Intercropping as One Cropping Option

To reduce the risk of a crop failure in a drought year, intercropping is a common practice of resource-poor farmers in the SAT. Intercropping can be defined as simultaneously growing two or more crops, with different canopy structure and growth period, in alternating rows or sets of rows.5 Although a wide range of crop combinations are practiced in the SAT, a combination of cereals and legumes is recommended, mainly due to the

Fig. 8.1.Monthly changes in temperature, potential evaporation and precipitation at Patancheru, Hyderabad, India, 17°38'N, 78°21E.3

Fig. 8.1.Monthly changes in temperature, potential evaporation and precipitation at Patancheru, Hyderabad, India, 17°38'N, 78°21E.3

economic value of legumes, high potential yield from the cereals and favorable effects of BNF on soil fertility. Among legumes as component crops in intercropping, pigeonpea is considered to be a promising choice6 because of its:

1. Having deep rooting systems to pump water and nutrients from deep soil layers;

2. Fixing substantial amounts of N in low fertility and dry environments;

3. Contributing high quality residue that recycles N and P benefits to subsequent crops;

4. Enhancing P availability by solubiliz-ing Fe-P, which allows it to grow under low-P status soil.

The productivity of intercropping is normally expressed with a land equivalent ratio (LER), which can be obtained by summation of yield ratio of each component crop in intercropping over monocropping. Under the appropriate crop combination and row arrangement, the LER can exceed unity, which means increased land productivity over monocropping. In the case of cereal/legume intercropping, in order to increase the LER the aim should be to minimize reduction in yield of the cereal, so that any yield from the legume will bring additional benefit over monocropping.

Intercropping is a system to increase resource utilization above and below ground by growing two or more crops with different growth patterns of shoots and roots. In monocropping, there may be times during the crop growing period when aerial resources (mainly light and CO2) and soil resources (mainly water and nutrients) are not properly utilized by crops. Because all the crops in a field grow at the same rate in monocropping, the crops may not be ready to utilize the resources at the initial stage, although they are available, and too much mutual competition may take place for too little resource at the later stage. Intercropping has been extensively examined in relation to solar radiation utilization. Appropriate planting densities and row arrangements have been proposed for every possible cropping combination to minimize competition for solar radiation. When it comes to resource sharing below ground, however, little work has been done, mainly because of technical difficulties in measuring resource dynamics and root system development in soils. Intercropping should be more closely researched from this aspect to increase utilization of soil resources.

The interactions between component crops in intercropping takes place not only above ground but also below ground. In pigeonpea-sorghum intercropping, there is evidence that the presence of sorghum in neighboring rows enhances N input from biological nitrogen fixation (BNF) into pigeonpea (Fig. 8.2). This would be explained by root interaction.2 Since sorghum is very active in N uptake from soil, it depletes most of the N from soils close to pigeonpea roots when sorghum roots are developed to the pigeonpea row. Because of lowered N content in soil, inhibition of BNF by inorganic N would be relieved. This finding suggests that the N balance in the system can be improved by proper management of the cropping systems through increased input from BNF, without requiring any investment.7

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