1. VI. Acknowledgements Corn Yield Responses to Plant Height Variability for Various Tillage Systems and Crop Rotations Christopher R. Boomsma, Jason C. Brewer, Judith B. Santini, Terry D. West, and Tony J. Vyn Department of Agronomy; Purdue University; West Lafayette, IN 47907 IV. Preliminary Conclusions The continuous corn, no-till treatment shows a significantly lower grain yield compared to the other three treatments in 10 out of 14 years (Figure 4). For the continuous corn, no-till treatment, 8 week plant height mean and variability are not associated with lower grain yield when grain yields are below an annual grand mean grain yield of ≈ 175 bu A -1, but may influence grain yield when grain yields are above an annual grand mean grain yield of ≈ 175 bu A -1 (Figures 4-6). An increase in 8 week plant height mean for the continuous corn, no-till treatment is associated with a decrease in grain yield (Figure 7). An increase in 8 week plant height variability for the continuous corn rotation is associated with a decrease in grain yield for the combined no-till and plow tillage treatments (Figure 8). A variety of non-treatment factors, such as temperature, rainfall, and planting date, may also influence plant height, plant height variability, and subsequently grain yield, and will therefore be investigated in future research. I. Introduction Background: The effects of various tillage systems and crop rotations on corn (Zea mays L.) growth and development have been studied extensively over the past twenty-five years. Many previous studies were conducted on a short-term basis (Wilhelm et al., 2004); however, a number of long-term studies were also performed. Many of these have principally focused on the effects of tillage and crop rotation on grain yield and mean plant height (Griffith et al., 1988; Kapusta et al., 1996; Vyn et al., 2000; West et al., 1996). As a result of past research, many agronomists and growers believe that lower corn grain yields in no-till versus conventional-till systems are generally associated with reduced mean plant heights at critical developmental stages throughout the growing season. However, mean plant heights may not be accurate morphometric indicators of decreased grain yields in no-till corn. This research, conducted over a 14 year period, therefore examines the early-season effects of both mean plant heights and plant height variability on grain yields using multiple tillage systems and two crop rotations. Hypotheses: 1)No-till grain yield reductions are greatest when plant height variability is high. 2)Early-season plant height variability is a more accurate indicator or predictor of grain yield response to tillage and crop rotation than early-season mean plant heights. Objective: To determine the effects of early-season plant height variability and mean plant heights on grain yields for various tillage systems and crop rotations. V. Literature Cited Griffith, D.R., E.J. Kladivko, J.V. Mannering, T.D. West, and S.D. Parsons. 1988. Long-term tillage and rotation effects on corn growth and yield on high and low organic matter, poorly drained soils. Agron. J. 80:599-605. Kapusta, G., R.F. Krausz, and J.L. Matthews. 1996. Corn yield is equal in conventional, reduced, and no tillage after 20 years. Agron. J. 88:812-817. Vyn, T.J., T.D. West, and G.C. Steinhardt. 2000. Corn and soybean response to tillage and rotation systems on a dark prairie soil: 25-year review. p. 1–10. In Proc. 15th Int. Soil Tillage Res. Org. Conf., Fort Worth, TX. 2–6 July 2000. Published by Int. Soil Tillage Organization. CD-ROM available from Soil Sci. Dep., Univ. of Wisconsin, Madison, WI. West, T.D., D.R. Griffith, G.C. Steinhardt, E.J. Kladivko, and S.D. Parsons. 1996. Effect of tillage and rotation on agronomic performance of corn and soybean: Twenty-year study on dark silty clay loam. J. Prod. Agric. 9:241-248. Wilhelm, W.W., J.M.F. Johnson, J.L. Hatfield, W.B. Voorhees, and D.R. Linden. 2004. Crop and soil productivity response to corn residue removal: A literature review. Agron. J. 96:1-17. II. Materials and Methods Figure 3: Fall plowing of soybean residue in preparation for a corn crop. Experimental Setup: Layout: Split-plot Split-block Design Four Blocks Hybrid: Beck’s 65X (114 Day) Seeding Rate: 26,100 plants A -1 Planting Date: Range: April 25 to May 22 Mean: May 5 Measurements: Grain Yield (bu A -1 ) Grain Moisture Content (%) Plant Population (plants A -1 ) 4 and 8 Week (after planting) Plant Heights (in) Statistical Analyses: All analyses were conducted using SAS ® PROC GLM. Years were considered a fixed effect. Block 1 plant measurements were omitted from analysis due to frequent flooding. 8 week plant height measurements were omitted in 1981 and 1987 due to data problems. Treatments: Crop Rotation (whole unit): Corn-Soybean (CS) Corn-Corn (CC) Tillage System (subunit): No-Till (NT) Plow (PL) Chisel Ridge-Till Year (split block): 1981 – 1994 8 week plant height coefficient of variation (CV) was log-transformed prior to analysis. All error terms were pooled (P>0.25) within even- and odd-year analyses. Even- and odd-year analyses were combined into a single 12- or 14-year model since the even- and odd-year error variances were homogeneous. Figures 4-8 present results for no-till and plow tillage treatments only. Figure 1: Spring, pre-plant comparison of a plow (left) and no-till (right) tillage treatment following a previous corn crop. Figure 2: Spring, pre-plant comparison of all tillage treatments following a previous corn crop. Figure 8: Figure 8 describes the relationship between annual grain yield and 8 week plant height CV for 12 years of the study. Key Results: Large 8 week plant height CVs are associated with predicted grain yields of approximately 145 bu A -1 or less. Yield is not influenced by the 8 week plant height CV for the corn-soybean rotation. Yield is not influenced by the 8 week plant height CV for the continuous corn rotation when only CVs less than 16% are considered. R 2 = 0.2074** III. Results Figure 4: Figure 4 presents the annual grain yield for each rotation-tillage treatment for all 14 years of the study. The years are ranked according to the grain yield grand mean of all four treatments. Key Results: The continuous corn, no-till treatment has a significantly lower yield for most years of the study. The continuous corn, no-till yields vary tremendously relative to the yields of all other treatments. Important Note: Error bars equal one-half of the least significant difference (LSD) at probability level 0.05. Means are significantly different where error bars do not overlap. Figure 5: Figure 5 presents the 8 week plant height mean for each rotation-tillage treatment for 12 years of the study. The years are ranked according to the grain yield grand mean of all four treatments. Key Results: The continuous corn, no-till treatment has a significantly lower 8 week plant height mean for 11 out of the 12 years of the study. The continuous corn, no-till 8 week plant height means vary relative to the means for all other treatments. Figure 6: Figure 6 displays the 8 week plant height CV (log 10 [%]) for each rotation-tillage treatment for 12 years of the study. The years are ranked according to the grain yield grand mean of all four treatments. Key Results: The continuous corn, no-till treatment shows a significantly higher 8 week plant height CV in 2 out of 12 years of the study. Figure 7: Figure 7 describes the relationship between annual grain yield and 8 week plant height mean for 12 years of the study. Key Results: Yield decreases 0.91 bu A -1 for each 1 inch increase in 8 week plant height mean for the continuous corn, no-till treatment. Yield is not influenced by the 8 week plant height mean for all other treatments. Factors other than the treatments may be influencing the continuous corn, no-till regression line. R 2 = 0.2815** Equipment and Materials: Beck’s Hybrids Purdue University Agronomy Center for Research and Education (ACRE) Funding: Purdue University Andrews Fellowship Purdue University Research Foundation