Crops remove fairly large quantities of nitrogen, phosphorus, and potassium from the soil. The yield from continuously cropped soils, decreases over time and ultimately it becomes uneconomical to cultivate them. In order to maintain the yield, it is, therefore, necessary to take measures such as reducing the drain on the soil by keeping it fallow, by allowing an interval between crops of different seasons, or adding nutrients to the soil in the form of manure and fertilizer. Early agricultural experiments showed the value of crop rotations that included a legume sod crop in the regular sequence. Such a system generally’ maintains productivity, and prevents soils degradation and nutrient depletion.
Crop rotation is the sowing of crops in a regular order, one after the other on the same land for a fix period keeping in view that the fertility of soil may not be adversely affected. Technically speaking, crop rotation is the raising of
crops from a piece of land in an order or succession so that the soil fertility is least suffered. Different crop rotation systems have been practiced in Pakistan from the time immemorial.
This system is in contrast with the practice of growing the same crop, year after year. The objective is to ensure increased crop production and have better quality crop produce by maintaining and increasing soil fertility and improving soil productivity through raising of different natured crops in an order from a piece of land. Modem crop rotation was established about the year 1730, in England.
Principles of crop rotation: There are some important botanical principles and management considerations involved in setting up crop rotations. The mechanics of setting up a good crop rotation can be summarized as follows:
I. Crops of the same natural order, that is, belonging to the same family should not follow each other.
2. Crops of the same root system (shallow or deep) should not follow each other.
3. Leguminous crops must be included in the rotation.
4. Green manuring and forage crops should be given a place in the rotation at regular intervals.
4. Crops requiring heavy tillage operations such as sugarcane, potatoes,should also be included.
5. Exhaustive crops should be followed by the restorative crops. Legumes and green manuring crops are restorative.
6. Alternating the crops susceptible to .certain soil-borne diseases with those crops that are resistant to diseases.
7. Apply manure and commercial fertilizers to that crop in the rotation which will make best’ use of them.
8. Have enough elasticity in the rotation so that if a disease destroys, for example, a perennial crop, another crop can be substituted, or if the expected price for a given crop drops, a crop with better prospects can be substituted.
A good rotation that provides for maintenance or improvement of soil productivity usually includes a legume to promote fixation of nitrogen, a grass or legume sod crop for maintenance of humus, a cultivated or intertilled crop for weed control, arid fertilizers. The choice of a rotation for a particular farm depends upon the crops adapted to the particular soil, climate, and economic conditions like the availability of labour, etc. Other factors that affect crop rotation are: irrigation facilities, market demands, and the prevalent system of farming. In addition, weeds, plant diseases, and insect pests may limit the kinds of crops to be grown in a locality.
Key Referene : General agriculture By Muhammad Akhtar Abbas