Compost Impacts On An Irrigated Potato Production System.

The addition of compost to cropping systems increases sustainability and crop productivity by building soil organic matter and improving soil quality. However, using organic amendments such as compost to increase crop production may also influence the competitive ability of agriculturally significant weeds that will reduce crop yield and quality. A field study was established in 2010 in Montcalm County to investigate the effect of compost on weed competition in potato. Three rates of cured dairy compost (0 kg C ha^-1, 4000 kg C ha^-1, and 8000 kg C ha^-1) were applied and incorporated to a 10 cm depth in late April, and ‘Snowden’ variety potatoes were planted mid-May. The starter fertilizer rate was adjusted based on expected compost N mineralization. Plots received three nitrogen (N) applications in addition to starter fertilizer at planting for a total of 205 kg N ha^-1. Plots were irrigated to maintain field capacity. Hairy nightshade, giant foxtail, or common lambsquarters seedlings were transplanted into the potato row at 5.3 weeds m row^-1 at cracking. Plant height and biomass were recorded bi-weekly. Potatoes were harvested and graded following vine senescence. Data was subjected to analysis of variance with significance determined at α<0.05. Adding 8000 kg C ha^-1 of compost increased total and marketable tuber yield by 15% when compared to the non-amended treatment. Weeds reduced potato yield, regardless of compost application. Observed yield differences were not due to N availability because each system was balanced for N application. The 8000 kg C ha^-1 compost treatment had higher levels of potassium, which implies potassium was limiting in the lower and no compost production systems. Compost addition did not increase weed biomass or weed seed production of any species compared to when no compost was applied. Common lambsquarters reduced potato yield by 48%, whereas giant foxtail and hairy nightshade reduced potato yield by 20%. Compost may increase potato yield without increasing the competitiveness of weeds.