Urea application enhances cadmium uptake and accumulation in Italian ryegrass.

Italian ryegrass (Lolium multifolorum Lam.) has a potential phytoextraction capacity for cadmium (Cd), which is considered as the most toxic heavy metal (HM) pollutant in the farmland. The promotion effect of urea application on Italian ryegrass growth has been clarified, while it is not clear whether and how urea application affects Cd accumulation in Italian ryegrass under Cd stress. A 2-year pot experiment was conducted to investigate the effect of urea application on Cd accumulation and related mechanisms by uptake inhibition and kinetics experiments. The results showed that both shoot biomass and Cd concentration under Cd stress were increased by up to 213.37% and 84.74% in 2016 and 38.15% and 47.11% in 2017 after urea application, respectively. The shoot Cd accumulation reached maximum value (910.23 and 630.09 µg pot-1 in 2016 and 2017, respectively) at the level of 300 kg ha-1 urea. Superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were significantly increased by urea application. Compared with control group, urea application significantly improved inhibition ratio of 2, 4-dinitrophenol (DNP) rather than LaCl3 and Ca2+. Cadmium uptake kinetics experiment showed that urea application significantly decreased the Km value and improved the α value (P < 0.01), but no significant effect on the Vmax value (P > 0.05). In conclusion, we proposed that the higher affinity to Cd2+ of the membrane transporter after urea application promoted the active uptake of Cd, which contributed to the effective Cd accumulation capacity in Italian ryegrass.

Adding sweet potato vines improve the quality of rice straw silage.

Rice straw and sweet potato vines are the main by-products of agricultural crops, and their disposal creates problems for the environment in the south of China. In order to establish an easy method for making rice straw silage successfully, experiments were conduct to evaluate fermentation quality and nutritive value of rice straw silages ensiled with or without sweet potato vine. Paddy rice straw (PR) and upland rice straw (UP) were ensiled alone or with sweet potato vines (SP) by a ratio of 1:1 (fresh matter basis), over 3 years. Compared with rice straw silages ensiled alone, the mixed-material silages (PR + SP, UR + SP) showed higher fermentation quality with lower propionic acid content and NH3 -N ratio of total N, and higher (P < 0.05) concentrations of lactic acid and acetic acid, resulting in decrease (P < 0.05) of dry matter loss and higher (P < 0.05) in vitro ruminal dry matter digestion. When the fermentation quality, chemical composition and in vitro rumen fermentation characteristics were considered, ensiling would be an effective way of utilization of rice straw and sweet potato vines in the regions where rice and sweet potato are harvested at same season, and the sweet potato vines have the potential to improve rice straw fermentation quality with low water soluble carbohydrate content in south of China.

Effects of chemical additives on the fermentation quality and N distribution of alfalfa silage in south of China.

In order to better utilize the last cut alfalfa harvested before killing frost in a high moisture environment, the effects of chemical additives on the quality of alfalfa silage were studied in south of China. The alfalfa was freshly harvested at branching stage, and wilted by dry matter content of about 300 g/kg (fresh matter basis). Silage was prepared by using a small-scale silage fermentation system, where sucrose, potassium citrate, sodium carbonate, formic acid, acetic acid and propionic acid were used as silage additives, and no additives served as control. These silos were stored at ambient temperature (5-20°C), and the silage qualities were analyzed after 120 days of fermentation. All additive treatments affected the chemical composition and N distribution, increased the water-soluble content and crude protein contents, decreased non-protein nitrogen (NPN) content, and enhanced the in vitro ruminal dry matter digestibility (except for sodium carbonate). Silages treated with organic acids were preserved with significantly (P < 0.05) lower pH value, ethanol content and NPN content compared with control. When the fermentation quality, chemical composition and N distribution were considered, the treatment with sucrose or organic acids resulted in high quality of alfalfa silage ensiled before killing frost, with formic acid having the best effect.