Raymond E. Knighton

Emerging national research needs for agricultural air quality

Over the next 50 years, the Earths human population is predicted to increase from the current 6.1 billion to more than 9 billion, creating a parallel increase in demand for agricultural commodities. Satisfying the demand for food is already driving changes in crop and livestock production methods that may have profound environmental effects. Increased consumption of animal protein in developed and developing countries, for example, has resulted in concentrated production of poultry and livestock, which has led to concentrated emissions of pollutants from these production facilities and has created regulatory concerns for agriculture. Development of land for nonagricultural uses has placed more pressure on marginal agricultural lands and has caused environmental degradation including the emission of trace gases (e.g., carbon,sulfur, and nitrogen species) into the atmosphere.

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.

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.