| Grazing and rangeland development for livestock production |
|Management of rangelands and other grazing lands of the tropics and subtropics for support of livestock production. Technical Series Bulletin No. 23|
|IV. The elements of productive grassland management.|
a. A comparatively dense cover of grasses and forage legumes on the land provides the best protection known against soil erosion from rainfall runoff, and against wind erosion. A around cover of grasses and legumes, also is the most effective method yet found for increasing infiltration of rains into the ground surface, and of holding it in the soil profile for use by plants for as long as it lasts. Further, water losses from the soil by direct evaporation, and by transpiration from leaves of plants is reduced by a grass-legumes cover on the soil. In general, the most effective use of water stored in the soil profile for production of usable for ace for livestock is that provided by a strong growth of forage grasses and legumes composed of species that are adapted to local climate and soil. Such plant cover is more efficient in use of water to grow forage than is true of brush and scrub trees. Where forage grasses and legumes are not adapted and do not survive in semi-desert regions, the browse plants may constitute the most efficient species for livestock support (See item 4.e.).
From the foregoing, it is evident that maintenance of a strong grass-legume cover will result in the most efficient use of rainfall in semi-arid and subhumid regions. Where overgrazing and other harmful management practices have denuded the land, the re-establishment of a grass-legume cover on the land should result in retention and utilization of rainfall that currently runs off and is lost, and produce the growth of forage in greater abundance than now occurs. It must become clear to the herders who use the land, that it can be made much more productive by prudent management.
When this relationship has been demonstrated by practical field trials, the users may then be persuaded to avoid over-stocking and to practice rotation grazing so that all range areas are allowed periods of "resting" and re-growth. This means that the herdsmen must focus attention on the land and forage supply and the means for protecting and nurturing it. It should become clear that the success of livestock enterprises depends on both the protection of land and forage resources and on the welfare of his livestock. The outlook for successful livestock enterprises without stabilized supplies of feed is forbidding. For herders in semi-arid and subhumid regions, this basic dependence of livestock on feed supplies is emphasized with every recurring drought.
b. Waterspreading is often a useful practice in both subhumid and semi-arid regions, as a means of controlling rainfall runoff that would otherwise be lost. By this practice, runoff water is diverted from stream channels or drainage courses that are normally dry but have flowing water after rains occur. The water spreading may have two functions: (1) increasing forage production by spreading the water over nearby smooth sloping land so that it infiltrates and is stored in the soil profile, and (2) reducing gulling and downstream flooding. Rangeland flood waterspreading systems are constructed so that operation is automatic whenever storms result in flood flows. The gentle slopes into which directed water is led should have fairly permeable soil to depths of 30 cm. or greater. Grades of I to 2% are preferred, but grades of 5% may be used if the soil is highly permeable. The water spreading system must be constructed to fit the local terrain. The essential features are a diversion barrier or berm and a system of meandering channels and dikes to direct the flow gradually down slope with sufficiently slow flow to allow infiltration into the soil profile. Dikes and/or furrows are placed to facilitate spreading on the area selected. Design of the water spreading system is best prepared by an agricultural engineer, particularly where costs of construction will be substantial. However, simple but effective waterspreading systems are found in some primitive regions, that have long been used both for crop production on limited areas, and for forage production. On well-designed systems, increased forage production has varied from three- to ten-fold where several natural floodings occur yearly.
c. Terracing to retain water on the land is feasible under some conditions. As in the case of waterspreading, runoff water is intercepted in the stream-bed, and is directed to a series of terraces that are stair-stepped down the slope. Dikes at terrace borders direct the flow across the slope to the entrance of the next terrace, and thence from terrace to terrace down slope. The design of such a system calls for technical expertise, and is warranted only where both the rainfall pattern and the soil type are such that increased production will exceed the cost when prorated over a period of years. Well-established sod of forage grasses and legumes should require very little maintenance effort, when the system has been established. This may be an important means of providing supplemental feed for livestock, that is not available otherwise.