Whether the enterprise is cotton, corn, cattle, or grain sorghum, water is essential for its production and the single most important aspect of production that determines yield. Said another way, “Water is all we sell in agriculture.” Therefore it is vital that growers manage rainfall and soil moisture properly. Of course, Mother Nature has to provide some first and after several tough growing seasons it seems that there is a little optimism back in our long range forecasts. However, we must also be prepared to capture it.
Effective rainfall refers to the percentage of rainfall which becomes available to plants and crops. It considers losses due to runoff, evaporation and deep percolation. There are several things that can be done to help minimize those loses before we get that next rain, although many variables like soil texture are out of our control. One inch of water that does not run off will wet a very coarse soil to 12 inches deep; but it will take more water to wet a loam, 1.5 to 2.0 inches and even more, 2.5 inches to wet a clay soil. Again this is assuming that no water runs off.
The mist, drizzle and showers which often amount to a quarter of an inch or less obviously do not run off and so the water has wet the soil. The only problem is that we can generally assumes the first 1/10 inch of rain is lost to evaporation and in most cases the soil is only wet ˝ to maybe an inch deep. The effective root zone of most plants is 3 feet. Generally, the water infiltration rate of clay is 2 to 6/10ths of an inch per hour. Therefore, we assume that any additional precipitation amounts above 2 inches are lost to runoff.
However, clay has a water storage capacity of between 2.5 to 4 inches per foot of soil. So with timely rainfall many of our clay soils can store up to 16 inches of rainfall within most plants root zone.
In addition to texture we can do little to control topography or the intensity of a rainfall event. However tillage practices, degree of crop residue, our rotation practices, and type of crop can be used to influence rainfall effectiveness. Cropping systems that enhance rainfall capture and storage during the season offer the most promise for increased dryland yields. Additionally, soil erosion is dramatically reduced.
The primary reason for any tillage operation should be to establish a proper seedbed for optimal germination and emergence. Any additional tillage operations waste water through evaporation. Deep chiseling or ripping should be done early and followed by another tillage operation to close up the ripped soil channels. Otherwise significant moisture can be lost from open chisel channels. Evaporation losses can be minimized by performing several tillage operations within a short time period. Tillage equipment connected to perform several operations per pass is especially effective in reducing evaporation loss.
Combining reduced tillage with rotation to high residue crops can increase the amount of crop residue left in the field. When adequate residues are available and conservation tillage is used water capture is enhanced. Increased levels of crop reside help protect the soil, slow water moment across a field and allow for greater infiltration. Residue also protects the soil surface from rain drop splash which can reduce soil erosion as well as reduce evaporation by covering a portion of the soil surface.
During the growing season, crop type also affects runoff. Logically, a wheat crop would have a lower average runoff than sorghum or cotton. Therefore, a no-till wheat crop would yield substantially less runoff than a conventional-till cotton crop.
Let’s hope that we continue to benefit from a little rainfall and we can capture it with a few of these practices.
Individuals with disabilities, who require an auxiliary aid, service or accommodation in order to participate in any of the mentioned activities, are encouraged to contact the County Extension Office eight days before all programs for assistance. Extension programs serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability or national origin.