Author
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Varvel, Gary |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/1/2000 Publication Date: 12/1/2000 Citation: VARVEL, G.E. CROP ROTATION AND NITROGEN EFFECTS ON NORMALIZED GRAIN YIELDS IN A LONG-TERM STUDY. AGRONOMY JOURNAL 92:938-941. 2000. Interpretive Summary: Agronomists have long recognized that spatial and temporal variability greatly affect crop production. Hybrid and variety development, fertilizer use, and irrigation where possible have been used successfully in many areas to reduce or minimize some of the effects of that variability. These practices have generally resulted in improved average yields over the long term, but little information is available on their effect on year to year variability. However, few studies are conducted for a long enough period of time where management system evaluations and assessments can be made. Questions about whether management systems are effective at reducing temporal variability were investigated using data from a long-term crop rotation study to determine effects of crop rotation and N fertilization practices in a rainfed environment. Sixteen years of grain yield data from an experiment with seven cropping systems (three monoculture, two two-year, ,and two four-year rotations) with three rates of N fertilizer are included in the study. Grain yields from 1983 through 1998 for each crop were normalized for each year. Overall analyses of the 16 years of normalized yield data were conducted to assess what effects cropping systems have on yield stability. These analyses demonstrated that crop rotation systems are more effective at reducing long-term yield variability than monoculture systems, even with N fertilizer. As expected, N fertility, obtained from either fertilizer or legumes in monoculture or rotation systems is probably one of the most, if not the most important aspect in maintaining yield stability. Technical Abstract: Effects of year to year variability in agricultural production systems have always been a concern, but few studies are conducted for a long enough period of time where management system evaluations and assessments can be made. Given this limitation, questions about whether management systems are effective at reducing temporal variability remains in production agriculture. These questions prompted investigation of a long-term crop rotation study to determine effects of crop rotation and N fertilization practices in a rainfed environment on grain yield stability. Sixteen years of grain yield data from an experiment with seven cropping systems (three monoculture, two two-year, and two four-year rotations) with three rates of N fertilizer are included in the study. Grain yields from 1983 through 1998 for each crop were normalized for each year and then combined, which resulted in a relative yield for all crops across all plots. Using these normalized yields, overall analyses of the 16 years of data were conducted to assess what effects cropping systems have on yield stability. These analyses demonstrated that crop rotation systems are more effective at reducing long-term yield variability than monoculture systems, even with N fertilizer. As expected, N fertility, obtained from either fertilizer or legumes in monoculture or rotation systems is probably one of the most, if not the most important aspect in maintaining yield stability. It also demonstrated that significant degrees of yield stability could be obtained in many of our cropping systems with proper management. |
