Temporal yield variability under conventional and alternative management systems
Year to year variation in yield is an inherent risk associated with crop production and many growers rely on intensive mechanical or chemical inputs to preserve crop yield in the face of fluctuating environmental conditions. However, as interest grows in alternative crop management systems which depend less on external inputs, determining the degree to which management systems can impact the temporal yield variability will help the development of sustainable agroecosystems. This study assessed average crop yields and temporal yield variability over a 12-yr period in four agricultural management systems that are part of a long-term cropping systems experiment at the W.K. Kellogg Biological Station (KBS) Long Term Ecological Research (LTER) site in southwestern Michigan. The four systems follow a corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and winter wheat (Triticum aestivum L.) 3-yr rotation under conventional (CT), no-till (NT), low-input (LI), or organic (ORG) management, and each crop phase was present in the rotation four times from 1993 to 2004. Yields were measured each year and crop yield variability was estimated using the coefficient of variation calculated separately for each crop phase. Averaged over the study period, yields in the CT and NT systems were similar across all crop phases of the rotation and of higher magnitude than the LI system only in the winter wheat phase of the rotation. Compared to the other three management systems, yields in the ORG system were lower in the corn and winter wheat phases of the rotation. Yields in the soybean phase were similar across the four management systems. Temporal yield variability differed among management systems and rotation phases and was highest in the ORG system during the soybean (CV = 48%) and winter wheat (CV = 33%) phases of the rotation. Compared to the CT system, yield variability was 40% lower in the LI (corn phase), 33% lower in the NT (soybean phase) and similar in the NT (corn and winter wheat phases) systems. Results of this study suggest that yield and temporal yield variability under alternative management systems such as no-till and low-input can be comparable to that in conventional systems. However, temporal yield variability can be as high or higher in organic cropping systems without external inputs of manure or compost.