Crop and tillage management effects on water flow and nitrate-nitrogen loss through subsurface drains

Data were collected from subsurface drains on 36, 0.4-ha plots at Iowa State University\u27s Northeast Research Farm near Nashua, IA to determine crop and tillage management effects on water flow and nitrate-N loss through subsurface drains. From 1990 to 1992, four tillage systems (chisel plow, moldboard plow, ridge till and no-till) were used with two crop rotations (continuous corn (Zea mays L.) and corn-soybean (Glycine max L. (Herr.)) rotation) and a single-spring fertilizer application. From 1993 to 1995, tillage systems were reduced to chisel plow and no-till, while fertilizer management changed to include single-spring fertilizer, spring-summer split fertilizer and fall manure application;The amount of nitrate-N lost in subsurface drainage was influenced more by subsurface drainage volume than nitrate-N concentration in drain effluent. Tillage had minimal effects on drainage volume, although no-till plots showed greater preferential flow than chisel plow plots. Significant differences in drain flow only occurred under continuous corn between 1990 and 1992, when the no-till system had higher drain flow than moldboard plow;Tillage affected nitrate-N concentrations in drain effluent during 1990 to 1992. Moldboard plow plots had higher concentrations than no-till plots possibly because of differences in bypass flow, denitrification and mineralization. Nitrate-N concentrations were not influenced by tillage after management systems were changed. However, plots where continuous corn had been grown for 15 yr had higher drain flows and nitrate-N losses in 1993 than where corn was planted into plots that had been rotated with soybean;Nitrate-N concentrations and losses were always higher with continuous corn than with corn-soybean rotation. Corn yields with split fertilizer applications were as high or higher than yields from single application treatments, but nitrate-N losses were essentially the same. Swine manure was difficult to apply at desired rates, resulting in wide variations in yield, nitrate-N concentrations and nitrate-N losses among years. This suggests that manure should be used to supply only a portion of crop nitrogen needs with additional fertilizer added based on late-spring soil nitrate tests

Fighting erosion in furrow irrigation

Despite the trend towards center pivot and drip irrigation, furrow irrigation is still used on almost half of the irrigated land in the US. However, soil erosion is an inherent problem when water flows over soil. Erosion causes problems within the field and off the field. Within a field, soil tends to erode from the upper end making furrows deeper. Erosion deposits soil on the bottom end, filling furrows and causing water to flood across rows. Severe erosion can expose plant roots. Fortunately, applying a small amount of polyacrylamide (PAM) to the furrow soil or with irrigation water almost eliminates erosion in irrigation furrows

Temperature, concentration, and pumping effects on PAM viscosity

As polyacrylamide (PAM) use in irrigated agriculture increases, new methods are being sought to accurately and automatically apply PAM with irrigation water. PAM is also beginning to be used in sprinkler irrigation. However, little information is available about flow characteristics of PAM solutions. This study was conducted to investigate temperature, concentration and pumping effects on viscosity of two agricultural PAM formulations: a dry powder and an inverse oil emulsion. Flow tests, using solutions prepared from the dry powder PAM, showed that viscosity decreased as flow rate increased for concentrations greater than 400 ppm. Thus, accurately predicting PAM viscosity at concentrations greater than 400 ppm is difficult because viscosity varies not only with concentration and temperature, but with flow conditions. Flow rate changes due to temperature fluctuations, however, should be minimal for the oil emulsion PAM over typical temperature ranges occurring under field conditions if tubing diameter is greater than 10 mm and tubing length is less than 1 m, which should be adequate for all surface irrigation applications. The two PAM products tested had similar viscosity relationships with temperature and concentration. PAM viscosity for solutions with concentrations < 24 ppm only increased about 5% relative to water for each 10 ppm increase in PAM concentration. Pumping a 2400 ppm PAM solution just once through a centrifugal pump reduced viscosity 15 to 20%; pumping five times reduced viscosity approximately 50%. The viscosity reduction is thought to result from breaking or shearing the PAM molecules, reducing its effectiveness to stabilize the soil surface and reduce soil erosion

Water temperature in irrigation return flow from the Upper Snake Rock watershed

Water returning to a river from an irrigated watershed could increase the water temperature in the river. The objective of this study was to compare the temperature of irrigation return flow water with the temperature of the diverted irrigation water. Water temperature was measured weekly in the main irrigation canal, 24 return flow streams and one ephemeral stream from 2005 to 2008 in the Upper Snake Rock (USR) watershed. The USR is an 82,000 ha watershed in southern Idaho, USA with about 60% of the area surface irrigated and the remaining area sprinkler irrigated. Median annual water temperatures in irrigation return flow streams were not greater than the water diverted from the river, suggesting that water flowing through the canal system and furrow irrigated fields does increase temperature. Water in seven of the 14 return flow streams that received flow from subsurface drains had significantly lower temperatures than the main canal in at least two years of the four years. Significant differences were generally only two to three degrees Celsius. Results of this study indicate that water can be diverted from a river for surface irrigation without increasing the temperature of the irrigation return flow

Irrigation: Erosion

Irrigation is essential for global food production. However, irrigation erosion can limit the ability of irrigation systems to reliably produce food and fiber in the future. The factors affecting soil erosion from irrigation are the same as rainfall—water detaches and transports sediment. However, there are some unique differences in how the factors occur during irrigation and in our ability to manage the application of water that causes the erosion. All surface irrigation entails water flowing over soil. Soil type, field slope and flow rate all affect surface irrigation erosion, with flow rate being the main factor that can be managed. Ideally sprinkler irrigation will have no runoff, but application rates on moving irrigation systems can exceed the soil infiltration rate, resulting in runoff and erosion. Using tillage practices to increase soil surface storage and selecting sprinklers with lower application rates will reduce sprinkler irrigation runoff. Irrigation can be managed to minimize erosion and maintain productivity

Tillage and crop rotation effects on subsurface drainage response to rainfall

A field study was conducted to determine if tillage and crop rotation affected subsurface drainage response to rainfall. An instrumentation system collected subsurface drain flow data from thirty-six, 0.4 ha plots during the 1993, 1994 and 1995 growing seasons. Response time, time-to-peak drain flow rate, drainage volume, peak drain flow rate and percent preferential flow were compared between two tillage systems (no-till and chisel plow) and two crop rotations (continuous corn and corn-soybean) for 23 drainage events over the three-year study. The influence of preferential flow was estimated for each drainage event using a hydrograph separation procedure based on subsurface drain flow rate changes

Evaluating WEPP-predicted furrow irrigation erosion

The Water Erosion Prediction Project (WEPP) model allows users to predict furrow irrigation erosion. However, an initial model evaluation showed that 1) WEPP default erodibility values had to be reduced for simulating furrow irrigation erosion and 2) the WEPP model overpredicted sediment transport capacity. Therefore, the purpose of this study was to investigate the applicability of the governing equations used in the WEPP model to calculate sediment detachment and transport. Sediment detachment data were collected from 53 irrigation furrows, 9 m long, on a Portneuf silt loam with flow rates varying from 2 to 50 L min-1 among furrows. Hydraulic shear measured in irrigation furrows varied from 0.4 to 1.7 Pa, which is less than the 2.6 to 8.8 Pa shear measured during WEPP rainfall simulation on the same soil. The linear relationship between shear and detachment rate used by the WEPP model may be appropriate for predicting both rainfall and furrow irrigation erosion as long as separate erodibility values are identified for furrow irrigation. A power function relating shear and detachment rate may allow one relationship to be used for both the low shear conditions in irrigation furrows and the high shear conditions in rills during intense rain storms. Although transport capacity could not be thoroughly evaluated with this data set, sediment detachment seemed to be limited by factors other than transport capacity,. Additional model evaluation is needed with data from other soils before changes to the model can be recommended or the model can be implemented for predicting furrow irrigation erosion

Seasonal changes in flow and nitrate-N loss from subsurface drains

Subsurface drainage from thirty-six, 0.4-ha plots was monitored for three years (1990 to 1992) from chisel plow, moldboard plow, ridge till, and no-till systems with continuous corn and corn-soybean rotations. Data were analyzed in four seasonal stages to determine variations in drain flows and nitrate-N contents in drain effluent. The hypothesis of this study was that differences among tillage systems would change during the monitoring season as rainfall patterns varied and as plots were fertilized and cultivated

Intercropping in maize silage versus solo-seeding for alfalfa establishment in Wisconsin and Idaho

Alfalfa (Medicago sativa L.) intercropping with maize (Zea mays L.) silage is being developed in the northern United States to improve the profitability and environmental sustainability of forage production. This study, conducted under rainfed conditions inWisconsin and semiarid irrigated conditions in Idaho, compared the establishment of alfalfa and dry matter yield of four intercropping systems to three conventional systems. The former systems included alfalfa interseeded at planting or the vegetative emergence (VE) stage of maize and grown with or without prohexadione growth retardant. The latter systems included alfalfa seeded in spring, summerseeded after barley (Hordeum vulgare L.), or late summer-seeded after maize silage. Spring seeded and interseeded alfalfa inWisconsin also received foliar fungicide and insecticide during establishment. During alfalfa establishment, yield of intercropped maize silage was 1.8- to 4.4-fold greater than spring-seeded alfalfa. Compared to spring-seeded alfalfa, interseeded alfalfa had similar or somewhat lower stand density but similar first cut yield the following year, provided that intercropped maize was harvested near September 1 to allow ample alfalfa fall regrowth. Shifting interseeding from maize planting to the VE stage decreased early-season alfalfa growth, but improved maize silage yield, with minor effects on alfalfa fall growth, stand density, and first cut yield. Prohexadione application had little impact on establishment or yield of interseeded alfalfa. While having high plant density, alfalfa seeded after barley or especially maize had less fall growth and low first cut yield. Overall, alfalfa establishment and yield of intercropping systems compared favorably with conventional systems