Nitrogen Mineralization Responses to Cropping, Tillage, and Nitrogen Rate in the Northern Great Plains

Nitrogen-mineralization rates are needed to accurately determine N fertilization requirements to meet plant needs while minimizing environmental contamination. A spring wheat (Triticum aestivum L.)-fallow (SW-F) system was compared with a spring wheat-winter wheat-sunflower (Helianthus annuus L.) (SW-WW-SF) system on a Temvik-Wilton silt loam (fine-silty, mixed Typic and Pachic Haploborolls) at three N rates (0, 22, and 45 kg ha‒1 for SW-F and 34, 67, and 101 kg ha‒1 for SW-WW-SF) under conventional, minimum, and no-tillage. After 10 yr, soil samples were incubated to determine N mineralization rates. Cropping intensity, N rate, and tillage intensity interacted to affect N-mineralization rates. Within the SW-F system N-mineralization rates in 0- to 0.05-m depth were 8.2 ± 0.8 kg ha‒1 wk‒1 in the fallow phase vs. 5.0 ± 0.7 kg ha‒1 wk‒1 in the crop phase under conventional tillage and were 6.2 ± 0.3 kg ha‒1 wk‒1 under minimum and no-tillage in both phases. The N-mineralization rates were 2.3 ± 0.4 kg ha‒1 wk‒1 in 0.05- to 0.15-m depth soils of the SW-F system. In spring wheat, N-mineralization rates in 0- to 0.05-m depth soil were 9.9 ± 0.8 kg ha‒1 wk‒1 in the SW-WW-SF system vs. 5.6 ± 0.4 kg ha‒1 wk‒1 in the SW-F system and in the 0.05- to 0.15-m depth were 3.6 ± 0.1 kg ha‒1 wk‒1 in the SW-WW-SF system vs. 2.4 ± 0.2 kg ha‒1 wk‒1 in the SW-F system Within the SW-WW-SF system, N-mineralization rates in the 0- to 0.05-m soil layer were 6.8 ± 0.5 kg ha‒1 wk‒1 under winter wheat vs. 9.9 ± 0.8 kg ha‒1 wk‒1 under spring wheat and 9.2 ± 0.6 kg ha‒1 wk‒1 under sunflower. In the 0.05- to 0.15-m soil layer, N-mineralization rates were 3.3 ± 1.0 kg ha‒1 wk‒1. More intensive cropping and conservation tillage increased N-mineralization rates in this soil and may ameliorate the decline in N fertility associated with crop-fallow systems

Corn Cobs On Deck for Cellulosic Feedstock

When energy officials proposed using crop residues to produce cellulosic ethanol, concerned soil scientists took to the fields to learn more about how these residues protect soil from erosion and enhance soil quality. Agricultural Research Service soil scientist Brian Wienhold focused on a single component of residue— the corncob. “We didn’t have data on how postharvest cob residues might protect soil quality,” says Wienhold, who works in the ARS Agroecosystem Management Research Unit in Lincoln, Nebraska. “But corncobs make up 20 percent of residue by weight, which means that the average U.S. production of corn could provide 40 to 50 million tons of cobs for feedstock every year.” Wienhold led colleagues in studies that compared runoff from no-till corn fields where postharvest crop residues were either removed or retained. The scientists also removed the cobs from half of the test plots that were protected by the residues. Then they generated two simulated rainfall events; the first occurred when the fields were dry, and the next occurred 24 hours later when the soils were almost completely saturated. During the first event, on plots where residue was removed, runoff began around 200 seconds after the “rain” began, whereas runoff in the residueprotected plots didn’t start until around 240 seconds after it started to “rain.” Runoff from the residue-free plots contained 30 percent more sediment than runoff from all the residue-protected plots. The presence or absence of cobs on the residue-protected plots did not affect sediment loss rates

Volatilization of Alachlor and Atrazine as Influenced by Surface Litter

A basic knowledge of how herbicide volatilization is influenced by agronomic practices is necessary if long-term detrimental impacts from herbicides are to be minimized. We measured cumulative herbicide volatilization losses in glass agroecosystem chambers to assess how surface residue conditions, simulated rainfall, temperature, and herbicide formulation affect volatilization of atrazine and alaehlor. Research results demonstrated that herbicide volatilization before water application was greater under mulched conditions, but decreased dramatically after the first irrigation. As a result, after 35 d cumulative volatilization of atrazine from a mulched soil surface was less than half that from bare soil for both formulations. Plant litter on the soft surface and encapsulated herbicides may be viable alternatives for reducing volatilization of some herbicides in humid regions

Managing Manure Phosphorus

Manure, a renewable resource, contains nutrients that are needed for plant growth. Phosphorus in manure can be utilized for crop production as a substitute for synthetic fertilizers. Phosphorus in manure can also be a source of surface or ground water contamination if not used properly. Increased P concentration can lead to eutrophication of surface waters. Management systems need to be developed to utilize manure P effectively without adverse effects on the environment

Increased abundance of arbuscular mycorrhizal fungi in soil coincides with the reproductive stages of maize

Arbuscular mycorrhizal (AM) fungi are recognized for their positive effects on plant growth, playing an important role in plant P nutrition. We used C16:1cis11 and C18:1cis11 fatty acid methyl ester (FAME) biomarkers to monitor the dynamics of AM fungi during the reproductive stages of maize (Zea mays L.) grown at high yield in Nebraska, USA. Two fields with four different levels of P availability were sampled throughout the reproductive stages. Chambers, made of PVC enclosed mesh fabric to allow passage of roots and hyphae(+R) or hyphae alone (-R) and amended with either KH2PO4 (+P) or distilled water (-P), were installed in the field at tasselling and removed after three, six and nine weeks. Our objectives were (i) to provide evidence for C allocation to AM fungi during the reproductive stages of high productivity maize and (ii) to link AM fungal growth dynamics with changes in soil P availability. We observed that initial AM FAME concentration was lower at sites with a high availability of P. During the reproductive growth of maize, AM biomarkers increased inside the chambers and were consistent with the biomarker increase observed in adjacent field soil. This confirms that there is C allocation from the plant to the symbiont during the reproductive stages of maize. We also observed a reduction in available P in +R and -R chambers. This observation implies that hyphae were as efficient as roots and hyphae in reducing the P concentration in chambers. These results demonstrate that AM fungi are active during the reproductive growth stages of maize and may benefit high productivity maize crops by facilitating P uptake

Distribution and Quantification of Antibiotic Resistant Genes and Bacteria across Agricultural and Non- Agricultural Metagenomes

There is concern that antibiotic resistance can potentially be transferred from animals to humans through the food chain. The relationship between specific antibiotic resistant bacteria and the genes they carry remains to be described. Few details are known about the ecology of antibiotic resistant genes and bacteria in food production systems, or how antibiotic resistance genes in food animals compare to antibiotic resistance genes in other ecosystems. Here we report the distribution of antibiotic resistant genes in publicly available agricultural and non-agricultural metagenomic samples and identify which bacteria are likely to be carrying those genes. Antibiotic resistance, as coded for in the genes used in this study, is a process that was associated with all natural, agricultural, and human-impacted ecosystems examined, with between 0.7 to 4.4% of all classified genes in each habitat coding for resistance to antibiotic and toxic compounds (RATC). Agricultural, human, and coastal-marine metagenomes have characteristic distributions of antibiotic resistance genes, and different bacteria that carry the genes. There is a larger percentage of the total genome associated with antibiotic resistance in gastrointestinal-associated and agricultural metagenomes compared to marine and Antarctic samples. Since antibiotic resistance genes are a natural part of both human-impacted and pristine habitats, presence of these resistance genes in any specific habitat is therefore not sufficient to indicate or determine impact of anthropogenic antibiotic use. We recommend that baseline studies and control samples be taken in order to determine natural background levels of antibiotic resistant bacteria and/or antibiotic resistance genes when investigating the impacts of veterinary use of antibiotics on human health. We raise questions regarding whether the underlying biology of each type of bacteria contributes to the likelihood of transfer via the food chain

NUTRIENTS IN RUNOFF FOLLOWING THE APPLICATION OF SWINE MANURE TO INTERRILL AREAS

The P content of swine manure can be reduced through the addition of feed supplements or the use of selected corn hybrids. This study was conducted to compare interrill runoff losses of P and N from three soils following the application of swine manure obtained from selected diets. The soils used in this investigation included a Hersh sandy loam, Pierre silty clay, and Sharpsburg silt loam. Simulated rainfall was applied during both initial and wet runs to a soil pan on which swine manure produced from low phytate corn (LPC), phytase added to the diet (PHY), or a traditional corn diet (TCD) was added. Additional experimental treatments included inorganic fertilizer and an untreated check. For the initial rainfall simulation run, concentrations of dissolved P, bioavailable P, and Total P were greater for the fertilizer treatment than any of the manure treatments. Use of manure from a LPC diet generally did not result in a reduction in N and P concentrations in runoff when compared with the TCD. Concentrations and total amounts of nutrients transported in runoff were affected by soil type. Changing the TCD to LPC and PHY diets to reduce the P content of manure did not significantly affect the total amounts of DP, BAP, or Total P transported in runoff, when simulated rainfall was applied soon after manure application

Soil Electrical Conductivity Classification: A Basis For Site-Specific Management In Semiarid Cropping Systems

Site specific management (SSM) has the potential to improve both economic and ecological outcomes in agriculture. Effective SSM requires strong and temporally consistent relationships between identified management zones, underlying soil physical, chemical and biological parameters defining yield potential, and crop yield. In a farm-scale (250 ha) experiment in semiarid northeastern Colorado, each of eight 31-ha fields was individually mapped for soil apparent electrical conductivity (ECa) and classified into four management zones (ranges of ECa). Soil analyses revealed a strong negative relationship between ECa zones and soil parameters associated with innate fertility (P ≤ 0.06). The objective of the present study was to further evaluate ECa as a basis for SSM by examining its relationship to actual yield using two years of yield maps for winter wheat (Triticurn aestivum L.) and corn (Zea mays L.). Within field wheat yields were strongly related to ECa, particularly when regressing mean wheat yields within ECa classes against mean ECa within ECa classes (r2 = 0.95 to 0.99). Yield response curves revealed a boundary line of maximum yield that decreased with increasing EC . In this semiarid dryland system, ECa-based management zones can be used in the SSM of wheat for: (1) yield goal determination, (2) soil sampling to assess residual fertilizer concentrations and soil attributes affecting herbicide efficacy, and (3) prescription maps for metering fertilizer, pesticide and seed inputs. Inconsistent relationships were found between ECa and corn yields indicating that, while soil factors controlled wheat yields, corn yields were more influenced by weather

Long-term no-till and stover retention each decrease the global warming potential of irrigated continuous corn

Over the last 50 years, the most increase in cultivated land area globally has been due to a doubling of irrigated land. Long-term agronomic management impacts on soil organic carbon (SOC) stocks, soil greenhouse gas (GHG) emissions, and global warming potential (GWP) in irrigated systems, however, remain relatively unknown. Here, residue and tillage management effects were quantified by measuring soil nitrous oxide (N2O) and methane (CH4) fluxes and SOC changes (ΔSOC) at a long-term, irrigated continuous corn (Zea mays L.) system in eastern Nebraska, USA. Management treatments began in 2002, and measured treatments included no or high stover removal (0 or 6.8 Mg DM ha-1 yr-1, respectively) under no-till (NT) or conventional disk tillage (CT) with full irrigation (n = 4). Soil N2O and CH4 fluxes were measured for five crop-years (2011 to 2015), and ΔSOC was determined on an equivalent-mass basis to ~30 cm soil depth. Both area- and yield-scaled soil N2O emissions were greater with stover retention compared to removal and for CT compared to NT, with no interaction between stover and tillage practices. Methane comprise

STATUS OF SOIL ELECTRICAL CONDUCTIVITY STUDIES BY CENTRAL STATE RESEARCHERS

Practical tools are needed to identify and advance sustainable management practices to optimize economic return, conserve soil, and minimize negative off-site environmental effects. The objective of this article is to review current research in non-saline soils of the central U.S. to consider bulk soil electrical conductivity (ECa) as an assessment tool for: (1) tracking N dynamics, (2) identifying management zones, (3) monitoring soil quality trends, and (4) designing and evaluating field-scale experiments. The interpretation and utility of ECa are highly location and soil specific; soil properties contributing to measured ECa must be clearly understood. In soils where ECa is driven by NO3-N, ECa has been used to track spatial and temporal variations in crop-available N (manure, compost, commercial fertilizer, and cover crop treatments) and rapidly assess N mineralization early in the growing season to calculate fertilizer rates for site-specific management (SSM). Selection of appropriate ECa sensors (direct contact, electromagnetic induction, or time domain reflectometry) may improve sensitivity to N fluctuations at specific soil depths. In a dryland cropping system where clay content dominates measured ECa, ECa -based management zones delineated soil productivity characteristics and crop yields. These results provided a framework effective for SSM, monitoring management-induced trends in soil quality, and appraising and statistically evaluating field-scale experiments. Use of ECa may foster a large-scale systems approach to research that encourages farmer involvement. Additional research is needed to investigate the interactive effects of soil, weather, and management on ECa as an assessment tool, and the geographic extent to which specific applications of this technology can be applied