Using Sod Crops to Improve Your Soil

Learn how rotating sod crops on your homestead can improve the soil, leading to larger harvests.
By Ken Kern
September/October 1972
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Information on the various types of sod crops and where they perform best.
ILLUSTRATION: KEN KERN
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Sod cropping as defined in this chapter is a balanced method of farming which permits maximum output of soil resources while at the same time maintaining and improving them. It is a method that contrasts with Row Cropping  in that sod cropping is basic to water and soil conservation, and essential—in rotation — for the maintenance of high level row crop production.

Without question, sod crops are the most important underdeveloped agricultural resource in the world today. This is true in spite of the fact that they have been around a long time: improved varieties such as alfalfa were known to the Persians and Romans before the time of Christ; clovers were grown in northern Europe in A.D. 800. There are at present 5,000 species of sod grasses in the world, and 1,500 of these are found in the U.S. This number does not include the hundreds of "natives" and weed varieties which agriculturalists refuse to include as economic to American fanning practice.

Due to the numbers involved, it is with some difficulty that we attempt a classification of sod cropping. Some crops are grown annually, some in rotation, and some permanently. Of the annuals, there are warm season and cool season varieties. Grasses are grown in companionship with other grasses or with legumes. And every plant species has an optimum soil and climate requirement. A high-producing sod crop may prove to be valueless on poor soil. And conversely, a sod crop considered undesirable in a productive soil-and-climatic-environment, may be highly regarded on a less desirable site: palatable short grasses like buffalo blue grama, silver bluestem, and sand dropseed are not grown to advantage on fertile sites.

Benefits of Sod Crops

Plant ecologists present the clearest perception of optimum plant development in the presentation of the Climax Growth concept. We are told that there is a subtle response between plants and changes in the environment. Individual plants become more abundant or less abundant in a community, depending upon soil and climate factors. One species is gradually replaced by another higher and more adapted variety, until finally vegetation attains the climax form characteristic of the soil and climate. This is a good explanation of why a climax sod crop is the only important soil builder of any consequence. When a native sod us plowed and put into rowcrop production, a climax has been destroyed but the soil remains productive for many years. When this happens in a humid forest situation the soil becomes unproductive after a few short years, of cultivation; the wider spacing of trees offers little root development and soil-aggregation buildup.

A sod growth, however, reaches climax as more and more topsoil is formed and accumulated. Each succession contributes to the next higher plant development. An example of California rangeland climax is illustrated below.

Climax succession is also apparent when overgrazed or cultivated land is abandoned and sod crops allowed to return: first, annual weeds (crab grass, pigweed, Russian thistle) appear; then so-called poverty grasses (wire grass, broom sedge) replace the native weeds; as the organic content of the soil increases, poverty grasses get so thick they cannot withstand their own competition. Thus, short-lived perennials like bunch grass appear and progress, finally, to semi-climax and climax grasses native to the region.

The importance that weeds play in this succession cannot be overstated. Weeds condition the soil; their vigorous root system opens up the soil, fiberizes it, and enlarges the feeding zone for the benefit of succeeding plants. Grass will return and thrive in a pasture situation only when weeds have first prepared the way; grass has the power to disperse the weeds once the environmental conditions are right.

The director of the Rocky Mountain Forest and Range Experiment Station, Dr. David Costello, studied the value of weeds on the western range. He found that weeds, surprisingly, made up the greater portion of cattle diet. Furthermore, perennial weeds and shrubs were found to have a higher crude protein content than native grasses. From Dr. Costello's research we deduce that low-protein grass pastures would best be grazed in summer when food values are highest. Superior pasture—containing abundant weeds and shrubs—should be grazed in late summer, fall and winter when the food value of grass is low. The nutrient value of standing grass herbage drops during fall and winter, because at that time nutrients drain back into the root zone, whereas the food value of browse plants remains high.

It was the Swiss dairymen who first demonstrated the value of harvesting immature forage. Alfalfa cut at a pre-bloom state has 28% protein and 12% mineral content; at full bloom it contains only 13% protein and 8% mineral. The Swiss also showed that grass under continuously heavy grazing is more nutritious than under light grazing. Frequent cutting promotes a continuous production of young, nutritious shoots. Young forage is more digestible and palatable as well.

I will show in the following chapter on row crops how their value depends primarily upon nitrogen and vitamin content. Now, except for the legume family, sod crops cannot accumulate large quantities of nitrogen. So it makes good agricultural sense to follow a sod crop (grass-legume mixture) with row crops (vegetables). This form of alternate husbandry is called Ley Farming, and it involves the full fertility cycle of crop-soil-animal relationship. A three-year sod cropping program rotates with a three-year row cropping. Ley farming becomes a rather good substitute for green manuring which may require a plowing under of the sod culture for possible soil enrichment.

Although it takes about seven acres of sod crops to equal the production of one acre of row crops, the nutrients supplied cost a fraction of the amount as that of row crops. The Bureau of Dairy Industry (USDA) made a four-year study of the relative cost of producing 100 pounds of totally digestible nutrients. It was found that the return from pasture crops per man-hour-labor is six times more than from corn, and ten times more than from barley.

And there is one other important sod-cropping statistic—this time provided by the Missouri Agricultural Research Station: on a land slope of three degrees, continuously cultivated soil erodes seven inches in 24 years; seven inches of continuously grown corn soil is eroded in 50 years; seven inches of continuously grown wheat soil is eroded in 100 years. But under continuously grown sod pasture it would take 3,000 years to erode seven inches of soil! It is little wonder that advocates of permanent pasture are so enthusiastic. Certainly every homestead would do well to include at least one permanent pasture. This pasture may be gown in companion with scattered tree crops as is often the case in southern forests of longleaf pine growing in open stands with an understory of sod crops. Most sod crops grow best and produce a higher protein level when grown in partial shade.

Although the major portion of permanent sod crops consists of perennial (self-seeding), and long-lived annuals, it may also include short-lived, aggressive and rapidly establishing species as Italian ryegrass. There is no hard-and-fast rule for determining optimum sod mixtures. Agriculturalists at one extreme favor "shotgun mixtures", the indiscriminate mixture of up to a dozen different species. Other experts advocate a two-seed, grass/ legume mix. Somewhere between these extremes lies essential, sod-growing knowledge usable by the small homesteader.

A well-balanced pasture community is analogous to well-made concrete: various plants combine to form a dense ground cover in the same way that sand and cement fill porous spaces around coarse aggregates. An example is the way broomgrass fills in around alfalfa, and ladino clover fills in around orchardgrass.

Since the time of George Washington ("Orchardgrass of all others is in my opinion the best mixture with clover") farmers knew that grass and legumes should be grown together. If grass is grown without a legume companion, nitrogen soil deficiency is likely and the crop will contain excessive energy-giving carbohydrates at the expense of mineral and protein content. If a legume pasture is seeded without a grass companion, more nitrogen becomes available than required; volunteer grasses and weeds will soon invade the legume. So in general it is prudent to sow half grass and half legume in a sod crop mixture. As mentioned in the previous chapter, legumes alone are able to obtain nitrogen from the atmosphere. Nitrogen is "fixed" by symbiotic bacteria which live in nodules on their roots. This is the reason why legumes are less sensitive than grasses to the level of nitrogen in the soil.  

It has been found that the presence of a legume in a sod culture increases the protein content of the companion grass. Corn, for instance, that is gown with soybeans has twice the nitrogen content. The protein content of timothy hay can be increased by growing it with alfalfa. Grass also grows at a faster rate when a companion crop of legume is present. The yield of a grass crop can be doubled when red clover is included in the sod mixture.

Determining Seed Mixtures

Seed mixtures and proportions must be determined with great care. A choice is influenced more by soil and climate than any other factor. Temperature, soil moisture, latitude, altitude, soil pH and rainfall are main considerations. Alfalfa does poorly on wet undrained soils where alsike clover thrives. Studies at the Wisconsin Experiment Station show that an acre of bromegrass/alfalfa mixture provides as much pasturage as 2 1/2 acres of bluegrass. With an oat/soybean mixture, only the oats germinate and grow; an oat/field pea mixture, however, gives a balanced crop. Bromegrass matures early and crowds out red clover; timothy matures too late to make a satisfactory stand with alfalfa. But bromegrass/alfalfa and timothy/red clover are excellent mixtures.

The best companion crop is the one that gives the least competition . . . grass and legume mixtures should produce together for best results. One naturally wishes to extend the grazing season to as much of a year-round program as possible. To do this it may be necessary to have two or more separate pasturesone for cool season sod crops, and one for warm season sod crops. Warm season crops begin growth in late spring, with most growth during the summer. Cool season crops are seeded in the winter and start growth early the following spring. A dormant period occurs here in midsummer, but growth resumes in early fall.

For some unexplainable reason sod crop seeds give greater yields when they have undergone a freezing action to break their dormancy period. So it is preferable to broadcast seed by hand or with the use of a hand-operated whirlwind seeder (e.g., Cyclone Seeder) in the early winter . . . seed that falls on the gound will be covered by the freezing and thawing action throughout the winter months. This dispenses with expensive seed-drilling equipment and springtime tractor compaction of the soil.

Mulch planting is as important to sod cropping as it is to tree and row cropping. Nothing will do more to insure a successful sod crop than a light mulch applied at the time of seeding. Mulch conserves surface moisture and delays seed germination until the soil is sufficiently warm. It also protects seedlings from excessive wind and sun and unwanted plant competition.

A properly managed sod crop progam requires no tillage, no fertilization, no burning. One can begin his pasture operation with a luxurious stand of tall weeds and brush. A mowing machine or stalk shredder is first used to cut or beat up and scatter top growth. Sod crop seeding is done directly in the remaining stubble. The heavy trash covering on the ground is highly desirable, and the tall stubble helps to protect young seedlings. Stubble offers no competition to young sod crops for moisture and soil nutrients.

Mowing is Essential for Successful Sod Cropping

Mowing is the one essential management practice for successful sod cropping. It satisfies a number of necessary sod culture practices by (1) allowing tough parts of the plant to decompose, thereby improving soil structure; (2) making hay or silage from clippings; (3) providing uniformity of gazing and consequently greater total production and (4) maintaining an immature and more nutritious stage of growth. Cease mowing activities in early fall so good ground cover can grow for fall and early winter gazing, and so that the sod crop can be into the winter dormant season with plenty of gowth left.

There is one important rule to remember when mowing or grazing sod crops: TAKE HALF AND LEAVE HALF. Overgrazing is to be deplored. A plant's food manufacturing ability should be constantly maintained.

The goal of any serious pasture program is one of providing for year-round gazing. This is obviously possible in milder or moister climates, but requires concentrated planning in places where the ground remains frozen or covered with snow much of the winter. Pastures are rarely productive for more than a few months at a time, so in northern climates two or more permanent pastures and perhaps several fields for raising supplementary feeds are required to "weather through" gazing stock. In some cases it may be advisable to incorporate ration grazing: a small strip of pasture is cut off from the main field each day. A movable electric fence is customarily used to ration the food.

Modern agribusiness methods for animal feeding limit, the animal to a "dry lot" situation, with sod crops harvested and brought to the animals throughout the year. It makes little sense for the small homesteader to grow, harvest, haul, process, store and then ration feed for his animals when the animal can provide these functions in a more comfortable and sanitary manner out in the pasture. And it has already been pointed out that the dry matter or immature sod crops are higher in protein and nutrients and more palatable than dry matter from mature crops harvested for hay or silage. Research at the Virginia Agricultural Experiment Station shows that the nutrient yield of pasture is 50% greater than for the same crops that were allowed to mature and then cut for hay. Let the animal harvest its own food—and let it spread its own manure.

Grazing Animals on Sod Crops

There is a final consideration in increasing the productiveness of sod crop pasturage: graze several combinations of animals on it simultaneously. Sheep and dairy cows do well on a pasture together; sheep will eat weeds and other plants refused by cows, and plants not required for high milk production. Goats tend to favor types of woody vegetation and are valuable in keeping brush from overtaking a pasture. It is a good practice to let beef cattle and hogs pasture together; hogs eat much of the vegetation overlooked or wasted by cattle.

At these northern regions where some form of winter feed supplement must be provided for, one has the choice of storing feed by drying or by silage. Each process has its pros and cons, so the best approach here is merely to acquaint the homesteader with some of the problems and prospects inherent in each method.

Hay-making involves mowing the crop, raking it into windrows, bailing or bunching, curing, leading, transporting and storing. As mentioned earlier, these processes exact about 50% of the nutrient value from the original crop. And if it rains during the haymaking process, molds may develop and plant nutrients may leach to lower the nutrient value even more. If the moisture content of hay is high at the time of storage (above 30%) heat will be generated during the time of storage. This heat destroys carotene and sometimes causes spontaneous ignition.

The loss of carotene in field-cured hay has stimulated agricultural re search toward improved curing processes. One such method of "barn curing" has been developed by the Virginia Experiment Station, with similar solutions proposed by the Tennessee Agricultural Experiment Station and T.V. A. Partially dried hay is placed over a duct system and hot air is forced out through the hay. Three to four times the amount of carotene is retained using this system of barn curing.

Despite the nutrient losses associated with hay-making, the small homesteader may still find it the most practical method for providing supplemental feed. For one thing the investment in equipment required to process loose hay is minimal. With a full mechanized setup, a ton of hay can be processed and stored by one man in two hours; with hand labor the same man can process and store a ton of hay in six hours. A mowing machine need be the only mechanical equipment required. Hand pitching hay onto a four-wheel trailer is fast and gratifying work. And unloading into a hay loft can be done with a small investment in power forks or slings.

Ensiling sod crops requires much more equipment and expensive storage facilities, though the storage size can be reduced considerably. Loose hay takes four times and baled hay two times as much space as an equivalent amount of dry matter in silage. Silage is not a new process: the Romans knew that crops could be preserved by excluding air. As chopped sod crops are placed in airtight silos, air is driven out by the settling and compaction of the crop. Fermentation takes place as oxygen is replaced by carbon dioxide. Natural carbohydrates are reduced to acids (lactic and acetic) by microbial action. After the oxygen is eliminated silage will keep almost indefinitely. For this reason it is important to force all air pockets out as the silo becomes filled.


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