiotic associations with Rhizobium bacteria in root nodules and convert atmospheric nitrogen into usable forms (ammonia). In an intercropping system involving a legume and a non- legume crop, part of the nitrogen fixed in the root nodules of the legume become available to the non- legume component crop. The presence of rhizospheric microflora and mycorrhiza on one species may lead to mobilization and greater availability of nutrients not only to the species concerned, but also to the associated species. It reduces the dependency on synthetic nitrogen fertilizers.
Complementary Resource Use
In intercropping, deep rooted crops are intercropped with shallow rooted crops with different time of peak nutrient demands. The shallow rooted crops extract nutrients and moisture from the upper soil layer and the crops with deep root system take up the nutrients and moisture from deeper layer of the soil as a result efficient utilization of soil nutrients and moisture is attained. It minimizes the competition for nutrients and water competition and maximizes the yield. Having deep root system, legumes can extract moisture and nutrients from deeper layer and hence does not compete with associated cereals (Das et al., 2016)
Improved Soil Fertility
Legumes produce good amount of foliage and quickly cover the soil. The foliage of leguminous plants and their deep root systems act as a good source of organic matter. Increase in the soil organic matter in turn enhancesthe soil microbial activity. This leads to improvement in nutrient cycling and availability. The higher the organic matter status, the more is the nutrient use efficiency. Decomposition of legume intercrop residues not only increase the soil organic matter but also release various plant nutrients and can correct micro nutrient deficiency. Excessive fertilizer use leads to nutrient losses, environmental pollution, and higher production costs.
Reduction in Nutrient Losses
The quick growth and better ground cover of the legumes reducessoil erosion, nutrient leaching and surface runoff. Moreover, the deep root systems of legumes bind the soil together and ensurethat more nutrients remain in the root zone.
Temporal Advantage
Temporal advantage in intercropping occurs when fast and slow growing crops are combined to utilize resources at different times, reducing competition and increasing total yield compared to sole crops. Fast-growing and short duration crops (e.g., legumes) are harvested before slow-growing, long-duration crops (e.g., maize) thus reducing resource competition.Different crops in the system can take up nutrients at different times, maximizing the overall uptake efficiency and leads to efficient nutrient utilization over time.
Weed suppression
Weeds usually absorb mineral nutrients faster than many crop plants and accumulate them in their tissues in relatively larger amounts. Nutrient removal by weeds leads to huge loss of nutrients in each crop season, which is often twice that of crop plants. For instance at early stages of maize cultivation, the weeds found to remove 9 times more of N, 10 times more of P and 7 times more of K. Moreover, in weedy fields, soil moisture may be exhausted by the time the crop reaches the fruiting stage, i.e., the peak consumptive use period of the crop, causing significant loss in crop yields. Intercropping especially with legumes helps to keep the weeds under control which otherwise would compete with the main crops for plant nutrients and moisture.
Living mulch
Mulching is the method of covering the surface of the soil with any decomposable material (grass, hay, paper, kitchen wastes, leaves, twigs, and plant residues) so that the soil is not exposed to the drying action of the sun or the desiccating action of the wind. Living mulch are plants which have good foliage cover like green gram, blackgram, groundnut, cowpea etc. They help with water conservation by preventing evaporation loss from soil, provides better infiltration and improves the water holding capacity of the soil. They also work as a temperature regulator of the soil. Mulch serves as an insulating layer for the soil so the temperature of the ground changes more slowly which enhance the nutrient use efficiency.
Advantages of Legume Intercropping
Agronomic Benefits
* Higher total productivity
* Yield stability under variable conditions
Soil Health Benefits
* Increased soil organic carbon
* Improved soil structure
Plant health benefits
* Increases the diversity or population of natural enemies
* Limits the outbreak of various pests and diseases
Economic Benefits
* Reduced fertilizer costs
* Higher net returns
Environmental Benefits
* Reduced greenhouse gas emissions
* Lower environmental pollution
Constraints and Limitations
* Competition if crops are not properly selected.
* Complex management practices.
* Difficulty in mechanization.
* Requires proper knowledge of crop combinations.
Criteria for Selection of Crops for Intercropping System
Care should be taken to select the crops with different growth habits, root growth, duration and families. The following points are to be considered while selecting crops for intercropping system.
* Tall growing crops with short growing crops.
* Bushy crops with erect growing crops.
* Fast growing crops with slow growing crops.
* Deep rooted crops with shallow rooted crops.
* Short duration crops with long duration crops.
* Legume crops with non-legume crops.
* Crops should have least allelopathic effect.
* Crops selectedshould beof differentfamilies toavoid pests and diseases.
Conclusion
Legume intercropping is a sustainable and efficient approach to enhance nutrient use efficiency in agriculture. By improving nitrogen availability, optimizing nutrient uptake, and enhancing soil health, it reduces dependency on chemical fertilizers while maintaining productivity.
The authors are College of Horticulture & Forestry, Pasighat, Arunachal Pradesh, Central Agricultural University, Imphal, Manipur