Compost Carryover and Cover Crop Effects in Dryland Organic Wheat.

Producers of dryland organic wheat struggle to maintain adequate soil fertility due to the high cost of organic soil amendments. This results in decreased yields, and a high amount of weather dependent variability of grain yield and quality. Cover crops are one option for improving soil organic matter and available nitrogen, but they also use valuable soil moisture, which can have a detrimental effect on crop yields. Amending the soil with compost is another option for organic producers, although in the past this has been dismissed due to high cost. Recent research documenting the long lasting compost carryover effect, or instances where the soil health benefits of a one-time addition of compost last for multiple years, may improve the economic outlook of this option. This study measures the interactions between cover crop mixes and a one-time, large amendment of compost, on cover crop biomass, weed suppression, wheat yield, and quality. The study is located on three certified organic wheat farms in a wheat-fallow rotation near Snowville, UT. The soil is a calcareous Thiokol silt loam cultivated using conventional tillage. Austrian winter pea/hairy vetch and Austrian winter pea/barley cover crop mixes were planted and measured in interaction with 0, 12.5, 25, and 50 MT/Ha compost treatments. Preliminary results indicate that in a dry year all cover crop mixes were detrimental to grain yield. Compost treatments however, were shown to be beneficial to yield in both dry and more particularly in wet years. Grain quality was unaffected by either treatment. It appears that cover crops may be beneficial to dryland organic wheat farmers only when rainfall is sufficient to replenish lost soil moisture. Amending the soil with compost may prove to be the most economical option for increasing soil fertility, especially when the long-term carryover effect is taken into account.