As the scale implies, good drainage usually means good growth, but red pine in Wisconsin suffers from needle droop disease in sands or sandy looms that have low water-holding ability. It is hard to find a rule that will apply generally to all sites and all strains of a species.

Littleleaf disease of shortleaf pine has been associated with poor aeration and imperfect drainage. A littleleaf hazard rating has been developed based on four observable soil characteristics degree of erosion, subsoil consistence, depth to zone of greatly reduced permeability, and subsoil mottling. This soil-rating system predicts which soils will support disease-free stands.

Soil management that minimizes soil disturbance, soil drying, and mortality of rootlets may reduce the birch die-back in the Northeastern States and in eastern Canada.

In a study carried out in New Brunswick, raising the average summer soil temperature 2 C. above normal, by the use of soil heating cables, caused rootlet mortality to rise from 6 percent to 60 percent the same year. The trees were healthy when the study began, but they soon showed typical dieback symptoms. The effects of excessive temperatures are worse on light, shallow soils.

In the West and North, especially in the Lake States, high temperatures of surface soil kill or injure newly planted seedlings, and mulch or other protection often is needed. Heat injury is much less frequent in the South, probably because the southern pines form bark very early and bark is an efficient insulator.

THE FERTILITY REQUIREMENTS of trees are not well understood, but they seem to vary greatly, especially among the pines. It is possible that mineral deficiencies are partly responsible for some loss of growth that is ascribed to fungi, drought, or excess water.

The most practical step in maintaining good fertility in forest soils is to build up and maintain a mull type of humus. The humus is like a sponge in absorbing water and helps hold mineral elements in the upper soil layers. It is the seat of the greatest microbiological activity and acts as a nutrient reservoir. Humus may be deficient in warm and hot climates because decomposition of organic matter proceeds rapidly and continues throughout the year. In cold climates with short growing seasons, slow decomposition may permit accumulation of litter and humus to such an extent that water, percolating through, becomes highly acid and leaches out minerals in the upper horizons.

Nitrogen fertilizers have often increased tree growth but are too expensive for general use in forests. Experiments in Washington have shown that carefully controlled applications of nitrogen can improve the quality of Douglas-fir grown for Christmas trees.

When fertilization becomes generally feasible, it may well be done by foliage application rather than through the soil. This will allow rapid applications to extensive areas and efficient use of the fertilizer. Broadcast applications of fertilizer can be detrimental. Weeds and grasses may respond vigorously to fertilizer and smother pine seedlings or rob them of soil moisture.

Some of the most extensive soil amendment and fertilizer tests conducted in the United States were made in connection with the littleleaf disease of shortleaf pine. Fertilization with 200 pounds of available nitrogen to the acre, from sodium nitrate or ammonium sulfate, prevented the onset of disease symptoms in healthy trees and improved diseased trees. Still better results were obtained when potassium and phosphorus were included.

The micronutrients the trace elements may increase tree growth even when applied in small amounts.

Many plantations of Monterey pine in Australia were growing very poorly except the trees next to fence rows. Investigation revealed that the soil was deficient in zinc but that the rainwater dissolved minute quantities of zinc from the galvanized fence wire. Growth in the entire stand was stimulated by adding tiny amounts of zinc to the soil.

Some elements are absolutely necessary in trace quantities but are toxic in slightly higher concentrations. In some agricultural soils in Florida, toxicity symptoms appeared when molybdenum was added every year for 5 Years instead of once every 5 years.

Levels of forest soil fertility can be raised temporarily by burning the litter and ground cover. Burning releases nonvolatile minerals, but the loss of potential humus may eventually cancel the immediate gain. Studies in California and Oregon indicated that only a small percentage of the land area of a burn actually receives a severe burn. Both pH and soil fertility are increased for a few years; if the soil erosion hazard is not increased, the survival and growth of planted tree seedlings may be excellent.

Fertility problems in the Lake States sometimes have been corrected by breaking a hardpan to release mineral elements. Plowing has proved to be highly satisfactory but cannot be done if the pan is too deep to be reached with a subsoil plow.

COMPACTION OF THE SOIL, so that roots cannot penetrate, sometimes is a problem. Some cultivated land in Mississippi has been abandoned because of compaction of soil and formation of plowsole. Cottonwoods are often planted in those areas. If the plowsoles are ripped with a chisel before trees are set out, the roots develop faster, and the available water is increased.

Repeated trampling by grazing cattle, especially when the soil is wet, can injure a site through destruction of organic matter, increased compaction, reduced storage of moisture, increased light intensity, lower humidity, and higher soil temperatures.

Heavy logging machinery should not be used on soils or in seasons when compaction is likely.

Synthetic soil conditioners may have use in restoring compacted soils in intensively used areas like parks, logging ramps, and campgrounds, but they have not yet proved practical for general forestry purposes.

SOIL STABILIZATION is usually no problem in undisturbed forests, but once the forest cover is removed, erosion and loss of storage capacity may take place. Stabilization difficulties are greatest in the mountainous areas, but they can be serious in flatlands, particularly in soils high in organic matter.

Logging sometimes improves the forest seedbed. On most sites, however, the danger of erosion requires that logging be carried out with minimum disturbance of the ground cover. Depending on the erosive character of the soils, logging in mountainous national forests is done under restrictions: Downslope logging usually is not permitted, grades are carefully planned, diversion ditches are essential, and the logging roads must be "put to bed" after they are abandoned.

Soil stabilization is especially important in the chaparral watersheds of southern California. The year after a fire, erosion may be 30 times greater than before. Sowing black mustard from airplanes is an economical and effective way to get some plant cover to hold the soil in place until the chaparral reoccupies the site.

MANAGEMENT Of Soils in forest nurseries is advanced further than management of forest soils.

Nurseries have a high per-acre value and can be treated intensively. Their soils are important because the success of plantings depends to a large extent on the use of thrifty, disease-free planting stock. Among the more troublesome nursery diseases are root rots, damping-off, nutritional deficiencies, frost-heaving, winterkill, drought, and heat injuries.

Proper drainage of wet nursery sites and care in the selection of water to be used for irrigation will decrease root rot and damping-off. Tile drains or open-ditch drains are effective, especially when the seedbeds also are elevated. The use of highly saline water for irrigation is unwise, as it may lower soil acidity and favor certain seedling diseases.

Nutrient deficiencies and chlorosis Commonly occur in nursery beds depleted by intensive use. Sawdust generally improves soil tilth and the vigor and size of seedlings. Amendments such as nitrogen, phosphorus, and potassium, however, must also be added. Complete fertilizers are more beneficial than applications of single elements unless the latter are special-purpose applications. If any chlorosis and stunting are evident, foliage sprays or soil applications of potassium, phosphorus, magnesium, manganese, and iron may give a favorable response.