Simulating soil nitrogen fate in irrigated crop production with mature applications

Dairy manure is commonly applied to irrigated agricultural crops in the Magic Valley Region of southern Idaho, which has reported to impact the quality of surface and ground water. In this study, we used the Root Zone Water Quality Model (RZWQM2) to provide information about the long-term implications of manure applications. RZWQM2 was first calibrated and validated using 4 years of data from a long-term study with annual and biennial manure application rates of 18 Mg ha-1, 36 Mg ha-1, and 52 Mg ha-1, along with a control and conventional fertilizer treatment for crop yield, soil water and soil N. The 4-yr crop rotation was spring wheat (2013), potato (2014), spring barley (2015), and sugar beets (2016). RZWQM2 simulated soil water content, crop yield, total soil nitrogen, and soil nitrogen mineralization effectively as PBIAS and RRMSE for soil water content and crop yields were within the acceptable range (± 25% for PBIAS and <1.0 for RRMSE). Nitrate in the soil profile was overestimated, however in the acceptable range for the validation treatments. The calibrated model was then run for 16 years by repeating the management practices of the 4-year scenarios (4 crop rotations) for all treatments and 24 years for the 52 T Annual treatment (6 crop rotations). The 16-year simulation results showed that nitrogen seepage from annual manure treatments (for example, 18 T Annual vs 18 T Biennial) was 2.0 to 2.3 times higher than the nitrogen seepage from the biennial manure treatments. Increasing manure applications from 18 T Annual to 52 T Annual increased N seepage an average of 3.2 times for the 16-year rotation. Nitrogen seepage increased dramatically in rotations 3 and 4 compared to rotations 1 and 2 in the sixteen-year simulation. The 24-year simulation results showed after manure had been applied annually for 16 years and then applications terminated, the amount of N seepage returned initial levels in 8 years. In conclusion, to maintain clean ground water, manure applications would be best applied biennially and high applications should be discouraged

Irrigation and Culm Contribution to Yield and Yield Components of Winter Wheat

Water is generally the limiting factor in U.S. Great Plains wheat (Triticum aestivum L.) production. With increasing demands for limited water, improving the efficacy of irrigation is critical. One technique is to irrigate during responsive stages of crop development, but few studies have examined this approach. This 2-yr study on a Nunn clay loam soil (fine, montmorillonitic, mesic Aridic Argiustoll) was designed to examine the effects of irrigation, based on stage of crop development, on winter wheat yield, yield components (on a plant basis), and specific culm responses. In the first year, the treatments were control (dryland), and irrigation at late jointing. In the second year, the treatments were dryland, irrigation at late jointing, irrigation at anthesis, and irrigation at both late jointing and anthesis. Irrigation at late jointing or anthesis significantly increased grain yield and the most important yield component (spikes per plant), as well as spikelets per plant, number of kernels per plant, and kernel weight per plant. The increased spikes per plant in the irrigation treatments, particularly with late-jointing irrigation, was due to reduced tiller abortion. Increased yield was primarily due to the contribution of more secondary tillers (T10, T11, T20, T21, T30, and T31) that produced spikes. The contribution of main stems to the total yield decreased from 92% to at most 86% with irrigation, although the dry weight of main-stem spikes increased with irrigation. The contribution to total yield of the main yield-producing tillers, T1 and T2, decreased from 20 to U% and W to U%, respectively, with irrigation. As with main-stem spikes, irrigation also increased T1 and T2 spike dry weight. Therefore, the production of secondary spikes due to irrigation treatments was not at the expense of main stem or primary tiller spikes. If only one irrigation can be applied, irrigation at late jointing- is recommended for central Great Plains conditions. due to its -greater effect on tiller survival. This implies that developmental and physiological processes at late jointing are critical in determining final grain yield, and water stress should be avoided at this growth stage

Evaluation of GPFARM for Simulation of Forage Production and Cow-Calf Weights

A modeling approach that assesses impacts of alternative management decisions prior to field implementation would reduce decision-making risk for rangeland and livestock production system managers. However, the accuracy and functionality of models should be verified before they are used as decision-making tools. The goal of this study was to evaluate the functionality of the Great Plains Framework for Agricultural Resource Management (GPFARM) model in simulating forage and cow-calf production in the central Great Plains. The forage production module was tested in shortgrass prairie using April-October monthly biomass values from 2000 through 2002 for warm-season grasses (WSG), cool-season grasses (CSG), shrubs, and forbs. The forage module displayed excellent (99% explained variance) agreement in the 2001 calibration year in tracking growth and senescence trends of WSG and CSG, which constitute the vast majority of the aboveground biomass. Less agreement (35%-39% explained variance) was observed for shrubs and forbs. The model-explained variances of biomass in 2000 and 2002 (verification years) were 80% for WSG, 67% for CSG, 78% for shrubs, and 82% for forbs. Further development is needed to improve predicted plant response to environmental stresses. The cow-calf production module was tested in northern mixed-grass prairie using June-November monthly average cow and calf weights from 1996 through 2001 for March-calving, moderately stocked Hereford pairs. Overall, GPFARM performed well and tracked cow (81% explained variance) and calf (94% explained variance) pre- and postweaning weights. The GPFARM model has functional utility for simulating forage and cow-calf production with satisfactory accuracy at semiarid-temperate sites, such as southeastern Wyoming and northeastern Colorado. Continued development will focus on improving plant response to environmental stresses and testing the model’s functionality as a decision support tool for strategic and tactical ranch management.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 2020Legacy DOIs that must be preserved: 10.2458/azu_rangelands_v58i3_bartlin