Dean D. Steele

Field Comparison of Irrigation Scheduling Methods for Corn

Irrigation scheduling for corn requires knowledge of methods for timing irrigation applications. A three-year field plot study of irrigation scheduling methods for corn was undertaken on a sandy loam soil near Oakes, North Dakota, using a randomized block design. The study was designed to assess the influence of the methods on grain yields and total irrigation amounts applied. The reference irrigation timing method was based on allowable root zone available water depletion (40%). The other irrigation timing methods used were: partial evapotranspiration (ET) (0.5 ¥ ET) replacement, crop water stress index (CWSI of 0.2, 0.4, and 0.6), measured soil matric potential (30 and 50 kPa), and growth model (CERES-Maize) estimates of dry matter accumulation and water use. In terms of crop yield per unit ET, the best method was the 50-kPa treatment. The 50-kPa method resulted in the maximum average yield of 12 200 kg ha–1 while achieving a statistically significant average reduction of 139 mm (40%) in irrigation application compared to the reference treatment. The nonreference methods, except for CWSI = 0.6, appear to offer the potential for significant irrigation water savings without significant yield reductions. The 0.6 CWSI treatment suffered a statistically significant yield reduction of 1 600 kg ha–1 (13%).

Irrigation scheduling methods for potatoes in the northern Great Plains

The successful irrigation of potatoes requires a knowledge of both irrigation application and scheduling methods. A four-year field study of four irrigation scheduling and application methods for Russet Burbank potatoes was undertaken on a sandy loam soil near Oakes, North Dakota. A randomized complete block statistical design was used to assess the influence of irrigation treatments on total yield, no. 1 grade yield, specific gravity, and total irrigation applied. For the reference treatment, above-ground drip irrigation (AGDI) was used to apply irrigations based on 40% depletion of root zone available water on an area basis. The other treatments were: (1) AGDI, basing scheduling on a crop water stress index (CWSI) of 0.2; (2) subsurface drip irrigation (SDI), basing scheduling on measured soil matric potentials (SMPs) of 30 kPa using a feedback and control system to automate irrigation applications; and (3) AGDI, basing scheduling on SUBSTOR-Potatoes (SUBSTOR) growth model estimates of water use. Because of high relative humidity and intermittent cloudiness, irrigations for the CWSI treatment were also scheduled based on SMP of 30 kPa at 0.3-m depth. Averages for yield (39.7 Mg ha–1), percentage no. 1 grade (76.1%), and specific gravity (1.086) did not differ between treatments. The reference treatment required an average of 220 mm irrigation water each year, significantly higher than the 167 mm for CWSI , the 129 mm for SDI, and the 149 mm for SUBSTOR. Improved irrigation methods can save water without compromising potato yield or quality. Tensiometer-based methods were preferred, while SUBSTOR has limited practicality for irrigation scheduling.

Irrigation management for corn in the northern Great Plains, USA

Abstract Irrigation management influences production costs and affects leaching of nutrients to groundwater. This study was conducted to compare irrigation scheduling techniques on a field-scale site and to determine whether significant irrigation water savings and equivalent yields could be achieved compared with the practices of other commercial growers in the local area. The effects of four irrigation scheduling techniques on seasonal irrigation water requirements and corn grain yields were studied for the 1990–1995 seasons at a field-scale (53.4 ha) site within the Oakes Test Area (OTA) of the Garrison Diversion Unit in southeastern North Dakota, USA. The four scheduling techniques, applied with field quadrants and seasons as dimensions of a modified Latin square statistical design, included irrigating based on tensiometer and infrared canopy temperature measurements, two water balance methods, and irrigating based on CERES–Maize estimates of plant-extractable soil water. No statistically significant differences in seasonal irrigation totals were found between irrigation scheduling methods or irrigation quadrants, while statistically significant differences were found for season. Corn grain yield was significantly affected by seasons, quadrants, and irrigation scheduling methods for both the current and previous seasons. Compared to other commercial growers in the OTA, this study maintained 5% higher yields and saved approximately 30% in irrigation inputs. Careful irrigation scheduling, based on any of the four techniques, offers the potential to reduce input costs for irrigated corn production in the area.

New Corn Evapotranspiration Crop Curves for Southeastern North Dakota

Accurate irrigation scheduling requires knowledge of crop water use. Crop curves are one means of irrigation scheduling. Crop curves are the ratio of actual crop water use to reference crop evapotranspiration presented as a function of an independent variable such as days past planting, phenological development, fraction of season, or cumulative seasonal heat units. Crop curves are commonly based on daily data from weighing lysimeters. In nonweighing lysimeters, soil moisture measurements may be taken at weekly or other nondaily intervals. We present four mean corn evapotranspiration crop curves based on 11 years of data from four nonweighing lysimeters. The crop curves are based on Jensen-Haise (J-H) or Penman-Allen (P-A) reference evapotranspiration (ETr) computations as functions of days past planting (DPP) or cumulative growing degree days (CGDD) since planting. The r2 and standard errors in the Kc estimates (SEKc) were 0.68 and 0.21, respectively, for the J-H DPP method; 0.54 and 0.25 for the J-H CGDD method; 0.62 and 0.24 for the P-A DPP method; and 0.52 and 0.27 for the P-A CGDD method. We also illustrate: 1) calculation procedures for development of crop curves based on nondaily soil moisture measurements; 2) a method of referencing each water balance period to the independent variable which does not bias the resulting crop curve forward or backward in time; and 3) the repercussions of using an insufficient number of significant digits in the crop curve polynomial coefficients. Reliable and unbiased crop curves should result from use of the methods described in this article.

Subsurface Drip Irrigation Systems for Specialty Crop Production in North Dakota

Subsurface drip irrigation (SDI) systems offer advantages over other types of irrigation systems for specialty crop production, including water savings, improved trafficability, and a drier canopy. This study was conducted to evaluate the performance of SDI, placed at 1.2-m (4-ft) lateral spacing and buried at 0.28-m (11-in.) depth, in a subhumid climate with severe winters. Effects on crop yield and crop quality of tape design (from five manufacturers) and position along 152-m (500-ft) lateral runs were investigated for three consecutive years on a sandy loam soil near Oakes, N. Dakota. In 1993, marketable and total sweet corn yields averaged 13.9 and 14.9 Mg ha–1 (6.20 ton ac–1 and 6.65 ton ac–1), respectively. In 1994, U.S. No. 1, U.S. No. 2, and total yields for winter squash were 17.7, 6.8, and 31.9 Mg ha–1 (7.90, 3.03, and 14.23 ton ac–1), respectively. In 1995, the cabbage yield averaged 98 Mg ha–1 (43.7 ton ac–1). Yields were measured at three transects [approximately 17, 76, and 136 m (56 ft, 250 ft, and 446 ft) from the upstream ends of the drip laterals] to determine effects of tape design on water distribution and corresponding yield. Yields did not differ statistically between designs for any transect in any year. Measured emitter discharge rates decreased dramatically with distance downstream from the start of the tape. This was attributed to friction losses in the tape, deformation of the normally circular cross-section of the tape by winter conditions, soil compaction from tillage operations, and calcium deposits. Subsurface drip irrigation tape appears durable enough to withstand winters in the northern Great Plains for multiple-season use, provided proper installation and maintenance procedures are followed.

Initiation of Irrigation Effects on Temporal Nitrate Leaching

Groundwater and surface water are significant resources for rural water supplies, and certain agricultural practices may have substantial effects on these resources. An 11-yr study was started in 1989 near Oakes, ND that continuously monitored NO 3 –N concentrations in subsurface water of a field that was converted from dryland to center-pivot irrigation in 1989. The vadose zone was monitored with four disturbed and 16 undisturbed-profile lysimeters, and the groundwater of the surficial aquifer was monitored with 18 sets of nested wells, which sampled shallow, intermediate, and deep depths. The depth to water table of the surficial aquifer was approximately 3 m and the saturated thickness extended to a depth of 7 m. Also, NO 3 –N levels from two subsurface drains were monitored. The time series NO 3 –N concentration data from each of the monitoring locations exhibited the similar three-phase trend where NO 3 –N concentrations first increased, then decreased, and finally reached a steady-state level that was maintained. The first and second phases of this trend were shorter (∼3 yr total) for the lysimeters and increased as the depth of observation increased (5 and 8 yr total for shallow and intermediate wells, respectively). Also, the peak NO 3 –N concentration decreased as the observation went deeper into the profile (ranging from 150 mg L −1 in lysimeters, to 50 mg L −1 in shallow wells, and to 40 mg L −1 in intermediate wells). The NO 3 –N levels in the deep wells averaged 0.48 mg L −1 , had a maximum of 1.59 mg L −1 , and exhibited a slight increase through time. The subsurface drainage NO 3 –N levels were an average of 77% lower than the groundwater concentrations, which may have been caused by biotic and abiotic reduction. The increase in NO 3 –N concentrations in subsurface waters as a result of the initiation of irrigation can be partially explained by the residual N in the soil from dryland agriculture. As soil moisture increased, the availability and mobility of nitrogen increased, which attributed to the flush of NO 3 –N through the soil profile.

IRRIGATION SCHEDULING METHODS FOR POPCORN IN THE NORTHERN GREAT PLAIN

Irrigation of popcorn requires knowledge of methods of applying and scheduling irrigations. A four-year field plot study of four application-scheduling methods for popcorn was undertaken on a sandy loam soil near Oakes, North Dakota (ND), using a randomized block design. The study was designed to assess the influence of the methods on grain yields, popped volumes, and total irrigation water amounts applied for “White Cloud” popcorn. The reference method used aboveground drip irrigation (AGDI) to apply water and a scheduling method based on estimates of when 40% depletion of root zone available water (40% D) would be reached. The other irrigation application-scheduling methods were: AGDI and scheduling based on plant temperature, i.e., crop water stress index (CWSI) of 0.4; subsurface drip irrigation (SDI) and scheduling based on measured soil matric potential (SMP) of 30 kPa using a feedback and control system to automate irrigation applications through an SDI system; and AGDI and CERES-Maize (CM) growth model estimates of water use. Due to difficulties in implementing the CWSI method (high relative humidity and intermittent cloudiness), irrigations were also scheduled based on tensiometer-measured SMP of 40 kPa at 0.3-m depth for the CWSI treatment. Compared to the 40% D method, all other methods achieved statistically significant (0.05 level) irrigation water savings for popcorn without significant reductions in yields or popped volumes. Four-year average irrigation water amounts were 235, 134, 142, and 156 mm for the 40% D, CWSI, SDI, and CM methods, respectively, with corresponding popcorn yields of 4.63, 4.33, 4.44, and 4.47 Mg ha–1 and popped volumes of 26.3, 28.0, 28.3, and 28.0 L kg–1.

Furrow vs hill planting of sprinkler-irrigated russet burbank potatoes on coarse-textured soils

Surface water runoff from the hill, where potatoes are planted, to the furrow may exacerbate potato drought sensitivity. Planting into furrows and constructing midrow ridges may improve water use efficiency and relieve water stress on potato by directing water toward, not away from, the plants. A 3-year field study was conducted to compare yields and tuber size distributions of furrow- and hill-planted potato (Solanum tuberosum L., ‘Russet Burbank’) on coarse-textured, well-drained soils under sprinkler irrigation. A split-plot experimental design with main plots of row orientation (N-S vs E-W) and subplots of planting method (hill and furrow) combined with two planting depths was used at two central North Dakota sites. Except for planting method and limiting the post-emergence cultivation in the furrow treatments, all cultural practices (fertilizer, irrigation, etc.) were identical and corresponded with conventional practices for hill planted potato. Row orientation did not affect yield for any tuber size category. Averaged over 3 years, furrow-planted potato produced 24% larger tubers (188 vs 151 g), 31% smaller yield for tubers <113 g (4.99 vs 7.21 Mg ha−1), 28% smaller yield for tubers 113 to 170 g (8.14 vs 11.3 Mg ha−1), 8% larger yields for tubers 170 to 283 g (18.0 vs 16.6 Mg ha−1), 103% larger yields for tubers 283 to 454 g (10.9 vs 5.36 Mg ha−1), 341% larger yields for tubers >454 g (2.65 vs 0.60 Mg ha−1), and 10% larger total yields (46.2 vs 41.9 Mg ha−1) compared with hill-planted potato. There were no differences in tuber specific gravity. Preliminary soil water measurements indicated an inter-row water-harvesting effect for furrow planting compared with hill planting. The furrow-planting method may offer significant potential for ameliorating the drought sensitivity of potato.ResumenEl agua que corre del camellón donde se siembra papa hacia el fondo del surco puede exacerbar la sensibilidad de la planta a la sequía. Sembrando en el fondo de los surcos y construyendo camellones centrales se puede mejorar la efficiencia en el uso del agua y aliviar el estrés si se dirige el agua hacia la planta y no al revés. Durante tres años se realizó un estudio de campo para comparar el rendimiento y distribución del tamaño de los tubérculos en pruebas donde se sembró papa (Solanum tuberosum L. ‘Russet Burbank’) en el surco y en el lomo del surco en suelo de textura gruesa, con buen drenaje y riego por aspersión. Se utilizó el diseño experimental de parcela dividida con la principal orientación de las hileras (N-S vs. E-O) y los métodos de siembra (lomo y surco) de las sub-parcelas combinado con dos profundidades en dos lugares cerca de North Dakota central. Con excepción del método de siembra y limitando las labores de cultivo de post-emergencia en los tratamientos en el surco, todas las labores culturales (fertilización, irrigación) fueron idénticas y correspondieron a las prácticas convencionales para siembra de papa en el lomo del surco. La orientación de las hileras no afectó el rendimiento ni la categoría de tamaño del tubérculo. El promedio de rendimiento de los tres años de papas sembradas en el fondo del surco fue del 24% de tubérculos más grandes (188 vs 151 g), 31% de menor rendimiento para tubérculos de <113 g (4.99 vs 7.21 Mg ha−1), 28% de menor rendimiento para tubérculos de 113 a 170 g (8.14 vs 11.3 Mg ha−1), 8% de mayor rendimiento para tubérculos de 170 a 283 g (18.0 vs 16.6 Mg ha−1), 103% de mayor rendimiento para tubérculos de 283 a 454 g (10.9 vs 5.36 Mg ha−1), 341% de mayor rendimiento para tubérculos >454 g (2.65 vs 0.60 Mg ha−1) y 10% de mayor rendimiento total (46.2 vs 41.9 Mg ha−1) en comparación con papa sembrada en el lomo del surco. No hubo diferencias en la gravedad específica del tubérculo. Las mediciones preliminares del agua del suelo indicaron un efecto del agua entre hileras al momento de la cosecha en comparación con la siembra en el lomo. El método de siembra en el surco puede ofrecer un significativo potencial para mejorar la sensibilidad de la papa a la sequía.

WATER BALANCE IRRIGATION SCHEDULING: COMPARING CROP CURVE ACCURACIES AND DETERMINING THE FREQUENCY OF CORRECTIONS TO SOIL MOISTURE ESTIMATES

Water balance methods are commonly used to schedule irrigations and use evapotranspiration (ET) functions and crop curves to estimate crop ET (ETc). Because the methods may over or underestimate ETc, field-measured values of available soil moisture content (SMC) are often used to correct or adjust estimates of soil moisture during the growing season. This study was conducted to (1) compare the accuracies of four crop curves, based on the Jensen-Haise reference ET method, for corn in the northern Great Plains, and (2) determine the need for and frequency of in-season corrections to SMC estimates. The comparisons were based on differences between estimated and measured SMC for the 1990, 1991, 1992, and 1994 seasons using nonweighing lysimeters near Oakes, North Dakota. The SMC data were compared to estimates using bias and absolute errors, r2, Friedman Rank Sums, and sign distributions. The SMC estimates were corrected to measured values at three frequencies: start of season only, approximately monthly, and approximately semimonthly. The crop curve based on days past planting was generally the most accurate, followed by the crop curve based on cumulative growing degree days. All of the methods tended to overestimate ETc. Selection of a correction frequency is more important than selection of a particular independent variable—days or weeks past emergence, days past planting, or cumulative growing degree days since planting—for a crop curve. For the crop curves, soil types, and climatic conditions of this study, none of the crop curves should be used without in-season SMC corrections on at least a monthly frequency, and semi-monthly corrections are preferred. The methods employed in this study can be transferred to other sites, climates, and crops.

Subsurface Drainage and Subirrigation Effects on Water Quality in Southeast North Dakota

Rising water tables, increased soil salinity, and poor trafficability have prompted rapid expansion of subsurface drainage in the Red River Valley of the North in eastern North Dakota and northwestern Minnesota. A conventional subsurface drainage (CD) and subirrigation (SI) field study was conducted in southeast North Dakota from 2008 to 2010 to investigate drainage and subirrigation effects on water quality. Water samples were collected biweekly from a sump pump structure (used as the water inlet and outlet) and 16 observation wells within the field. Water quality variables included chloride (Cl-), electrical conductivity (EC), total dissolved solids (TDS), sodium adsorption ratio (SAR), sodium (Na+), orthophosphate (PO4-P), ammonium (NH4-N), nitrite and nitrate (NOx-N), Kjeldahl nitrogen (TKN), and total nitrogen (TN). A three-factor partially nested design and a general linear model with random effects were employed to compare the effects of water management treatment, distance to drain, and well locations (soil heterogeneity) on water quality. The most significant water quality difference was found at the outlet structure, where a significant difference (p < 0.001) between the CD and SI water was found for all ten variables. The water quality of the drainage water was better than the subirrigation water from the aquifer, except for the NOx-N, EC, and TDS concentrations. Well water Cl- concentrations inside the field were significantly greater in SI compared with CD water; EC, TDS, SAR, and Na+ were not. In contrast, EC, TDS, SAR, and Na+ were significantly higher at two well locations, indicating that soil heterogeneity affected the water quality. Due to SI practice, a significant difference for Cl-, SAR, and Na+ was found between the locations closest to and farthest from the drains during the SI practice, which implies that the SI process may cause soil properties to change in the future. Overall, well locations significantly affected PO4-P, NOx-N, and TN, indicating that the soil physical and chemical properties affected the water quality, and these effects could overcome the difference due to different water treatments.