This study quantified the effects of tillage (moldboard plowing [MP], ridge tillage [RT]) and nutrient source (manure and commercial fertilizer [urea and triple superphosphate]) on sediment, NH4+ -N, NO3- -N, total P, particulate P, and soluble P losses in surface runoff and subsurface tile drainage from a clay loam soil. Treatment effects were evaluated using simulated rainfall immediately after corn (Zea mays L.) planting, the most vulnerable period for soil erosion and water quality degradation. Sediment, total P, soluble P, and NH4+ -N losses mainly occurred in surface runoff. The NO3- -N losses primarily occurred in subsurface tile drainage. In combined (surface and subsurface) flow, the MP treatment resulted in nearly two times greater sediment loss than RT (P < 0.01). Ridge tillage with urea lost at least 11 times more NH4+ -N than any other treatment (P < 0.01). Ridge tillage with manure also had the most total and soluble P losses of all treatments (P < 0.01). If all water quality parameters were equally important, then moldboard plow with manure would result in least water quality degradation of the combined flow followed by moldboard plow with urea or ridge tillage with urea (equivalent losses) and ridge tillage with manure. Tillage systems that do not incorporate surface residue and amendments appear to be more vulnerable to soluble nutrient losses mainly in surface runoff but also in subsurface drainage (due to macropore flow). Tillage systems that thoroughly mix residue and amendments in surface soil appear to be more prone to sediment and sediment-associated nutrient (particulate P) losses via surface runoff.

Low spring soil temperatures commonly restrict the early growth of corn (Zea mays L.) in the northern Corn Belt. A quantitative assessment of the effects of tillage and residue management practices on soil temperature would improve tillage recommendations in this region. The effect of tillage and surface residue cover on seedbed soil temperatures and subsequent corn growth were studied at four sites in the northern Corn Belt that differed widely in soil characteristics including drainage, texture, slope, and organic matter content. Tillage systems included no‐tillage, chisel plow, moldboard plow, paraplow, ridge plant, and wheeltrack plant. A wide range of surface residue cover was imposed on each system at three sites. Corn emergence and leaf number to the six‐leaf stage were closely related to percent in‐row cover and air temperature growing degree days (air GDD) through their mutual relationship to soil temperature growing degree days (soil GDD) at all sites. For a given site and year, percent in‐row cover following planting was the major factor affecting corn growth rate until the six‐leaf stage. Corn planted under high percent residue cover required more time and consequently more air GDD to reach the six‐leaf stage. This added time represents a growth delay that can be expressed as the additional air GDD required to reach the six‐leaf stage. Such delays were related to increased grain moisture and decreased corn grain yield when net cumulative air GDD were less than the threshold value of 1319 and water stress was minimal. In‐row residue cover due to tillage and previous crop can have a major impact on the growth and development of corn in the northern Corn Belt. These factors should be considered in selecting tillage systems in this region.

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Increasing groundwater nitrate concentrations in potato (Solanum tuberosum L.) production regions have prompted the need to identify alternative nitrogen management practices. A new type of polymer-coated urea (PCU) called Environmentally Smart Nitrogen (Agrium, Inc., Calgary, AB) is significantly lower in cost than comparable PCUs, but its potential to reduce nitrate leaching and improve fertilizer recovery has not been extensively studied in potato. In 2006 and 2007, four rates of PCU applied at emergence were compared with equivalent rates of soluble N split-applied at emergence and post-hilling. Additional treatments included a 0 N control, two PCU timing treatments (applied at preplant or planting), and a soluble N fertigation simulation. Nitrate leaching, fertilizer N recovery, N use efficiency (NUE), and residual soil inorganic N were measured. Both 2006 and 2007 were low leaching years. Nitrate leaching with PCU (21.3 kg NO(3)-N ha(-1) averaged over N rates) was significantly lower than with split-applied soluble N (26.9 kg NO(3)-N ha(-1)). The soluble N fertigation treatment resulted in similar leaching as PCU at equivalent N rates. Apparent fertilizer N recovery with PCU (65% averaged over four rates) tended to be higher than split-applied soluble N (55%) at equivalent rates (p = 0.059). Residual soil N and NUE were not significantly affected by N source. Under the conditions of this study, PCU significantly reduced leaching and tended to improved N recovery over soluble N applied in two applications and resulted in similar N recovery and nitrate leaching as soluble N applied in six applications.

Application of manure on soils having high P test has raised concerns over the eutrophication of lakes and rivers. The objective of this study was to evaluate the effects of one time application of 164 kg P ha−1 from solid beef (Bos taurus L.) manure on soil Olsen P dynamics, P uptake by corn (Zea mays L.) grain, and P losses as total P (TP), particulate P (PP), and dissolved molybdate reactive P (DMRP) in both snowmelt and rainfall runoff under ridge tillage (RT) and moldboard plow (MP) systems from 1992 to 1994. Soil P was consistently higher in the manure than no manure treated plots (17.9 vs. 12.3 mg kg−1 in 1993 and 23.7 vs. 13.8 mg kg−1 in 1994). Phosphorus uptake was greater from the manure than no manure treated plots (24.5 vs. 19.8 kg ha−1 and 23.5 vs. 18.8 kg ha−1). Annual PP and TP losses were either similar or lower from manure than no manure treated plots. Particulate P losses by rainfall runoff were lower from the RT vs. MP systems (0.25 vs. 1.95 kg ha−1 in 1993 and 0.06 vs. 0.65 kg ha−1 and 1994). The opposite was apparent for DMRP losses in snowmelt, which were higher from the RT than MP system (0.11 vs. 0.01 kg ha−1 and 0.14 vs. 0.03 kg ha−1). The RT system is an environmentally better system than the MP system due to its substantial reduction in annual PP and TP losses.

As potato (Solanum tuberosum L.) production increases in the North‐Central Region of the USA, so does the potential for deep seepage of nitrogenous compounds into the ground water. The objectives of this 2‐yr study were to determine how different irrigation schemes (sprinkler and drip), irrigation triggers (70 and 40% of the available soil water [AW] remaining), drip placement (at the soil surface or buried at 25‐cm depth), and various N sources (urea, sulfur‐coated urea [SCU], and turkey [Meleagris gallopavo] manure) and timings (three‐ vs. five‐N splits) affect percolation and NO3 leaching. As expected, water percolation was generally higher from the sprinkler‐irrigation than from the drip‐irrigation treatments. Within the sprinkler irrigation, percolation was higher when irrigated at 70% than at 40% of AW remaining. Small but frequent irrigation in drip treatments helped reduce water percolation. Within irrigation treatments, 70% AW had the most N leaching, followed by 40% AW and the drip, the last two treatments being about the same. The trend in N leaching among fertilizer treatments was similar for various irrigation methods. Splitting N applications five times vs. three times reduced N leaching from unforeseen rains. Sulfur‐coated urea reduced N leaching, whereas turkey manure‐amended treatments showed no significant difference in N leaching compared with the urea‐N treatment. In conclusion, alternatives such as 40% deficit irrigation, five‐N application splits, drip irrigation, S‐coated urea, and turkey manure not only reduce N leaching but also have a minimal impact on potato tuber yield and tuber quality.

Controlled release fertilizers, especially polymer‐coated urea (PCU), have been shown to reduce nitrate (NO3) leaching while maintaining potato (Solanum tuberosum L.) yields, but cost has been prohibitive. A new type of PCU (Environmentally Smart Nitrogen, Agrium, Inc., Calgary, AB) is less costly than previous PCUs, but its effectiveness on potato production has not been extensively studied. A 2‐yr field study was conducted on loamy sand to evaluate the effect of this PCU on Russet Burbank tuber yield and to determine if it is economically comparable to soluble N sources. Several N rates of PCU applied at emergence were compared with two split applications of soluble N at equivalent rates. Additional treatments examined N application timing of PCU and a fertigation simulation with urea/ammonium nitrate. Petioles and midseason soil samples were collected to determine N status during the season. Overall, PCU and soluble N at equivalent N rates were found to have similar total and grade A yields and net monetary returns. The optimal N rate that resulted in maximum net returns was 251 and 236 kg N ha−1 as soluble N and PCU, respectively. Petiole NO3 concentrations were typically higher with soluble N early in the season and higher with PCU later in the season. Soil NO3 determined in samples collected in late June was found to be a better predictor of yield and potential N need than those collected in mid‐ to late July. Overall, PCU may reduce or eliminate the need for split applications of N on coarse‐textured soils.

A study was conducted on a Verndale sandy loam soil (coarse loamy over sandy, mixed, frigid Udic Argiboroll) during 1991 and 1992 at Staples, MN, to assess the influence of irrigation scheduling and N source and rate on corn (Zea mays L.) yield and nitrate leaching. Nitrogen sources were urea and turkey manure. Soils were irrigated to field capacity (i) at a fixed trigger deficit throughout the season, or (ii) at a variable trigger deficit based on crop growth stage. Leaching losses were calculated from measured daily fluxes of water percolation and soil water NO3‐N concentrations and from a seasonal N mass balance. Based on yield response curves, maximum corn grain yields were obtained at 202 and 234 kg N ha−1 urea in 1991 and 1992, respectively. This resulted in growing season leaching losses of 72 and 55 kg N ha−1 in 1991 and 1992, respectively. The rate at 95% of the maximum crop yield is suggested to substantially reduce nitrate leaching past the root zone. Using this guideline, nitrate leaching would be reduced by 35% compared with nitrate leaching at the maximum yield. When a variable available water deficit was used to schedule irrigation compared with a fixed deficit schedule (at 95% of maximum yield N rate), nitrate leaching was reduced 46%. At equivalent N rates, turkey manure produced equal or greater crop yields as that from urea applications; however, nitrate leaching was equal to or less than urea.