Intercropping

Santalla M, De Ron AM, Escribano MR (1994) Effect of intercropping bush bean populations with maize on agronomic traits and their implications for selection. Field Crop Res 36 185-189... 

Keywords Allelopathy Cover crops Crop residues Intercropping Mulching Organic farming Weeds... 

Allelopathic interactions of plants can provide weed control by (a) use of allelopathic crops as cover crops, mulches or green manure, (b) use of allelopathic plants in crop rotations, (c) crop mixtures and intercropping, (d) varieties with strong allelopathic potential, and (e) use of allelopathic crop water extracts and other agents. 

Fig. 14.3 One of the most common examples of intercropping - oat with red clover (Trifolium pratense L.). Oat provides early competition with weeds while the clover is established the clover blocking out light to the soil the oat also takes up excess nitrogen that would otherwise stimulate the weed growth... 

Intercropping is most successful when the two crops have the complementary growth and resource needs, e.g., Italian ryegrass (L. multiflorum Lam.) was too competitive with the timothy grass (Phleum pratense L.), therefore it should not be recommended as a companion crop for timothy establishment (Jefferson et al. 2000). 

Intercropping may facilitate weed control if intercrops are more weed competitive than sole crops or are able to suppress weed growth through allelopathy (the weed species is more susceptible to such phytotoxin than crops). If intercrops do not suppress weeds more than sole crops, they should provide yield advantages due to better utilization of resources or by converting resources than in case of sole crops (Liebman and Dyck 1993). 

An example, when intercropping suppressed the weed growth more than sole, is a leek (Allium ampeloprasum var. porrum (L.) J.Gay) - celery (Apium graveo-lens L.) intercrop sown in a row-by-row layout decreased relative soil cover of weeds by 41%, reduced the density and biomass of groundsel (Senecio vulgaris L.) by 58% and 98%, respectively, and increased the total crop yield by 10% (Baumann et al. 2000). Increased weed suppression and the crop yield were also demonstrated in cereal-legume intercrops in many different environments (Ofori et al. 1987). 

The main disadvantages of intercropping are competition between crops possible damage of the other crop during the harvest of one crop component complication of mechanization and cultivation decrease of symbiotic nitrogen fixation in legumes caused by plant competition for resources (Soon et al. 2004). 

Intercropping with trap or catch crop against parasitic plants is often practiced in resource-poor regions but as parasitic plants it has considerable success. This approach is more effective than use of pesticides, cheap and environmentally... 

Cowpea (Vigna unguiculata (L.) Walp.), green gram (Vigna radiata (L.) Wilczek), crotalaria (Crotalaria ochroleuca G. Don), sweet potato (Ipomoea batatas (L.) Lam.) Intercropping Khan et al. 2007... 

O. crenata Forsk. Oat (Avena sativa L.) Intercropping Femandez-Aparicio et al. 2007... 

Except direct use of allelopathic crops as cover crops, smother crops, and intercrops, applications of allelopathy for weed control include the use of allelopathic residues as an herbicide agent, e.g., pellets flours, water extracts, etc. The most common example of crop residue utilization is application of straw on the soil surface (mulching), e.g., rice straw inhibited germination of field bindweed (Convolvulus arvensis L.), winter wild oat (Avena ludoviciana Durieu), and little-seed canarygrass (Phalaris minor Retz.) (Lee et al. 1991 Tamak et al. 1994 Young et al. 1989). 

Baumann DT, Kropff MJ, Bastiaans L (2000) Intercropping carrots and leeks to suppress weeds. Weed Res 40 359-374... 

Liebman M, Dyck E (1993) Crop rotation and intercropping strategies for weed management. Eco Appl 3 92-122... 

Rusinamhodzi L, Murwira CHK, Nyamangara Cl (2006) Cotton-cowpea intercropping and its N2 fixation capacity improves yield of a subsequent maize crop under Zimbabwean rain-fed conditions. Plant Soil 287 327-336... 

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