Arable Cropping & the Environment - a guide

1. Rotation 

A well-planned crop rotation helps reduce input requirements, pollution and soil erosion. It boosts profit and enhances landscape and biodiversity.

Principles

Planning lies at the heart of integrated cropping. This means planning a rotation over several years. The approach can bring benefits, including more efficient use of land, labour, machinery and other resources. Integrated cropping can also improve weed, pest and disease control with reduced risk of resistance and result in cost savings. In terms of outputs, a well-planned rotation allows more high-yielding first wheat crops following break crops and affords opportunities to enhance quality.

The ‘ideal’ rotation

An ideal rotation would include a balance of crops from different crop groups – cereals, legumes, root crops and broad-leaved arable crops – with no group occupying more than half the land area at any time. A diverse crop rotation aims to break cycles of pests and diseases, improve weed control options, provide sufficient crop cover to prevent erosion and improve nutrient cycling and soil condition. The consequences of different rotations on soils and nutrients can be assessed, forming the basis for choosing ones which have less environmental impact.

Potential problems

Options can be limited. Root crops demand heavy investment in machinery and production. Quotas and contracts limit other crops, eg sugar beet, vining peas and certain field vegetables. Some crops are less profitable than others although they may give benefits elsewhere in the rotation. Soil type can also be limiting. For instance, spring crops are difficult to establish on heavy land. Economics have a major influence on crop choice.

Some practical suggestions 

  • Avoid long runs of winter cereals.
  • Maximise the benefits of break crops, eg through improved grass weed control, even if only occasional.
  • Calculate gross margins over running 5-year periods, not just on the basis of single years.
  • Choose break crops with care, making sure that you have a market before the crop is sown.

Interactions

Soils                         **

The level and intensity of cultivations depends on rooting structure and tilth required for chosen crop. Potatoes require very deep cultivations to create beds and ridges, while cereals and oilseed rape can be direct drilled into stubble.

Previous crop residues and soil structure also influence cultivation needs. In particular, large quantities of cereal chaff and straw hamper establishment of following crops.

Harvesting can cause soil compaction, especially if heavy machinery is used to lift roots on wet soils late in the year. After harvest, crop volunteers can be controlled, eg volunteer potato tubers rot if left exposed to frost on the soil surface; oilseed rape volunteer seed should be left on the surface to reduce dormancy and encourage germination and then be cultivated or sprayed off.

Carefully-managed cover crops have minimum impact on subsequent establishment. However, they may reduce soil moisture for spring-sown crops, lock up N during crop establishment and harbour slugs.

Establishment        *

Market choice is the key influence on crop and variety selection. Rotation affects crop quality (eg milling wheats with high N needs usually follow a break crop) and disease incidence. Varietal diversification reduces disease pressure.

Sowing date, seed rate and variety choice are all affected by local climatic conditions.The busy autumn and harvest workloads can be eased by crop and variety selection.

Nutrition               ***

Phosphate, potash, magnesium and other nutrient needs depend on soil reserves and crop offtakes. Fertility can be maintained at acceptable levels by applications to receptive crops.

Nitrogen is applied crop-by-crop, according to crop needs, previous crop residues, soil organic matter reserves and atmospheric deposition. Crops with low N demand, eg spring rape, can reduce fertiliser inputs over the whole rotation. Legumes fix nitrogen and can leave high crop residues. Good rotational management utilises the fertility in crop residues.

Farmyard manure can replace inorganic fertiliser and benefit soil fertility. Solid manures can be applied overwinter to stubbles provided leaching is avoided. When spread in liquid form, care must be taken to avoid run-off.

Cover crops can reduce N leaching over-winter, but N release may be unpredictable later in the season.

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