Cropping systems: sequential, relay, mixed and multiple cropping
How crops are arranged in time and space: the main cropping systems of the world, cropping intensity, and how to compare systems by equivalent yield.
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A field is not managed one crop at a time. Over a year, and over several years, a farmer decides which crops follow which, whether two grow together, and how intensively the land is used. That arrangement, the cropping system, shapes soil fertility, pests, water use, labour and income more than any single season's decisions.
Cropping systems are a basic topic in agronomy and farming systems courses. Exams expect the vocabulary, examples from around the world, and a few calculations such as cropping intensity and equivalent yield.
The vocabulary
- Cropping pattern: the crops grown and their arrangement in time and space on a farm or in a region, often given as the proportion of area under each crop.
- Cropping system: the cropping pattern together with its management and its interactions with farm resources, technology and other enterprises.
- Monocropping (monoculture): the same crop grown on the same land year after year.
- Crop rotation: different crops grown in a planned sequence on the same field over several years.
- Multiple cropping: growing more than one crop on the same land in a year. It has two forms:
- Sequential cropping: crops follow one another with no overlap. Two crops a year is double cropping, three is triple cropping, four is quadruple cropping.
- Intercropping: two or more crops grow on the same land at the same time, as mixed, row, strip or relay intercropping.
- Relay cropping: the second crop is sown into the first before it is harvested, using the overlap to gain time.
- Ratoon cropping: a crop regrows from the stubble of the previous harvest, as in sugarcane, some rice, banana and pigeonpea.
Some major cropping systems of the world
| System | Where it is important | Notes |
|---|---|---|
| Rice–wheat | the plains of South Asia and parts of China | about 25 million hectares; tight turnaround between crops, groundwater depletion, residue burning and soil structure problems after puddled rice |
| Rice–rice (and rice–rice–rice) | irrigated deltas and plains of South-East and East Asia | very high productivity; intensive water and nutrient use |
| Maize–soybean rotation | the North American Corn Belt, parts of South America and China | the legume supplies nitrogen and breaks cereal pest cycles |
| Soybean–maize double cropping ("safrinha") | central Brazil | a second maize crop sown immediately after soybean in the same rainy season |
| Cereal–legume intercropping | sub-Saharan Africa, Latin America | maize with beans, cowpea or pigeonpea; sorghum or millet with cowpea or groundnut |
| Wheat–fallow and cereal–legume rotations | dryland regions of Australia, North America, West Asia and North Africa | fallow or legumes store moisture and nitrogen for the next cereal |
| Sugarcane with ratoons | tropical and subtropical lowlands worldwide | a plant crop followed by one or more ratoons over several years |
| Mixed crop–livestock systems | smallholder farms on every continent | crops feed animals, manure feeds crops |
Measuring intensity
Cropping intensity measures how many crops a piece of land carries in a year:
The net cropped area is the physical area sown at least once in the year; the gross cropped area counts land again each time it is sown.
Cropping intensity on a farm
A 100 ha farm sows all 100 ha in the wet season, 60 ha again in the dry season with irrigation, and 20 ha with a short pulse crop before the next wet season.
- Net cropped area = 100 ha.
- Gross cropped area = 100 + 60 + 20 = 180 ha.
- Cropping intensity = 180 ⁄ 100 × 100 = 180 per cent.
A farm with one crop a year on all its land has a cropping intensity of 100 per cent; double cropping of all land gives 200 per cent. Irrigation is usually what lifts intensity above 100 per cent in seasonally dry climates.
Comparing systems with different crops
How do you compare a rice–wheat system with a rice–potato–mungbean one? Yields of different crops cannot simply be added. Two common approaches:
- Crop equivalent yield: convert every crop's yield into the yield of one reference crop by price. Rice equivalent yield (REY) = Σ (yield of crop × price of crop ⁄ price of rice). Wheat equivalent and maize equivalent yields are used in the same way.
- Land equivalent ratio (LER), for intercrops: the land needed as sole crops to match the intercrop's yields.
Systems are also compared by production efficiency (kg of produce per hectare per day of field occupation), net returns, water productivity, energy use, and sustainable yield index over several years.
Rice equivalent yield of a system
A rice–wheat system yields 5.0 t/ha of rice and 4.0 t/ha of wheat. Rice sells at 18 currency units per 100 kg and wheat at 20.
- Wheat converted to rice equivalent: 4.0 × 20 ⁄ 18 = 4.44 t/ha.
- System REY = 5.0 + 4.44 = 9.44 t/ha of rice equivalent.
A rice–potato–mungbean system with 4.6 t rice, 20 t potato (price 8 per 100 kg) and 1.0 t mungbean (price 60 per 100 kg) gives 4.6 + 20 × 8 ⁄ 18 + 1.0 × 60 ⁄ 18 = 4.6 + 8.89 + 3.33 = 16.8 t/ha REY, much higher gross output, though costs, labour and risk must also be compared.
Choosing a cropping system
The best system for a place depends on:
- Climate and water: length of the growing season, rainfall pattern, irrigation, frost.
- Soil: texture, drainage, fertility; puddled soils suit rice but not the following upland crop.
- Markets and prices, and the household's own food needs.
- Labour, machinery and capital, especially the tight windows between crops in intensive systems.
- Pests, diseases and weeds, which build up under monoculture and are broken by diversity.
- Sustainability: soil organic matter, nutrient balance, groundwater, residue management and greenhouse gas emissions.
Diversifying intensive cereal systems with legumes, oilseeds, vegetables or fodder is a common goal of agricultural policy in many countries, for soil health, nutrition and income.
Key points
- A cropping system is the arrangement of crops in time and space with its management; the cropping pattern is the crops and their areas.
- Multiple cropping includes sequential cropping (double, triple) and intercropping (mixed, row, strip, relay); rotation spreads crops over years; ratoon crops regrow from stubble.
- Major world systems: rice–wheat, rice–rice, maize–soybean rotation, soybean–maize double cropping, cereal–legume intercrops, cereal–fallow rotations in drylands.
- Cropping intensity = gross cropped area ⁄ net cropped area × 100.
- Systems are compared by crop equivalent yield, LER, production efficiency, returns and resource use.
What the exams ask
- School-leaving and entrance papers: definitions of cropping pattern, cropping system, monocropping, multiple, sequential, relay, mixed and intercropping, with examples.
- Degree and research-fellowship entrances: calculating cropping intensity, equivalent yields and LER; major cropping systems and their problems; principles of choosing crops.
- Professional and policy examinations: diversifying cereal systems, sustainability of intensive systems, and planning cropping systems for irrigated and rain-fed areas.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
What is the difference between mixed cropping and intercropping?
Mixed cropping is one kind of intercropping, in which crops are sown together with no row arrangement. Intercropping also includes row, strip and relay arrangements.
Is monoculture always bad?
It is simpler and suits specialised machinery and markets, but it tends to build up pests, diseases and weeds, deplete particular nutrients and lower soil organic matter. Rotations and diversity usually make systems more resilient.
What is a ratoon crop?
A crop that regrows from the base of the previous crop after harvest, without replanting, such as sugarcane, some rice and pigeonpea. Ratoons save seed and time but often yield less than the plant crop.
Sources
- Reddy, S. R. Principles of Agronomy. Kalyani Publishers, latest edition. Chapters on cropping systems.
- Francis, C. A. (ed.) Multiple Cropping Systems. Macmillan, 1986.
- Ladha, J. K. et al. "How extensive are yield declines in long-term rice–wheat experiments in Asia?" Field Crops Research 81, 159–180 (2003).
- Dobermann, A. and Fairhurst, T. Rice: Nutrient Disorders and Nutrient Management. IRRI and PPI, 2000.
- FAO. Save and Grow: A Policymaker's Guide to the Sustainable Intensification of Smallholder Crop Production. FAO, 2011.
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