Soil moisture and water thrifty crops

Timely rainfall is more critical than normal this growing season. Only the northeast corner of South Dakota has been removed from the drought designation (U.S. Drought Monitor), though it is still abnormally dry. Only 28% of subsoil moisture in the state is rated adequate to surplus in the latest USDA-NASS Crop Progress And Condition Report. Growers abandoning winter wheat and seeding a spring crop may want to consider the answers to these questions: 1) Are some crops thriftier with water and 2) did some crops in 2012 deplete soil moisture more than others?

Some crops have a lower crop water use threshold or need less water before the first harvested bushel is produced by the crop. For example, sunflower and grain sorghum water use thresholds are 50% and 63% of the corn water use threshold, respectively (Table 1). This means these crops require significantly less water to produce harvestable yield compared to corn. Also, crops with longer growing seasons and greater rooting depths have the greatest ability to deplete soil moisture like alfalfa. However, fallow period length and residue cover are two additional interactions to consider. The length of fallow period between the previous crop and the crop you will be planting next, i.e. shorter between corn after soybeans compared to corn after wheat. Research in Brookings, SD has shown greater soil moisture and higher corn yields following wheat than soybean in drier years (Pikul Jr. et al., 2012). Low residue producing crops and a crop with lower carbon to nitrogen ratio residue that decomposes faster may not able to conserve as much soil moisture through reduced soil water evaporative losses. Regional studies have compared and contrasted various crops grown in South Dakota for soil moisture depletion ranking, maximum rooting depth, and water use threshold values shown in Table 1.

Producers across the Midwest realized firsthand in 2012 that the continuous corn yield penalty can be larger in drier years compared to corn in rotation with soybeans. Understanding the ability of the previous crop to deplete soil moisture and the crop water use threshold values can provide some basic agronomic guidelines to improve profitability on the farm, especially under dry or drought conditions.

If growers are considering abandoning winter wheat and attempting to plant a late-spring seeded cash crop, strongly consider sorghum and sunflowers given their lower water use threshold (Table 1). Please remember to check the most recent herbicide label for rotational crop restrictions prior to planting a different crop than intended.

References

· Copeland, P.J., R.R. Almaras, R.K. Crookston, and W.W. Nelson. 1993. Corn-soybean rotation effects on soil water depletion. Agron. J. 85:203-210.

· Merrill, S.D., D.L. Tanaka, J.M. Krupinsky, M.A. Liebig, and J.D. Hanson. 2007. Soil water depletion and recharge under ten crop species and applications to the principles of dynamic cropping systems. Agron. J. 99:931-938.

· Pikul Jr., J.L., S.L. Osborne, and W.E. Riedell. 2012. Corn yield and nitrogen- and water-use under no-tillage rotations. Comm. Soil Sci. Plant Anal. 43:2722-2734.

· Stone, L.R. Stone, A.J. Schlegel, A.H. Khan, N.L. Klocke, and R.M. Aiken. 2006. Water supply: Yield relationships developed for study of water management. J Nat. Resour. Life Sci. Educ. 35:161-173.