Jeffrey S. Strock

Challenges and opportunities for mitigating nitrous oxide emissions from fertilized cropping systems

Nitrous oxide (N2O) is often the largest single component of the greenhouse-gas budget of individual cropping systems, as well as for the US agricultural sector as a whole. Here, we highlight the factors that make mitigating N2O emissions from fertilized agroecosystems such a difficult challenge, and discuss how these factors limit the effectiveness of existing practices and therefore require new technologies and fresh ideas. Modification of the rate, source, placement, and/or timing of nitrogen fertilizer application has in some cases been an effective way to reduce N2O emissions. However, the efficacy of existing approaches to reducing N2O emissions while maintaining crop yields across locations and growing seasons is uncertain because of the interaction of multiple factors that regulate several different N2O-producing processes in soil. Although these processes have been well studied, our understanding of key aspects and our ability to manage them to mitigate N2O emissions remain limited.

Drainage water management for water quality protection

L and drainage has been central to the development of North America since colonial times, with the first organized drainage efforts occurring as early as the 1600s (Evans et al. 1996). Drainage has been encouraged to improve public highways, reduce public health risks, promote increased crop yield and reduced yield variability, reduce surface runoff and erosion, and increase land value. Agricultural drainage includes artificial subsurface drainage and surface drainage. Most agricultural producers improve the drainage on their land for better trafficability, to enhance field conditions, to facilitate timely planting and harvesting operations, and to help decrease crop damage from saturated soil and standing water during the growing season. Agricultural drainage improvement also decreases year-to-year variability in crop yield, ensuring consistent production. Increasingly, agricultural drainage is being targeted as a conduit for pollution, particularly nutrient pollution (Needelman et al. 2007). Considerable resistance exists in some regions to the expansion of drainage systems despite their importance to food production, with up to 50% of the cropland in some states under artificial drainage. However, because drainage ditches and subsurface drainage systems convert diffuse flows from the landscape into concentrated flows, they also provide opportunities for precision conservation, the targeting of specific practices to…

Downstream approaches to phosphorus management in agricultural landscapes: Regional applicability and use

This review provides a critical overview of conservation practices that are aimed at improving water quality by retaining phosphorus (P) downstream of runoff genesis. The review is structured around specific downstream practices that are prevalent in various parts of the United States. Specific practices that we discuss include the use of controlled drainage, chemical treatment of waters and soils, receiving ditch management, and wetlands. The review also focuses on the specific hydrology and biogeochemistry associated with each of those practices. The practices are structured sequentially along flowpaths as you move through the landscape, from the edge-of-field, to adjacent aquatic systems, and ultimately to downstream P retention. Often practices are region specific based on geology, cropping practices, and specific P related problems and thus require a right practice, and right place mentality to management. Each practice has fundamental P transport and retention processes by systems that can be optimized by management with the goal of reducing downstream P loading after P has left agricultural fields. The management of P requires a system-wide assessment of the stability of P in different biogeochemical forms (particulate vs. dissolved, organic vs. inorganic), in different storage pools (soil, sediment, streams etc.), and under varying biogeochemical and hydrological conditions that act to convert P from one form to another and promote its retention in or transport out of different landscape components. There is significant potential of hierarchically placing practices in the agricultural landscape and enhancing the associated P mitigation. But an understanding is needed of short- and long-term P retention mechanisms within a certain practice and incorporating maintenance schedules if necessary to improve P retention times and minimize exceeding retention capacity.

Plant Growth Component of a Simple Rye Growth Model

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-atmosphere simulation model, RyeGro, was developed to quantify the probabilities that a winter rye cover crop will reduce artificial subsurface drainage nitrate-N losses given climatic variability in the region. This article describes the plant growth submodel of RyeGro, Grosub, which estimates biomass production with a radiation use efficiency-based approach for converting intercepted photosynthetically active radiation to biomass. Estimates of nitrogen (N) uptake are based on an empirical plant N concentration curve. The model was calibrated with data from a three-year field study conducted on a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, Minnesota. The model was validated with data measured from a field trial in St. Paul, Minnesota. The cumulative rye aboveground biomass predictions for the calibration years differed by -0.45, 0.09, and 0.16 Mg ha-1 (-17%, 9%, and 32%), and the plant N uptake predictions differed by -10.5, 8.0, and 4.0 kg N ha-1 (-16%, 30%, and 21%) from the observed values. The predictions of biomass production and N uptake for the validation year varied by -1.4 Mg ha-1 and 16 kg N ha-1 (-27% and 24%) from the values observed in the field study, respectively. A local sensitivity analysis of eight input parameters indicated that model output is most sensitive to the maximum leaf area index and radiation use efficiency parameters. Grosub demonstrated the capability to predict seasonal aboveground biomass production of fall-planted rye in southwestern Minnesota within an accuracy of ±30% in years when production exceeds 1 Mg ha-1 by mid-May, and to predict seasonal rye N uptake within ±25% of observed values.

Phosphorus availability and early corn growth response in soil amended with turkey manure ash.

Incinerating turkey manure is a new option in the USA to generate renewable energy and to eliminate environmental problems associated with manure stockpiling. Incineration produces turkey manure ash (TMA) with a nutrient content of 43 g phosphorus (P) kg−1 and 100 g potassium (K) kg−1. We conducted a greenhouse pot study using a low P (6 mg kg−1) and high K (121 mg kg−1) soil/sand mixture with a 7.0 pH to evaluate early growth response of corn (Zea mays L.) to TMA. A control and five rates based on P (5.6, 10.9, 16.5, 21.9, and 27.2 mg kg−1) and respective K contents in TMA were compared with triple-superphosphate and potassium chloride fertilizer. Plant height and stalk thickness at 24 and 31 days after emergence (DAE) were greatest with the fertilizer, but no differences were detected at the final sampling (52 DAE). Regardless of nutrient source, plant biomass increased with P rate. Because of faster initial plant development, corn dry matter 52 DAE was 15 to 20% greater with fertilizer than with TMA. Corn tissue P concentration was greater with TMA than with fertilizer, but P uptake was similar. Tissue micronutrient concentrations were greatest for the control. Bray 1 P appeared to extract excessive amounts of P in TMA-amended soil, whereas soil P levels with the Olsen extractant provided an estimate of plant-available P that was consistent with plant response. Based on this first approximation, we conclude that TMA is a potential source of P for field crops. Field studies are required to determine recommended application rates.

What does it take to detect a change in soil carbon stock? A regional comparison of minimum detectable difference and experiment duration in the north central United States

Variability in soil organic carbon (SOC) results from natural and human processes interacting across time and space, and leads to large variation in the minimum difference in SOC that can be detected with a particular experimental design. Here we report a unique comparison of minimum detectable differences (MDDs) in SOC, and the estimated times required to observe those MDDs across the north central United States, calculated for the two most common SOC experiments: (1) a comparison between two treatments, e.g., moldboard plow (MP) and no-tillage (NT), using a randomized complete block design experiment; and (2) a comparison of changes in SOC over time for a particular treatment, e.g., NT, using a randomized complete block design experiment with time as an additional factor. We estimated the duration of the two experiment types required to achieve MDD through simulation of SOC dynamics. Data for the study came from 13 experimental sites located in Iowa, Illinois, Ohio, Michigan, Wisconsin, Missouri, and Minnesota. Soil organic carbon, bulk density, and texture were measured at four soil depths. Minimum detectable differences were calculated with probability of Type I error of 0.05 and probability of Type II error of 0.15. The MDDs in SOC were highly variable across the region and increased with soil depth. At 0 to 10 cm (0 to 3.9 in) soil depth, MDDs with five replications ranged from 1.04 g C kg−1 (0.017 oz C lb−1; 6%) to 7.15 g C kg−1 (0.114 oz C lb−1; 31%) for comparison of two treatments; and from 0.46 g C kg−1 (0.007 oz C lb−1; 3%) to 3.12 g C kg−1 (0.050 oz C lb−1; 13%) for SOC change over time. Large differences were also predicted in the experiment duration required to detect a difference in SOC between MP and NT (from 8 to >100 years with five replications), or a change in SOC over time under NT management (from 11 to 71 years with five replications). At most locations, the time required to detect a change in SOC under NT was shorter than the time required to detect a difference between MP and NT. Minimum detectable difference and experiment duration decreased with the number of replications and were correlated with SOC variability and soil texture of the experimental sites, i.e., they tended to be lower in fine textured soils. Experiment duration was also reduced by increased crop productivity and the amount of residue left on the soil. The relationships and methods described here enable the design of experiments with high power of detecting differences and changes in SOC and enhance our understanding of how management practices influence SOC storage.

Buffers and Vegetative Filter Strips

First paragraph: This chapter describes the use of buffers and vegetative filter strips relative to water quality. In particular, we primarily discuss the herbaceous components of the following NRCS Conservation Practice Standards

Turkey Manure Ash Effects on Alfalfa Yield, Tissue Elemental Composition, and Chemical Soil Properties

A power plant that utilizes turkey manure as fuel to produce energy was built in Benson, Minnesota, and started full energy production in 2007. The plant was built to meet legislative requirements governing the use of renewable sources to generate energy in Minnesota. Although the use of turkey manure as biofuel generates energy, it also results in turkey manure ash (TMA) as a by‐product that contains phosphorus (P), potassium (K), sulfur (S), and zinc (Z) as well as other essential and nonessential elements. A 2‐year study was conducted to compare TMA with triple‐superphosphate and potassium chloride fertilizers as a source of nutrients for alfalfa (Medicago sativa) at three locations: Lamberton, Morris, and Appleton, Minnesota. The soils at Lamberton and Appleton were acidic with P and K concentrations ranging from medium‐high to very high, whereas the soil at Morris was alkaline with high concentrations of P and K. The experiment consisted of a control (0 P and 0 K) and annual and split applications of TMA and fertilizer. Annual TMA and fertilizer rates were 84 kg P2O5 ha−1, 118 kg K2O ha−1, and 34 kg S ha−1. Split rates were 42/42 kg P2O5 ha−1, 59/59 kg K2O ha−1, and 17/17 kg S ha−1. However, because of an overestimation of citrate‐soluble P in 2005 for the TMA, the total amount of available P applied with the TMA for the 2‐year study was 168 kg P2O5 ha−1 compared with 286 kg P2O5 ha−1 for the fertilizer. In the first year, fertilizer resulted in greater alfalfa biomass yield than TMA and the control, whereas in the second year, alfalfa yields with TMA and fertilizer were similar and both more than the control. In 2005, TMA resulted in more copper (Cu) and S tissue concentrations than the fertilizer. In 2006, application of both sources increased tissue P and S concentrations compared with the control. The TMA increased tissue Cu concentration and Zn plant uptake compared with fertilizer. Bray P1–extractable soil P concentrations were less with TMA and control treatments than with the fertilizer treatments. Ammonium acetate–extractable soil sodium (Na) concentrations were greater with TMA than with fertilizer and the control. By the second year, both ash and fertilizer treatments resulted in more K uptake than the untreated control with no difference in K uptake between the two sources or time of application. Both sources were effective in increasing P uptake compared with the untreated control. TMA was shown to be an effective source of nutrients for alfalfa production.

Controlled drainage to improve edge-of-field water quality in Southwest minnesota, USA

Wet, poorly drained soils throughout the northern Cornbelt are often artificially drained to improve field conditions for timely field operations, decrease crop damage resulting from excess water conditions, and improve crop yields. Drainage has also been identified as a contributing factor to water quality impairments in surface waters. Our objective was to quantify drain flow volume, nitrogen and phosphorus loss, and grain yield from a conventional free-drainage (FD) compared to a controlled drainage (CD) system in Minnesota, USA. A field study was conducted from 2006-2009 on a tile-drained Millington loam soil (fine-loamy, mixed, calcareous, mesic Cumulic Haplaquoll). The field site consisted of two independently drained management zones, 15 and 22ha, respectively. The project used a paired design approach to statistically evaluate treatment effects. During the calibration period (2006-2007) each zone was managed the same. The treatment phase of the experiment began in 2008 with one zone managed in FD mode and the other managed in CD mode. During the two year treatment period (2008-2009) drain flow volume was reduced on average 63%, 141 to 52 mm. There was also evidence that annual nitrate-nitrogen, total phosphorus, and ortho-phosphorus loads were reduced by 61, 50, and 63%, respectively. However, the reasons for a 33% increase in flow weighted mean total phosphorus concentration under controlled drainage are unclear. The use of CD showed environmental benefits compared to FD but has not resulted in a consistent yield benefit at this site to date.

Standardized research protocols enable transdisciplinary research of climate variation impacts in corn production systems

The important questions about agriculture, climate, and sustainability have become increasingly complex and require a coordinated, multifaceted approach for developing new knowledge and understanding. A multistate, transdisciplinary project was begun in 2011 to study the potential for both mitigation and adaptation of corn-based cropping systems to climate variations. The team is measuring the baseline as well as change of the systems carbon (C), nitrogen (N), and water footprints, crop productivity, and pest pressure in response to existing and novel production practices. Nine states and 11 institutions are participating in the project, necessitating a well thought out approach to coordinating field data collection procedures at 35 research sites. In addition, the collected data must be brought together in a way that can be stored and used by persons not originally involved in the data collection, necessitating robust procedures for linking metadata with the data and clearly delineated rules for use and publication of data from the overall project. In order to improve the ability to compare data across sites and begin to make inferences about soil and cropping system responses to climate across the region, detailed research protocols were developed to standardize the types of measurements taken and the specific details such as depth, time, method, numbers of samples, and minimum data set required from each site. This process required significant time, debate, and commitment of all the investigators involved with field data collection and was also informed by the data needed to run the simulation models and life cycle analyses. Although individual research teams are collecting additional measurements beyond those stated in the standardized protocols, the written protocols are used by the team for the base measurements to be compared across the region. A centralized database was constructed to meet the needs of current researchers on this project as well as for future use for data synthesis and modeling for agricultural, ecosystem, and climate sciences.