SOIL MANAGEMENT ON FARM PASTURES

Horace J. Harper

THE KIND of soil management to use in establishing or improving pastures and meadows on farms in the natural grassland area depends primarily on climatic environment and character of the soil.

The average annual rainfall varies from 40 inches in the eastern part of the tall-grass country to less than 15 inches in the western part of the short-grass region. A high proportion of the prairie soils that developed under the influence of a humid climate are acid and are low in available phosphorus. Acid, low-phosphate soils occur frequently also in the eastern part of the Reddish Prairie soil region. On many of them fertilizer and lime are needed.

Acid soils seldom occur in the northern part of the subhumid portion or in the semiarid portion of the natural grass-land area. Chernozem, Chestnut, Reddish Chestnut, and Brown soils found there usually are high in available plant nutrients. Consequently methods for pasture improvement will be limited to tillage requirements for reseeding cultivated land and procedures that increase the efficiency of rainfall.

Soils in the eastern part of the natural grassland area are higher in organic matter and nitrogen than similar soils farther west in the same latitude. Temperature, however, has a greater influence than rainfall on the quantity of organic matter in the natural grassland area.

Soils in the northern part of the area contain two to three times as much organic matter and nitrogen as soils of similar texture in the southern part. The organic matter content of southern grassland soils is relatively low, except in the blackland areas (Rendzina soils), where a high content of clay and lime has provided a favorable environment for the accumulation of organic matter.

A high proportion of the pastures in the humid and subhumid part of the areas are on shallow soil or on slopes too steep to cultivate. Much of the cultivated land has been damaged by erosion, and soils that were originally deep are now too shallow for cultivation. A grass cover can be established on them but yields will be poor unless fertility can be improved. Several grasses will grow on them, but the forage is usually low in protein and deficient in available phosphorus. Where a grass-legume mixture cannot be readily established, pasture improvement is a slow process, especially on low-nitrogen soils.

The response of grasses to soil improvement practices on shallow soils depends largely on the porosity of subsurface layers. Occasionally subsoils are too sandy to hold water. On such soils and on shallow soils with impervious subsoils, plant growth will be restricted by lack of moisture even in a humid climate. Increased income will not be sufficient to pay the cost of soil improvement on this type of land. On deeper soils, pasture improvement can be an important factor in increasing farm income.

Different parts of a pasture may respond differently to the same type of soil management. A soil survey will indicate areas where the physical character of the land may or may not be favorable for more intensive use.

Disking or shallow plowing is a part of the treatment needed to establish native or introduced grasses on formerly cultivated land or on low-producing pastures that do not respond quickly to controlled grazing. The forage-producing capacity of the sod-bound pastures composed principally of Kentucky bluegrass, bromegrass, or Bermuda-grass can be increased by early spring tillage. Spring plowing also stimulates forage production in Johnsongrass pastures where rootstock vigor has been decreased by soil packing. Stirring the soil hastens the decay of organic matter and indirectly provides more nitrogen and other nutrients for plant growth.

Low-producing Kentucky bluegrass pastures in the northeastern part of the natural grassland area can be improved by a combination of tillage, liming, fertilization, and reseeding to adapted legumes or maybe timothy and bromegrass. Plowing these pastures about 3 inches deep in late fall will destroy many of the bluegrass plants and provide a more favorable condition for the development of introduced grasses and legumes. Renovating and reseeding a southern Iowa pasture increased beef production 35 pounds an acre over untreated land. This treatment plus lime increased production 85 pounds per acre.

In Oklahoma and Texas many low-producing weedy pastures east of the 30-inch rainfall belt should be plowed and planted to Bermuda-grass, lespedeza, and hop clover. In the lower rainfall areas, cool season grasses, such as weeping lovegrass, should be planted on a firm seedbed in the southern part and crested or western wheatgrass in the northern part of the natural grassland area to lengthen the grazing season.

Pasture renovation is needed also to obtain more rapid benefits from the application of limestone. Limestone applied on the surface of a pasture sod dissolves very slowly and maximum benefit is not obtained for several years. When lime is applied to a pasture that has been stirred 3 or 4 inches deep by disking or shallow plowing, it can be thoroughly mixed with the surface soil by double disking. Phosphate or mixed fertilizer can also be applied more effectively on a loose soil.

Pasture land on long slopes may be damaged by gully erosion when the vegetative cover is destroyed by disking or plowing and torrential rainfall occurs before a grass cover can be reestablished. Narrow terrace ridges constructed at 8-foot or 10-foot vertical intervals, with a variable grade of 0.1 to 0.3 percent fall per 100 feet, can be used to intercept runoff and prevent soil loss in areas where danger from soil erosion is likely.

Legumes are the key to pasture and meadow improvement where climatic conditions are favorable for their growth. Soils must contain more lime for alfalfa and sweetclover to grow successfully in a grass mixture, than for clover. A neutral soil also provides a more favorable condition for the release of plant nutrients locked up in the soil organic matter as a result of a more rapid growth of soil microorganisms. Although the addition of lime to an acid soil may increase the liberation of plant nutrients from the decay of soil organic matter, the residues produced from an increased growth of a legume-grass mixture will return more organic matter and nitrogen to the soil than would have been returned on unlimed land. Legumes will also replace losses of nitrogen that may occur as a result of increased biological activity when lime is applied to acid pasture land containing no legumes.

Lime must also be applied to replace calcium removed from pasture soils by the leaching effect of rainfall and to neutralize the acids produced when protein in soil organic matter or legume residue decays. If lime is not applied, acid-sensitive legumes eventually will disappear, and growth of acid-tolerant legumes will be poor. However, many natural grassland soils are high in lime content and can continue to produce excellent yields of legumes for a long time before forage production will be seriously reduced by soil acidity or calcium deficiency.

Sweetclover has the highest lime requirement of the legumes normally planted in pasture mixtures. This crop will produce maximum yields in neutral to slightly alkaline soils. Data published in Ohio Agricultural Experiment Station Bulletin 588 show that alfalfa and red, mammoth, and alsike clovers produce maximum yields in a neutral soil, and higher yields in slightly alkaline soils than in moderately acid soil.

Experimental studies at different locations over the Prairie soil area show that the white clover will grow very well in slightly acid soil when other conditions such as drought do not limit plant development. Many winter legumes, such as big and little hop clover, bur-clover, black medic, and Persian clover, will make an excellent growth on slightly acid soil; but lime must be applied to produce maximum yields on moderately acid or strongly acid soil. Big and little hop clover will grow on poorer land than other winter legumes, partly because of their lower potassium requirement.

Common lespedeza is more acid tolerant than Korean lespedeza. Maximum yields of Korean lespedeza will usually not be obtained on moderate to strongly acid soils unless lime is applied.

Soils low in available phosphorus should be fertilized with superphosphate to provide more favorable conditions for the growth of a legume-grass mixture on pasture land where the physical character of the soil is favorable for deep moisture penetration and root development. The phosphorus content of legume crops is frequently 25 to 50 percent higher than that of native grasses. Many grasses will make a good growth on low-phosphate soils where legumes will fail. Alfalfa has a higher soil phosphorus requirement than red, alsike, or white clovers, or sweetclover.

Korean lespedeza is less responsive to phosphate fertilization than winter legumes. Maximum growth occurs during summer months when a considerable quantity of organic phosphate is released by the decay of soil organic matter. Because of this condition and also because of summer drought which frequently limits the growth of lespedeza, response from phosphate fertilization is quite variable. Lespedeza can feed on relatively insoluble forms of mineral phosphate in the soil. However, the phosphorus content of forage produced on very poor soils is frequently below minimum requirements for the growth of livestock.

Recent studies at the Southeast Pasture-Fertility Research Station near Coalgate, Okla., indicate that the fertilizer cost of a pasture improvement program can be reduced and the efficiency of fertilization increased by drilling superphosphate in 14-inch rows. The legume seeds were dropped on the soil above the fertilized zone in this experiment. Ryegrass was planted between the fertilized rows because the phosphorus requirement of this crop is much lower than that of hop, Persian, and white clovers, and black medic. Less fixation of phosphorus will occur on many soils when the fertilizer is drilled in 14-inch rows as compared with a similar quantity of fertilizer applied broadcast.

Rock phosphate drilled in rows 14 or 16 inches apart at the rate of 150 pounds an acre between drill rows of spring oats has produced excellent yields of sweetclover on phosphorus-deficient soils where lime has been applied to correct soil acidity. The quantity of sweetclover seed can also be reduced by scattering it on the surface of the soil above the fertilized zone. A good temporary pasture can be produced on cultivated land at a relatively low cost for phosphate fertilizer. A modification of this procedure is needed in areas where crop response from soil-improving factors may be low because of limited rainfall. A larger area of soil must be provided under such conditions to supply the moisture needed for the survival of legume seedlings. Width of soil between plants rather than depth may be the important limiting factor under many conditions.