Forages Fit Uncertain Water Supplies
Forages are a flexible and well-adapted choice among irrigated field crops when irrigation supplies are uncertain.
The
continuing drought is causing many irrigators to struggle over crop planting
decisions. Their struggle stems from the uncertainty over the total amount
of water supplied and whether that water will be available throughout
the season or only during the spring and early summer run of water. Many
traditional field crops need the certainty of available water throughout
the growing season and especially during each crop’s critical growth
period. Applying irrigation water to forage fields may be the best choice
this year because of their inherent responsiveness to water and adaptability
under mid and late summer water shortages.
Forage crops can be harvested at any growth stage and thus escape drought induced crop failures through early harvest. Secondly, established perennial forages will remain viable during drought periods only to re-initiate growth upon resumption of soil available moisture from either rainfall or irrigation. And finally, annual forages may be seeded as a relatively inexpensive opportunity crop or to utilize limited irrigations.
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| Figure 1. Forage yield vs. water use |
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| Figure 2. Grain yield vs. water use |
Forage crops have a linear water response relationship without an initial irrigation requirement (Figure 1). On the other hand, grain and oilseed crops require a minimum quantity of water for plant establishment prior to filling the crop’s yield potential (Figure 2). Forages have the advantage in having a harvestable unit produced for each additional inch of water supplied.
When the supply of irrigation water is insufficient to supply the full seasonal water requirements of alfalfa or other cool season forage it is recommended to irrigate fully in the spring. For alfalfa, the first cutting should be emphasized with the possibly to take later cuttings should irrigation water supplies continue to be available. It is not advisable to try to “spread out” an insufficient water supply and deficit-irrigate for the entire season. Forage production is significantly reduced when plants are forced into and out of dormancy with regularity. The amount of irrigation water required per ton of alfalfa is less for the first cutting than for the second or third (Table 5). Temperatures are cooler in the spring and the chance of rainfall is greater. First-cutting yields usually surpass later cuttings.
Similarly, moderate temperatures create favorable growth conditions in September, especially in Colorado’s high plains region and western slope river valleys. In these areas, the average first killing freeze, below 24º F are normally expected in late October or in many years well into November. In these areas, when water is available, a mid to late August irrigation can be beneficially applied and utilized for a fall harvest.
Research and field experience throughout the west have demonstrated that irrigation water can be withdrawn or reduced following the first cutting without significantly reducing stand density or yields the following year. Soil moisture deficit forces alfalfa into drought-induced dormancy. The stand usually fully recovers when it receives adequate water the next production season.
Small grains can be seeded in the early spring and winter wheat can all be harvested as a forage crop. These cool season grasses can be used to utilize winter stored soil moisture and efficiently use precipitation and early season irrigations to produce good tonnages and high quality forages. Wheat, barley, and triticale, haying should be completed before these grasses enter the boot stage of development. Oats can be swathed for haying up until the mid-dough stage of development, but care should be taken that the oat glumes do not begin to dry and initiate tanning. Care over livestock health issues, grass tetany and cow asthma should be taken when grazing these spring grains.
Warm season forages can be seeded in the late spring in many low elevation areas of Colorado as an opportunity crop. Forage sorghum, sorghum x sudan hybrids, and forage millets are often seeded in both dryland and irrigated fields. They have an advantage in that, once established, they can persist through weeks of heat and drought until significant rainfall occurs or irrigation is applied. Similarly to alfalfa, their growth and harvest potential is dependent upon crop evapotranspiration which is directly affected by precipitation and irrigation supplied soil water. Warm season forages can be very productive and quality can be good if harvested (repeatedly) during vegetative stages of growth. However, as a rule, warm season grasses tend to have higher lignin contents than cool season grasses and should be marketed accordingly.
As with all non traditional forages, make sure that the forages can be utilized on farm or that a buyer is reasonably secured before planting these forages. In addition, pay attention that the quality desired by the buyer is realized through proper swathing and haying timing. The producer and the buyer can negotiate the forage price over the balance of harvest quality and production.
