Agriculture for Engineers 4 (3+1)

Lesson 29. Crop Rotation

29.2 CROP ROTATION

The farmers are in the habit of growing different crops according to their needs and facilities, but it is necessary for them to know more about it. Crop rotation is a process of growing different crops in succession on a piece of land in a specific period of time, with an object to get maximum profit from least investment without impairing the soil fertility.

29.3 PRINCIPLES OF CROP ROTATION

There are certain accepted principles based on which the crops should be selected for crop rotation.

1. The crops with tap roots should be followed by those which have fibrous root system. This helps in proper and uniform use of nutrients from the soil and the roots do not compete with each other for the uptake of nutrients.
2. The leguminous crops should be grown after non-leguminous crops because legumes fix atmospheric nitrogen into the soil and add more organic matter to the soil; while on the other hand, non-legumes are fertility depleting crops. Apart from this, the nutritional requirements of these crops are different, e.g. legumes need more phosphate and less nitrogen while non-legumes need more of nitrogen and relatively low phosphorus. Thus a combination of these crops helps the farmers in reducing their cost of cultivation.
3. More exhaustive crop should be followed by less exhaustive crops because crops like potato, sugarcane, maize etc. need more inputs such as better tillage, more fertilizers, greater number of irrigations, more insecticides, pesticides and better care than crops like oil seeds, pulses etc. which need relatively less or little of the above mentioned inputs.
4. Selection of the crops should be demand based i.e. the crops which are needed by the people of the area and by the family members should be chosen so that the produce can be easily sold at a higher price.
5. The selection of crops should be problem based e.g. On sloppy lands which are prone to soil erosion, an alternate cropping of erosion promoting (erect growing crops like millet, etc.) and erosion resisting crops like legumes, should be adopted.
6. Under dry farming or partially irrigated areas  the selection of crops should be such which can tolerate the drought similarly in low lying and flood prone areas the crops should be such which can tolerate water stagnation e.g. paddy, jute etc.
7. The selection of crops should suit the farmers’ financial conditions.
8. The crops selected should also suit the soil and climatic conditions.
9. The crops of the same family should not be grown in succession because they act like alternate hosts for insects, pests and disease pathogens. Thus, the control of insects, pests and diseases becomes a perennial problem. Apart from this, types of weeds found, are associated with various crops and selection of the same type of crops in rotation encourages weed problems in the field viz. Johnson grass grow with gramminaceous crop throughout year.
10. An ideal crop rotation is one which provides maximum employment to the family and farm labour, the machines and equipments are efficiently used and all the agricultural operations are done timely.

 29.4 ADVANTAGES OF CROP ROTATION

An ideal crop rotation has the following advantages:

1. Agricultural operations can be done timely for all the crops because of less competition. The supervisory work also becomes easier.
2. Soil fertility is restored by fixing atmospheric nitrogen, encouraging microbial activity, avoiding accumulation of toxins (HCN etc.) and maintaining physic-chemical properties of the soil. The soil may also be protected from erosion, salinity and acidity.
3. An ideal crop rotation helps in controlling insects, pests and diseases. It also controls the weeds in the fields e.g. continued growing of berseem encourages chikori (kasani) infestation in the field and repeated wheat culture increase wild oats and Phalaris infestation but an alternate cropping of berseem and wheat helps in controlling kasani as well as wild oats and Phalaris. This is because of taking several cuttings of berseem, the wild oats and Phalaris are also cut and in the wheat the chikori (kasani) is controlled by 2,4-D spraying but if some plants are left, they keep on growing and before they set into seeds, the wheat crop is harvested. Thus all these weeds are controlled along with many other weeds associated with wheat and berseem crops.
4. Proper utilization of all resources and inputs could be made by following crop rotation. The family and farm labour, power, equipment and machines are well employed throughout year.
5. The farmer gets a better price for his produce because of its higher demand in the locality or market.
6. Growing crops of different root depths avoids continues depletion of nutrients from same depths e.g. the deep rooted crops take nutrients from deeper zone and during that period the upper zone gets enriched. Similarly the surface feeding roots take nutrients from upper zone when lower zone gets enriched. Thus nutrients of entire soil mass are fully utilized and cost of cultivation is reduced.
7. Best utilization of residual moisture, fertility and organic residues is made by growing crop of different nature.
8. Ideal crop rotation improves percolation, soil structure and reduces chances or creation of hard pan in sub-soil zone.
9. Some crop plants are found to produce photoalexins when they get infected by diseases. Repeated cultivation of such crops results in harmful effects over crop plants and lower crop yield is obtained.

The family needs of feed, food, fuel, fibre, spices, condiments, sugar, etc. are fulfilled. The farmers keep on getting some income constantly from their cropping which improves their socio-economic status and it also facilitates future crop planning.

Growing different crops is very beneficial but sometimes the desired crops cannot be grown because of certain governing factors. The factors which affect the selection of crops are agro-climatic factors (soil and climate), irrigation, availability of bullock and other powers, market facilities and type of farming and customs in neighbouring areas.