Crop Growth, Lint Yield, and Pest Population Dynamics in Cotton Under Conservation Cropping Systems.

Conservation cropping systems are being developed for cotton that has traditionally been grown on raised beds with several soil- disturbing tillage passes in the San Joaquin Valley (SJV) of California.  These beds are irrigated by flood, furrow, or sprinkler systems and have limited options for crop rotation.  Overhead (OH) and subsurface drip irrigation (SDI) systems are two water conserving techniques being tested in combination with reduced tillage and strategic crop rotations in the SJV.  However, crop growth, yield, soil temperature, moisture, and pest population dynamics in these new cropping systems have not been documented.  Therefore, a study was initiated in 2010 to compare  these parameters in a conservation tillage silage wheat- cotton-silage wheat-cotton rotation with OH or SDI systems.  The cotton was a Roundup Ready Acala variety.  The experimental design was a randomized complete block with irrigation systems as treatments.  Data were analyzed using ANOVA procedures and significance was determined at an alpha of 0.05.  The use of OH or SDI allowed flat-planting of cotton and made crop rotation feasible.  Results in 2011 showed that crop growth parameters and yield were generally similar in the OH and SDI systems.  However, the top 15 cm of the soil in the OH plots was wetter and cooler than the SDI plots at most sampling dates during the growing season. The SDI plots had a greater spider mite (Tetranychus sp.) population but lower weed densities than the OH plots.  The study is being continued in 2012.