FERTILIZERS FOR GRASS IN ROTATIONS

W. V. Bartholomew

GRASS CROPS in the rotation can be made to provide more pasture and hay and to impart a greater influence upon soil productivity if prudent use is made of fertilizers.

Let us examine some principles that determine the best use of fertilizer the most efficient use, that is, in order to get the greatest benefit from grass crops. Four points are a part of such an examination : The peculiar nutrient needs of the crop or crops to be grown, the ability of the soil to supply the necessary nutrients to the plants, the tendency of the fertilizer to be lost by leaching, and the capacity of the soil to fix in unavailable form the elements applied in the fertilizer.

Soils vary greatly with regard to the kind and quantity of fertility elements they can supply to the growing crop. Alfalfa, a crop that can be grown in the several climatic regions of the United States if soil conditions are adequate, is an illustration. Alfalfa requires good drainage and moderate to high levels of soil fertility. In the Southeast, lime, phosphate, potash, and some of the minor elements as well must be applied to the soil for alfalfa production. Good yields can be obtained on the better soils of the North Central region with little fertilization usually only moderate to small applications of lime and phosphate. In some of the Western irrigated regions alfalfa has been grown extensively without fertilization. The soils of the West are normally calcareous and initially were generally high in fertility.

Soils differ locally as well as between regions. In some areas the local differences may be marked. The fact that one farmer gets excellent results by the use of high rates of fertilizer is not always an indication that his neighbor a few miles away can get similar results. Such local contrasts in soil fertility are common in the East.

For the better grass crops the nutrient requirements are high. This thesis runs counter to the belief that grasses, because they are soil builders, find their best use in soil conditions of low fertility. Some grass crops will survive and grow on poor soils, but abundant experimental data, supported by extensive practical experience have shown that grass crops, those that can grow on poor soils as well as those needing high minimum levels of fertility, respond markedly to the application of fertilizer.

An example of the capacity of non-leguminous grass crops to respond to nitrogen is provided by the Virginia Agricultural Experiment Station: Orchardgrass yields were increased from 1,099 pounds an acre where no nitrogen was added to 5,099 pounds when a hundredweight of nitrogen was applied. The protein yields in pounds per acre in the two treatments were 99 and 528 pounds per acre, respectively.

In South Dakota the average yield of several adapted grasses from experiments in four counties was 1,964 pounds an acre when no fertilizer was applied; 3,093 pounds when only nitrogen was used; and 3,240 pounds when nitrogen was added along with phosphorus.

Alfalfa yields in Michigan were increased from 3,032 pounds an acre when no fertilizer was used to 5,502 pounds where 500 pounds of 0-16-10 were applied. In an experiment in Sussex County, New Jersey, alfalfa yielded 3,118 pounds an acre without fertilization and 8,603 pounds when 370 pounds of bone meal and 200 pounds of potash were applied.

Some grass crops have a wide fertility tolerance. Such crops as peanuts, soybeans, lespedeza, and kudzu are effective foragers for plant nutrients and therefore can survive on poor soils and successfully compete with other associated crops under adverse fertility conditions. They grow best, however, under conditions of moderate to high fertility, and when they are grown on poor soils they have been found to respond markedly to additions of fertilizer. When such crops are grown on poor soils without fertilization, they contribute most by their limited fixation of nitrogen or by prevention of soil erosion they neither conserve fertility nor hasten its liberation from the soil minerals. They merely postpone the time when it must be added to the soil as fertilizer if soil productivity is to be maintained.

Such crops as tobacco and cotton, when they follow soybeans and peanuts, commonly develop severe potash deficiency symptoms. This results from the high nutrient requirements of the peanuts and soybeans and their ability to take up large quantities of plant nutrients even at low levels of fertility.

The plant nutrients removed in a year's growth of grass harvested for hay are more than double the amounts contained in a crop of cotton or corn grain and more than three times the amount removed with a crop of small grain. A 3-ton crop of alfalfa contains about 140 pounds of nitrogen, 35 pounds of phosphoric acid, and 135 pounds of potash. A 3,000-pound crop of timothy contains about 40 pounds of nitrogen, 15 pounds of phosphoric acid, and 45 pounds of potash.

The grass and hay crops adapted to poor soils are also high in mineral elements. Each ton of peanut or soybean hay removes from the soil about 10 pounds of phosphoric acid and 25 pounds of potash. A 1,500-pound crop of peanuts and the accompanying 2,000 pounds of hay remove approximately 16 pounds of phosphoric acid and 56 pounds of potash.