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United States Department of Agriculture

Agricultural Research Service


Location: Cropping Systems and Water Quality Research

2012 Annual Report

1a. Objectives (from AD-416):
Objective 1: Evaluate and optimize production systems for irrigated cotton, corn, and rice to optimize WUE under variable weather conditions that are expected to become more variable with impacts of climate change while considering the constraints of timing for field operations, a limited growing season, and increasingly limited water supplies. 1a: Determine crop coefficient for sprinkler irrigated rice. 1b: Determine water/yield relationships for sprinkler-irrigated rice and cotton. 1c: Compare drought-tolerant corn hybrids to those currently grown. 1d: Develop database of water use variation among rice production systems. Objective 2: Evaluate the suitability of variable-rate center pivot irrigation for crop production on variable soils and in varying weather conditions to determine potential costs and benefits for producers. 2a: Determine the utility of soil apparent electrical conductivity (ECa) and topographic variables for defining management zones to develop prescriptions for VRI management. 2b: Determine the optimum irrigation schedule for rice under center pivot irrigation over a range of sand contents. Objective 3: Evaluate the quality of runoff from irrigated cropland to determine current and potential environmental risks and develop guidelines and BMPs to reduce impact of irrigated agriculture on water quality degradation. 3a: Determine nutrient content of runoff from surface drained land in the lower Mississippi River basin. 3b: Develop guidelines for fertigation for center pivots in humid and sub-humid regions. 3c: Determine greenhouse gas (GHG) emissions associated with different water management strategies for rice production and options for reducing. 3d: Develop a variable source N application system utilizing controlled release nitrogen (CRN) technology to reduce N losses in furrow irrigated cotton.

1b. Approach (from AD-416):
Scientists from both ARS and MU conduct crop production research in southeast Missouri relating to irrigated crop production and irrigation management. This research will include studies on agricultural experiment stations as well as on cooperator's farms. Project results will be documented in scientific and extension publications and will be presented at a variety of international, national, regional, and local meetings.

3. Progress Report:
This was the second year of the Agreement and efforts were aimed at continuing and refining ongoing studies. Projects investigated irrigated crop production in the upper Mississippi Delta region. With the certification of the parent project in February, variable rate irrigation (VRI) studies and additional crops were included. (1) A 152 meter (m) center pivot irrigation system was adapted to allow VRI application, with ten independent zones of approximately equal area. A 113 m center pivot system was also adapted to allow VRI application, with independent control of each of 48 nozzles. Rice studies were conducted under both systems, as well as cotton and soybean. Using VRI, the rice experiment had irrigation applications of 8, 10, and 12 millimeter (mm) starting at 13 mm soil water deficit and 12, 15, and 18 mm starting at a drier 19 mm deficit. For cotton and soybeans, VRI was used to make 0, 6, 13, 19, 25, and 32 mm applications starting at a 44 mm deficit. Resulting yields will allow testing and refining of previously developed crop coefficient functions. In addition to use in existing irrigation scheduling programs, the researchers are developing a smartphone application to aid farmers in scheduling irrigation. Another planned rice irrigation study was modified to allow crop rotation to improve weed problems resulting from multiple years of rice production and a study of VRI system performance was initiated. A 154 m center pivot system equipped with seven equal-area zones along the pivot lateral was studied to evaluate application uniformity, confirm nozzle pulsing rates used to achieve variable application, and evaluate timing influence on application uniformity. Application depths were measured using rainfall collectors spaced along the pivot lateral at 1.5 m increments from approximately 79 m from the pivot point through 152 m. Tests were conducted based on American Society of Agricultural and Biological Engineers Standard with pulsing rates ranging from 40 to 100 percent in 20 percent increments. All collectors were measured and adjusted to meet the Standard requirements. Flow rate of the center pivot was measured. The initial run evaluated uniformity at 100 percent sprinkler capacity (i.e. no pulsing), with application depth values used to calculate coefficients of uniformity for the pivot lateral. Pivot speed was set at the panel and verified by timing system movement for each tower in the field. Cycle times were measured and compared to the prescription value as set on the control panel for each test. To measure uniformity during the pulse rate change, seven rows of collectors were placed on the field to measure application depth. Measured water volumes were compared to determine how closely application depth matched the prescription amount. Pulsing rates of 40, 60, 80, and 100 percent were evaluated and additional variations will be examined as needed. (2) Cotton measurements were continued in two ongoing studies. The adjustable mobile sensor system used to measure spatially referenced canopy temperature, reflectance, and height, and temperature and relative humidity of air above the crop was modified and additional reflectance sensors were added for inter-row measurements. The new system was tested in corn and cotton studies. (3) Rice yield response has been evaluated with biochar applications under different water management practices from the field scale experiment. A conventional US Southern long-grain rice variety (i.e., Wells) was drill seeded under conventional conditions on a Sharkey soil. Rice hull and biochar were broadcast and incorporated 4 months prior to seeding. Each plot was harvested with a plot combine with an on-board weighing system. In 2011, rice yield on a rain-fed system was significantly lower than other water management systems. Otherwise, no significant difference of rice yield was found between flooded and intermittent drainage systems. Further studies of yield response to biochar application may be considered with environmental impacts, such as greenhouse gas emission, carbon sequestration, and soil and water quality studies. (4) Three soil types (soils amended with different amounts of biochar) and four insecticide treatments (non-treated, two seed treatments, and a foliar application) were included. Water samples were collected at 24, 48, and 72 hours after flooding was established. Water samples were placed in a freezer and held for analysis. (5) On-farm studies were conducted to evaluate the effectiveness of controlled release nitrogen (CRN) fertilizers relative to traditional nitrogen fertilizer programs for furrow irrigated cotton production. In 2011, large scale strip trials were conducted on three furrow irrigated commercial cotton production fields. The treatments used encompassed mixtures of CRN and urea ranging between 100% of each product. Cotton leaf petiole samples were collected during the growing season to determine differences in nitrogen status among treatments and seed cotton yield was determined by the weight from each plot at the gin. An additional small scale trial was also conducted. The 2011 yield results indicated CRN fertilizers did not show significant yield increase; however, environment benefits and labor and fuel efficiency should be considered. CRN applied preplant can save subsequent fuel and labor associated with standard split N applications. Although there were significant differences in fiber quality, only strength and micronaire would result in premiums and discounts. There were no consistent responses among treatments with fiber quality; therefore, the fiber quality appeared more affected by environment than fertilizer treatments. (6) A worksheet was developed for calculating the amount of fertilizer or other ag chemical based on the speed setting on the pivot. In 2011, a relatively late corn planting date (12 May) and mechanical failures of the irrigation system resulted in fairly low yields and no significant differences among the fertigation treatments. The study was modified for 2012 to allow the fertigated blocks to receive nitrogen while being irrigated by using small injectors on selected nozzles. Three contiguous risers were set up to apply the nitrogen with yield being taken out from the middle rows. However, problems with the well and existing sprinkler package caused both poor distribution and inadequate pressure to allow an induced pressure differential sufficient for the injector to work properly. Pump and system tests were conducted early in the season to choose another orifice size. Even though the distribution uniformity improved and the flow rate increased, the pressure needed to allow the system to work in a controlled method could not be obtained even after changing to a larger diameter water supply hose. Therefore, fertigation was planned using a well-head injector and injecting nitrogen into treatments as needed with other sprinklers closed off. In addition, soybean fungicide applications will be compared by two methods, traditional and chemigation, with a non-treated check.

4. Accomplishments

Last Modified: 06/27/2017
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