Earl D. Vories

Soybean growth and yield response to saturated soil culture in a temperate environment

Saturated soil culture (SSC) is a production system developed in semiarid tropical Australia that reportedly increases soybean (Glycine max L. (Merr.)) yield above that obtained with conventional irrigation. With SSC, water is maintained in furrows between beds from early vegetative stages until maturity. The objective of this research was to evaluate SSC of soybean as an option in temperate regions for rotations in a rice-based production system. Soybean was sown in 1994 and 1995 at Keiser, Arkansas, on 15 cm high beds, spaced 1 m apart in fields precision-graded to 0.15% slope. In 1994, the cultivars were Hutcheson (MG V) and Manokin (MG IV), and in 1995, the cultivars were Asgrow 6297 (MG VI) (A6297) and Hartz 5545 (MG V) (H5545). In both years, the irrigation treatments were nonirrigated, furrow-irrigated at a 50 mm soil water deficit, and SSC. In agreement with reports from Australia, the SSC treatment resulted in leaf yellowing after treatments were established, this yellowing was associated with a lag in biomass and N accumulation in comparison with the furrow-irrigated treatment in 1994. In 1995, N accumulation rate decreased in SSC during the acclimation period, but there was no effect on biomass accumulation rate. In contrast to reports from Australia, yield was not increased by the SSC treatment. In 1994, seed yield from the SSC treatment averaged across cultivars was 40% below that from the furrow-irrigated treatment. A similar yield decrease for the SSC treatment was observed in 1995 for H5545. For A6297, however, the SSC yields and furrow-irrigated yields did not differ. In 1994 for both cultivars and in 1995 for H5545, there was a strong negative response of seed yield to depth of water in the furrow of the SSC treatment. It was concluded that there is no yield advantage from a SSC management system compared to furrow irrigation at the Arkansas site. A positive yield response of SSC may be limited to arid environments where warm temperatures and high irradiance levels contribute to overcoming the detrimental effects of SSC following treatment establishment.

Response of cotton to different soil water deficits on clay soils

SummaryCotton was grown under sprinkler irrigation on a silty clay soil at Keiser, Arkansas, for the 1987, 1988 and 1989 growing seasons. Irrigation treatments consisted of maximum soil water deficits (SWD) of 25, 50 and 75 mm and a nonirrigated control. While the irrigated treatments were significantly different from the control for plant height and total seedcotton yield, significant differences among the three irrigated treatments were only observed for plant height. Yields were significantly lower in 1989 than in the other two years of the study, due in part to later planting. The 3-year averages for total seedcotton yield were 3280 and 2870 kg ha−1 for irrigated and nonirrigated, respectively, for an average increase corresponding to irrigation of 416 kg ha−1 or 14.5% of the nonirrigated yield. The maximum increase was observed in 1988 as 602 kg ha−1 or 20.6% of the nonirrigated yield for that year. The 75 mm allowable SWD was the most efficient treatment and resulted in a 3-year average of 3.85 kg ha−1 additional seedcotton (above the nonirrigated) harvested for each 1 mm of irrigation applied. Maintaining the SWD below a 75 mm maximum required an average of four irrigations and 110 mm of irrigation water per year.

Scheduling Irrigation on Non-Flooded Rice

While continuous-flood irrigation, the most common method for US rice production, can have a fairly high application efficiency, factors such as soil variability and the size of most Mid-South farming operations combine to reduce the efficiency in many cases. Center pivot irrigation is one potential way to reduce water use in some cases and bring rice into the crop rotation in other situations. Rice was produced at the University of Missouri Delta Research Center Marsh Farm at Portageville in 2009 and 2010 and irrigated every other day with a 150-m-long center pivot irrigation system. An experimental crop coefficient function was developed and included in a beta version of the Arkansas Irrigation Scheduler to estimate the daily soil water deficit (SWD) and daily short grass reference evapotranspiration (ETo) was calculated from weather data collected on site. Weather conditions were warmer and much drier in 2010 and ETo was higher each month. In 2009, there were a total of 34 days with irrigation and 414 mm of water applied. In 2010, there were a total of 45 days with irrigation and 503 mm of irrigation water applied. The AIS appeared to respond as expected with the frequent irrigation; therefore, the next phase of the project will use the beta version of the AIS to schedule irrigations based on allowable SWD. The findings should indicate whether the current crop coefficient in the AIS is adequate and allow producers a system for scheduling center pivot irrigation on rice.