Gyles W. Randall

Nitrate Losses to Surface Water Through Subsurface, Tile Drainage

Publisher Summary This chapter focuses on the linkage between subsurface tile drainage of agricultural lands and nitrate in surface waters, and the effect of uncontrollable factors and controllable factors on nitrate losses to subsurface drainage. Subsurface drainage is a common water management practice in highly productive agricultural areas with poorly drained soils that have seasonally perched water tables or shallow groundwater. This management practice increases crop productivity, reduces risk, and improves economic returns to crop producers. Agricultural drainage water has been identified as a major contributor to the nitrate-N loading of receiving waters. Research conducted at widely different scales of watershed basins point to the fact that agricultural systems do affect nitrate levels in river waters. Long-term, subsurface drainage research, which integrates the effects of climatic variability, soil properties, and various cropping systems, is vital to understanding of nitrate losses to subsurface drainage.

Combining chlorophyll meter readings and high spatial resolution remote sensing images for in-season site-specific nitrogen management of corn

The chlorophyll meter (CM) has been commonly used for in-season nitrogen (N) management of corn (Zea mays L.). Nevertheless, it has limited potential for site-specific N management in large fields due to difficulties in using it to generate N status maps. The objective of this study was to determine how well CM readings can be estimated using aerial hyper-spectral and simulated multi-spectral remote sensing images at different corn growth stages. Two field experiments were conducted in Minnesota, USA during 2005 involving different N application rates and timings on a corn-soybean [Glycine max (L.) Merr.] rotation field and a corn-corn rotation field. Four flights were made during the growing season using the AISA Eagle Hyper-spectral Imager and CM readings were collected at four or five different growth stages. The results indicated that single multi-spectral and hyper-spectral band or vegetation index could explain 64–86% and 73–88% of the variability in CM readings, respectively, except at growth stage V9 in the corn-soybean rotation field where no band or vegetation index could explain more than 37% of the variability in CM readings. Multiple regression analysis demonstrated that the combination of 2–4 broad-bands or 3–8 narrow-bands could explain 41–92% or 61–94% of the variability in CM readings across the two fields and different corn growth stages investigated. It was concluded that the combination of CM readings with high spatial resolution hyper-spectral or multi-spectral remote sensing images can overcome the limitations of using them individually, thus offering a practical solution to N deficiency detection and possibly in-season site-specific N management in large continuous corn fields or at later stages in corn-soybean rotation fields.

Performance of dicyandiamide in the north central states

Abstract The effectiveness of the nitrification inhibitors, nitrapyrin and dicyandiamine, in reducing nitrogen loss from soil and preventing reduction in crop yield was evaluated in field studies conducted over dozens of site years in Illinois, Iowa, Minnesota, and Wisconsin on corn, wheat, and a vegetable crop, potato. Both chemicals were effective in retarding the nitrification of ammoniacal fertilizers, including nitrogen from liquid animal manures, but this inhibitor did not always result in yield increases above that obtained with equivalent amounts of nitrogen applied without inhibitor. Greatest benefits for nitrification inhibitor use was obtained on coarse‐textured soils under conditions that were conducive to nitrate nitrogen loss when nitrogen was applied at rates not considered to be excessive.

Nitrogen Application Timing, Forms, and Additives

First paragraph: Wet, poorly drained soils throughout North America and Europe are often artificially drained with subsurface tile systems to remove excess (gravitational) water from the upper 1 to 1.2 m soil profile. Improved crop production that often results from drainage is in large part due to better physical conditions for field operations and a deeper unrestricted root zone for greater crop rooting, nutrient uptake, and yields. Removal of excess water by drainage lessens the potential for anaerobic conditions and consequently reduces the potential for nitrate to be lost from the soil profile by the process of denitrification. The combination of greater soil organic matter N mineralization with increased aerobic soil conditions, less N lost via denitrification, and increased transport of subsurface water results in higher nitrate concentrations in the receiving surface water bodies. Watersheds containing similar production systems and soils without subsurface drainage generate lower nitrate concentrations because anaerobic conditions exist more frequently. Under anaerobic conditions, denitrification predominates, resulting in nitrate losses as N gas to the atmosphere as well as economic losses to the farmer because of reduced available N.

Effect of manure on accumulation of dry matter, nitrogen, and phosphorus by soybean

Manure application for soybean [Glycine max (L.) Merr.] production is being considered by livestock producers, but the manures influence on dry matter (DM), nitrogen (N), and phosphorus (P) accumulation is not well documented. The objectives of this study were to measure N, P, and DM accumulation patterns and quantities by three genetically-different soybean varieties. Two preplant, sweep-injected manure application rates and a control were main plot treatments and three soybean varieties were subplots at seven experimental sites in 1996 and 1997. Starting in mid-June and continuing on a 15-d schedule until maturity, whole-plant samples were collected, dried, weighed, and analyzed for N and P. Plant DM increased with increasing manure rates at each sampling after mid-June. Nitrogen concentration differences among manure rates were greatest early in the season and diminished with time, whereas P concentration differences were consistent throughout the sampling period. Compared to the control treatment, manure resulted in an average of 25% more N accumulation at the first sampling date, 35% more at the second sampling, 42% at the third sampling, and then steadily decreased to a 10% increase at the final sampling date. Similar to N accumulation, mean P accumulation differences between the control and the manure treatments increased to 27% at the third sampling and then gradually decreased to 14% by the final sampling date. The overall effect of variety was minimal, yet statistically significant, and interactions between manure rate and variety were not found. Applying manure for soybean increased end-of-season accumulation of DM, N, and P by 9, 10, and 14%, respectively, compared to the non-manure treatment.

Optimum placement of phosphorus for corn/soybean rotations in a strip-tillage system

Strip tillage, a conservation tillage system using very reduced tillage, is attracting much attention throughout the corn-growing regions of the United States. In the northern parts of the Corn Belt, strip tillage often replaces no-till systems on the more poorly drained soils because it provides a warmer tilled seedbed for early planting and faster early growth while maintaining substantial amounts of erosion-minimizing plant residue between the tilled strips. Another benefit of strip tillage is the need for only one field operation between soybean harvest and spring planting—that is, fall strip tillage accompanied by deep-placement of fertilizer phosphorus (P) and potassium (K) in a band 15 to 18 cm (6 to 7 in) deep in the strip. No preplant tillage is needed. From an environmental perspective, deep-band placement is considered to be ideal in terms of eliminating nutrient stratification and reducing the potential for surface runoff of fertilizer P, which can easily occur when fertilizers are broadcasted on the soil surface of no-till systems. From an agronomic perspective, fertilizer placement 10 to 13 cm (4 to 5 in) directly below where the seed will be planted is thought to be ideal in terms of fertilizer P and K use efficiency, early

Seepage from deep bedded and poultry litter systems.

Abstract The work reported indicates that there could be a potential of ground water pollution by NO3‐N from turkey facilities built on both sandy and clay soils. At four different depths (30.54, 61.08, 91.62, and 122.16 cm), the NO3‐N levels for the clay soil were 1572, 497, 66, and 28 ppm, and those for the sandy soil were 293, 425, 324, and 164 ppm, respectively. No significant P increases were observed but there did exist a significant increase of K in the topsoil for both clay and sandy turkey structures. The results show that swine hoop houses with less than three or four years of age may not pose a threat to groundwater pollution due to the leaching of nutrients. The only dairy feedlot sampled in this study, although it has been used for more than 20 years, did not show leaching of NO3‐N and P. However, it did show a significantly elevated concentration of potassium in the topsoil, as compared to the background sample. More sites should be investigated to verify this.