[Characteristics of soil nitrate accumulation and leaching under different long-term nitrogen application rates in winter wheat and summer maize rotation system.]

Winter wheat and summer maize were the main crops in the North China Plain. While intensive farming system could generally achieve high yield, the perennial large amounts of nitrogen (N) fertilization application cause environmental problems including NO₃^--N accumulation and leaching at deep soil layer. Here, the effects of different N application rates on soil NO₃^--N accumulation and leaching in winter wheat-summer maize cropping system were investigated from 2010 to 2016 at Qingyuan County, Hebei Province, China. There were five treatments with N application rates at 0 (N₀), 100 (N₁₀₀), 180 (N₁₈₀), 255 (N₂₅₅) and 330 (N₃₃₀) kg·hm^-2. Results showed that crop yield and soil N status significantly varied among treatments for both wheat and maize after each harvest, respectively. Soil NO₃^--N were accumulated during winter wheat growing season and leached to deeper soil during summer maize growing season. Moreover, the soil NO₃^--N accumulation amount in the 90 to 180 cm soil profile decreased with the decreases of N inputs (N₃₃₀ > N₂₅₅ > N₁₈₀ > N₁₀₀ > N₀). Soil NO₃^--N could be leached to 990 cm soil depth. There were six NO₃^--N accumulation peaks in the soil profile, with the peaks presenting at deeper soil profile with higher N fertilization rate. The deepest peak appeared at 840 cm soil depth with the N application rate of 330 kg·hm^-2. From the distribution of NO₃^--N accumulation in the soil profile, only around 10% of total NO₃^--N was accumulated between 0-90 cm soil depth, while the rest accumulated below 90 cm, which could not be largely absorbed by plants. Therefore, NO₃^--N leaching during summer maize growing season was serious and it was greater with higher N fertilization rate which might lead to increased risk of underground water contamination. In terms of balanced crop yield and soil NO₃^--N accumulation, the rate of 180 kg·hm^-2 would be the optimum one in areas with similar cultivation and environmental conditions to the present study.

[Effects of different cultivation patterns on yield, nitrate accumulation and nitrogen balance in winter wheat and summer maize rotation system.]

This study investigated the impacts of four cultivation patterns including farmer practice, high yield and high efficiency practice, super high yield practice, and super high yield and high efficiency practice on yields, soil nitrate and nitrogen (N) balances in 3 winter wheat-summer maize rotations with straw returning in Hebei Province. Results showed that the super high yield practice was identified with greatest winter wheat and summer maize yields, followed by high yield and high efficiency practice, and super high yield and high efficiency practice, which were all greater than that of farmer practice. The N use efficiency of high yield and high efficiency practice was significantly greater than the other cultivation patterns. The total nitrate accumulation in 0-400 cm soil of these cultivation patterns reached 768.4-1133.3 kg·hm^-2, where 80%-85% of the accumulated nitrate were in 90-400 cm soil. Meanwhile, the nitrate leaching was observed in all cultivation patterns and nitrate accumulation peaks at 120-150 cm and 270-330 cm were found. Soil nitrate content of high yield and high efficiency practice was less than 30 mg·kg^-1 and generally lower than other cultivation patterns, which to some extent reduced the environmental risk. In addition, nitrate surplus in 0-90 cm soil during winter wheat season was lower than that during summer maize season, and the high yield and high efficiency practice had the lowest apparent nitrogen loss. Overall, the high yield and high efficiency practice was evaluated to be the best cultivation pattern in consi-deration of yield, nitrogen use efficiency and nitrate accumulation in soil, but there was still certain achievable improvement potential.

Methylation analysis of CXCR1 in mammary gland tissue of cows with mastitis induced by Staphylococcus aureus

Mastitis is the most important disease in the global dairy industry, and causes large economic losses. Staphylococcus aureus is one of most common pathogens that cause bovine mastitis. CXCR1 has been implicated as a prospective genetic marker for mastitis resistance in dairy cows; CXCR1 expression significantly increases when cows have mastitis. To investigate the mechanisms involved in its increased expression, bisulfite sequencing polymerase chain reaction (PCR) was used to detect the methylation status of CXCR1 CpG island, and quantitative fluorescence PCR was used to detect CXCR1 expression in bovine mammary tissue induced with S. aureus in three Chinese Holstein cows. No CpG island was found for bovine CXCR1 in the upstream 2-kb region, whereas one CpG island that contained 13 CpG sites was found in exon 1 of CXCR1. All of the CpG sites were under hypermethylation from 90 to 100% in the mammary tissues. When the mammary gland mRNA expression of CXCR1 was 12.10-fold higher in infected cow quarters than in uninfected quarters, the methylation levels of the CpG site at position 519 were significantly lower in the infected quarters than in the uninfected quarters. Pearson correlation analysis showed that the methylation level at position 519 was significantly negatively correlated with the CXCR1 mRNA expression level (P < 0.05). These results indicate that the methylation of the CpG site at position 519 may regulate CXCR1 expression in cows with mastitis induced by S. aureus, but further studies are needed to elucidate the mechanisms involved.