Supplements and growth promotants containing steroid hormones are routinely administered to beef cattle to improve feeding efficiency, reduce behavioral problems, and enhance production. As a result, beef cattle manure will contain both synthetic steroids as well as a range of endogenous steroids including androgens, estrogens, and progestogens. A two-year controlled study was conducted in which beef cattle were administered steroid hormones via subcutaneous implants and feed additives and the occurrence of 16 endogenous and synthetic steroid hormones and metabolites was evaluated in runoff from beef cattle feedlots and in manure and soil collected from feedlot surfaces. Samples were extracted and analyzed using liquid chromatography tandem mass spectrometry for metabolites of the synthetic androgen trenbolone acetate, 17α-trenbolone, 17β-trenbolone, for the nonsteroidal semisynthetic estrogen agonist, α-zearalanol, and the synthetic progesterone melengesterol acetate, as well as a wide range of endogeneous estrogens, androgens, and f usarium metabolites. Synthetic steroids including trenbolone metabolites and melengestrol acetate were detected in fresh manure and in feedlot surface soils from cattle administered synthetic steroids at concentrations up to 55 ± 22 ng/g dry weight (dw) (17α-trenbolone) and 6.5 ± 0.4 ng/g dw (melengesterol acetate). Melengesterol acetate was detected in 6% of runoff samples from feedlots holding cattle administered synthetic steroids at concentrations ranging up to 115 ng/L. The presence of melengesterol acetate in runoff from beef cattle feeding operations has not been previously reported. Synthetic steroids were not detected in manure or runoff from control cattle. A wide range of endogenous hormones were detected in runoff and feedlot surface soils and manure from cattle given synthetic steroids and from control cattle, with no statistically significant differences in concentration. These results indicate that runoff from confined animal production facilities is of environmental and public health concern regardless of the use of growth promotants.

Careful management of both N fertilizer and irrigation water is required to minimize NO−3 leaching below the root zone in irrigated corn (Zea mays L.) production. Practices related to management of fertilizer N and irrigation water were evaluated in a series of studies conducted at 79 sites in Nebraska, from 1984 through 1988. Practices evaluated included N credit from NO−3 in soil, N credit from NO−3 in irrigation water, realistic yield goal selection, and irrigation scheduling according to crop water use. Nitrogen was applied in field length strips at the recommended rate, and at rates 50 lb N/acre above and below the recommended rate. Groundwater NO−3‐N concentrations at sites ranged from 0.5 to 46.1 ppm. The procedure for determining the recommended fertilizer N rate provided adequate N without reducing yields. Averaged over 79 sites, yield goal was 170 bu/acre; recommended fertilizer N rate was 130 lb/acre; yield was 173 bu/acre; and fertilizer N reduction due to accounting was 45 lb N/acre. Because of the often high NO−3‐N concentrations in irrigation water and substantial amounts of NO5 in soil (ranging from 15–265 lb/acre in 4 ft), grain yield was relatively insensitive to fertilizer N rate. With average values for soil and irrigation water N credits, increasing the fertilizer N rate by 100 lb/acre increased yield by only 1.3%. Decreasing the fertilizer N rate by 50 lb/acre decreased yield by only 2.6%. At the three primary N rates used in these studies (−50, 0, and 50 deviation from the recommended rate), irrigation water NO−3‐N concentration, irrigation water amount, and soil NO−3 level all influenced yield more than fertilizer N rate.

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Highlights Irrigation is key to the productivity of Great Plains agriculture but is threatened by water scarcity. The irrigated area grew to >9 million ha since 1870, mostly since 1950, but is likely to decline. Changes in climate, water availability, irrigated area, and policy will affect productivity. Adaptation and innovation, hallmarks of Great Plains populations, will ensure future success. Abstract. Motivated by the need for sustainable water management and technology for next-generation crop production, the future of irrigation on the U.S. Great Plains was examined through the lenses of past changes in water supply, historical changes in irrigated area, and innovations in irrigation technology, management, and agronomy. We analyzed the history of irrigated agriculture through the 1900s to the present day. We focused particularly on the efficiency and water productivity of irrigation systems (application efficiency, crop water productivity, and irrigation water use productivity) as a connection between water resource management and agricultural production. Technology innovations have greatly increased the efficiency of water application, the productivity of water use, and the agricultural productivity of the Great Plains. We also examined the changes in water stored in the High Plains aquifer, which is the region’s principle supply for irrigation water. Relative to other states, the aquifer has been less impacted in Nebraska, despite large increases in irrigated area. Greatly increased irrigation efficiency has played a role in this, but so have regulations and the recharge to the aquifer from the Nebraska Sand Hills and from rivers crossing the state. The outlook for irrigation is less positive in western Kansas, eastern Colorado, and the Oklahoma and Texas Panhandles. The aquifer in these regions is recharged at rates much less than current pumping, and the aquifer is declining as a result. Improvements in irrigation technology and management plus changes in crops grown have made irrigation ever more efficient and allowed irrigation to continue. There is good reason to expect that future research and development efforts by federal and state researchers, extension specialists, and industry, often in concert, will continue to improve the efficiency and productivity of irrigated agriculture. Public policy changes will also play a role in regulating consumption and motivating on-farm efficiency improvements. Water supplies, while finite, will be stretched much further than projected by some who look only at past rates of consumption. Thus, irrigation will continue to be important economically for an extended period. Sustaining irrigation is crucial to sustained productivity of the Great Plains “bread basket” because on average irrigation doubles the efficiency with which water is turned into crop yields compared with what can be attained in this region with precipitation alone. Lessons learned from the Great Plains are relevant to irrigation in semi-arid and subhumid areas worldwide. Keywords: Center pivot, Crop water productivity, History, Sprinkler irrigation, Subsurface drip irrigation, Water use efficiency.

Abbreviations: C1, first-year corn; C2, second-year corn; CC, continuous corn; CS, cornsoybean rotation; DNM, difference in nitrogen rates at maximum yield; FRV, fertilizer replacement value; HI, harvest index; NHI, nitrogen harvest index; NRE, nitrogen recovery efficiency; NUE, nitrogen use efficiency.