The practice of growing one crop variety in pure stands on a field is referred to as sole cropping. In this practice, only one crop variety occupies the land at a time.
Meanwhile, The alternative practice of growing two or more crops simultaneously on the same field is called inter-cropping. The various crops in the inter-crop do not necessarily have to be sown or harvested at the same time, the main requirement is that they are on the field at the same time for a significant part of their growing periods.
Types of inter-cropping
- Row inter-cropping: this is when the various crops are grown in separate rows
- Mixed cropping: this is when the various crops are grown intermingled more or less at random with each other.
- Relay inter-cropping: this is when a second crop variety is sown between the stands of an existing sole crop just before the first crop is harvested. As such, both the first and second crops spend most of their field as sole crop, and grow together on the field for only a brief period.
Factors that determine the crops combination and spatial arrangement
- Tillage practices: when ridges have been made, the , the spatial arrangement of the various crops may be determined by particular needs of each crop. For example, yam which requires a deep layer of tilled soil, is planted at the top of the mounds, while rice because of its high moisture requirement, is planted in the lower ground between the mounds. Other crops such as maize, pumpkins and melons are planted at intermediate positions between the rice and the yams.
- The crop the farmers considers as target crop and which one is considered a subsidiary influence the proportion of the crops.
- Nature of the crops themselves: a few strands of pumpkin or melon occupy a lit of land and have high economic yield, whereas rice strands, foe example, would have to be much more numerous to be meaningful.
Evaluating yield from inter-cropping
The relative yield of each component crop in an inter-cropping situation is the yield of that component in the inter-cropping situation divided by what that crop would have yielded as a sole crop, covering the same area as the inter-crop and managed at the same level.
Suppose, for example, that a field with a crop combination of maize and cow-peas yields 1.5 tonnes/hectare of maize and 0.25 tonnes/ha. Of cow-peas. If the expected sole crop yield of maize is 2.0 t/ha and that of cow-peas is 0.5 t/ha. Then the relative yield of maize is 1.5/2.0 =0.75 and the relative yield of cow-peas is 0.25/0.50=0.50.
The sum of the relative yields of the various component crops in the inter-crops in the inter-crop is sometimes called the relative yield total. A little reflection of how many times the land area used for inter-crop would be required to produced the same yields of the component crops when they are grown as sole crops. The relative yield total is therefore more conventionally referred to as land equivalent ratio (LER).
LER = relative yield of crop A and relative yield of crop B + relative yield of crop n
In the maize/cow-peas combination considered above the LER = 0.75 + 0.25 = 1.25. An LER greater than 1.0 implies that for that particular crop combination, inter-cropping yielding more than growing the same number of stands each crop as sole crops. An LER of less than 1.0 implies that the inter-cropping was less beneficial than cropping.
LER can also be calculated based on the monetary value of the yield obtained from the various inter-crop and sole crop situation and make comparisons on the basis.
Calculating LER by comparing the total energy value of the yield in kilo calories in various situations and compared the values to determine which arrangement was most beneficial.
Advantages of inter-cropping
- In a carefully planned inter-cropping the LER is usually greater than one. This means that there is yield advantage in growing crops together than growing each one separately. This advantage may rise from several sources.
- The crops may complement one another in their use of field time. The period of their peak demands for light, water, nutrients and other resources may differ, so that in general there is a more efficient utilization of the resources available. For example, during the two or three month that yam takes to sprout and establish adequately on the field, a quick inter-crop of maize or melon would beneficially utilize the field resources during this period.
- The component crop may complement each other in their use of space. For example, an inter-crop of a deep rooted crop can exploit various horizons of the soil.
- An inter-crops may be able to utilized resources which the main crop may not be able to utilized or which may even be disadvantageous to it.
- Certain crops may exert specific beneficial effect on others. For example, plantains inter-cropped with young cocoa seedlings provide shade for the seedlings. Similarly, in an inter-crop of a legume with a cereal crop, the cereal would benefit from the nitrogen fixed by the legumes.
- By having many crops growing simultaneously on the field the farmers is more or less buffered against failure of one of the crop.
- Inter-cropping allows for a more uniform distribution of labour throughout the year.
- When one component of an inter-crop combination fails, the other combinations are able to utilized the resources that would have been available to the failed crop, and so yield better than they would have done otherwise. In other words there is yield stability.
- The spread of diseases and pests is less rapid than in sole cropping. This is probably because the mean distances between the plants of the same component crops are greater. In many instances, the other component crops are not susceptible to the particular disease or pest afflicting one component and may act as physical barriers to the spread of diseases and pest
Disadvantages of inter-cropping
- Since many crops exist together on the field, it is not possible to tailor production practices to the needs of any particular crop.
- Control of pests and diseases is particularly difficult because pesticides which have been development to control a disease on one particular component crop may have deleterious effect on other crops in the combination.
- It is difficult to mechanize operations such as planting, weeding and harvesting.
Read Also: Sowing Guide for Different Kind of Crops