Growth analysis methods are useful tools for describing plant response to environmental variations (Rad- ford, 1967; Hunt, 1982). The objective of this study was (NT) often appear smaller than those grown with conventional tillage to test our hypothesis that a combination of compensa-(CT), yet they produce similar grain yield. Our objective was to test the hypothesis that the early-season growth depression is offset by tory growth and changes in plant development are recompensatory growth and changes in plant development. A 2-yr field sponsible for stable grain yield in the face of reduced study was conducted at Urbana, IL, on a long-term tillage experiment. early-season plant growth for soybean on a high organic Grain yield, moisture, protein, and oil content were similar for CT matter, well-structured soil in the central Corn Belt. and NT treatments. Total plant, stem, leaf, and pod dry biomass were all initially about 15 to 20% greater under CT, but the difference MATERIALS AND METHODS declined until about R5 or R6; thus, compensatory growth did occur. At the initiation of sampling (V2) crop growth rate was about 20% Field Procedures greater under CT, but the difference declined until about R2. The Field studies were conducted during the summers of 1993 advantage shifted to NT until about R6. Leaf area index (LAI) was and 1994 at the Agricultural Engineering Research Farm of greater for CT until about R4. Net assimilation rate was greater for the University of Illinois at Urbana-Champaign. This study NT until about R5. Increases in early-season crop growth rate for CT was superimposed on a long-term tillage experiment in a corn was due to increased LAI. Greater crop growth rate for NT late in [(Zea mays (L.)]-soybean rotation that was established in 1986 the season was due to increased net assimilation rate. Leaf weight on a Thorp silt loam field (fine-silty, mixed, mesic Argiaquic ratio was larger for the CT crop until about R6. Specific leaf area Soybean [Glycine max (L.) Merrill] plants grown with no-tillageArgialbolls) with 3.1% organic matter and a pH of 6.7. From was less in CT than NT. This work supports our hypothesis that the six tillage systems included in the long-term tillage expericompensatory growth and alterations in plant development occur ment, we selected two for this study: conventional tillage and when soybean is grown in NT systems and helps to explain why grain no-tillage. The CT consists of fall moldboard plowing (20-25 yield does not decrease with NT even though early-season growth cm deep) of corn residue followed by spring disking (7.5-10 is affected.cm deep) and field cultivating in preparation for soybean. The NT, by definition, has no tillage or cultivation. The experiment design is a complete randomized block with four replications,
Two varieties of winter rapeseed (Brassica napus) (Cobra and Liborius) were planted at Brownstown, IL to evaluate the effect of planting date, nitrogen (N) rate, N application timing, and tillage on grain yield and oil content of the grain, grain moisture, plant lodging, winter survival, and plant N content. Results indicated that planting rapeseed approximately one to two weeks prior to winter wheat in this region is preferable to planting earlier. Grain yield showed a significant linear increase with delayed planting date from 25 August to 24 September. Grain yield also increased quadratically with increasing N rate (with an optimum of about 250 kg N/ha) and increased (0.15 Mg/ha) due to splitting the N fertilizer into two even applications. An increase in grain yield was accompanied by an increase in grain moisture with Liborius (late maturing) having significantly greater grain moisture than Cobra. Winter survival increased linearly with delayed planting date but, was accompanied by a significant quadratic increase in plant lodging. Chisel, as compared to disk tillage, increased plant lodging slightly, but decreased winter survival slightly. Neither delayed planting, N rate, nor splitting of spring N affected oil content. Liborius produced significantly more oil than did Cobra.
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