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United States Department of Agriculture

Agricultural Research Service


Location: Cropping Systems and Water Quality Research

2013 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 third 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 2012, variable rate irrigation (VRI) studies and additional crops were included. (1) In 2012 we initiated a test evaluating Management Allowable Depletion irrigation treatments for center pivot irrigated rice and cotton based on calculated evapotranspiration (ET) from on-site weather station data using the Arkansas Irrigation Scheduler. For rice, three irrigation rates at two timing intervals were compared. Much of the season was required to install the variable rate irrigation (VRI) system, with ten independent zones of approximately equal area and a variable frequency drive (VFD) for the pump, and the equipment installation work kept us from irrigating as often as needed for the hot and dry conditions. Before July 16, all plots were irrigated equally but less than the recommended amount; after the VRI installation was completed we 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 the rice study. The irrigation rates corresponded to 80, 100, and 120% replacement, respectively, of the estimated ET. For cotton, VRI was used to make 0, 6, 13, 19, 25, and 32 mm applications starting at a 44 mm deficit corresponding to 0, 25, 50, 75, 100, and 125% replacement, respectively, of the estimated ET. For rice, the negative impact of high temperatures during pollination causing blank hulls was observed again in 2012 as we saw in 2011 and the problem was exacerbated by the irrigation shortfalls during VRI system installation. No significant irrigation treatment effects were observed for rice or cotton, but during the period before July 16, the hottest and driest part of the 2012 growing season, all treatments were irrigated uniformly. Tissue samples showed that silicon content in rice straw was below critical levels and silicon deficiency is thought to be a factor in inconsistent center pivot rice yields. Rice grain produced with center pivots has lower arsenic levels than flooded rice but is prone to silicon deficiency. In May 2013, we applied 1450 kg calcium silicate/ha from a steel mill in Pennsylvania to the test field. Soil phosphorus, potassium and pH were at optimum levels. Nitrogen (N) was applied as dry urea at first tiller growth stage and supplemented with UAN fertigation. In addition to using existing irrigation scheduling programs, the researchers are developing a smartphone application to aid farmers in scheduling irrigation. A second center pivot system was also adapted to allow VRI application, with independent control of each of 48 nozzles. Rice cultivar and silicon studies and a soybean irrigation study similar to the cotton study were conducted under the system. No significant irrigation effect was observed for the soybeans, but as with the cotton, the study area was uniformly irrigated for part of the season as the VRI system was installed and tested. Late in the season the diesel power unit and line-shaft turbine pump were replaced with a new pumping plant consisting of submersible electric pump, VFD, and remote monitoring and control system. Sensors for monitoring electric power were obtained in 2013 to supplement the sensors for pressure, flow, and depth-to-water that were originally installed with the system. When all of the sensors have been installed and calibrated the system will provide much information on the aquifer and the performance of the pump, and VFD. The performance of a center pivot with VRI technology was tested to evaluate application uniformity within and between adjacent zones and to evaluate the zonal application depth when changing application percentages during pivot rotation. Uniformity tests were conducted in accordance with ASABE Standard S436.1. The three span center pivot was divided into six VRI zones. Tests were conducted within sprinkler zones 3, 4, 5, and 6 as the first two zones were too close to the pivot point to perform multiple tests in a given time frame allowing the pivot to move completely over all the collectors. Wind speed was measured at 5 min intervals at less than 5 m/s for the duration of the testing. The first test evaluated application uniformity of the pivot with the solenoid valves 100% open during the entire test as the baseline uniformity (91.2%). A second test three weeks later showed a similar uniformity of 93.5%. Inspection of the volumes of water within each of the sprinkler zones showed that the uniformity in all but one sprinkler zone was greater than 90%. The findings of the tests were the basis of a poster presentation and corresponding proceedings article (ARIS log number 295177) for the 2013 ASABE Annual International Meeting. (2) Cotton measurements were continued in three ongoing studies and measurements were also made in a corn study. 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 for 2013 to include a smaller, more rugged infrared thermometer and two new reflectance sensors were added for additional above-row and inter-row measurements. The new system was used in a cotton study in 2013 and a second data-collection session is planned. Results from a three year cotton study that ended with the 2012 growing season were compiled and analyzed and the findings were the basis of a presentation and corresponding proceedings article (ARIS Log Number 296282) for the 2013 ASABE Annual International Meeting. The article is currently being expanded for submission to Applied Engineering in Agriculture. (3) 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 2012, large scale strip trials were conducted on two furrow irrigated commercial cotton production fields. Two treatments were included in 2012: 100% urea and 25% urea, 75% CRN. As in 2011, the 2012 yield results indicated CRN fertilizers did not show a significant yield increase; however, environmental benefits and should be considered and in 2013 an additional study was started to compare nitrogen content in runoff water between urea- and CRN- fertilized cotton plots. (4) Fifteen years of data from the annual Bootheel Irrigation Survey were compiled and in examining 138 field-years of results, fertigation was shown to increase yield for corn irrigators using pivots by 12 kg/ha. The field 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 poor water distribution and inadequate pressure to allow an induced pressure differential sufficient for the injectors to work properly. Pump and system tests were conducted early in the season to choose another orifice size, the lateral was re-nozzled to increase the distribution uniformity, and a larger-diameter water supply hose was installed. 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. Furthermore, the buried guide wire for the lateral was apparently damaged by lightning causing it to periodically lose continuity, but repair crews could never find the fault. A temporary fix was discovered, but was not reliable and later irrigation applications included errors. In 2012, two related studies were started. One used the corn plants in the study to evaluate a heat unit-driven model to predict the growth stages and canopy closure. This research will allow crop coefficient (Kc) values to be automatically calculated from local historic weather files. A second study compared various N rates on fields following soybeans and corn and indicated an average 15 kg/ha yield increase when following soybeans.

4. Accomplishments

Last Modified: 06/26/2017
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