Increased streamflow and its associated impacts on water quality have frequently been linked to changes in land use and land cover (LULC) such as tile drainage, cultivation of prairies, and increased adoption of soybeans (Glycine max) in modern day cropping systems. This study evaluated the relative importance of changes in precipitation and LULC on streamflow in 29 Hydrologic Unit Code 008 watersheds in the upper midwestern United States. The evaluation was done by statistically testing the changes in slope and intercept of the relationships between ln(annual streamflow) versus annual precipitation for the periods prior to 1975 (prechange period) and after 1976 (postchange period). A significant shift either in slope or intercept of these relationships was assumed to be an indication of LULC changes whereas a lack of significant shift suggested a single relationship driven by precipitation. All 29 watersheds showed no statistical difference in slope or intercept of the relationships between the two periods. However, a simpler model that kept the slope constant for the two periods showed a slight upward shift in the intercept value for 10 watersheds in the postchange period. A comparison of 5 year moving averages also revealed that the increased streamflows in the postchange period are mainly due to an increase in precipitation. Minimal or the lack of LULC change impact on streamflow results from comparable evapotranspiration in the two time periods. We also show how incorrect assumptions in previously published studies minimized precipitation change impacts and heightened the LULC change impacts on streamflows.

High N fertilizer and irrigation amounts applied to potato (Solanum tuberosum L.) on coarse-textured soils often result in nitrate (NO3) leaching and low recovery of applied fertilizer N. This 3-yr study compared the effects of two rates (140 and 280 kg N ha(-1)) of a single polyolefin-coated urea (PCU) application versus split applications of urea on 'Russet Burbank' potato yield and on NO3 leaching and N recovery efficiency (RE) on a loamy sand. Standard irrigation was applied in all years and excessive irrigation was used in another experiment in the third year. At the recommended rate of 280 kg N ha(-1), NO3 leaching during the growing season was 34 to 49% lower with PCU than three applications of urea. Under standard irrigation in the third year, leaching from five applications of urea (280 kg N ha(-1)) was 38% higher than PCU. Under leaching conditions in the first year (> or = 25 mm drainage water in at least one 24-h period) and excessive irrigation in the third year, PCU at 280 kg N ha(-1) improved total and marketable tuber yields by 12 to 19% compared with three applications of urea. Fertilizer N RE estimated by the difference and 15N isotope methods at the 280 kg N ha(-1) rate was, on average, higher with PCU (mean 50%) than urea (mean 43%). Fertilizer N RE values estimated by the isotope method (mean 51%) were greater than those estimated by the difference method (mean 47%). Results from this study indicate that PCU can reduce leaching and improve N recovery and tuber yield during seasons with high leaching.

Anaerobic soil conditions resulting from flooding often enhance release of phosphorus (P) to overlying water. Enhanced P release is well documented for flooded acidic soils; however, there is little information for flooded alkaline soils. We examined the effect of flooding and anaerobic conditions on P mobilization using 12 alkaline soils from Manitoba that were either unamended or amended with solid cattle manure. Pore water and floodwater were analyzed over 8 wk of simulated flooding for dissolved reactive P (DRP), Ca, Mg, Fe, and Mn. As expected, manured soils had significantly greater pore and floodwater DRP concentrations than unamended. Flooding increased pore water DRP concentrations significantly in all soils and treatments except one manured clay in which concentrations increased initially and then decreased. Floodwater DRP concentrations increased significantly by two-to 15-fold in 10 soils regardless of amendment treatment but remained relatively stable in the two soils with greatest clay content. Phosphorus release at the onset of flooding was associated with the release of Ca, Mg, and Mn, suggesting that P release may be controlled by the dissolution of Mg and Ca phosphates and reductive dissolution of Mn phosphates. Thereafter, P release was associated with release of Fe, suggesting the reductive dissolution of Fe phosphates. Differences in pore water and floodwater DRP concentrations among soils and amendment treatments and the high variability in P mobilization from pore water to floodwater among soils indicate the need to further investigate chemical reactions responsible for P release and mobility under anaerobic conditions.

In the 1990s, restrictions on incineration encouraged the forest industry in western Canada to develop new uses for their wood residuals by product. One such use was as a replacement for cereal straw bedding in southern Alberta's beef cattle (Bos taurus) feedlot industry. However, use of carbon (C)-rich bedding, such as wood chips, had implications for subsequent composting of the feedlot manure, a practice that was being increasingly adopted. In a 3-yr study, we compared composting of wood chip-bedded manure (WBM) and barley (Hordeum vulgare L.) straw-bedded manure (SBM). There were no significant differences in temperature regimes of SBM and WBM, indicating similar rates of successful composting. Of 17 physical and chemical parameters, five showed significant (P < 0.10) differences due to bedding at the outset of composting (Day 0), and 11 showed significant differences at final sampling (Day 124). During composting (10 sampling times), seven parameters showed significant bedding effects, 16 showed significant time effects, and four showed a Bedding x Time interaction. Significantly lower (P < 0.10) losses of nitrogen (N) occurred with WBM (19%) compared with SBM (34%), which has positive implications for air quality and use as a soil amendment. Other advantages of WBM compost included significantly higher total C (333 vs. 210 kg Mg(-1) for SBM) and inorganic N (1.3 vs. 1.0 kg Mg(-1) for SBM) and significantly lower total phosphorus (4.5 vs. 5.3 kg Mg(-1) for SBM). Our results showed that wood chip bedding should not be a problem for subsequent composting of the manure after pen cleaning. In combination with other benefits, our findings should encourage the adoption of wood chips over straw as a bedding choice for southern Alberta feedlots.

Soil phosphorus (P) cycling in agroecosystems is highly complex, with many chemical, physical, and biological processes affecting the availability of P to plants. Traditionally, P fertilizer recommendations have been made using an insurance‐based approach, which has resulted in the accumulation of P in many intensively managed agricultural soils worldwide and contributed to the widespread water quality issue of eutrophication. To mitigate further environmental degradation and because future P fertilizer supplies are threatened due to finite phosphate rock resources and associated geopolitical and quality issues, there is an immediate need to increase P use efficiency (PUE) in agroecosystems. Through cultivar selection and improved cropping system design, contemporary research suggests that sufficient crop yields could be maintained at reduced soil test P (STP) concentrations. In addition, more efficient P cycling at the field scale can be achieved through agroecosystem management that increases soil organic matter and organic P mineralization and optimizes arbuscular mycorrhizal fungi (AMF) symbioses. This review paper provides a perspective on how agriculture has the potential to utilize plant and microbial traits to improve PUE at the field scale and accordingly, maintain crop yields at lower STP concentrations. It also links with the need to tighten the P cycle at the regional scale, including a discussion of P recovery and recycling technologies, with a particular focus on the use of struvite as a recycled P fertilizer. Guidance on directions for future research is provided. Core Ideas There is an urgent need to increase P use efficiency in agroecosystems. Crop yields could be maintained at lower than recommended soil test P concentrations. Both the quantity and quality of organic matter influence P availability. Further research on ability of organic P to supply P to crops is needed. Struvite has the potential to fill an important niche in P recycling.

Ackerman, J. N., Zvomuya, F., Cicek, N. and Flaten, D. 2013. Evaluation of manure-derived struvite as a phosphorus source for canola. Can. J. Plant Sci. 93: 419–424. There is growing interest in the treatment of swine manure to mitigate water quality issues related to phosphorus (P) from livestock operations. Precipitation of P as struvite (MgNH4PO4·6H2O) is a potential strategy to achieve this. The overall objective of this growth room study was to evaluate the effect of manure-derived struvite (MDS) on canola growth and P recovery efficiency. Pure struvite (PS), monoammonium phosphate (MAP), and polymer-coated monoammonium phosphate (PCMAP) were applied to canola plants in plastic pots containing 2 kg of a sandy loam soil. Biomass yields for MDS and PS were similar at all P rates (mean = 7.6 g pot−1) and significantly smaller than those for MAP and PCMAP (mean = 9.3 g pot−1). Differences in P uptake among P sources were detected at the highest P rate where P uptake was significantly greater for MAP and PCMAP (mean = 22.7 mg P pot−1) than for the struvite forms (mean = 16.4 mg P pot−1). Our results show that although P uptake was similar for the struvites and commercial fertilizers at P2O5 rates of 38 mg pot−1 or lower, biomass yield per unit of P taken up was smaller for the struvites. This may be due to lower initial solubility of the struvites in the alkaline (pH 7.7) soil used in this experiment, which gave an early stage growth advantage to canola fertilized with MAP and PCMAP. These results suggest that it may be necessary to supplement struvite with soluble P fertilizers, such as MAP, if applied on soils such as that tested in this study.

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Land application of manure is a common practice in the Upper Midwest of the United States. Recently, there have been concerns regarding the effect of this practice on water quality, especially when manure is applied during winter over frozen soils. A study undertaken on a Rozetta silt loam (fine-silty, mixed, superactive, mesic Typic Hapludalfs) at Lancaster, WI, evaluated the effects of tillage and timing of manure application on surface and subsurface water quality. The daily scrape and haul liquid dairy manure was applied either in the fall (before snow) or in winter (over snow with frozen soil underneath) to be compared with no manure under two tillage systems (no-till and chisel-plowing). In this paper, we report results on the effects of the above treatments on mineral N leaching. Percolation and mineral N leaching during the nongrowing season were, respectively, 72 and 78% of the annual losses, mainly because of the absence of plant water and N uptake. Percolation was generally higher from no-till compared with chisel-plow but there was no significant effect of tillage on mineral N concentration of the leachate or mineral N losses via leaching. Mineral N leaching was statistically higher from the manure-applied vs. no-manure treatment, but there was no difference between winter-applied manure and no-manure treatments. There were significant tillage by manure interactions with fall manure application followed by chisel-plowing resulting in highest N leaching losses. Averaged over the two years, N leaching rates were 52, 38, and 28 kg N ha(-1) yr(-1) from fall-applied, winter-applied, and no-manure treatments, respectively. These results show that there is substantial N leaching from these soils even when no fertilizer or manure is applied. Furthermore, fall-applied manure followed by fall tillage significantly increases N leaching due to enhanced mineralization of both soil and manure organic N.