Agronomic, ecological, and economic trade-offs among different dryland organic transition cropping systems

Many studies have compared various aspects of conventional production with organic production; however, very few studies have been conducted to investigate the trade-offs among different organic transition schemes. The organic transition phase is a three-year period when a cropping system must be free of the synthetic fertilizers and pesticides commonly used in conventional agriculture. During this transition period, the crops produced do not qualify as certified organic, and price premiums cannot be obtained. A farmer may also be vulnerable to economic losses due to weed and pest infestations, inadequate soil fertility, and dockage penalties due to poor crop quality. The objective of our study is to determine how utilizing crop rotations may reduce any economic losses during the transition period, while building soil fertility through the use of green manures to maximize gains when the farm becomes certified organic. Nine transitions systems were designed to integrate legumes or forages for fertility building (nitrogen), and to provide opportunities for mechanical weed management to control weeds and deplete the soil weed seed bank. In summary, spring pea grown for grain was prone to insect pests and weed infestations, whereas winter pea grown for a green manure greatly aided the building of soil fertility and suppression of weeds. Winter pea green manure did result in significantly higher nitrate nitrogen in the lower portion of the soil profile than the other systems. The alfalfa forage system provide some net positive income during the transition phase and resulted in the highest spring wheat yields in the first year of organic production.   A reduced tillage system consisting of sweep plow + rotary harrow + rotary hoe worked well to manage annual weeds, but did not effectively suppress perennial weeds such as field bindweed.