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Abstract: Nitrogen (N) management is critical in optimizing potato yield and quality and reducing environmental pollution. Six N rates from 34 to 270kgha−1, and different timing of N application were used in a 3-year field experiment to contrast SPAD-502 chlorophyll meter and QuickBird satellite imagery data against the conventional petiole sampling technique for assessing canopy N status. Overall treatment variations in SPAD readings were consistent with those in petiole nitrate-nitrogen (NO3-N) concentrations. However, the ability of the SPAD meter to detect treatment differences varied with growth stage and growing season. Severe N deficiency was detected about 1 month after emergence with SPAD readings, but as early as 2 weeks after emergence with petiole NO3-N concentrations. Petiole NO3-N concentrations tended to differentiate more treatment variations than SPAD readings at all growth stages except at hilling. N deficiency was detected with QuickBird image-derived vegetation indices (VIs) at the hilling stage in 2002, but not in 2003. At the post-hilling stage, treatment differences in VI values were minimal and insignificant except very late in the growing season. SPAD meters could be used as an indirect method for detecting N deficiency at the hilling stage when making supplemental N applications, but they are not as sensitive as the petiole sampling method. The sensitivity of QuickBird imagery to canopy N variations needs to be further tested with more pixel data. However, cloud interference and high cost of images could limit the use of QuickBird data in making timely management decisions. [Copyright &y& Elsevier]

Aims: Soil microbiomes and their interactions with crop plants are important drivers of agricultural health and productivity. Our objective was to examine short-term responses of soil microbiota to agricultural management (i.e. cover cropping and nitrogen fertilization). Methods: Following three years of cropping, soil samples were collected from replicated field plots at two southern Minnesota field sites (Lamberton and Waseca). We used amplicon-based gene sequencing (ITS2 and 16S rRNA V4) to investigate short-term soil fungal and bacterial community responses to cover crops and urea-nitrogen (N) fertilization (0, 80, 100, and 120% of recommended rates) in a corn (Zea mays)-soybean (Glycine max) cropping system planted with and without cover crops. Results: We found that rates of N-fertilizer applied, more than cover crops, significantly impacted soil chemical properties at both sites. Different cropping or N fertilization treatments did not lead to strong differences in fungal or bacterial alpha (local) diversity. At both sites, cover crop was a significant predictor of fungal community compositions and specific fungal and bacterial taxa were significantly impacted by cover crops. While, N fertilization was not a strong predictor of community compositions, urea-N additions, at any rate, resulted in changes in the relative abundances of the fungal phyla Glomeromycota in addition to a number of bacterial phyla. Conclusions: Our findings suggest that after three years of cropping, fungal communities respond to cover crops, while bacterial community responses may depend on soil chemical conditions. [ABSTRACT FROM AUTHOR]

Transport of nitrogen and phosphorus from agricultural and urban landscapes to surface water bodies can cause adverse environmental impacts. The main objective of this long-term study was to quantify and compare contaminant transport in agricultural drainage water and urban stormwater runoff. We measured flow rate and contaminant concentration in stormwater runoff from Willmar, Minnesota, USA, and in drainage water from subsurface-drained fields with surface inlets, namely, Unfertilized and Fertilized Fields. Commercial fertilizer and turkey litter manure were applied to the Fertilized Field based on agronomic requirements. Results showed that the City Stormwater transported significantly higher loads per unit area of ammonium, total suspended solids (TSS), and total phosphorus (TP) than the Fertilized Field, but nitrate load was significantly lower. Nitrate load transport in drainage water from the Unfertilized Field was 58% of that from the Fertilized Field. Linear regression analysis indicated that a 1% increase in flow depth resulted in a 1.05% increase of TSS load from the City Stormwater, a 1.07% increase in nitrate load from the Fertilized Field, and a 1.11% increase in TP load from the Fertilized Field. This indicates an increase in concentration with a rise in flow depth, revealing that concentration variation was a significant factor influencing the dynamics of load transport. Further regression analysis showed the importance of targeting high flows to reduce contaminant transport. In conclusion, for watersheds similar to this one, management practices should be directed to load reduction of ammonium and TSS from urban areas, and nitrate from cropland while TP should be a target for both. [ABSTRACT FROM AUTHOR]

Commercial sweet corn (Zea mays convar. saccharata var. rugosa) production has a proportionally high potential for nutrient loss to waterways, due to its high nitrogen (N) requirements and low N use efficiency. Cover crops planted after sweet corn can help ameliorate N lost from the field, but farmers are reluctant to utilize cover crops due to a lack of economic incentive. Pennycress (Thlaspi arvense L.) is a winter annual that can provide both economic and environmental benefits. Five N-rates (0, 65, 135, 135 split and 200) were applied pre-plant to sweet corn. After the sweet corn harvest, pennycress was planted into the sweet corn residue with two seeding methods and harvested for seed the following spring. Residual inorganic soil N (Nmin), pennycress biomass, biomass N and yield were measured. The nitrogen rate and seeding method had no effect on pennycress yield, biomass, or biomass N content. The nitrogen rate positively affected Nmin at pennycress seeding, wherein 200N plots had 38–80% higher Nmin than 0N plots, but had no effect on Nmin at pennycress harvest. Control treatments without pennycress had an average of 27–42% greater Nmin. In conclusion, pennycress can act as an effective N catch crop, and produce an adequate seed yield after sweet corn without the need for supplemental fertilization. [ABSTRACT FROM AUTHOR]