• Authors:
    • Kratochvil, R. J.
    • Forrestal, P. J.
    • Meisinger, J. J.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 1
  • Year: 2012
  • Summary: Evaluation of corn ( Zea mays L.) N management and soil residual NO 3-N late in the growing season could provide important management information for subsequent small grain crops and about potential NO 3-N loss. Our objective was to evaluate the ability of several late-season corn measurements, which have been advocated to assess N management, to identify sites with elevated soil residual NO 3-N. These crop-based measurements were collected at three reproductive phases and included normalized difference vegetative index (NDVI) at 10 site-years and green-leaf number and chlorophyll (SPAD) meter readings at six of these sites. The corn stalk nitrate test (CSNT) and postharvest soil residual NO 3-N were measured at all sites. Four levels of N were applied, ranging from N deficient (0 or 67 kg N ha -1) to excessive (269 kg N ha -1). The CSNT was positively ( p<0.001) correlated with residual NO 3-N, although residual NO 3-N was not always low at CSNT values <2.0 g NO 3-N kg -1, where drought reduced production. Drought stress was a major factor influencing excess N supply and residual soil NO 3-N. Canopy measurement values at growth stages R3-R4, including NDVI, which can be measured remotely, were effective indicators of drought stress. Across sites, relative canopy readings best predicted relative grain yield when collected at R3-R4, underscoring the importance of reference strips. Use of remotely measured NDVI would allow policymakers to identify drought sites in the late summer and target them for cover crop planting, thus reducing potential winter NO 3-N losses in humid regions.
  • Authors:
    • Eigenberg, R. A.
    • Hubbard, R. K.
    • Powell, J. M.
    • Torbert, H. A.
    • Woodbury, B. L.
    • Albrecht, S. L.
    • Sistani, K. R.
    • Wienhold, B. J.
    • He, Z. Q.
    • Larkin, R. P.
    • Griffin, T. S.
    • Vandemark, G.
    • Honeycutt, C. W.
    • Fortuna, A. M.
    • Wright, R. J.
    • Alldredge, J. R.
    • Harsh, J. B.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 1
  • Year: 2012
  • Summary: Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy ( Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha -1. Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.
  • Authors:
    • Lakshmanan, P.
    • Robinson, N.
    • Brackin, R.
    • Holst, J.
    • Schmidt, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 155
  • Year: 2012
  • Summary: Addressing the limited knowledge of nitrogen (N) pools in tropical agricultural soils and the need to reduce N losses from these systems, we analysed soluble organic and inorganic N in two Hydrosols under sugarcane. Concentrations of ammonium and nitrate spanned ~3 - orders of magnitude (0.2-41.0 mg ammonium-N, 0-10.7 mg nitrate-N kg -1 soil) with the highest concentrations detected within 2-3 months of fertiliser application. Soluble amino acids spanned 1-order of magnitude (0.22-2.42 mg amino acid-N kg -1 soil) and accounted for up to 70% of the low-molecular weight N. Amino acid concentrations were usually highest in the wet season and uniform across soil depth, indicating that amino acids are generated throughout the studied profile. We compared soluble and dissolved (free) N in the soil solution in a subset of samples. In soil solution, amino acid, ammonium and nitrate concentrations averaged 20, 265 and 1820 M, respectively, corresponding to ~10% (amino acids), ~20% (ammonium) and ~100% (nitrate) of the soluble N pool. We calculated an annual gross amino acid flux in the dissolved N pool in the order of 2-6 tons N ha -1 yr -1 in the upper 40 cm of soil. We discuss whether amino acids can significantly contribute to the N demand of sugarcane.
  • Authors:
    • Yagi, K.
    • Xu, H.
    • Ma, J.
    • Liu, G.
    • Ji, Y.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 94
  • Issue: 1
  • Year: 2012
  • Summary: A 2-year field experiment was conducted to study effects of application rate of controlled-release fertilizer (CRF) and urea on N2O emission from a wheat cropping system. Two kinds of N fertilizers, CRF and urea, and four application rates (0, 100, 200 and 270 kg N ha(-1)) were used. Results indicate that the application of either urea or CRF, increased total N2O emission during the wheat growing period linearly from 32 to 164 %, with increasing N rate (p < 0.05), compared to the zero N control, and the increase was less significant in CRF than urea treatments. Compared with urea, CRF significantly reduced N2O emission by 25-56 % during the wheat growing period (p < 0.05), and the effect was more significant when N rate was higher. Grain yield increased in a power pattern from 24 to 43 % in urea treatments and from 30 to 45 % in CRF treatments with increasing N rate (p < 0.05). Specific N2O emission (N2O emission per unit of yield) increased linearly from 31 to 114 % in urea treatments (p < 0.05), and from 2 to 50 % in CRF treatments (p < 0.05), with increasing N rate. Compared with urea, CRF significantly inhibited specific N2O emission (p < 0.05), and the effect increased with increasing N rate. Peaks of N2O emission did not occur immediately after fertilization, but did immediately after rainfall events. CRF released fertilizer-N slowly, prolonging nitrogen supply and reducing peaks of N2O fluxes stimulated by rainfall. The application rate of CRF could be reduced by 26-50 % lower than that of urea for mitigating N2O emission without sacrificing grain yield. We would not risk any significant loss of wheat yield while achieving economic and environmental benefits by reducing urea or CRF application rate from 270 kg to 200 kg N ha(-1).
  • Authors:
    • Moyo, B. H.
    • Chirwa, P. W.
    • Khumalo, S.
    • Syampungani, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 157
  • Year: 2012
  • Summary: This paper reviews the agroecosystems and agricultural biodiversity in Southern Africa and highlights the importance of the agricultural landscape in biodiversity conservation and the important role that the traditional farming systems play in conserving biodiversity. The review established that agrobiodiversity is of great importance to both small scale and large commercial farmers in Southern Africa through its provision of ecosystem services. The paper also highlights the significant loss of agrobiodiversity as a result of human population pressure and the transition from traditional mixed farming systems which is characterized with high agrobiodiversity, to modern monoculture farming resulting in decline of species diversity. Although concerted efforts are being made to promote the sustainable use and management of this agrobiodiversity, there need to have a multi-stakeholder approach so that conservation efforts are successful, a role that is currently played by the SADC Plant Genetic Resources Centre in Southern African conservation of agrobiodiversity.
  • Authors:
    • Kunkel, K.
    • Reddy, K. R.
    • Gao, W.
    • Xu, M.
    • Liang, X. Z.
    • Schmoldt, D. L.
    • Samel, A. N.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 3
  • Year: 2012
  • Summary: Climate variability and changes affect crop yields by causing climatic stresses during various stages of the plant life cycle. A crop growth model must be able to capture the observed relationships between crop yields and climate stresses before its credible use as a prediction tool. This study evaluated the ability of the geographically distributed cotton growth model redeveloped from GOSSYM in simulating U.S. cotton ( Gossypium hirsutum L.) yields and their responses to climate stresses during 1979 to 2005. Driven by realistic climate conditions, the model reproduced long-term mean cotton yields within 10% of observations at the 30-km model resolution across virtually the entire U.S. Cotton Belt and correctly captured the critical dependence of their geographic distributions on regional climate characteristics. Significant correlations between simulated and observed interannual variations were found across 87% of the total harvest grids. The model also faithfully represented the predictive role of July to August air temperature and August to September soil temperature anomalies on interannual cotton yield changes on unirrigated lands, with a similar but weaker predictive signal for irrigated lands as observed. The modeled cotton yields exhibited large, positive correlations with July to August leaf area index. These results indicate the model's ability to depict the regional impact of climate stresses on cotton yields and suggest the potential predictive value of satellite retrievals. They also provide a baseline reference for further model improvements and applications in the future study of climate-cotton interactions.
  • Authors:
    • Wang, P. J.
    • Zhao, J. S.
    • Wu, J. S.
    • Ruan, L. L.
    • Hu, R. G.
    • Iqbal, J.
    • Lin, S.
  • Source: Agriculture Ecosystems and Environment
  • Volume: 146
  • Issue: 1
  • Year: 2012
  • Summary: Red soil may play an important role in nitrous oxide (N 2O) emissions due to its recent land use change pattern. To predict the land use change effect on N 2O emissions, we examined the relationship between soil N 2O flux and environmental determinants in four different types of land uses in subtropical red soil. During two years of study (January 2005-January 2007), biweekly N 2O fluxes were measured from 09:00 to 11:00 a.m. using static closed chamber method. Objectives were to estimate the seasonal and annual N 2O flux differences from land use change and, reveal the controlling factors of soil N 2O emission by studying the relationship of dissolved organic carbon (DOC), microbial biomass carbon (MBC), water filled pore space (WFPS) and soil temperature with soil N 2O flux. Nitrous oxide fluxes were significantly higher in hot-humid season than in the cool-dry season. Significant differences in soil N 2O fluxes were observed among four land uses; 2.9, 1.9 and 1.7 times increased N 2O emissions were observed after conventional land use conversion from woodland to paddy, orchard and upland, respectively. The mean annual budgets of N 2O emission were 0.71-2.21 kg N 2O-N ha -1 year -1 from four land use types. The differences were partly attributed to increased fertilizer use in agriculture land uses. In all land uses, N 2O fluxes were positively related to soil temperature and DOC accounting for 22-48% and 30-46% of the seasonal N 2O flux variability, respectively. Nitrous oxide fluxes did significantly correlate with WFPS in orchard and upland only. Nitrous oxide fluxes responded positively to MBC in all land use types except orchard which had the lowest WFPS. We conclude that (1) land use conversion from woodland to agriculture land uses leads to increased soil N 2O fluxes, partly due increased fertilizer use, and (2) irrespective of land use, soil N 2O fluxes are under environmental controls, the main variables being soil temperature and DOC, both of which control the supply of nitrification and denitrification substrates.
  • Authors:
    • Zhang, X. Y.
    • Studdert, G.
    • Morras, H.
    • Huffman, T.
    • Duran, A.
    • Kravchenko, Y. S.
    • Burras, C. L.
    • Liu, X. B.
    • Cruse, R. M.
    • Yuan, X. H.
  • Source: Canadian Soil Science
  • Volume: 92
  • Issue: 3
  • Year: 2012
  • Summary: Mollisols - a.k.a., Black Soils or Prairie Soils - make up about 916 million ha, which is 7% of the world's ice-free land surface. Their distribution strongly correlates with native prairie ecosystems, but is not limited to them. They are most prevalent in the mid-latitudes of North America, Eurasia, and South America. In North America, they cover 200 million ha of the United States, more than 40 million ha of Canada and 50 million ha of Mexico. Across Eurasia they cover around 450 million ha, extending from the western 148 million ha in southern Russia and 34 million ha in Ukraine to the eastern 35 million ha in northeast China. They are common to South America's Argentina and Uruguay, covering about 89 million and 13 million ha, respectively. Mollisols are often recognized as inherently productive and fertile soils. They are extensively and intensively farmed, and increasingly dedicated to cereals production, which needs significant inputs of fertilizers and tillage. Mollisols are also important soils in pasture, range and forage systems. Thus, it is not surprising that these soils are prone to soil erosion, dehumification (loss of stable aggregates and organic matter) and are suffering from anthropogenic soil acidity. Therefore, soil scientists from all of the world's Mollisols regions are concerned about the sustainability of some of current trends in land use and agricultural practices. These same scientists recommend increasing the acreage under minimum or restricted tillage, returning plant residues and adding organic amendments such as animal manure to maintain or increase soil organic matter content, and more systematic use of chemical amendments such as agricultural limestone to replenish soil calcium reserves.
  • Authors:
    • Lin, X. M.
    • Hubbard, K. G.
    • Yang, X. G.
    • Liu, Z. J.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 11
  • Year: 2012
  • Summary: Northeast China (NEC) is not only one of the major agricultural production areas in China, but it is also the most susceptible to climate variability. This led us to investigate the impact of climate change on maize potential yield and yield gaps in this region, where maize accounts for about 30% of the nation's production. The APSIM-Maize model was calibrated and validated for maize phenology and yields. The validated model was then used to estimate potential yields, rain-fed potential yields, and yield gaps for assessing the climate impacts on maize productivity in NEC. During maize growing seasons from 1981 to 2010, the analysis indicates a warming trend all across NEC, whereas the trends in solar radiation and total precipitation tended to decrease. When the same hybrid was specified in APSIM for all years, a simulated increase of maximum temperature resulted in a negative impact on both potential yield and rain-fed potential yield. A simulated increase in minimum temperature produced no significant changes in potential or rain-fed potential yield. However, the increase of minimum temperature was shown to result in a positive impact on the on-farm yield, consistent with our finding that farmers adopted longer season hybrids for which the increase in minimum temperature provided better conditions for germination, emergence, and grain filling during night time. The gap between potential and rain-fed potential yields was shown to be larger at locations with lower seasonal precipitation (<500 mm). Our results indicate that regions with the largest yield gaps between rain-fed potential and on-farm yields were located in the southeast of NEC. Within NEC, on-farm maize yields were, on average, only 51% of the potential yields, indicating a large exploitable yield gap, which provides an opportunity to significantly increase production by effective irrigation, fertilization, herbicide, and planting density in NEC.
  • Authors:
    • Lucas, S. T.
    • Weil, R. R.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 4
  • Year: 2012
  • Summary: Permanganate (KMnO 4) oxidizable C (POXC), an estimate of labile soil C, was evaluated for use as a soil test to identify soils that may respond positively to soil organic matter (SOM) management. We hypothesized that soils lower in POXC would be more likely than soils higher in POXC to show increased crop productivity in response to practices that increase SOM. At four sites, paired fields of the same soil but contrasting management history (cropping vs. sod) were studied. Fields with sod history tested higher in total organic C (TOC) and POXC than fields with cropped history. Permanganate-oxidizable C was strongly related to TOC ( r=0.94). We examined crop stover, grain, and biomass responses to two cover crop treatments within each field: winter rye ( Secale cereale L.) or no rye. After at least 1 yr of treatment, there was a significant negative correlation between relative stover response to rye and POXC ( r=-0.60) at sites with finer textured soils. After at least 2 yr of treatment, crop responses to rye showed a significant negative correlation with POXC and TOC. The strongest relationships to POXC occurred in the stover response at two sites with finer textured soils (Keedysville: r=-0.74; Holtwood: r=-0.84). Permanganate-oxidizable C was comparable to TOC at predicting crop responses to rye. These results suggest that POXC may be a useful test for identifying soils where improved SOM management is likely to improve productivity. The rapid, simple POXC methodology enables on-site or laboratory soil testing.