Impacts of cover cropping and tillage on weed populations and soil nutrients in a sub-Arctic environment

Abstract

One of the biggest challenges for organic crop and vegetable producers is weed control. Traditional practices, such as cover cropping and tilling, aid in controlling weeds on fallow land. However, both methods can impact soil nutrient availability. For producers in sub-Arctic regions with a limited growing season, such as interior Alaska, these practices would remove valuable farm land from production for at least a year and potentially impact soil nutrients. The objective of this study was to determine cover cropping and tilling intervals that would reduce weed seedbank size without negatively influencing soil nutrient availability and taking land out of production for multiple growing seasons. A two year (2008 and 2009) study at two interior Alaska farms (UAF-AFES and Rosie Creek) measured weed density, weed seedbank size, and extractable macro and micro soil nutrients at two soil depths (0-15 cm, 15-30 cm) among seven treatments: continuous tillage (TILL), continuous cover crop (CC), tillage + middle season cover crop (TC), and cover crop + middle season tillage (CT). Two species, Hordeum vulgare L. (Albright barley) and Pisum sativum subsp. Arvense (Austrian winter field peas) were planted as cover crops. Field weed estimates were measured prior to treatment applications (tillage or planting) followed by soil core samples post treatment for weed seedbank analysis. Soil cores were collected for soil nutrient analysis at the beginning, middle and end of the growing season. In 2008 at UAF-AFES, weed density among treatments were different mid-season (p<0.05) and the subsequent growing season (p<0.05), TILL and TC treatments reduced weed populations. Weed seedbank size was different among treatments the subsequent growing season (p<0.05). In 2008 at Rosie Creek, only the subsequent growing season were there differences among treatments (p<0.05). In 2009 both study sites had no differences among treatments at any sample period. Extractable soil nutrients varied among location, year and soil depth. The highest concentrations of nitrate (NO₃-N) were measured in the tillage treatments and the lowest concentrations of NO₃-N were measured in the cover crop barley treatments (p<0.05). The research suggested that continuous tillage and tilling through the first half of the growing season has a greater impact on reducing the weed population, but can impact soil nitrate concentrations. Producers may be able to till and cover crop within one growing season, but this is highly dependent on weed density and there may be a loss of soil available nutrients for subsequent crops.