Effects of Continuous Applications of Digested Pig Biogas Slurry on Brassica napus Yields and Rapeseed Quality

Applying biogass slurry, rich in nutrients, could promote crop growth and yields. However, there is little information available about its long-term effects on plants. A three-year experiment was designed to evaluate the effects of biogas slurry applications on yields and quality of rape(Brassica napus) at Guyi Town, Qionglai City, Sichuan Province. The results indicated that over years the rape yields decreased in the treatments with chemical fertilizer, but significantly increased with biogas slurry applications. The highest yields can be obtained in the treatments with biogas slurry rates of 101 250～132 500 kg·hm-2, which was applied 37% for the base fertilizer, 47% for seed bed, and 16% for bolting stage. The rape yields were 157.54%, 365.50%, 254.10% higher in biogas slurry than in CK(only water application)treatments and 38.26%, 55.50%, 155.57% higher than in chemical fertilizer in 2010, 2011, and 2012, respectively. The contents of protein, oil, oleic acid, erucic acid and ghccesino of the rapeseeds were at the best levels in biogas slurry treatments. The content of oil in the rapeseeds was higher than the national level I standard, while the content of erucic acid was less than1%, meeting the international standard. Also, the applications of biogas slurry maintained the contents of mineral elements, such as Fe, Mn, Cu, Zn, Ca, and Mg, at a higher level than other treatments.