Intercropping

The degree of spatial and temporal overlap in the two crops can vary somewhat, but both requirements must be met for a cropping system to be an intercrop. Numerous types of intercropping, all of which vary the temporal and spatial mixture to some degree, have been identified. Mixed intercropping Mixed intercropping consists of multiple crops freely mixed in the available space. In the 21st century, it remains a common practice in Ethiopia, Eritrea, Georgia, and a few other places. Freely mixed intercropping has been practiced for thousands of years. In medieval England, farmers mixed oat and barley, which they called dredge, or dredge corn, to make livestock feed. French peasants similarly ground wheat and rye together to make pain de méteil, or bread of mixed grains. Ease of harvesting and buyer preferences led later farmers to plant single-species fields instead. Row crops A row crop is a crop that can be planted in rows wide enough to allow it to be tilled or otherwise cultivated by agricultural machinery, machinery tailored for the seasonal activities of row crops. Such crops are sown by drilling or transplanting rather than broadcasting. They are often grown in market gardening (truck farming) contexts or in kitchen gardens. Growing row crops first started in Ancient China in the 6th century BC. Temporal Temporal intercropping uses the practice of sowing a fast-growing crop with a slow-growing crop, so that the fast-growing crop is harvested before the slow-growing crop starts to mature. This can provide greater yield than either crop alone. Further temporal separation is found in relay cropping, where the second crop is sown during the growth, often near the onset of reproductive development or fruiting, of the first crop, so that the first crop is harvested to make room for the full development of the second. Crop rotation is a related practice but is not a form of intercropping, as the different crops are grown in separate growing seasons rather than in a single season. Alley cropping Alley cropping has crop strips alternating with rows of closely spaced tree or hedge species. Normally, the trees are pruned before planting the crop. The cut leafy material - for example, from Alchornea cordifolia and Acioa barteri - is spread over the crop area to provide nutrients. In addition to nutrients, the hedges serve as windbreaks and reduce erosion. Weed control is inherent to alley cropping, by providing mulch and shade. Inga alley cropping offers an alternative to the ecologically destructive slash and burn cultivation. It increases yields and is more sustainable as it allows the land to be cultivated repeatedly, eliminating the need for slash and burn to get fertile plots. Inga trees, native to Central and South America, grow well on acid soils of tropical rainforest or former rainforest. They are leguminous, fixing nitrogen into a form usable by plants. The leaves form a thick mulch that protects both soil and roots from sun and rain. The trees form a thick canopy that cuts off light from the weeds below, and withstand annual pruning. The technique was developed and trialled by tropical ecologist Mike Hands in Costa Rica in the late 1980s and early '90s. He showed that the tough leaves of the Inga tree decomposed quickly enough to be useful as a mulch. == Potential benefits ==