Crop Rotation

Rotation is a very old practice for reducing soil borne problems. Many nematodes, soil borne disease organisms, and insects can reproduce and survive on only a few plants. Repeatedly planting a field with the same crop without interruption will enable any organism, which reproduce successfully on that crop to continue to increase. Rotation to non-host crops may cause many of those pests to cease reproduction and allow natural mortality factors to reduce their numbers. By carefully planning the sequence of crops to be planted in a particular field, it is often possible to avoid excessive build-up of pests that are important to all of the major cash crops in the cycle. In a few instances, it is even possible to include a crop in the rotation that will help to control pests that have built up in preceding crops in the cycle. Pangola digitgrass has been used as a rotation crop to control burrowing and root knot nematodes in vegetables. In India the practice of rotating of vegetable crops with cereal crops is being practiced to reduce the load of root knot nematode in the subsequent vegetable crop in gardenland ecosystem. Similarly in wetland, banana is rotated with rice crop to minimize the nematodes affecting both crops. Particularly in Tami Nadu one of the recommendation for the management of potato cyst nematode is inclusion of non-host crops namely garlic, turnip, beetroot, radish, carrot, wheat etc as five-year crop rotation to reduce the nematode infestation level.

A cultural practice that receives far less attention than it deserves is the immediate destruction of crop roots at the conclusion of the cropping season. It is a practice heavily emphasized in some areas of the country for high value crops such as tobacco. Fields should be tilled as soon as possible after harvest to kill all plants in the field and destroy their roots. Nematodes, soil borne diseases, and many soil borne insects will continue to feed and multiply on crop root systems as long as they remain alive. Hence the destruction of rice stubbles at least during second season is advocated to suppress rice white tip nematode population in Tamil Nadu. Similarly timely harvest of groundnut also helpful to check the lesion nematode population as the delay in the harvest for a week will lead to increase in nematode population heavily.

In certain cases, flooding or fallowing may be used to help reduce number of nematode pests. Flooding has long been practiced for control of root knot nematodes. It is practical only where the water level can be controlled easily and maintained at a high level for several weeks. It is also important to consider the possibility that flooding may actually spread some soil borne pests, if the water source is likely to contain disease causing fungi such as Fusarium or nematodes such as soybean cyst nematode. Where flooding can be practiced, alternating periods of about 2 or 3 weeks of flooding, drying, and flooding again are apparently much more effective than a continuous period of flooding. The soil should be worked during the periods of drying to increase aeration and drying of soil and to prevent weed growth while the soil is exposed. Flooding probably kills nematodes by providing a long period without host plants rather than by some direct physical effect on the nematodes. Fallowing refers to leaving a field with no plants on it for a prolonged period. Most nematodes will decrease after a period of time without an adequate host plant. Exposure to extremely high temperatures in the surface levels of the soil during the hot summers may also reduce numbers of many kinds of nematodes. However, fallowing may be objectionable from a soil management viewpoint, because of the risk of losing soil organic matter, increased danger of erosion, and loss of productive time. If fallowing is being used to help reduce nematode numbers, the field should be cultivated regularly to prevent growth of weeds and to expose new portions of the soil to the effects of drying and heating. If weeds are allowed to grow without control in a "fallow" plot, many kinds of nematodes may be able to survive and reproduce on the weeds, making the practice ineffective.