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CONSERVATION TILLAGE HANDBOOK SERIES
Winter Cover Crops for Irrigated Sandy Soils
Controlling wind erosion on sandy soils can be difficult. The particle size distribution and lack of aggregation or stable clods makes them extremely susceptible to erosion by the wind. Growing cover crops, utilizing plant residues, reducing field lengths, establishing wind breaks and increasing surface roughness are possible methods of controlling wind erosion on these soils. Each of these methods have advantages and disadvantages depending on climatic and field conditions and are sometimes used together. In the Columbia Basin, sandy soils maybe so low in organic matter and high in content of fine sand that the practice of surface roughening is not effective. Windbreaks can be effective but require time, effort and the correct soil and moisture conditions for establishment. Reducing the length of fields is an effective practice but may not be practical because size of irrigation equipment and machinery. The use of plant residues can be effective if sufficient residue remains after harvest. Winter cover crops are an effective method of erosion control when the proper species are selected and care is taken to establish a vigorous stand.
Vance Pumphrey, Oregon State University agronomist, Pendleton, has evaluated winter cover crops adapted to the Columbia Basin in the Hermiston, OR, area. He has observed that the effectiveness of cover crops is less than maximum because the choice of crops is limited and often fall plantings fail to make adequate growth to protect the soil surface.
Selecting Winter Cover Crops
Desirable characteristics of an effective winter cover crop are: (1) a growth habit that provides sufficient ground cover to protect the soil, (2) the ability to grow under cool conditions, (3) a high degree of winter hardiness and (4) not to cause a major problem for spring cropping. Pumphrey states that species can differ in all these characteristics. Consequently, all these factors are important to consider when selecting a cover crop. In his research, Pumphrey has evaluated these characteristics in several species. His observations are summarized in Table 1. Conclusions that Pumphrey draws from his observations on cover crops are:
1. The more upright growth habit of tillering winter wheat and winter barley provides better soil protection than the more prostrate growth habit of rye and triticale.
2. Barley and wheat pose less of a volunteer problem than do either rye or triticale.
3. Hairy and smooth vetch are both delicate, fragile plants that are easily damaged by soil abrasion (sandblasting).
4. Growth of winter cereals during cool temperatures is better than that of the vetches.
5. The massive growth of hairy vetch commonly observed in May can be misleading as to the amount of soil protection provided during cooler months.
6. Seedlings and young plants of Austrian winter peas are more upright and sturdier than those of vetch.
Table 1. Observations on species evaluated as winter cover crops, Hermiston, OR (Pumphrey, OSU, Pendleton).
If cereals are grown as cover crops, Pumphrey recommends the cultivars commonly grown for grain. He warns that using cereals can perpetuate plant diseases and if conservation tillage or no-till is being practiced, a contact herbicide is needed in the spring to eliminate the cover crop and weeds.
To establish adequate ground cover before winter, planting dates are important. Table 2 shows the effect that planting dates have upon the adequacy of ground cover. At locations in the Columbia Basin, where climatic conditions differ from those of Hermiston, OR, planting dates should be adjusted accordingly.
Pumpbrey describes a unique method of controlling wind erosion in asparagus fields. Winter annual weeds such as tumble mustard, shepherd's purse and downy bromegrass are controlled within the row with herbicides but are allowed to grow between rows. These weeds are clipped as necessary to contain their growth within acceptable size for asparagus production. These weeds provide protection for both soil and asparagus from the wind. Using weeds eliminates the expense of establishing cover crops and problems with establishment and winter kill.
Sandy soils in the irrigated areas of the Columbia Basin are highly susceptible to wind erosion. Several methods of control are feasible; the use of winter cover crops is among these. Because of the cool growing conditions usually encountered in the fall and winter, species that have high potential for rapid establishment and growth under a broad range of planting conditions are preferred. Commonly grown cultivars of winter barley and winter wheat are the best choices among winter cereals. These varieties possess the necessary growth habits, and seed is readily available at a minimum cost. Among noncereal species, Austrian winter pea is recommended because of its greater growth in cool weather, nitrogen fixing ability, more upright growth habit and low probability of becoming a pest. Regardless of the choice of cover crop, planting dates should be early enough to permit establishment and adequate ground cover.
Table 2. Growth of several winter cover crops planted at three dates, Hermiston, OR (Pumphrey, OSU, Pendleton).
us: Hans Kok, (208)885-5971
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