Francisco J. Arriaga

A fast method for determining soil particle size distribution using a laser instrument

The sieve-pipette is the standard method for determining soil particle size distribution (PSD) because it is precise and reproducible. However, this method requires considerable time. Light diffraction methods for determining PSD are fast, but there is no standard procedure and often, results do not agree precisely with the pipette. The objective of this study was to develop a simple and fast procedure for sample handling and treatment of light diffraction method. A commercially available laser-light diffraction instrument was used. Soil samples were loaded dry into the instrument for ease and speed. A combination of chemical and physical dispersion within the instrument was found to be convenient and effective. Time required to analyze a sample was at most 15 min. Reproducibility between different operators was good, with S.E. ranging from 0.2% to 3.6%. Furthermore, we attempted to identify optimal values for the real refractive index and imaginary refractive index used in the optical model for light diffraction. Values of 1.42 and 0.001 for real refractive index and imaginary refractive index, respectively, were found to give acceptable results when compared with the pipette method. The light diffraction method was not significantly different from the pipette method for sand (P = 0.084), silt (P = 0.743), and clay (P = 0.052). Correlation between the light diffraction and pipette method for sand, silt, and clay was acceptable (R2 = 0.88, 0.80, and 0.69, respectively). The light diffraction technique does not have a perfect agreement with the pipette method, but it provides data rapidly and was reproducible. This method can be very valuable when a large number of samples need to be analyzed for relative comparisons between different sites.

SOIL PHYSICAL PROPERTIES AND CROP PRODUCTIVITY OF AN ERODED SOIL AMENDED WITH CATTLE MANURE

Erosion changes soil properties, especially physical properties, mainly because it removes surface soil rich in organic materials and exposes lower soil layers. In 1988, a study was established to determine the effects of soil erosion and long-term manure applications on selected soil physical properties and corn (Zea mays L.) production. After 10 years of annual manure applications, soil core samples were collected in 7.6-cm increments at three depths, 0 to 7.6, 15 to 22.6, and 30 to 37.6 cm, to determine soil bulk density (&rgr;b), hydraulic conductivity of saturated soil (Ks), and water retention. Bulk density and Ks increased slightly with erosion level. Water retention did not change in the surface 7.6 cm, but it did decrease with increasing erosion level at deeper depths. Long-term application of manure decreased &rgr;b by 10%, whereas Ks was doubled in the top 7.6 cm of soil. Manure increased soil-water retention capacity and decreased differences in water retention between erosion levels, especially at low suctions (0 to 20 kPa). Soil carbon content correlated well with water retention and &rgr;b. Corn grain yields in 1997, 1998, and 1999 were 15, 6, and 14% less, respectively, in the severe than in the slight erosion phase. Long-term manure additions increased corn grain yields by 19% in 1998 and by 25% in 1999. Increased yield from manure additions was likely related to an enhancement in water retention. Results from this study show that long-term manure application is a possible management alternative for restoring the physical properties and crop productivity of eroded soil.

New roller crimper concepts for mechanical termination of cover crops in conservation agriculture

Rollers crimpers have been used in conservation agriculture to terminate cover crops; however, excessive vibration generated by the original straight-bar roller design has delayed adoption of this technology in the United States. To avoid excessive vibration, producers generally reduce operating speeds that increase the time needed to perform the field operation. The objectives of this research were to identify roller crimper designs that terminated rye cover crops consistently, resulted in soil moisture conservation after use, and minimized vibrations when operated in the field. Six different roller types were developed and tested at 3.2 and 6.4 km h - 1 in Alabama field experiments during the 2006, 2007 and 2008 growing seasons. All roller types were used alone and one also in combination with glyphosate. Rye mortalities were evaluated 1, 2 and 3 weeks after rolling and compared with the check (non-rolled standing rye). Soil volumetric moisture content (VMC) was measured at the day of rolling, and then at 1, 2 and 3 weeks after rolling. Vibration was measured on the rollers’ and tractor’s frames during operation. Mortality for rolled rye 2 weeks after rolling was at least 98% compared with 96% for the check in 2006, 93% for rolling compared with 75% for the check in 2007, and 94% for rolling compared with 60% for the check in 2008 (P < 0.10). There were no consistent differences in rye mortality across roller types (without glyphosate) and speeds. VMC for soil in non-rolled rye plots was consistently lower than in rolled rye plots, averaging 3% compared with 7% 2 weeks after rolling in 2006, and 4% compared with 8% in 2008. During 2007, VMC was affected by severe drought conditions, and differences between roller treatments were detected but minor. The - 1 - 2 straight-bar roller generated the highest vibration on the tractor’s frame at 6.4 km h (0.71 m s , RMS), which exceeded International Standards (International Standard Office (ISO)). At 6.4 km h - 1 , new roller designs generated significantly lower acceleration levels from 0.12 to 0.32 m s - 2 on the tractor’s frame and were below detrimental effects on health ‘health limits’ classified by ISO. Overall, 2 weeks after rolling, all roller designs effectively terminated rye above 90%, which is the recommended termination level of rye to plant a cash crop into residue mat, while protecting soil surface from water loss. New roller designs generate less vibration than the original design and can be used safely at higher operating speeds.

Climate-induced reduction in US-wide soybean yields underpinned by region- and in-season-specific responses

The United States is one of the largest soybean exporters in the world. Production is concentrated in the upper Midwest1. Much of this region is not irrigated, rendering soybean production systems in the area highly sensitive to in-season variations in weather. Although the influence of in-season weather trends on the yields of crops such as soybean, wheat and maize has been explored in several countries2–6, the potentially confounding influence of genetic improvements on yields has been overlooked. Here we assess the effect of in-season weather trends on soybean yields in the United States between 1994 and 2013, using field trial data, meteorological data and information on crop management practices, including the adoption of new cultivars. We show that in-season temperature trends had a greater impact on soybean yields than in-season precipitation trends over the measurement period. Averaging across the United States, we show that soybean yields fell by around 2.4% for every 1 °C rise in growing season temperature. However, the response varied significantly among individual states, ranging from −22% to +9%, and also with the month of the year in which the warming occurred. We estimate that year-to-year changes in precipitation and temperature combined suppressed the US average yield gain by around 30% over the measurement period, leading to a loss of US

Impact of Rye Rolling Direction and Different No-Till Row Cleaners on Cotton Emergence and Yield

11 billion. Our data highlight the importance of developing location-specific adaptation strategies for climate change based on early-, mid- and late-growing season climate trends.

Hedgerow Pruning Effects on Light Interception, Water Relations and Yield in Alley-Cropped Maize

Cover crops have been recognized as a vital component of conservation agriculture. However, cover crops must produce substantial biomass to be effective. Because of the large amount of residue produced by many cover crops, they must be managed appropriately to avoid planting problems. Roller-crimpers have been used to manage cover crops by flattening them and creating a thick mat over the soil surface. A study was conducted to determine the effect of different rolling directions (parallel, diagonal, and perpendicular to cotton planting direction) using a roller/crimper, three different commercial row cleaners (Dawn, Dawn without coulter, and Yetter), and no row cleaner on cotton (Gossypium hirsutum L.) stand, emergence rate, yield, and net returns. The study was conducted at two Alabama locations with a replicated strip plot design. Presented results illustrate two growing and harvest seasons (2004 and 2005). Rye (Secale cereale L.) was chosen as the cover crop due to its potential to produce large amounts of biomass and its popularity with Alabama producers. Rye was rolled at the soft dough growth stage and terminated using Roundup (glyphosate). Data showed that parallel rolling with respect to the planting direction for cotton produced the highest cotton stand and yield in both years. In 2004, the Yetter row cleaner resulted in higher cotton stand and yield for both locations when compared with the Dawn row cleaner. However, in 2005, the Dawn row cleaner resulted in a greater cotton yield than the Yetter. Based on the emergence rate index (ERI), the most rapid emergence was observed with parallel rolling and both row cleaners. The slowest emergence rate was observed with perpendicular and diagonal rolling and no row cleaners. Parallel rolling minimized accumulated rye residue on the row cleaners and minimized the cleaning time for the row cleaners. General findings from this research are: for tall rye producing large biomass, parallel rolling and Dawn or Yetter row cleaners are recommended. For shorter rye producing low biomass, no row cleaners were required for rolled rye with the parallel rolling direction, or cotton could be planted into standing rye using Dawn or Yetter row cleaners. Regardless of the height and amount of rye residue and the row cleaner type, the perpendicular and diagonal rolling directions are not recommended.

Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exchange in conventional and no-tillage systems.

Abstract In alley cropping, trees and crops compete for light, nutrients, and water. However, there is little information on how hedgerow pruning would impact light interception, water relations, and yield in a maize (Zea mays L.)-mimosa (Albizia julibrissin Durazz) alley-cropping system. Competition between mimosa hedgerows and maize was measured under alley cropping on a compass loam sand in Shorter, AL. Treatments were established in a randomized complete block design and consisted of no pruning or pruning at 30, 30 + 60 and 30 + 90 days after maize planting (DAP) and at 5 cm and 50 cm pruning heights. To minimize competition for nutrients, 189 kg N ha−1, 9 kg P ha−1, and 73 kg K ha−1 were applied. Reduction in photosynthetically active radiation (PAR) was assessed periodically. Water status in maize was assessed using a steady state porometer to measure maize leaf stomatal conductance and transpiration rate. PAR was lower in maize rows closest to hedgerows (ROW1) than in second maize rows from hedgerows (ROW2) especially after 60 DAP. After the 90 DAP pruning, 30 + 90 DAP pruning treatment gave significantly lower stomatal conductance (CD) and transpiration rate (TR) in maize leaves than did 30 DAP or 30 + 60 DAP treatments. ROW1 had high CD and TR, which suggests greater water loss that might reduce final yields. Pruning increased PAR, maize grain and stover yields compared to no-pruning plots. Pruning twice gave higher grain and stover yields than did no-pruning controls. Pruning at 5 cm height gave higher maize yield than pruning at 50 cm. On average, ROW1 had 24% lower yield than did ROW2. Interaction of treatment by row was highly significant. Yield in ROW1 was more affected by pruning treatments than in ROW2. After 90 DAP, 30 + 90 DAP pruning treatment had lowest shade, followed by pruning treatment 30 + 60 DAP at 5 cm height. Pruning at 90 DAP and pruning at 5 cm height reduced competition for water and light. Hedgerow pruning can increase light interception and reduce water stress in the maize crop.

Management of Pigweed (Amaranthus spp.) in Glufosinate-Resistant Soybean in the Midwest and Mid-South

Increasing atmospheric CO(2) concentration has led to concerns about potential effects on production agriculture. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional tillage and no-tillage) to elevated CO(2). The study used a split-plot design replicated three times with two management systems as main plots and two atmospheric CO(2) levels (ambient and twice ambient) as split plots using open-top chambers on a Decatur silt loam soil (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.] rotation with winter fallow and spring tillage practices. In the no-tillage system, sorghum and soybean were rotated, and three cover crops were used [crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)]. Over multiple growing seasons, the effect of management and CO(2) concentration on leaf-level gas exchange during row crop (soybean in 1999, 2001, and 2003; sorghum in 2000, 2002, and 2004) reproductive growth were evaluated. Treatment effects were fairly consistent across years. In general, higher photosynthetic rates were observed under CO(2) enrichment (more so with soybean) regardless of residue management practice. Elevated CO(2) led to decreases in stomatal conductance and transpiration, which resulted in increased water use efficiency. The effects of management system on gas exchange measurements were infrequently significant, as were interactions of CO(2) and management. These results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO(2)-enriched environments during reproductive growth.

Quantifying the Impact of Seasonal and Short-term Manure Application Decisions on Phosphorus Loss in Surface Runoff

Pigweeds are among the most abundant and troublesome weed species across Midwest and mid-South soybean production systems because of their prolific growth characteristics and ability to rapidly evolve resistance to several herbicide sites of action. This has renewed interest in diversifying weed management strategies by implementing integrated weed management (IWM) programs to efficiently manage weeds, increase soybean light interception, and increase grain yield. Field studies were conducted across 16 site-years to determine the effectiveness of soybean row width, seeding rate, and herbicide strategy as components of IWM in glufosinate-resistant soybean. Sites were grouped according to optimum adaptation zones for soybean maturity groups (MGs). Across all MG regions, pigweed density and height at the POST herbicide timing, and end-of-season pigweed density, height, and fecundity were reduced in IWM programs using a PRE followed by (fb) POST herbicide strategy. Furthermore, a PRE fb POST herbicide strategy treatment increased soybean cumulative intercepted photosynthetically active radiation (CIPAR) and subsequently, soybean grain yield across all MG regions. Soybean row width and seeding rate manipulation effects were highly variable. Narrow row width (≤ 38 cm) and a high seeding rate (470,000 seeds ha−1) reduced end-of-season height and fecundity variably across MG regions compared with wide row width (≥ 76 cm) and moderate to low (322,000 to 173,000 seeds ha−1) seeding rates. However, narrow row widths and high seeding rates did not reduce pigweed density at the POST herbicide application timing or at soybean harvest. Across all MG regions, soybean CIPAR increased as soybean row width decreased and seeding rate increased; however, row width and seeding rate had variable effects on soybean yield. Furthermore, soybean CIPAR was not associated with end-of-season pigweed growth and fecundity. A PRE fb POST herbicide strategy was a necessary component for an IWM program as it simultaneously managed pigweeds, increased soybean CIPAR, and increased grain yield. Nomenclature: Glufosinate; pigweed, Amaranthus spp.; soybean, Glycine max (L.) Merr. Las especies del género Amaranthus están entre las especies de malezas más abundantes y problemáticas en los sistemas de producción de soja en el medio oeste y el sur medio debido a sus características de crecimiento prolífico y su habilidad para evolucionar rápidamente resistencia a varios sitios de acción de herbicidas. Esto ha renovado el interés en la diversificación de estrategias de manejo de malezas implementando programas de manejo integrado de malezas (IWM) para manejar eficientemente a las malezas, que incluyan una mayor intercepción de luz por parte de la soja a la vez que se aumente el rendimiento de grano. Se realizaron estudios de campo a lo largo de 16 sitios-años para determinar la efectividad de la distancia entre hileras, densidad de siembra, y la estrategia de herbicidas, como componentes de un IWM en soja resistente a glufosinate. Los sitios fueron agrupados de acuerdo a las zonas óptimas de adaptación según los grupos de madurez (MGs) de la soja. Al promediar todas las regiones MG, la densidad y altura de Amaranthus, al momento de la aplicación POST del herbicida, y la densidad, la altura y la fecundidad de Amaranthus al final de la temporada, fueron reducidas en programas IWM que usaron una estrategia de herbicidas PRE seguidos por (fb) POST. Además, un tratamiento con una estrategia de herbicidas PRE fb POST aumentó la intercepción acumulativa de radiación fotosintéticamente activa (CIPAR) de la soja y subsecuentemente el rendimiento de grano de la soja al promediar todas las regiones MG. Los efectos de la distancia entre hileras y la densidad de siembra de la soja fueron altamente variables. Hileras angostas (≤ 38 cm) y una alta densidad de siembra (470,000 semillas ha−1) redujeron la altura y la fecundidad al final de la temporada en forma variable entre las regiones MG al compararse con hileras anchas (≥ 76 cm) y densidades de siembra de moderadas a bajas (322,000 a 173,000 semillas ha−1). Sin embargo, las hileras angostas y las altas densidades de siembra no redujeron la densidad de Amaranthus al momento de la aplicación de herbicida POST o al momento de la cosecha de la soja. Al promediar todas las regiones MG, la CIPAR de la soja aumentó al disminuir la distancia entre hileras e incrementar la densidad de siembra. Sin embargo, la distancia entre hileras y la densidad de siembra tuvieron efectos variables sobre el rendimiento de la soja. Adicionalmente, la CIPAR de la soja no estuvo asociada con el crecimiento ni la fecundidad de Amaranthus al final de la temporada. Una estrategia que use herbicidas PRE fb POST fue un componente necesario para que el programa IWM simultáneamente manejara malezas Amaranthus e incrementara la CIPAR de la soja y su rendimiento de grano.

Cover Crop Biomass Harvest Influences Cotton Nitrogen Utilization and Productivity

Agricultural phosphorus (P) management is a research and policy issue due to P loss from fields and water quality degradation. Better information is needed on the risk of P loss from dairy manure applied in winter or when runoff is imminent. We used the SurPhos computer model and 108 site-years of weather and runoff data to assess the impact of these two practices on dissolved P loss. Model results showed that winter manure application can increase P loss by 2.5 to 3.6 times compared with non-winter applications, with the amount increasing as the average runoff from a field increases. Increased P loss is true for manure applied any time from late November through early March, with a maximum P loss from application in late January and early February. Shifting manure application to fields with less runoff can reduce P loss by 3.4 to 7.5 times. Delaying manure application when runoff is imminent can reduce P loss any time of the year, and sometimes quite significantly, but the number of times that application delays will reduce P loss is limited to only 3 to 9% of possible spreading days, and average P loss may be reduced by only 15% for winter-applied manure and 6% for non-winter-applied manure. Overall, long-term strategies of shifting manure applications to low runoff seasons and fields can potentially reduce dissolved P loss in runoff much more compared with near-term, tactical application decisions of avoiding manure application when runoff is imminent.