4 Ah .^.<^1'*^^'' '^^ ^^'Hic'à'^. A Manual on Conservation of .Soil and Water HANDBOOK FOR PROFESSIONAL AGRICULTURAL WORKERS UNITED STATES DEPARTMENT OF AGRICULTURE Soil Conservation Service . Agriculture Handbook No. 61 Prefac e All over the world people are becoming more and more aware of the importance of keeping their agricultural land permanently productive. They are coming to realize that productive land is the source of human sustenance and security—that it is basic to the welfare of people every- where at all times. Essential foods, vegetable oils and fats, leather, fibers required for cloth- ing and cordage, forage for livestock—these are indispensable products, and for our supply of them we are dependent entirely or largely on the soil. Wood products, tobacco, and various other agricultural products come also from the soil. In order to keep the land productive, a good conservation program is imperative. Soil and water conservation is the basis of such a program, and also helps improve land impoverished by erosion and overuse—makes it more productive so that it can support more people. For effective conservation of soil and water, we must treat and use the various kinds of land according to their capability and need. To do this it is necessary to study the land carefully, so as to be able to fit conservation practices and structures to the various kinds of land. These measures can be used singly on some of the more stable land, but more often than not they must be used in combinations that will mutually support one another and thereby give greater strength, durability, and productiveness to the land. Moreover they must be used within the eco- nomic limitations and in accordance with the facilities of farmers. Soil conservation stores more of the runoff from excess rainfall in the reservoir of the soil for subsequent crop use; and this much water is kept out of streams, thereby contributing to flood reduction. Today these techniques of soil and water conservation are being prac- ticed in many countries with much benefit to great numbers of people. Agriculturists throughout the world now generally agree that a change- over from wasteful to protective and fruitful land use and farming methods should be brought about as quickly as possible. It must be brought about, that is, if individual nations and the world as a whole are to build a healthy economy, with agricultural production wherever possible adequate to feed, clothe, and shelter the people and to supply materials required in time of emergency. Soil erosion is the most serious and prevalent disease of the land. Vast areas have been so damaged that they no longer can be used to grow any- thing of value to human beings. Much of the good land that remains is in danger, from overuse and improper use. Populations are expanding nearly everywhere, and pressure on the land is heavier than ever before. The primary purpose of soil and water conservation is to prevent soil erosion and heal its scars where it has not advanced too far to respond to curative methods. This involves, in many instances, changing the uses to which land is put. It has been found, in fact, as stated previously, that the first requisite to conservation of land is to fit the crop—whether culti- vated crops, trees, or grazing plants—to the capabilities of the soils and the water available. Equally important is the use of engineering and agro- nomic practices which, conjointly, will control and conserve water and counteract the erosive action of both water and wind on the soil. In conjunction with these two basic principles, there must be put back into the soil what is taken out—organic matter, nitrogen, the mineral plant foods. And proper amounts of moisture for plant growth must be maintained through sound conservation measures, including irrigation I where it is needed and is feasible. Also, the many machines and tools now coming into use over the world must be used according to the capa- bility and need of the land, otherwise both the machines and the land are likely to suffer. , It IS on these premises that modern soil conservation has been planned and developed. Its ultimate objective is to achieve a sustained-yield type of agriculture based on principles and practices that will protect and im- prove land while it is being used, rather than one that will further deplete or destroy its productive capacity. This handbook explains the causes, processes, and consequences of soil erosion and depletion, and describes the major soil- and water-conservation measures which, when applied to the land in correct combinations, will greatly reduce or prevent soil erosion, improve fertility, and increase yields. Soil conservation is an international concern. Eroded and impoverished land that was formerly productive is now scattered throughout nearly all countries. Responsibility for care of the productive land rests on all the people of a country. This handbook was prepared for the use of officials, technicians, and agriculturists interested in controlling wind and water erosion and making better use of rainfall available and irrigation water throughout the world. The practices and recommendations are based very largely on the experience and technical publications of the Soil Conservation Service of the United States Department of Agriculture and other agencies in this and other Departments. Further details can be had by consulting technical publications issued in the United States and other countries. II CONTENTS Page What is soil erosion 1 Erosion bv rainfall and running water 7 Erosion by wind 17 Erosion—past, present, and future 21 Classifying land capability 23 Facts obtained in the field 24 Significant variations in land features 24 The classification scheme 26 Land-capability classes 26 Subclasses and units 28 Land suited for cultivation 29 Land not suited for cultivation 38 Land not suited for cultivation, grazing, or woodland 43 Using the physical inventory 45 Choosing practices to fit the land 45 A conservation farm plan 46 Preventing and controlling gullies 49 Woodland improvement 60 Tree planting 60 Woodland management 69 Terracing 79 Terracing and agronomic control measures 80 Hvdraulics of terrace design 81 Velocities in terrace channels 82 Tvpes of terraces 83 planning the terrace system 89 Terrace specifications 96 Terrace staking, realinement, and marking 98 Terrace construction 100 Farming terraced land 102 Stripcropping 108 Rotations 110 Contour tillage and terraces Ill Liming, fertilizing, and manuring 112 Stubble-mulch farming 112 Width of strips 112 Grass waterways 113 Managing stripcropped fields 114 Cover crops 117 Soil-depleting, soil-conserving, and soil-building crops 121 Soil-depleting crops 121 Soil-conserving crops 122 Soil-building crops 123 Pasture improvement 126 Selecting land for pasture 127 Pasture on land suited for cultivation 127 Land that should be put in pasture 128 Seedbed preparation and seeding 129 Treatment of newlv seeded pastures 130 Cultivating and resccding 130 Liming and fertilizing 130 Controlling weeds and brush 131 Effect of methods and intensity of grazing 132 Effect of burning pastures 133 Drainage of pasturcland 133 Pastures compared with harvested crops 133 Grazing practices and livestock management 135 III Rangeland improvement ■« j-iy The grazing Joad j-in Time for grazing ,,q Roration grazing , q Grazing distribution Reservoirs or ponds Spring development y Wells l''^ Reseeding 1'*'' Noxious plants 1''5 Water conservation 147 Contour furrows 147 Pitting 148 Water spreading 150 Reserve feed supplies 151 Conservation irrigation 153 Wasted water, damaged land 154 Problems can be solved 155 Conservation irrigation on the farm 156 Irrigation methods to fit the land, crops, and watet supply 156 Preparing land for conservation irrigation 163 Irrigation-distribution system on the farm 163 Improving the water supply 164 Farm drainage J66 How drainage helps 166 How land is drained ißy Planning a drainage system Igg The outlet 268 Surface drainage i gq Structures used with open ditches 274 Underground drainage -.-j-. Constructing tile drains JOT Maintenance of farm drains , q. Conservation nurseries , q^ Selecting nursery site Tq^ Maintaining soil fertility 7^^ Selecting suitable conservation plants ÍQ7 Production procedures " Winter storage of nursery stock ' ' i^? Grass and legume seed production ^ ^ 206 Issued June 1954 IV What Is Soil Erosion? of all the gifts of nature, none is more indispensable to man than soil. Lying over the rocky core of the earth at different depths, this complex mixture of animal, vegetable, and mineral matter is one of the four prime requisites for life. Along with sunlight, air, and water, soil nourishes all plantlife and supports human life and most animal life. Without it, this planet of ours would be as barren as the moon. Since the dawn of time, soil has been on the move. Rain and wind have scoured away almost constantly at the earth's surface and transported soil particles from place to place. In this way stream channels have been carved out, river deltas have been built up, and whole landscapes have gradually been transformed. But under a protective cover of grass, trees, or other thick-growing vegetation, the rate of soil removal has always been exceedingly slow—no faster, generally, than the normal rate of soil creation. This favorable soil balance prevailing under natural conditions was disturbed almost from the moment when man first started to till the earth for food. Clearing away the wild growth and breaking the ground surface with crude implements, the primitive farmer and his successors unwittingly speeded up the rate of soil removal. But farming probably went on for centuries before soil erosion became a recognizable human problem. It was only when population pressures forced the cultivation of steep slopes or unstable soils that people began to realize dimly that the earth can rapidly waste away unaer the impact of rain and wind.