Systems Approach Critical to Agroecosystems Management.

Sustainable dryland agriculture in the semi-arid Great Plains of the US depends on achieving economic yields while maintaining soil resources.  The traditional system of conventional tillage wheat-fallow was vulnerable to excessive soil erosion which resulted in excessive organic matter loss.  No-till has allowed for increased cropping and less fallow.  Optimizing the cropping system depends on environmental factors such as mean annual precipitation (MAP) and potential ET (PET) along with soil types working in concert with robust systems management.  A long term cropping systems experiment was established in 1985 to identify systems that maximize the use of precipitation by collecting data across gradients of 1)PET sites, 2)soils (across landscapes) and 3) cropping intensities.   The 4^th variable is time whereby the minimum length of the study is derived by the longest rotation in the study.  Each phase of each cropping system is represented each year.  Since the maximum rotation length is  4 years  all systems are back to their starting phase in year 12 and 24, (1997 and 2009) of the study, which permitted a comprehensive evaluation of the annualized production for each of the cropping systems.   Systems can be compared within a PET site and soil or pooled soils within each location or over all locations and soils.  This study has been designed to 1) determine if cropping system sequences with fewer summer fallow periods are feasible; 2) quantify the relationships among climate, soil type, and cropping sequences; 3) quantify the long-term  effects of no-till on soil structural stability, microbial  populations, and nutrient cycling along with  organic C and N; 4) identify cropping systems that will minimize soil erosion; and 5) develop a data base across climatic zones that will allow the economic assessment of the different management systems and provide a long-term data source to improve soil and crop models.