Charles S. Wortmann

Soil organic carbon: The value to soil properties

Maintaining or improving soil properties is becoming increasingly important to sustain modern agriculture under increasing demands to preserve biodiversity and environmental quality. Enhancing the inherent capacity of a soil to buffer changes against anthropogenic stresses and extreme climatic events such as droughts, intense rainstorms, heat waves, and floods is also a priority. Managing soil organic carbon (SOC) through optimized management practices is one strategy to enhance soil ecosystem services. Increasing organic C storage in the soil not only sequesters atmospheric C but often enhances soil physical, chemical, and biological processes and properties. Soil organic C has been widely discussed in terms of C sequestration, but its benefits on soil processes and properties have received less attention in recent years. Thus, this article discusses (1) the value of SOC to soil properties and (2) potential for increasing SOC through management. SOIL CARBON DYNAMICS The balance between C inputs and outputs is important to SOC change. Inputs include aboveground and belowground crop residues, animal manure, compost, and others, whereas outputs are losses through water and wind erosion, gas fluxes associated with microbial and plant respiration, and deep leaching. How fast residues decompose following the well-known exponential decay function depends…

Farmer research: Conventional experiences and guidelines for alternative agriculture and multi- functional agro-ecosystems

Abstract Crop producers are challenged to operate profitably, use resources efficiently, meet high standards of quality and protect theenvironment, while sustaining rural economies and societies. Cropping systems are generally fine-tuned and improvedthrough changes that have small effects which can often be verified only through research. The processes and successes oftwo farmer research projects were studied. Results of these studies, information from other sources and the authors’reflections on their own experiences were integrated to develop guidelines for the implementation of farmer researchprojects for alternative agriculture and multi-functional agro-ecosystems with diverse stakeholders. Surveys were mailed to118 farmers currently or previously participating in a farmer research project, and to 15 advisors. Responses show thatinvolvement in a farmer research project was profitable, stimulating, enjoyable and worthwhile, despite a substantial timerequirement. Tillage and soil fertility research had greater impact on annual farm profit than research on other topics.Farmers and advisors emphasized the importance of the farmers’ roles in identification of research topics, research planningand implementation, and interpretation of the results. Replicated trials conducted over 2 or 3 years were recognized asnecessary to adequately verify practices for the corn–soybean rotation of eastern Nebraska, USA. Such trials may need to becomplemented with alternative research approaches for improving alternative agriculture and multi-functional agro-ecosystems where knowledge about some system components is relatively scarce and there is a need to evaluate long-termeffects. In conclusion, organized farmer research is an efficient means to cropping system improvement. Guidelines aregiven for initiation and implementation of farmer research projects.

Nutrient dynamics in a climbing bean and sorghum crop rotation in the Central Africa Highlands

Bean (Phaseolus vulgaris L.) is a major crop in Eastern and Southern Africa, but yields are low. Climbing bean is much more productive than bush bean and is gaining importance with small scale farmers. Our objectives were to: compare nutrient balances with climbing and bush bean in a grain sorghum (Sorghum bicolor L.) based crop rotation system; and to determine the effect of management alternatives on the productivity of the subsequent crop. Different yearly crop rotations alternating sorghum with another crop were compared over six seasons in the highland area of southwestern Uganda at a steeply sloping, terrace site with clayey, acidic soil. The rotation treatments were climbers, bush bean, non-nodulating bush bean, and wheat (Triticum aestivum L.) with the whole plant harvested, and climbers with only pods harvested. Yield of climbing bean exceeded bush bean yield by 120% over three seasons. Sorghum yielded most grain in the rotation with climbing bean where only pods were harvested, while yield did not differ for the other treatments. Nutrient balances were more negative for the climbing bean rotations than for bush bean rotation. Nitrogen derived from the atmosphere was estimated to be 40% of plant N for both climbing and bush bean using the difference method, but 57% using the15N abundance method. Of the total N removed in crop harvest over the six season period, a greater proportion was estimated to be derived from the atmosphere for the climbing bean rotations than for bush beans.

Maize-nutrient response information applied across Sub-Saharan Africa

The profit potential for a given investment in fertilizer use can be estimated using representative crop nutrient response functions. Where response data is scarce, determination of representative response functions can be strengthened by using results from homologous crop growing conditions. Maize (Zea mays L.) nutrient response functions were selected from the Optimization of Fertilizer Recommendations in Africa (OFRA) database of 5500 georeferenced response functions determined from field research conducted in Sub-Saharan Africa. Three methods for defining inference domains for selection of response functions were compared. Use of the OFRA Inference Tool (OFRA-IT; http://agronomy.unl.edu/OFRA) resulted in greater specificity of maize N, P, and K response functions with higher R2 values indicating superiority compared with using the Harvest Choice Agroecological Zones (HC-AEZ) and the recommendation domains of the Global Yield Gap Atlas project (GYGA-RD). The OFRA-IT queries three soil properties in addition to climate-related properties while the latter two options use climate properties only. The OFRA-IT was generally insensitive to changes in criteria ranges of 20–25% used in queries suggesting value in using wider criteria ranges compared with the default for information scarce crop nutrient response functions.

Sweet Sorghum as a Bioenergy Crop for the US Great Plains

Sorghum (Sorghum bicolor L. Moench), including sweet sorghum, is widely adapted to diverse and often marginal crop production environments. Sweet sorghum stalks have high sugar content compared with other sorghum types and has potential for producing ethanol to be mixed with gasoline or for producing ethyl tert-butyl ether, an octane additive to gasoline. Sweet sorghum was introduced to the United States for syrup production in the 1850s (Winberry, 1980). Production peaked following sugar shortages during World War II at about 136 million L yr-1 of syrup in 1946 (Hunter & Anderson, 1997), but thereafter declined because of low sugar prices and inadequate production efficiency. Sweet sorghum can be competitive with corn (Zea mays L.) and grain sorghum for ethanol yield when grain yield is less than 9 Mg ha-1, and is comparatively efficient in nitrogen use (Smith & Buxton, 1993). Sweet sorghum can easily substitute for corn or grain sorghum in many cropping systems. Currently, most ethanol produced in the U.S.A. is from the starch of corn grain with the support of federal subsidies. Energy gains with production of ethanol from grain are modest, typically ranging from 30 to 130% depending on N use efficiency, ethanol plant efficiency, and the efficient use of the distillers grain co-product. Sweet sorghum can be produced at less cost than corn, often with higher energy gains (Smith & Buxton, 1993). Rather than producing starch, sweet sorghum carbohydrates are stored in the stalk as sugar, with sugar concentrations of 8-20% (Rains et al., 1990). Conversion of sugar to ethanol requires less energy than starch as much energy is used to depolymerize the starch. Sweet sorghum has demonstrated potential to produce up to 6000 L ha-1 of ethanol in Iowa and Colorado U.S.A. (Smith & Buxton, 1993), equivalent to ethanol from approximately 20 Mg of corn grain. However, estimated ethanol yields were on average 33% more with grain of corn and grain sorghum compared with sugar of sweet sorghum for seven rainfed site-years in Nebraska U.S.A. (Wortmann et al, 2010). Seasonal availability, the need to transport and store much mass, and storability of sweet sorghum constrain sweet sorghum as a bio-energy crop. In planning for bio-fuel production, long-term sustainability of cropping systems must be considered. Sustainability of a cropping system is very much dependent on production environment and resource availability. In one study comparing the sustainability of different bioenergy crops, sweet sorghum, along with oil palm (Elaeis guineensis L.) and sugarcane (Saccharum spp.) for biofuel, were found to be more sustainable in comparison to

Integrated soil fertility management in sub-Saharan Africa.

1Lilongwe University of Agriculture and Natural Resources, Bunda Campus, P.O. Box 219, Lilongwe, Malawi 2KALRO-Kabete, P.O. Box 1473300800, Nairobi, Kenya 3IPNI-Sub-Saharan Africa Program, P.O. Box 30772-00100, Nairobi, Kenya 4CSIR-Soil Research Institute, Academy Post Office, Kwadaso-Kumasi. Ghana 5Department of Soil Science, Faculty of Agriculture/Institute for Agricultural Research, Ahmadu Bello University, Zaria Nigeria 6Institut d’Economie Rurale, B.P. 258, Rue Mohamed V, Bamako, Mali 7Institut de l’Environnement et de Recherches Agricoles (INERA), O4 BP 8645 Ouagadougou 04, Burkina Faso 8Rwanda Agriculture Board, P.O. Box 5016, Kigali, Rwanda 9Institut National de Recherche Agronomique du Niger (INRAN), BP 240, Maradi, Niger 10CABI, Canary Bird 673, Limuru Road Muthaiga, PO Box 633-00621, Nairobi, Kenya 11279 Plant Science, University of Nebraska-Lincoln, Lincoln, NE 68583-0915, USA

Multisite Evaluation of APEX for Water Quality: II. Regional Parameterization

Phosphorus (P) Index assessment requires independent estimates of long-term average annual P loss from fields, representing multiple climatic scenarios, management practices, and landscape positions. Because currently available measured data are insufficient to evaluate P Index performance, calibrated and validated process-based models have been proposed as tools to generate the required data. The objectives of this research were to develop a regional parameterization for the Agricultural Policy Environmental eXtender (APEX) model to estimate edge-of-field runoff, sediment, and P losses in restricted-layer soils of Missouri and Kansas and to assess the performance of this parameterization using monitoring data from multiple sites in this region. Five site-specific calibrated models (SSCM) from within the region were used to develop a regionally calibrated model (RCM), which was further calibrated and validated with measured data. Performance of the RCM was similar to that of the SSCMs for runoff simulation and had Nash-Sutcliffe efficiency (NSE) > 0.72 and absolute percent bias (|PBIAS|) < 18% for both calibration and validation. The RCM could not simulate sediment loss (NSE < 0, |PBIAS| > 90%) and was particularly ineffective at simulating sediment loss from locations with small sediment loads. The RCM had acceptable performance for simulation of total P loss (NSE > 0.74, |PBIAS| < 30%) but underperformed the SSCMs. Total P-loss estimates should be used with caution due to poor simulation of sediment loss. Although we did not attain our goal of a robust regional parameterization of APEX for estimating sediment and total P losses, runoff estimates with the RCM were acceptable for P Index evaluation.

Multisite Evaluation of APEX for Water Quality: I. Best Professional Judgment Parameterization

The Agricultural Policy Environmental eXtender (APEX) model is capable of estimating edge-of-field water, nutrient, and sediment transport and is used to assess the environmental impacts of management practices. The current practice is to fully calibrate the model for each site simulation, a task that requires resources and data not always available. The objective of this study was to compare model performance for flow, sediment, and phosphorus transport under two parameterization schemes: a best professional judgment (BPJ) parameterization based on readily available data and a fully calibrated parameterization based on site-specific soil, weather, event flow, and water quality data. The analysis was conducted using 12 datasets at four locations representing poorly drained soils and row-crop production under different tillage systems. Model performance was based on the Nash-Sutcliffe efficiency (NSE), the coefficient of determination () and the regression slope between simulated and measured annualized loads across all site years. Although the BPJ model performance for flow was acceptable (NSE = 0.7) at the annual time step, calibration improved it (NSE = 0.9). Acceptable simulation of sediment and total phosphorus transport (NSE = 0.5 and 0.9, respectively) was obtained only after full calibration at each site. Given the unacceptable performance of the BPJ approach, uncalibrated use of APEX for planning or management purposes may be misleading. Model calibration with water quality data prior to using APEX for simulating sediment and total phosphorus loss is essential.

Manure Phosphorus Fractions: Development of Analytical Methods and Variation with Manure Types

Abstract Manure phosphorus (P) extraction and storage procedures were evaluated, and manure types were characterized for extractable P. The objectives of this research were to evaluate manure P extraction and sample storage procedures and to characterize manure types for water‐extractable P (WEP) and NaHCO3 P (BiEP). Manure P was extracted at dry matter–to–water extraction ratios of 0.5 g/200 mL, 2 g/200 mL, 2 g/20 mL, and 20 g/200 mL. Shaking times of 0.5 h, 1 h, or 2 h were evaluated along with filter paper types (Whatman No. 42, Whatman No. 40, and 0.45‐µm). Single or sequential extractions and repeated extractions with water or NaHCO3 were also compared on various manure sources. Manure types were treated as replications in the analysis of variance to reduce the probability of making a Type I error in applying the results to diverse manure types. Dry matter–to–water extraction ratios more concentrated than 1 g/100 mL removed less P than extraction at 1 g/200 mL, which removed a similar percentage of total P (TP) as 0.5 g/200 mL ratio. A single extraction with a 1 g/200 mL or more dilute ratio with 1 h of shaking time was found to give a good estimate of extractible P. Extracted manure P was similar for three sequential extractions of 1 g/100 mL dilution ratio compared to one extraction with 1 g/300 mL. Filter paper type did not affect the amount of P extracted. Phosphorus extraction was more consistent with samples stored dry as compared to refrigerated or frozen conditions. Extractible P in swine manure, as a percentage of TP, was more than for other manure types.

Irrigated Soybean Can Have a Small Response to Nitrogen Applied During Early Reproductive Growth

Abstract High-yield soybean ( Glycine max L.) has a high rate of N uptake during grain fill which may exceed N available from biological N fixation and mineralization of soil organic N. Other research findings show a low probability of response to N applied at early grain fill for yield 60 bu/acre yield are inconsistent. The effect of applying N and S to the soil at early podfill was determined in Nebraska by conducting 56 irrigated trials, including 44 with mean yield >60 bu/acre. Mean yield increases with 27 lb/acre N applied and >60 bu/acre yield were 2.5 bu/acre in south-central, 1.6 bu/acre in northeast, and not significant in southeast Nebraska. There was no added yield with applying 54 compared with 27 lb/acre N or with the addition of 4.5 lb/acre S. Variations in soil properties and in leaf N and S concentrations were not related to yield or the response to applied N. Depending on the grain to fertilizer price ratio, application of N at early pod fill may be profitable, especially if the cost of application is low such as through fertigation.