Tillage operations in orchards should be reduced to a minimum necessary to prepare land for irrigation and to plant and control cover crops and weeds at strategic intervals. Implements that penetrate the soil more than 4 or 5 inches may greatly injure tree roots.

Oil sprays to control interplanted vegetation in orchards have become common. They largely eliminate soil cultivation, especially in orchards irrigated by sprinkling. Oil sprays kill the vegetation and leave it as a mulch on the soil surface; the mulch aids soil granulation and encourages feeder roots near the soil surface. Reduced tillage may reduce soil compaction.

To wet the soil as uniformly as possible, irrigation furrows in orchards should be broad, shallow, and spaced at about 3-foot intervals between the tree rows. Border and basin systems often are used where the land is nearly level or has a uniform slope. Overhead sprinkling is used widely, and the practice is increasing. Special nozzles that throw the water out below the branches are used.

While trees draw water from soil depths of 5 feet or more, most feeder roots are in the upper 2 feet, and this zone should not be permitted to dry out between irrigations.

Organic matter is maintained in orchards through applications of farm manure and green manure. Rye, vetch, and sweetclover have been used extensively. Objections to sweetclover are its excessive growth and the fact that its demand for plant nutrients and soil moisture coincides with the peak demands of trees. Winter vetch and Austrian winter peas avoid competition with trees and give a good supply of organic matter by late spring or summer.

Alfalfa is used extensively for soil cover in apple and pear orchards. For peaches, apricots, and cherries grown on moderately coarse-textured soils, alfalfa furnishes undesirable competition for water and nutrients. Unless it is properly managed, alfalfa may encourage harmful insects, such as the tree leafhopper. Alfalfa is particularly helpful in orchards where chlorosis is a problem. Where alfalfa is grown, the top growth should be left in the orchard and worked into the soil, rather than harvested for hay.

Rye, mustard, and other nonlegumes need supplemental nitrogen for growth and decomposition. In central Washington, 200 pounds of ammonium sulfate an acre is recommended just before rye is planted.

For berries and grapes, it is usually not feasible to grow interplanted crops to maintain or build up organic supply. For these crops, soil organic matter should be built to a maximum before plantings are made. Supplemental additions can be made during the growth period as manure or mulches.

Irrigated fruit crops in the region have shown deficiencies of many elements. Nitrogen deficiencies are general. Phosphate deficiencies are not common, but some phosphate is widely used as an aid to cover and green manure crops between trees. Potassium is usually adequate although some growers believe potash improves quality.

Other elements frequently deficient are iron, zinc, manganese, and boron. Nitrogen deficiencies are typified by light-green color in leaves and reduced growth and vigor of plants. There is no one rule to determine application rates of nitrogen fertilizers. A common plan is to add sufficient nitrogen to give the desired average length of annual terminal growth. A 12-inch growth is considered desirable for bearing peach trees in Washington. Optimum annual growths for many apple varieties have been suggested in some areas. A second plan is to add as much nitrogen as possible without seriously reducing fruit color or quality.

The preferred time for nitrogen applications varies with areas and types of fruit. Early spring or fall applications are generally favored for deciduous fruits. Late-summer treatments delay ripening and may increase frost damage by encouraging late growth. Actual annual treatments are 60 to 120 pounds of fertilizer nitrogen an acre. Most mixed fertilizers for established fruits contain about twice as much nitrogen as phosphate.

VEGETABLE CROPS are grown throughout the region, but extensive commercial production is limited to population centers and areas with moderate to long growing seasons. Vegetable crops generally are expensive to produce and market.

Deep, well-drained, sandy soils are preferred for winter and early planted vegetable crops. Medium-textured soils, mucks, and even light clays often are used for warm-season crops. Soils that are difficult to cultivate should be avoided because land planted to vegetable crops must be frequently worked.

A few vegetable crops, such as table beets, kale, and asparagus, produce well in rather saline soils. In general, though, saline soils are not adapted to large yields of high-quality produce.

Topography also is a major consideration. Many vegetables need careful control of soil moisture. Labor costs for irrigation often are high. The land should be nearly level or of a moderate, even grade to permit uniform wetting.

Many vegetables have small seeds and need a clean, firm, moist seedbed. Good, uniform stands must be obtained to maintain essential quality and yield. Crooked, uneven rows and rough land interfere with cultivation.

In areas with severe winters, clay loams and clay soils should be fall plowed if early vegetables are to be planted in the spring. The yield and quality of peas, lettuce, and other crops are greatly reduced when planted so late that growth must extend into hot weather.

Vegetable crops differ appreciably in rooting depth and irrigation requirements. Because different crops have different irrigation requirements, water should be available on demand.

Many vegetable crops remove large amounts of plant nutrients from the soil, so that liberal fertilization is necessary. Farm manure is customarily applied to vegetables if it is available. The most usual ratio of fertilizer for vegetables in this region is 1-1-0 or 2-1-0. Potassium is added more often to vegetable soils than for other crops. Tomatoes often crowd the growing season, and nitrogen is used conservatively to limit prolonged vegetative growth and delayed ripening of the fruit. The most usual fertilizer for tomatoes has a 1-2-0 ratio; if they are planted following alfalfa, no nitrogen is used.

SOIL-MANAGEMENT RESEARCH in the grazing-irrigated region since 1945 has emphasized the advantages of combining desirable practices. Improper tillage operations that cause soil compaction may nullify improved fertilizer and irrigation practices.

H. B. Peterson and J. C. Ballard reported studies with combinations of irrigation water and nitrogen fertilizer needed for maximum yields of sweet corn in northern Utah.

Without nitrogen fertilizer, there was little response to increased frequency of irrigation. With nitrogen fertilizer, but with no change in irrigation, yields increased only moderately. But when the nitrogen fertilizer treatment was increased to 200 pounds of elemental nitrogen to the acre and a continuous supply of moisture was maintained in the root zone, the yield increased nearly 300 percent.