Response of Irrigated Potato (Solanum tuberosum L.) to Green Manure Cover Crops.

Green manure cover crops preceding potatoes have been reported to improve potato tuber yield and quality depending on the type of the preceding crop. Studies were conducted in Colorado, USA, to evaluate the effect of twelve green manure cover crops on potato tuber yield, tuber size distribution, and quality of the Russet Norkotah potato variety. Barley (B), barley + compost (B+C), sunflower (S), sordan 79 (SD), sordan 79 with the above ground biomass removed for hay (SDH), sorghum sudan (SS), canola (C), mustard (M), peas (P), and annual rye grass (RY), were the green manure crop treatments that preceded the 2008 potato crop. SS, C, and RY were replaced with radish (R), sordan mix (sordan 79 + radish; SM), and winter wheat (WW), for the green manure cover crop treatments that preceded the 2009 potato crop. A wet fallow ground (fallow) was maintained as a control plot. In 2008, potato planted after SDH produced 20% higher total tuber yield than the average of all other treatments. Maximum marketable tuber yield was obtained when potatoes were planted after SDH, B, and RY. Potatoes that followed P and fallow produced more tuber external defects.  In 2009, maximum total and marketable tuber yields were produced when B, S, SDH, SM, WW, and fallow preceded potatoes. B, B + C, P, and R produced tubers with the highest percentage of external defects. Fallow, B, B + C, P and WW produced more tuber internal defects and tuber rot. Data from these studies indicate that green manure cover crops can be used to influence tuber size distribution in potatoes. When potato is preceded by sordan 79 with the above ground biomass removed for hay, or by sunflower, maximum tuber yields are obtained with less tuber defects.