Box 2 - Planning High TDN Yields for Livestock

The TDN (total digestible nutrients) available to livestock from feed and forage is the key to profitable animal husbandry in technically advanced lands. A high TDN yield is best gained from select cultivars, of course. Yet there are options, and systems must be chosen in view of such local conditions as moisture availability, length of growing season, soil type, slope, and so on. On good land that has been progressively cropped, 11 metric tons of TDN per hectare (about 5 tons of TDN per acre) can be obtained either from 56 metric tons of corn silage, 15 metric tons of corn, or 22 metric tons of alfalfa hay. Which route is best? Or if a meadow can be harvested for silage instead of for hay, to yield an additional 25% of TDN, does the added expense justify this choice?

On poorer lands, especially on slopes unsuited to cultivation, yields may amount to only a bit more than 3 metric tons of TDN per hectare (about 1.5 tons per acre). This type of land may be most efficiently exploited by letting livestock graze rather than by trying to produce the 18 metric tons of silage or 4.5 metric tons of grain needed to match this TDN yield. Cost of inputs (fertilizer and capitalization of technology) for high yields on poor land may be so great that intensive cropping may not be the most efficient use! Urging a highly responsive forage such as alfalfa (each metric ton of which removes about 50 kilograms of lime, 6 kilograms of phosphate, and 22 kilograms of potash from the soil) to maximum production on poor soil might require doubling of inputs for an increase of only 50% in output! Adding grass to alfalfa may reduce TDN yields, but may still be the wisest course for protection of soil on slopes.

Obviously, management is a vital factor. Proper timing of fertilization is important, not only to provide maximum yields when needed, but to control the botanical composition of the pasture. Choice of cultivar is significant. For example, white clover may prove to be better on a shallow soil (if moisture is not limiting) than deeperrooted alfalfa or red clover, which are ordinarily more productive. Where moisture is insufficient for maximum corn yields, sorghum may be preferable, or, on stony hills perhaps tall fescue forage. In the southern United States, Coastal bermudagrass, which provides a high TDN yield on good soil, would be inferior to bahiagrass on poor land.

Maximum advantage is not taken of TDN opportunities if a pasture is undergrazed. Yet rotational grazing to allow recovery from overgrazing can increase TDN yields by 50%. If corn is harvested in the milk stage it may yield only two thirds as much energy as silage feed made from the same corn allowed to mature to the dent stage. Yet, delaying alfalfa harvest can impair nutritive quality so much that 50% additional feed grain may be required for equivalent animal weight gain. But too early (or too frequent) cutting of alfalfa can hurt the stand and increase the weeds!

Obviously, managing modern forage production intelligently requires no little technical knowledge. Profitable farming is not for the untrained.