• Authors:
    • Kabenge, I.
    • Irmak, S.
    • Sharma, V.
    • Kilic, A.
  • Source: Transactions of the ASABE
  • Volume: 54
  • Issue: 3
  • Year: 2011
  • Summary: Understanding the relationship between the spatial distribution of precipitation and crop yields on large scales (i.e., county, state, regional) while accounting for the spatial non-stationarity can help managers to better evaluate the long-term trends in agricultural productivity to make better assessments in food security, policy decisions, resource assessments, land and water resources enhancement, and management decisions. A relatively new technique, geographically weighted regression (GWR), has the ability to account for spatial non-stationarity with space. While its application is growing in other scientific disciplines (i.e., social sciences), the application of this new technique in agricultural settings has not been practiced. The geographic information system (GIS), along with two different statistical techniques [GWR and conventional ordinary least square regression (OLS)], was utilized to analyze the relationships between various precipitation categories and irrigated and rainfed maize and soybean yields for all 93 counties in Nebraska from 1996 to 2008. Precipitation was spatially interpolated in ArcGIS using a spline interpolation technique with zonal statistics. Both measured and GWR- and OLS-predicted yields were correlated to spatially interpolated annual (January 1 to December 31), seasonal (May 1 to September 30), and monthly (May, June, July, August, and September) precipitation for each county. Statewide average annual precipitation in Nebraska from 1996 to 2008 was 564 mm, with a maximum of 762 mm and minimum of 300 mm. Mean precipitation decreased gradually from May to September during the growing season. County average yields followed the same temporal trends as precipitation. When the OLS regression model was used, there was a general trend of linear correlation between observed yield and long-term average mean annual total precipitation with a varying coefficient of determination (R 2). For rainfed crops, 67% of the variability in mean yield was explained by the mean annual precipitation. About 23% and 17% of the variability in mean yield was explained by mean annual precipitation for irrigated maize and soybean, respectively. However, the performance of the GWR technique in predicting the yields from spatially interpolated precipitation for irrigated and rainfed maize and soybean was significantly better than the performance of the OLS model. For both rainfed maize and soybean, 77% to 80% of the variation in yield was explained by the mean annual precipitation alone. For irrigated crops, 42% of the variation in the yield was explained by the mean annual precipitation. For rainfed crops, there was a strong correlation between seasonal precipitation and yield, with R 2 values of 0.73 and 0.76 for maize and soybean, respectively. The mean annual total precipitation was a better predictor of rainfed maize yield than rainfed soybean yield. On a statewide average, July precipitation as a predictor had the greatest correlation with yields of both maize and soybean. June, July, and August precipitation had greater impact on maize yield than on soybean under rainfed conditions due to more sensitivity of maize to water stress than soybean. For irrigated yields, July precipitation had more impact on soybean yield than on maize. The performance of the GWR technique was superior to the OLS model in analyzing the relationship between yield and precipitation. The superiority of the GWR technique to OLS is mainly due to its ability to account for the impact of spatial non-stationarity on the precipitation vs. yield relationships.
  • Authors:
    • Jaynes, D. B.
    • Malone, R. W.
    • Singer, J. W.
    • Ma, L.
  • Source: Agricultural Water Management
  • Volume: 98
  • Issue: 10
  • Year: 2011
  • Summary: Studies quantifying winter annual cover crop effects on water quality are mostly limited to short-term studies at the plot scale. Long-term studies scaling-up water quality effects of cover crops to the watershed scale provide more integrated spatial responses from the landscape. The objective of this research was to quantify N loads from artificial subsurface drainage (tile drains) in a subbasin of the Walnut Creek, Iowa (Story county) watershed using the hybrid RZWQ-DSSAT model for a maize (Zen mays L.)soybean [Glycine max (L.) Merr.] and maize-maize-soybean rotations in all phases with and without a winter wheat (Triticum aestivum L.) cover crop during a 25-year period from 1981 to 2005. Simulated cover crop dry matter (DM) and N uptake averaged 1854 and 36 kgha(-1) in the spring in the maize-soybean phase of the 2-year rotation and 1895 and 36 kg ha(-1) in the soybean-maize phase during 1981-2005. In the 3-year rotation, cover crop DM and N uptake averaged 2047 and 44 kg ha(-1) in the maize-maize-soybean phase, 2039 and 43 kg ha(-1) in the soybean-maize-maize phase. and 1963 and 43 kg ha(-1) in the maize-soybean-maize phase during the same period. Annual N loads to tile drains averaged 29 kg ha(-1) in the maize-soybean phase and 25 kg ha(-1) in the soybean-maize phase compared to 21 and 20 kg ha(-1) in the same phases with a cover crop. In the 3-year rotation. annual N loads averaged 46, 43, and 45 kg ha(-1) in each phase of the rotation without a cover crop and 37, 35, and 35 kg ha(-1) with a cover crop. These results indicate using a winter annual cover crop can reduce annual N loads to tile drains 20-28% in the 2-year rotation and 19-22% in the 3-year rotation at the watershed subbasin scale over a 25-year period. Published by Elsevier B.V.
  • Authors:
    • Skaggs, K. E.
    • Irmak, S.
  • Source: Transactions of the ASABE
  • Volume: 54
  • Issue: 3
  • Year: 2011
  • Summary: The lack of knowledge and data on the driving forces of nighttime (nocturnal) evapotranspiration (ET) for various vegetation surfaces under different climatic and management conditions led this study to investigate the magnitude of nighttime ET (ET night) and its interactions with other nighttime surface energy fluxes, i.e., soil heat flux (G night), sensible heat flux (H night), and net radiation (R n_night), and microclimatic variables, i.e., wind speed at 3 m (u 3_night), vapor pressure deficit (VPD night), and air temperature (T night). Soybean [( Glycine max (L.) Merr.)] canopies under two different irrigation methods in subsurface drip- and center-pivot irrigated (SDI and CP) fields in south central Nebraska were studied. Hourly energy flux and meteorological data from the SDI field for the 2007 and 2008 seasons and from the CP field for 2008 were analyzed. The study period was divided into five sub-periods based on plant and canopy development to evaluate nighttime energy balances and driving forces at various plant growth and development stages. The five sub-periods are: pre-planting (from mid-March to plant emergence, EM), early season (from emergence to full canopy cover, leaf area index, LAI
  • Authors:
    • Armstrong, S. D.
    • Hernandez-Ramirez, G.
    • Smith, D. R.
    • Bucholtz, D. L.
    • Stott, D. E.
  • Source: Soil Science Society of America Journal
  • Volume: 75
  • Issue: 3
  • Year: 2011
  • Summary: Recent efforts have attempted to establish emission estimates for greenhouse gas (GHGs) from agricultural soils in the United States. This research project was conducted to assess the influence of cropping system management on non-CO(2) GHG emissions from an eastern Corn Belt Alfisol. Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotation plots were established, as were plots in continuous management of native grasses or sorghum-sudan-grass [Sorghum bicolor (L.) Moench nothossp. drummondii (Steud.) de Wet ex Davidse]. Greenhouse gas fluxes were monitored throughout each growing season from 2004 through 2007. Fluxes of N(2)O were significantly correlated with soil temperature (P
  • Authors:
    • Hyde, J.
    • Mortensen, D. A.
    • Barbercheck, M. E.
    • Smith, R. G.
    • Hulting, A. G.
  • Source: Agronomy Journal
  • Volume: 103
  • Issue: 1
  • Year: 2011
  • Summary: In the mid-Atlantic region, the demand for organic dairy has provided incentives for farmers to transition their land to organic feed grain production. At the same time, interest in minimum-tillage organic production is growing. Two field experiments were conducted to assess the effects of a first year cover crop and tillage system on weed populations, cash crop yield, and net returns over the 3-yr transition period in a cover crop-soybean (Glycine max (L.) Merr.)-corn (Zea mays L.) feed grain rotation. The cover crop treatments were rye (Secale cereale L.)-hairy vetch (Vicia villosa Roth) (hereaft er RYE) and timothy (Phleum pratense L.)-red clover (Trifolium pratense L.) (hereaft er TIM). Tillage system treatments were moldboard plow (full tillage, FT) and chisel plow (minimum tillage, MT). Across both experiments, soybean yields ranged from 1190 to 3721 kg ha(-1). Corn grain yields were affected by tillage in the first experiment only, and were 59% higher in FT (9370 kg ha(-1)) compared to MT (5906 kg ha(-1)). Weed abundance was primarily affected by tillage, with densities in corn being 244% higher in MT compared to FT. Cumulative net returns in the first experiment were profit-generating in systems where TIM was the initial cover crop (mean = U.S. $ 317 ha(-1)). Mean cumulative net returns were positive in three of the four treatment combinations in the second experiment (U.S. $ 74-299 ha(-1)). Improved strategies for minimizing the costs associated with fertilization and management of weeds in minimal tillage will be necessary to improve the profitability and sustainability of reduced-tillage organic systems.
  • Authors:
    • Tadesse, T.
    • Narumalani, S.
    • Wardlow, B. D.
    • Swain, S.
    • Callahan, K.
  • Source: GIScience & Remote Sensing
  • Volume: 48
  • Issue: 3
  • Year: 2011
  • Summary: Eight-day composite Terra-MODIS cumulative LST and NDVI timeseries data were used to analyze the responses of crop and grassland cover types to drought in Nebraska. Four hundred ninety 1 km pixels that included irrigated and non-irrigated corn and soybeans and three grassland cover types were selected across the state of Nebraska. Statistical analyses revealed that the majority of the land cover pixels experienced significantly higher daytime and nighttime LSTs and lower NDVI during the drought-year growing season ( p
  • Authors:
    • Czymmek, K. J.
    • Chase, L. E.
    • Ketterings, Q. M.
    • Swink, S. N.
    • van Amburgh, M. E.
  • Source: Journal of Soil and Water Conservation
  • Volume: 66
  • Issue: 1
  • Year: 2011
  • Summary: New York (NY) has dairy, cash grain, fruit, and vegetable industries located in close proximity to water, making it important to optimize manure and fertilizer use for both economic production of crops and protection of the environment. The gross phosphorus (P) balance for NY (manure and fertilizer P minus crop P removal) estimated for 2006 was +1.7 kg ha(-1) (+1.5 lb ac(-1)), indicating that, on a statewide basis, P is in balance. Our objectives in this study were to (1) estimate state, regional, and county-level gross nitrogen (N) balances for NY for 2007; (2) evaluate N balance trends over time (1987, 1992, 1997, 2002, and 2007); (3) estimate nonlegume cropland (net) N balances for 2007; and (4) quantify the potential impact of improved herd nutrition and manure incorporation on N balances. The 2007 NY gross N balance for nonlegume cropland was +62 kg ha(-1) (+55 lb ac(-1)). Long Island and western NY had the highest N balances (+101 and +77 kg ha(-1) [+90 and +69 lb ac(-1)], respectively) reflecting N fertilizer use for horticultural and/or cash grain crops (both regions) and presence of a concentrated dairy industry (western NY). The Chesapeake Bay watershed and Lake Champlain Basin counties had gross N balances below +28 kg ha(-1) (+25 lb ac(-1)). The statewide N balance decreased from +125 kg ha(-1) (+112 lb ac(-1)) in 1987 to +62 kg ha(-1) (+55 lb ac(-1)) in 2007, largely driven by a decline in N fertilizer use between 1987 and 1992. The statewide N balance dropped to -38 kg ha(-1) (-34 lb ac(-1)) when manure N losses in the barn and storage system and at land application were taken into account. Given a nearly zero P balance, a negative N balance indicates the need for best management practices that increase N use efficiency of manure and fertilizer and/or add N from other sources (cover crops, greater reliance on N fixation, shorter rotations). Improvement in herd nutrition through precision feeding has the potential to increase N use efficiency of surface applied manure and thus reduce N loss to the environment. However, such improvements will also reduce the total amount of N excreted and decrease the N:P ratio of the manure. Best management practices that reduce N loss in the barn and storage system, increase manure and fertilizer N uptake efficiency, and/or reduce N needs will be essential in order to balance N and P for the long-term sustainability of NY agriculture.
  • Authors:
    • Dobermann, A. R.
    • Shapiro, C. A.
    • Tarkalson, D. D.
    • Wortmann, C. S.
    • Ferguson, R. B.
    • Hergert, G. W.
    • Walters, D.
  • Source: Agronomy Journal
  • Volume: 103
  • Issue: 1
  • Year: 2011
  • Summary: Nitrogen use efficiency (NUE) is of economic and environmental importance. Components of NUE were evaluated at in 32 irrigated corn (Zea mays L.) trials conducted across Nebraska with different N rates and where the previous crop was either corn (CC), drybean ( Phaseolus vulgaris L.) (CD), or soybean [Glycine max (L.) Merr.] (CS). The mean grain yield with adequate nutrient availability was 14.7 Mg ha -1 When no N was applied, measured soil properties and irrigation water N accounted for <20% of the variation in plant nitrogen uptake (UN). Mean fertilizer N recovery in aboveground biomass was 74% at the lowest N rate compared with 40% at the highest N rate, a mean of 64% at the economically optimal nitrogen rate (EONR), and least with CD. Agronomic efficiency of fertilizer N averaged 29 kg grain kg(-1) N at EONR and was also least with CD. Partial factor productivity of N averaged 100 kg grain kg(-1) N at EONR, and was greater with CS compared with CC and CD. Aft er harvest, residual soil nitrate nitrogen (RSN) in the 0- to 1.2-m depth ranged from 21 to 121 kg ha(-1) and increased with N rate. Mean RSN was 88, 59, and 59 kg ha(-1) for CD, CC, and CS, respectively. High corn yields can be achieved with high NUE and low RSN by management to maximize profitability in consideration of yield potential, and by applying N at the right amount and time.
  • Authors:
    • Tyler, D. D.
    • Jaja, N.
    • McClure, M. A.
    • Yin, X. H.
    • Hayes, R. M.
  • Source: Agronomy Journal
  • Volume: 103
  • Issue: 3
  • Year: 2011
  • Summary: The relationship between corn ( Zea mays L.) yield and plant height has been poorly documented in major corn production systems. This study was conducted to assess the relationship of corn yield with plant height under four major corn production systems at Milan, TN from 2008 through 2010. Six N treatments at rates of 0, 62, 123, 185, 247, and 308 kg N ha -1 with four replications were evaluated in a randomized complete block design in the following corn production systems: nonirrigated corn after corn, nonirrigated corn after soybean [ Glycine max (L.) Merr.], nonirrigated corn after cotton [ Gossypium hirsutum (L.)], and irrigated corn after soybean. The regression of corn yield with plant height was significant and positive at 6-leaf growth stage (V6), 10-leaf growth stage (V10), and 12-leaf growth stage (V12), and mostly became stronger as plant growth progressed from V6 to V10 and to V12 under an exponential model in the four corn production systems for all 3 yr. In general, corn yield was strongly related with plant height measurements made at V10 and V12. Factors affecting the responses of plant height measured at V6, V10, and V12 or/and yield to the N treatments may have contributed to the variations of determination coeffient ( R2) values across years. In conclusion, corn yield may be predicted with plant height measurements collected during V10 to V12. This prediction provides a physiological basis for the utilization of high resolution plant height measurements to guide variable-rate N applications within the field on corn at around V10 and to more accurately estimate yield for earlier grain marketing purposes.
  • Authors:
    • Schultz, R. C.
    • Zaimes, G. N.
  • Source: Ecological Engineering
  • Volume: 37
  • Issue: 11
  • Year: 2011
  • Summary: Extensive land-use changes in Iowa have increased erosional processes and the amount of fines deposited on stream beds. Large amounts of fines cover the other bed substrate that are essential habitat for invertebrates and fish. In Iowa and other agricultural Midwestern states, riparian conservation land-uses are being established to minimize sediment inputs to streams. This study compared stream bed substrate composition in reaches adjacent to: riparian forest buffers, grass filters, row-cropped fields, pastures with cattle fenced out of the stream and continuous, rotational and intensively grazed rotational pastures, in three regions of Iowa. The objective was to examine the impacts of the adjacent riparian land-uses on stream bed substrate composition. The percentages of fines in this study ranged from: 36 to 63% in the central region; 10 to 31% in the northeast region; and 22 to 85% in the southeast region. The high percentage of fines in most stream bed reaches indicates high embeddedness. The high embeddedness resulted in the few significant differences in substrate percentages among riparian land-uses. Decades of agricultural land-uses have heavily impacted stream beds and only significant reductions in surface and bank erosion at the watershed scale can begin to reverse this trend. There were indications that riparian forest buffers and to a lesser degree, pastures with cattle fenced out of the stream, could decrease fines resulting in a more diverse substrate composition. Overall, more targeted approaches for the establishment of conservation land-uses in combination with other restoration practices (e.g. in-stream enhancements) are required to successfully decrease fines on stream beds. (C) 2011 Elsevier B.V. All rights reserved.