The conventional (i.e. USDA) method of irrigation and water management is wasteful.
A brief presentation of the Hydrologic Cycle was included in the preceding chapter. My intention was to impress the reader with an important concept: water is a function of the land. Like the land, and things which grow on the land, water too has been badly misused. We may settle in arid regions where streams flow only during cold, non-growing seasons. So we have to divert water from stream channels or impound it behind dams. Then we over-irrigate, causing nitrate leaching and the establishment of pathogenic fungi. Commercial fertilizers and poisonous sprays are then used to counteract these evils. Or we may farm the rich bottom land—but must first drain the meadows and valleys of stored water. The tile drainage systems employed lower the water table and contribute to down-stream flooding. We may cut or burn forests and native grass to graze cattle or plow the land. Then soil-depleting cultivated plants replace native vegetation: tillage practices leave the land stirred up and exposed to the ravages of wind and rain. Agriculture then becomes, for the most part, an occupation dealing with floods and drought, erosion and infertility, insects and diseased plants.
Consequently, as a function of the land, water and water management become very closely interrelated to soil and the way in which soil is used. Organisms and plant roots living in the soil remove oxygen and respire carbon dioxide. This free movement of carbon dioxide out, and oxygen into the soil is a first criterion of healthy plant growth. Standing surface water, for instance, may contribute to crop damage by impeding this action. Flooded soil encourages undesirable bacterial transformations: when soil aeration is poor, plant roots have difficulty in excreting carbon dioxide, and beneficial aerobic (airborne) microorganisms cannot function. Anerobic (waterborne) micro-organisms then take over and reduce valuable nitrates to toxic nitrite and gaseous nitrogen.
A leaching action—caused from excessive rainfall or irrigation—also contributes to an impoverished soil-condition by washing essential nitrates through the soil profile. The effect of percolating water on a soil's nutrient reserve depends a lot on the structure and texture of the soil. Heavy (clay type) soils will hold more water without nutrient leaching. The structural aggregates of heavy soils retain nutrients as they allow water, to drain around them.
Tillage operations also impede plant growth—mostly through compaction of the soil. Heavy equipment compaction reduces oxygen diffusion as well as obstructing root growth. Contrary to popular opinion, even light tillage wastes more soil moisture than it saves. As particles of soil are stirred up by tillage equipment, all sides are exposed to the air—which permits that much more moisture to evaporate. No more moisture is available to a crop which is cultivated than is available to a comparable crop uncultivated. One despairs at the wasted effort in "dust mulching": once a dry layer is formed on the surface of the soil, no amount of hoeing or cultivating can appreciably reduce the evaporation rate. And the common practice of lightly cultivating immediately after irrigation can be even more detrimental to a crop. Cultivated soils tend to cake and crust on wetting and drying: few empty pores remain where oxygen can diffuse, and water is held against drainage. Cultivation destroys surface "feeder" roots. And for other reasons, too, (which will be detailed in the following chapter) the Roto Tiller is seen as the most undesirable piece of equipment employed on most "organic" homesteads.
A proper water management program can be established once one understands the basic principles of water usage in relation to the growing plant and in relation to the soil. When it rains—or when one irrigates—old air is forced out and new air is pulled into the soil by the downward water movement. In its passage through the atmosphere, water absorbs traces of carbon dioxide which make it slightly acid. Certain minerals are thereby partially dissolved by this acidity: water acts as a solvent for the carbon dioxide and oxygen that the plant obtains from the atmosphere. Water is also the medium through which the plant obtains nitrogen and mineral nutrients from the soil to the plant and combines with nutrients entering plant leaves directly from the air.
In a "good" soil (as defined in the following chapter on Soil Management) water is quickly absorbed. A certain amount of reserve is held in the soil by a sponge effect (2/3 saturation is considered an optimum water content of most soils). Excess water is held in the water table. The minimum permissible depth of the water table depends upon the crop being grown: fruit trees, for instance, require a deeper water table than does grass.
The first principle, then, of proper water management is to increase the subsoil water storage capacity at depths where it will be free from evaporative losses. Water in subsoil depths should benefit the plant through a low "capillary" feeding of the root system. When one realizes that wheat, beans and peas, for instance, use about 200 pounds of water for every pound of dry matter produced, one can better appreciate the importance of this dynamic subsoil water storage. Again, the amount of water transpired for each pound of dry matter produced is much less on good soils than on poor ones.
As water transpires from a leaf, it has to absorb heat in order to vaporize. This is one way by which water regulates the temperature in a plant. During the middle part of a sunny day, the photosynthesis process can be reduced by sprinkling the plants during this hot, midday period.
The cooling effect of midday sprinkling consequently reduces respiration and increases net photosynthesis. The time-worn advice about sprinkling only during the cool evening hours of the day is just one more old-wives' tale.
It doesn't take a very long farming experience in a semi-arid region to fully appreciate some basic water management concepts. For one thing, one should try to control as many environmental growth factors as possible—so that water becomes the one limiting factor. Someone found that the application of manure to unfertile soil reduced from 500 gallons to 300 gallons of water required to produce 1 pound of corn. Proper fertilization is essential for an extensive and vigorous root development—which is in turn necessary for an effective exploitation of subsoil moisture. Surface evaporation can be significantly limited by mulch planting.
More will be said about mulch planting in ensuing chapters, but to the extent that mulch saves water and soil, it should be touched upon here. Mulch planting is the planting of new crops directly in the residue of the previous crop without prior land preparation. Crop residues left on the soil through winter helps to conserve water through absorption, and also in the form of accumulated snow that would otherwise be blown off.
Contour farming is becoming widely used on sloping land. Planting on the contour naturally reduces the velocity of water movement: more water is conserved through soil infiltration and percolation.
Crop management practices can become further methods of controlling environmental growth factors. The earliest safe planting date should find seed in the ground. This enables the seedlings to utilize accumulated winter moisture and at the same time lowers the evapo-transpiration rate. Crop sequence is also important: shallow rooted row crops like corn do not fully utilize available soil moisture; deep rooted crops like grains do. So one is prudent to follow-up a corn crop with grain or alfalfa, which will benefit from the soil moisture untapped by the corn.
Fallowing is a common farming practice where the distribution of rainfall is uneven and sparse. The land is not cultivated, but allowed to store water for use by the next crop. That is, one crop is grown from moisture received in 2 years. Fallowing is an inefficient method of moisture conservation, but does illustrate the extent to which water can be stored in a heavy soil.
It is well-nigh impossible to indicate how much water a given plant requires during its growing season. For one thing, soil properties have a great bearing on moisture retention: the coarser the particle, the less water it will hold. Sandy soils have a capacity of less than 1-inch of available water for a foot depth, whereas clay soils retain more than 3 inches. For a vegetable garden, an equivalent of 1-inch of rain is considered adequate in a single downpour: a garden 1/10 acre in size requires 3000 gallons! Most vegetables require .10 to .20 inches of water a day or about 3 to 9 inches a month. Research at Kansas Experiment Station disclosed some interesting facts about irrigation: wheat seeded in dry soil yielded 5 bushels per acre; where the soil was wet 1 foot deep, the yield was 9 bushels; soil wet 2 feet deep yielded 15 bushels; soil wet 3 feet deep yielded 27 bushels.
The competition between plants for available water is fierce. Small plants, for instance, have little chance for survival when they are within reach of tree roots. Crop yields can be increased in very dry seasons by increasing the distance between rows. This reduces the demand for water during the early part of the growing season, which therefore increases the amount of soil water available as the plant approaches maturity. In cases where land is plentiful and water scarce, it has been found to be more efficient to irrigate a large area with a small amount of water, than it is to irrigate a small area with a small amount of water. Seven inches of water on 4 acres produces three times the crop yield of 30 inches applied to 1 acre. Irrigation is a Pandora's box: its use raises the lid of many problems. These problems are associated mainly with soil management: drainage, soil structure, aeration, leveling, organic matter, mineral deficiency and toxicity, salt accumulation and general soil infertility. As pointed out in the previous chapter, water development has subtle but far-reaching influences: the hydrologic balance can be easily upset by man tampering with his environment. Introducing irrigation into a valley is an especially good example of how this balance can be upset. More particularly, one's homestead soil and plant population can be adversely affected—especially in arid regions. Irrigation water contains salt. Most of the water applied evaporates—either through the plant or on the soil surface. The salt remains, and must be washed away into the subsoil below the root zone, or into drainage canals. About one-fourth the amount of water used in irrigation is thus used to wash the salt out of the growing zone. And with the bath water goes the baby: most irrigated soils suffer severe nitrogen and phosphate deficiencies caused from the leaching of plant nutrients.
An accurate prediction of a soil's drainage requirements thus becomes the first element in selecting land for irrigation. As previously illustrated, water drainage through a sandy soil is .more than twice as rapid as through a heavy, clay soil. Soil depth, degree of land slope, and regularity of topography also influence irrigation procedure. Any amount of land leveling can be very expensive. Sandy soils which erode readily should be limited to low slopes. Clay and gravelly soils can be irrigated on steeper slopes without so much danger from erosion.
Actual water supply is another, equally important consideration for the selection of an irrigation method. Supply should, of course, be adequate and reliable. A small, constant-flow stream is adaptable to sprinkler irrigation whereas a large intermittent stream is adaptable to surface irrigation. To achieve the maximum utilization of soil and water, deep rooting into the subsoil should be encouraged. Light irrigations applied frequently will restrict root penetration and increase the degree of drought damage when dry periods occur.
Soil and water factors favor one or another of six different methods of irrigation: Wild Flooding, Basin, Border, Furrow, Sprinkler, and Subirrigation.
A small farm pond is practically an essential requirement of every owner-built homestead. As a reservoir, it becomes ideal for any type of crop-irrigation program. It can be used for livestock watering, for raising fish, ducks and geese. The fringe benefits of a farm pond are many: for recreational uses the pond can function for summer swimming and winter skating. It also serves as a convenient water source in case of fire.
Without question there have been more unsuccessful pond building attempts than successful ones. Reasons for failure are many and varied. There isn't space here to go into all the engineering details of small dam construction, but some of the obvious criteria should at least be mentioned.
Keep several things in mind when choosing a pond site. First, seek a site that offers the maximum amount of storage area with smallest dam practicable. Ideally the site will be located at a point higher than the homestead for possibilities of gravity-flow irrigation. A steep-sided valley where the stream runs slow is ideal: the greater cross sectional rise the shorter the dam; the flatter the longitudinal section the further upstream water will be impounded.
Second, investigate the geological strata closely. A concrete dam is a practical consideration where outcropping of granite or basalt extend across the valley or near the surface or where a good rock foundation is present. Other types of loose rock outcroppings along the banks should be avoided. Sometimes a shallow layer of soil will cover objectionable gravel and shattered rock. Ideally, for an earth fill dam, a site having a large percentage of clayey material with some silt or sand should be chosen. Too much clay causes cracks when dry and slippage when wet; too much sand causes seepage percolation.
An adequately designed spillway is most important in farm pond construction. The purpose of the spillway is to carry away surplus runoff: it may consist of a mechanical-type control or a drainage ditch planted to some protective ground cover. This latter type spillway should be clear of the dam and cut out of solid ground.
Farm pond management is another very much involved topic and again will only be briefly touched upon here. A pond managed for wildlife, fish, and recreation should be fenced. This will protect the spillway, fill, and pond-edge from livestock trampling. A sharp bank should be maintained around the perimeter of the pond to avoid warm and stagnant water. Water less than 2 feet deep has little value for fish, and shallow water encourages mosquito and weed growth.
Tree, shrub, and deep-rooted legume growth should be discouraged from growing on the fill. Trees planted around the pond should be coniferous varieties, not broadleafed, to minimize evaporation. A row of correctly placed conifers will reduce evaporation losses by sheltering the pond from winds which might otherwise ruffle the surface of the water. A wave action increases the evaporation manifold. Wave action and rain action are the major sources of erosion in a pond.
Erosion from rain may be a fitting subject on which to end this chapter. Erosion is like pollution: it suggests some grave mismanagement practice at some distant point of origin. With erosion, it is the whole system of agri-business which is at fault. Rains, for instance, are heaviest during that part of the growing season when row crops are least able to provide ground cover. This fact suggests a different practice, one that allows a ground cover and row crop growth simultaneously. Some far-sighted agriculturalists found that when weeds were grown with corn, the corn yield increased.
Weeds are not the water robbers that people once imagined them to be: they are actually conditioners of the soil. Weed growth can open up the soil and enlarge the feeding zone of other crops. Crop roots will follow weed roots deep into the subsoil in search of water.
A proper water management requires that the soil is used within its capacity. One's homestead may be sectioned into crop land, pasture, woodlot, and wildlife refuge depending upon soil structure and depth, movement of water and air through the soil, land slope, and susceptibility to water and wind erosion. A complete thesis on soil management is called for at this time. This will be presented in the following chapter.