Page 284 - Nutrient Management Planning Guide

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Cropping Practices to Reduce Nutrient Losses in Runoff

winter wheat. Winter cereals for water erosion control should be planted as early as possible to maximize growth and soil cover before the dormant period. They can then be terminated in spring with herbicide and planted to spring crops or left and harvested as a winter crop. Spring cereals planted in late summer or early fall will also provide good winter cover and may substitute for winter cereals in some situations.

Green Manures

Green manuring is the practice of growing and

terminating a short-term crop, which can include cereals, oilseeds and legumes, part way through the growing season. A green manure crop is grown to provide short-term ground cover during the growing season reducing the risk of erosion and runoff.

Traditionally, green manuring was used prior to the availability of nitrogen fertilizers to boost soil fertility. Legumes such as peas, lentils, or clovers, which “fix” atmospheric nitrogen are the preferred options for manuring because the residues from these crops have a high concentration of nitrogen that is readily released for subsequent crops.

The traditional practice is to bury crop biomass, which returns most of the fixed nitrogen and plant material to the soil. To provide protection from surface erosion, however, some crop residue must be left on the soil surface. This can be accomplished by either desiccating the crop using herbicides or by haying the crop.

Perennial Forages in Crop Rotations

Including perennial forages in long-term crop rotations is perhaps one of the most effective ways to minimize soil and nutrient losses from runoff. Perennial forages can be grown on poorer soils or on sites where slope is a serious constraint. This allows these areas to remain productive while minimizing erosion.

They provide dense ground cover, which protects the soil from erosion through buffering against raindrop impact filtering soil from runoff and slowing the speed of runoff thereby altering its erosive potential. In addition, the fibrous roots hold the soil in place.

Forages improve soil structure improving the ability for water to infiltrate into the soil and reduce runoff and erosion. Soil structure is improved through contributions to the soil organic matter pool as well as through the root structure of forages which tends to be finer than annual crops and creates a large number of small channels in the soil.

Conservation crop rotations designed to address erosion concerns typically alternate forages with cereals and oilseeds or legumes. Including legumes in the rotation will also boost soil nitrogen levels and improve soil fertility. Legumes can return about 60% of the plant material and nitrogen to the field. Perennial forage crops that are hayed can be added to the crop rotation to mine surplus nutrients such as phosphorus and potassium reducing the risk associated with nutrient build-up in the soil.

Forages can be successfully established by direct seeding. Forage stands can be terminated using herbicides and then an annual crop can be direct seeded into the field minimizing the exposure or bare ground and reducing the negative affects of tillage operations of increasing the risk of erosion and nutrient loss.

Retaining Crop Residues

Crop residues include straw, chaff and roots. Crop type and yield influence the amount of crop residue produced (Table 8.2.3). Leaving or returning crop residue to the land can help reduce runoff related soil and nutrient loss.

more info

For more information on the benefits of conservation fallow is available in the following online document, accessible through Ropin’ the Web.

AF. 1993. Summer fallow •

and soil conservation. Agdex 570-3.

The PFRA with AAFC also has information relating to the economics of conservation fallow in the following online document:

PFRA. 2006. Economics of •

conservation fallow. www.agr. gc.ca/ pfra/soil/swork3.htm