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Articles by Alexandra N. Kravchenko
Total Records ( 2 ) for Alexandra N. Kravchenko
  Dieudonne N. Baributsa , Eunice F. Foster , Kurt D. Thelen , Alexandra N. Kravchenko , Dale R. Mutch and Mathieu Ngouajio
  The increasing cost of nitrogen fertilizer and the need for a N source for low-input and organic farmers have led to the increased exploration of legume cover crops as an alternative to N fertilization. Reliable cropping strategies are needed to enhance legume cover crop use as a N source. Interseeding legume cover crops into corn (Zea mays L.) can affect corn yield and cover crop dry matter. This study, conducted at the Kellogg Biological Station in Hickory Corners, MI, from 2002 to 2005, evaluated (i) the impact of interseeded cover crops on corn yield at various corn densities (37,500 to 75,000 plants ha–1) and (ii) the effect of corn density on cover crop dry matter (DM) when corn was interseeded with red clover (Trifolium pratense L.) or chickling vetch (Lathyrus sativus L., var. AC Greenfix). Interseeded cover crops did not affect corn yield at any corn density. Interseeded cover crop DM decreased as corn density increased. The subsequent spring, red clover DM was similar regardless of previous corn density; AC Greenfix did not regrow. Interseeded cover crops produced less DM than monoculture cover crops. Cover crops can be interseeded into corn densities up to 75,000 plants ha–1 without corn yield reduction and still produce substantial DM the subsequent spring. Interseeding corn with red clover could be used in low-input farming systems to reduce N fertilizer costs, especially in developing countries and in organic farming systems.
  Xuewen Huang , Li Wang , Lijian Yang and Alexandra N. Kravchenko
  Crop yields are highly variable spatially and temporally as a result of complex interactions among topography, weather conditions, and management practices. The objective of this study was to analyze the effects of management practices on the relationship between crop yields and precipitation and crop yields and topography using 10 yr of yield data from a long-term corn (Zea mays L.)-soybean [Glycine max (L.) Merr.]-wheat (Triticum aestivum L.) rotation experiment in southwest Michigan. The four agronomic treatments studied were chisel plowed with conventional chemical inputs (CT), no-till with conventional chemical inputs (NT), chisel plowed with low chemical input and a winter leguminous cover crop (CTL), and organic-based chisel plowed with a winter leguminous cover crop (CTO). A nonparametric (spline) regression was used to characterize the relationship between the maximal yields, as characteristics of yield potential, and a wetness index (WI), as an integrative characteristic of topographical features related to water flow, and to compare the yield differences between the treatments across a range of the WI values. Variability of yields in NT and CTO systems was better explained by precipitation in early spring and during pollination and grain fill than that in CT and CTL. No-till and CTL tended to produce higher maximal yields than CT at the summit/steep-sloped areas (lower WI), while at intermediate and high WI levels the differences between them were inconsistent. The CTL often produced higher maximal yields than CTO at low and intermediate WI values, while the difference between them was mostly not significant at high WI levels (depression areas). The nonparametric spline regression algorithm used in the study was robust and efficient in comparing the yield differences between treatments across a range of WI values.
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