Crop Rotations

Why has crop rotation reduced?
Historically, crop rotation was a critical farming practice to maximise soil fertility and achieve satisfactory weed and disease control. As agricultural systems modernised, the need for crop rotation reduced with the availability of relatively cheap artificial fertiliser and crop protection products to control disease, weeds and insects. Monocultures consisting of continuous winter wheat and spring barley became common. The reduced availability of profitable Break crops e.g. sugar beet has accelerated this process.

Advantages of Monoculture
• Development of expertise in growing one crop.
• Specialisation with fixed cost (particularly machinery) and reduced labour demand.
• Matching a crop to the most suitable specific fields or blocks of land with logistical (size, shape, distance) and agronomic benefits.
• Avoids the need to find markets for less popular crops

Advantages of Rotation

• Higher yields e.g. typically a crop of winter wheat grown after oilseed rape will yield 1.5 tonne/ha (0.6 tonnes/ac) more than a second continuous crop of winter wheat.

• Reduced expenditure on crop nutrition, disease, pest and weed control e.g. a reduction of 25Kg/ha (20 units/ac) Nitrogen required to grow a crop of winter barley after beans compared to continuous cereals.

 

• Increase in soil structure and organic matter content
• Spreads the workload
• Increased biodiversity

 

Assessing rotations

Assessing the benefits of a crop rotation is not as simple as comparing the returns from a single cereal crop grown after a break crop with those from a continuous cereal crop. The costs and returns of the break crop must be taken into account. A proper comparison examines the costs and outputs of the entire rotation. Individual farms will have different rotations that suit them due to soil type, disease pressure and cropping history.

 

Below we compare the costs and returns of three different types of rotations:

  • Continuous cereals
  • Break crop
  • Combination of break crop and cereal rotation

 

*Note yields in the examples below are estimated from previous 5 year averages; costs and crop prices as per Teagasc crop margins publication 5-9-13

 

While these are three simple rotations and would need to be adapted to suit individual farms, plus the gross margins of the individual crops are greatly influence by the yields achieved and the prices of the crops; they highlight the potential benefit of rotations.

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