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Title:   Author  item
                                            Jaradat, Abdullahitem
                                            Archer, Daviditem
                                            Johnson, Janeitem
                                            Van Kempen, Stephenitem
                                            Wagner, Stevenitem
                                            Eklund, James
  Submitted to: Meeting Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 7/28/2004
                                    Publication  Date: 9/1/2005
                                    Citation: Jaradat, A.A., Archer, D.W., Johnson, J.M., Vankempen, S.J., Wagner, S.W., Eklund, J.J. 2005. Sampling strategies for crop yield assessment within and among crop rotations. Proceedings of the Seventh International Conference on Precision Agriculture, July 25-28, 2004, Minneapolis, Minnesota. 2005 CDROM.Interpretive Summary: Long-term experiments are needed to determine yield trends, estimate nutrient dynamics and balances, understand changes in yield, predict soil carrying capacity and assess system sustainability. Researchers and farmers, particularly in the upper Midwest, realized that research is needed to identify cropping systems that simultaneously improve the economic and social viability of farmers and rural communities while protecting the environment and improving or maintaining the natural resource base. Multilevel sampling and monitoring at the single plant, plants per unit area and experimental plot levels were designed to quantify the spatio-temporal dynamics of alfalfa, corn, soybeans and wheat crops in 192 geo-referenced experimental plots, their responses to alternative cropping systems, tillage and fertility treatments. Results of the long-term study will be of value to farmers and researchers in order to (1) determine which management factors and plant attributes affect crop yield estimates based on main- and sub-plot sampling and (2) identify the hierarchy of constraints to plant growth, development and yield of corn, soybean and wheat within a cropping sequence context.
                                Technical Abstract: Long-term two and four year crop rotations were designed to provide reliable information to formulate long-term strategies for crop sequencing that optimize crop and soil use options in the upper Midwest. Multilevel sampling and monitoring at the single plant, plants per unit area and experimental plot levels were designed to quantify the spatio-temporal dynamics of corn, soybean and wheat crops in 192 geo-referenced main plots (MP) and their responses to alternative cropping systems, tillage and fertility treatments. Baseline soil information and crop yield were collected from all 192 plots during 2002 and 2003. Data on plant grain area (G) per m**2, plant height (Ht), midday differential canopy temperature (D) during the growing season, yield per plant and its components and yield per m**2 at harvest were collected in 2003 from two geo-referenced sampling sites (SP) within each of 16 plots per crop. The multivariate data set was analyzed with the objective to identify the hierarchy of constraints to plant growth, development and yield and to refine the sub sampling strategy in future years. Averaged over crops, SP-based grain variance was 94.5% higher than the MP-based; however, SPs were more efficient than MPs in detecting crop-specific significant yield differences due to management factors. Conventional system, conventional tillage and N fertilizer resulted in highest grain yield, whereas organic system, strip tillage and no N fertilizer resulted in lowest grain yields. Yield-limiting factors were crop-specific, with strip tillage and no N fertilizer highly limiting corn yield, and organic system and no N fertilizer being the most limiting factors in soybean and wheat. G, Ht and D loaded highly on two components explaining >80.0% of variability in grain yield. However, relative importance of G and Ht in explaining yield variability decreased and that of D increased with successive samplings during the growing season.


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