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Aims: Kura clover living mulch (KCLM) is thought to provide in-season nitrogen (N) to the cash crop. Because of interactions between cropping system and crop performance, the magnitude of in-season N inputs from KCLM cannot be quantified using common N rate research methods. We aim to quantify the timing and magnitude of these N inputs using clover biomass and decomposition data. Methods: This research measured the temporal distribution of clover biomass with intensive sampling, vertical biomass distribution using bead tracer analysis, and residue decomposition using in situ litter bags. These data were used as inputs to a model that estimated the in-season N contributions from KCLM. Results: Our results found that spring management contributed 7–23 kg N ha−1 during the first 6 weeks of the growing season, while shade suppression contributed 59 – 84 kg N ha−1 from mid-June to mid-October. Daily N inputs peaked on 8 August at 1.14 kg N ha−1 d−1. When these estimates were added to fertilizer N inputs and analyzed against crop N uptake, we found that the maize took up 88% of the total N inputs and fertilizer recovery efficiency was 56%. Conclusions: This study provides a methodology which generates estimates that may be used in research related to N cycling and management in KCLM and other legume intercropping systems. [ABSTRACT FROM AUTHOR]

Row establishment is important to mitigate competition with maize (Zea mays L.) seedlings in a kura clover (Trifolium ambiguum Bieb.) living mulch (KCLM). This study investigated the effect of row-establishment and fertilizer nitrogen (N) rate on maize yield and N uptake in a KCLM system in Arlington, WI, and Rosemount, MN, during the 2021 growing season. Row establishment treatments included rotary zone tillage (RZT), shank strip-tillage (ST), and banded herbicides (BH), each evaluated at six N rates from 0 to 225 kg N ha-1. Extended periods of moderate and severe drought were experienced during the study period. The Arlington and Rosemount sites received 64 and 63% of the normal precipitation between 20 Apr. and 31 Oct. 2021, but poor distribution and higher temperatures at Rosemount elevated drought severity indices at that site. Grain yields at Rosemount were 3.6 Mg ha-1, whereas Arlington produced yields that matched expectations for the area (10Mg ha-1). Row establishment affected maize grain yield differentially at each site, where, under severe drought conditions, BH maximized maize yield, whereas under moderate drought conditions, the higher level of tillage (RZT) maximized maize yield. These responses are most likely attributed to reduced moisture loss in the row-zone of the BH treatment and the greater level of clover suppression in the RZT treatment and their interactions with specific weather conditions at the research sites. Results from this study indicate that row establishment methods in a KCLM cropping system should be considered with spring environmental conditions and the expected weather outlook. [ABSTRACT FROM AUTHOR]

The US Corn Belt is a global hotspot of atmospheric ammonia (NH3), a gas known to adversely impact the environment and human health. We combine hourly tall tower (100 m) measurements and bi‐weekly, spatially distributed, ground‐based observations from the Ammonia Monitoring Network with the US National Emissions Inventory (NEI) and WRF‐Chem simulations to constrain NH3 emissions from April to September 2017–2019. We show that: (1) NH3 emissions peaked from May to July and were 1.6–1.7 times the annual NEI average; (2) average growing season NH3 emissions from agricultural lands were remarkably similar across years (3.27–3.64 nmol m−2 s−1), yet showed substantial episodic variability driven by meteorology and land management; (3) dry deposition was 40% of gross emissions from agricultural lands and exceeded 100% of gross emissions in natural lands. Our findings provide an important benchmark for evaluating future NH3 emissions and mitigation efforts. Key Points: Rare multiyear tall tower and ground‐based ammonia measurements were combined with WRF‐Chem to constrain emissions from the US Corn BeltMonthly ammonia emissions peaked in May through July and were 1.6–1.7 times the annual NEI averageEpisodic low WRF‐Chem bias versus tall tower observations underscore the importance of weather and land management as emission drivers [ABSTRACT FROM AUTHOR]

Abstract Kura clover (Trifolium ambiguum Bieb.) perennial living mulch is a farming practice designed to pair water quality services and row crop production. In this system, rows are mechanically or chemically killed within a perennial kura clover stand to create a suitable environment for planting a crop. However, yields are often reduced relative to conventional, fully-tilled systems. This hypothesis was tested by using a novel rotary zone tillage unit (RZT) that creates 45 cm wide tilled strips with a depth of 8 cm for each row, with rows spaced 76 cm apart. We compared RZT to three row preparation strategies that have been commonly used in living mulch systems: herbicide band kill (BK), and shank tillage (ST), also known as strip tillage. Shank tillage produced bands that were 40 cm wide and 5 cm deep. We monitored kura clover health, soil moisture & temperature, corn (Zea mays L.) emergence, corn development, and corn yield in all three row preparation strategies over two growing seasons. In 2015, corn grown in RZT plots emerged and developed faster than corn grown in ST plots, but this did not lead to a difference in grain or stover yield. However, in 2016, corn grown in RZT plots not only emerged and developed faster, but also produced 4.0 Mg ha−1 more grain and 3.5 Mg ha−1 more stover biomass than corn grown in ST and BK plots. Kura clover biomass was not affected by treatment in either year. We conclude that rotary zone tillage is a promising row preparation strategy in kura clover living mulch for corn production with minimal herbicide use. [ABSTRACT FROM AUTHOR]

Net CO2 exchange data of legume crops at 17 flux tower sites in North America and three sites in Europe representing 29 site-years of measurements were partitioned into gross photosynthesis and ecosystem respiration by using the nonrectangular hyperbolic light-response function method. The analyses produced net CO2 exchange data and new ecosystem-scale ecophysiological parameter estimates for legume crops determined at diurnal and weekly time steps. Dynamics and annual totals ofgross photosynthesis, ecosystem respiration, and net ecosystem production were calculated by gap filling with multivariate nonlinear regression. Comparison with the data from grain crops obtained with the same method demonstrated that CO2 exchange rates and ecophysiological parameters of legumes were lowerthan those of maize (ZeamaysL.) but higherthanforwheat (TriticumaestipumL.) crops. Year-round annuallegume crops demonstrated a broad range of net ecosystem production, from sinks of 760 g CO2 m-2 yr-1 to sources of -2100 g CO2 m-2 yr-1, with an average of -330 g CO2 m-2 yr-1, indicating overall moderate CO2-source activity related to a shorter period of photosynthetic uptake and metabolic costs of N2 fixation. Perennial legumes (alfalfa, Medicago sativa L.) were strong sinks for atmospheric CO2, with an average net ecosystem production of 980 (range 550-1200) g CO2 m-2 yr-1. [ABSTRACT FROM AUTHOR]

Recent proliferation of large dairies has prompted concern regarding environmental impacts of associated corn silage production and high-rate manure application. Our objectives were to compare environmental impacts and forage production of monocrop corn (kZea mays L.) silage and rye (Secale cereal/L.)-corn silage double-crop systems with multiple corn planting dates and high-rate manure application near Morris, MN. From 2007 to 2009, corn for silage was seeded into a silt loam as a monocrop in early and mid-May and as a double-crop after rye in mid-May and early June. Manure was fall applied annually at average total N and P rates of 393 and 109 kg ha-1 respectively. Double-cropping reduced total forage dry matter (DM) yield 2 of 3 yr and reduced corn DM yield 15 to 25%. Soil NO3-N to 90 cm accumulated at an average rate of 71 kg N ha-1 yr-1 with monocropping, but accumulation was not observed with double-cropping. Soil organic C concentration from 0 to 5 cm increased in the monocrop (18%) and double-crop (26%) systems over 3 yr. Average soil solution NO3-N concentration was high with monocropping (52 mg L-1) and double-cropping (37 mg L-1) but estimated leaching load averaged only 8 kg ha-1 yr-1. Fall and spring ground cover was often less than 10% with monocropping but was usually greater than 30% with double-cropping. The primary environmental concerns identified for monocrop corn silage were soil NO3-N buildup and inadequate ground cover. Double-cropping addressed each concern but often decreased forage production. [ABSTRACT FROM AUTHOR]

A winter rye (Secale cereale L.) cover crop can be seeded after corn (Zea mays L.) silage to mitigate some of the environmental concerns associated with corn silage production. Rye can be managed as a cover crop by chemical termination or harvested for forage. A field study was conducted in Morris, MN in 2008 and 2009 to determine the impact of killed vs. harvested rye cover crops on soil moisture and NO3-N, and to monitor the impact of the rye on subsequent corn yield. Corn for silage was seeded either after winter fallow (control), after a rye cover crop terminated 3 to 4 wk before corn planting (killed rye), or after a rye forage crop harvested no more than 2 d before corn planting (harvested rye). Soil moisture after killed rye was similar to the control, but after harvested rye was 16% lower. Available soil NO3-N was decreased after both killed rye (35%) and harvested rye (59%) compared to the control. Corn biomass yield after killed rye was similar to the control, but yield following harvested rye was reduced by 4.5 Mg hat. Total forage biomass yield (silage + rye) was similar for all treatments. This work demonstrates that the environmental benefits of a winter rye cover crop can be achieved without impacting corn yield, but the later termination required for rye forage production resulted in soil resource depletion and negatively impacted corn silage yield. [ABSTRACT FROM AUTHOR]

Abstract: Climate change and economic concerns have motivated intense interest in the development of renewable energy sources, including fuels derived from plant biomass. However, the specter of massive biofuel production has raised other worries, specifically that by displacing food production it will lead to higher food prices, increased incidence of famine, and acceleration of undesirable land use change. One proposed solution is to increase the annual net primary productivity of the existing agricultural land base, so that it can sustainably produce both food and biofuel feedstocks. This might be possible in corn and soybean production regions through the use of winter cover crops, but the biophysical feasibility of this has not been systematically explored. We developed a model for this purpose that simulates the potential biomass production and water use of winter rye in continuous corn and corn–soybean rotations. The input data requirements represent an attempt to balance the demands of a physically and physiologically defensible simulation with the need for broad applicability in space and time. The necessary meteorological data are obtainable from standard agricultural weather stations, and the required management data are simply planting dates and harvest dates for corn and soybeans. Physiological parameters for rye were taken from the literature, supplemented by experimental data specifically collected for this project. The model was run for a number of growing seasons for 8 locations across the Midwestern USA. Results indicate potential rye biomass production of 1–8Mgha−1, with the lowest yields at the more northern sites, where both PAR and degree-days are limited in the interval between fall corn harvest and spring corn or soybean planting. At all sites rye yields are substantially greater when the following crop is soybean rather than corn, since soybean is planted later. Not surprisingly, soil moisture depletion is most likely in years and sites where rye biomass production is greatest. Consistent production of both food and biomass from corn/winter rye/soybean systems will probably require irrigation in many areas and additional N fertilizer, creating possible environmental concerns. Rye growth limitations in the northern portion of the corn belt may be partially mitigated with aerial seeding of rye into standing corn. [Copyright &y& Elsevier]

Maintaining crop production levels with reductions in terrestrial greenhouse gases requires strategic residue and nitrogen (N) fertilizer management. Our objectives were to: (1) quantify the effect of nitrogen N application rate on N losses; (2) examine the role of residue returned on N transformation and losses; and (3) verify the capability of the NCSWAP/NCSOIL model to simulate the dynamics of N and 15N in the soil–plant system. Data obtained from a long-term continuous corn study on a silt loam soil, with two N levels (20 and 200 kg N/ha), with two types of residue management (residue harvested, -R; and residue returned, +R) was used to calibrate the model. The model accurately predicted 15N in the plant and soil organic matter (SOM) at the 0- to 15-cm and 15- to 30-cm depths for both fertilizer rates and residue managements. Concentrations of 15N in the corn and SOM were higher for the 20 than 200 kg N/ha treatments. Greater dilution of the 15N with nontracer fertilizer added at the higher fertilizer rate was responsible for differences in 15N concentrations in the plant. The predicted cumulative N loss during a 30-year simulation indicates more nitrate leaching past the 1-m depth for -R than +R treatments, while higher denitrification rates were predicted for the +R than -R. The simulated cumulative effect of residue returned on denitrification over 30 years predicted increased cumulative N losses from 1320 to 1705 kg N/ha and 1333 to 2574 kg N/ha for the low and high N application rates, respectively. Better synchronization of N release from residue and addition of N fertilizer with plant-N uptake would minimize leaching and denitrification. [ABSTRACT FROM AUTHOR]

Kura clover (Trifolium ambiguum) is a perennial living mulch species that can be used in conjunction with zone tillage to reduce nitrogen pollution, maintain ground cover, and provide nitrogen to crops. In such systems, kura clover is maintained between crop rows by limiting tillage only to within-row areas. However, the effect of zone-tilled living mulches on soil quality and nutrient cycling in these distinct regions is relatively unexplored. We examined three pools of labile soil organic matter (SOM): microbial biomass, particulate organic matter (POM), and permanganate oxidizable carbon (POXC). Soil samples were collected from both within-row and between-row locations of a zone-tilled kura clover living mulch at three time points per year: before spring zone tillage, approximately ten days after spring zone tillage and corn (Zea mays) planting, and at corn harvest in 2015 and 2016. In 2016, POM and POXC decreased within rows relative to between-row regions after tillage, suggesting that zone till management stimulated decomposition of readily available SOM to effectively localize nutrient cycling in this region and slow mineralization between rows where living kura clover remained. This work shows that zone-tilled living mulches may be a promising avenue for enhancing the synchrony of nutrient mineralization specifically within crop rows, while maintaining year-round ground cover between rows. [ABSTRACT FROM AUTHOR]

Kura clover living mulch (KCLM) systems have been previously investigated for their incorporation into upper Midwestern row crop rotations to provide ecosystem services through continuous living cover. Reductions in soil erosion and nitrate loss to surface and groundwater have been reported, but factors affecting agronomic performance and nutrient management are not well defined. To achieve realized environmental benefits, research must develop agronomic management techniques, determine economic opportunities, and provide management recommendations for row crop production in KCLM systems. Two experiments were conducted in 2017 and 2018 to determine the response to N fertilizer application for maize production in KCLM. The first-year maize experiment followed forage management, and the second-year maize experiment followed maize after forage management. Eight fertilizer N treatments ranging from 0–250 kg N ha−1 were applied to each experiment and grain and stover yields were compared to conventionally managed maize hybrid trials that were conducted nearby. First-year maize did not need fertilizer N to maximize yield and profitability in either growing season, and second-year maize required a fertilizer N rate near local University guidelines for maize following soybean. The net economic return from maize grain and stover in the KCLM averaged over first and second-year maize experiments and 2017 and 2018 growing seasons were $138 ha−1 greater than the conventional comparison. [ABSTRACT FROM AUTHOR]

• We calculated field-scale net ecosystem C balances for forage and grain rotations. • C loss was threefold greater from continuous silage maize than soybean-grain maize. • Alfalfa reduced C loss by 23% relative to continuous silage maize. • Winter rye cover copping and liquid dairy manure improved C-balances marginally. • Every Mg of crop residue C left in-field improved C balances by +0.9 Mg C ha−1. Intensification of the US dairy industry has driven increased reliance on maize (Zea mays L.) silage as a primary forage source in place of perennial forages such as alfalfa (Medicago sativa L.). Using 29 site-years of eddy covariance, plant, and manure measurements, we calculated net ecosystem C balances (NECB) for two silage maize-based forage cropping systems and a soybean-maize grain rotation. We found that C losses were over threefold greater from continuous silage maize (-4.9 Mg C ha−1 yr−1) than from the predominant grain cropping system in the region, the soybean-maize rotation (-1.3 Mg C ha−1 yr−1). Including alfalfa in rotation reduced C losses by 23% relative to continuous silage maize, but net losses were still observed (-3.8 Mg C ha−1 yr−1). For every megagram of crop residue C left in-field, net C balances increased by +0.9 Mg C ha−1. A winter rye (Secale cereale L.) cover crop and applications of liquid dairy manure marginally improved C-balances but were insufficient to offset C losses in respiration and crop harvest. Increasing manure application rates could bring these systems to a net equilibrium C balance but would also result in soil N and P surpluses and unacceptable loss of nutrients to air and water. Since 1980, over 800,000 hectares of alfalfa have been lost across the Upper Midwest US, and C export in harvested maize grain and silage have increased dramatically. This shift implies a substantial reduction in SOC on forage cropped soils in the region. [ABSTRACT FROM AUTHOR]