It is observed that during the last decade there is decline in yield in mono-cropping system where same crops are grown on same land in repeated cycles. Mono-cropping system causes weeds and diseases problem in crops because every year or every season, same crops left behind the weed seeds as well as disease causing organism in same land. Mono-cropping system exhausted the nutrients from soil which are essential for plants/crops growth.
There is a well-known strategy against mono-cropping system which uplifts the yield of crops, increases the soil fertility, cause weeds and disease control. The strategy is known as “Crops Rotation”. Crops rotation means “growing of crops, every year, on the same land, one after each other, so that the fertility of land is least affected”. Rotation of crops has received full attention during the past number of years.
Crops rotation is a tool used to manage population level, soil born plants, diseases causing organisms and soil fertility level. It is acknowledged that there is no specific rotation which is standard for all agro-ecological zones. Rotation of crops is varying from place to place, time to time, and with climatic condition. Rotation of suitable crops depends upon;
• Water use
• Land use
• Labour availability
• Inputs available
• Nutrients availability
• Weeds and disease levels in field
The best crops rotation is that, which vary from field to field on the same farm from year to year. Every rotation of crops contains certain criteria, following are pin the points should be kept in mind for crops rotation.
• Long rooted crops should be followed by shallow rooted crops. i.e. Sugarcane followed by cotton
• Follow short term crops after long term crops.
• Follow crops with low nutrient demands after crops with high nutrient demand so that soil fertility maintain.
• Grow green manure/ cover crops for nitrogen-fixation in crops rotation (e.g., clover, alfalfa) with heavy feeding crops (e.g., corn) to take advantage of nitrogen supply.
• Rotate the location of annual crops each year this is especially suitable for vegetables like peppers, eggplants, tomatoes, potatoes, etc.
• Same family crops should be avoided during crops rotation.
• Always grow some crops that will produce and leave a large amount of residue/biomass that can be incorporated into the soil to help maintain soil organic matter levels.
• When growing a wide diversity of crops, attempt to group crops into blocks according to the following criteria:
a) Plant family
b) Similar timing/maturation periods
c) Type of crop (i.e., root vs. fruit vs. leaf crop)
d) Crops with similar cultural requirements (e.g., irrigation, plastic mulch, dry farmed, planted to moisture crops, etc.)
• Grow deep-rooted crops (e.g., sunflower, fava beans, etc.) that may access nutrients from lower soil horizons.
• Use cereals as a break crop to interrupt the disease cycles of oilseeds and pulses.
• Use different cereals such as wheat, barely, triticale, oats and rye in the rotation.
• Do not plant cereals more than two years in a row
• Sow disease-free seed and resistant varieties for added protection.
Mostly farmers not follow crop rotation as recommended. They use it for short cycle/duration.
Benefits of crops rotation are as follow:
Crop rotation has many agronomic, economic and environmental benefits compared to monoculture cropping. Crops rotation leads to enhance the soil fertility and help to optimize the water use by crops on sustainable basis i.e. corn crop is now grown in two-year rotations with soybeans or three-year rotations with soybeans and wheat. These short, two- to three-year rotations rarely include pastures, cover crops, or green manures lead to increase soil fertility as well as yield.
Suitable crops rotation also reduces soil erosion. Crop rotation may limit the growth of populations of agricultural pests including insects, nematodes, and diseases caused by bacteria, viruses, and fungi through regular interruption and replacing crop host species with different plant species that do not serve as hosts.
The use of specific crop and cover crop rotations may also be used to control pests through allelopathy, an interference interaction in which a plant releases into the environment a compound that inhibits or stimulates the growth or development of other organisms. I.e. in mono-cropping, in spring lettuce continuous weeds were observed. To control weeds, follow the spring lettuce with fast growing summer cover crops such as soybean or cowpea. This will lead to control of weed to satisfactory level, using catch crops which make efficient use of nutrient input.
Crops diversification can be achieved through crops rotation. Long term rotation of cover crops using perennial grasses lasting 6 month to one year or more may contribute to add organic material in soil and enhance soil microbial activity which causes soils fertile. The improvement of soil physical properties through crop rotation and organic matter accumulation may improve water-holding capacity and drainage characteristics. Hence yield also increases in crop rotation pattern as compared to mono-cropping system economically.
Finally farmers adopted this strategy world-wide but there is need to boost its level. This agronomic practice was developed to produce high yields by replenishing soil nutrients and breaking diseases and pests cycles. To ensure sustainable farming crop rotation with legumes or cover crops must be introduced instead.
The author is M.Sc. (Hons.) Agronomy, Department of Agronomy, University of Agriculture, Faisalabad, Pakistan. He can be reached at <abi2840@gmailcom>