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Streptococcus agalactiae is one of the important causative agents of bovine mastitis. Studies on molecular epidemiology, virulence factors and antimicrobial susceptibility profiles of S. agalactiae isolates from mastitis in China are scarce. Thus, this study was carried out to investigate prevalence of S. agalactiae associated with subclinical mastitis, to determine antimicrobial susceptibility profile, and to analyze their phenotypic and genotypic profiles. Capsular serotypes and genotypes by multilocus serotyping and virulence genes (hemolysin III, C-β protein, C-α protein, surface protein rib, hyaluronate lyase, and C5a peptidase) were determined using molecular assays. Additionally, susceptibility of S. agalactiae isolates to antimicrobial agents was accessed through standard disc diffusion method. A total of 2225 milk samples were collected from 21 large dairy herds located in 10 provinces of China. Overall, 133 (14.1%) S. agalactiae isolates were recovered from 946 (42.5%) subclinical mastitis milk samples. Serotype Ia and ST103 were the most prevalent serotypes and genotypes. Five of the six virulence genes were detected in 22.6% isolates with only two virulence genes and 6.8% of isolates with three genes. There were no significant geographical differences in the distribution of virulence genes. Moreover, 63.9% of S. agalactiae exhibited resistance to levofloxacin, 3.8% isolates were resistant to cefepime, 2.3% were resistant to chloramphenicol and ampicillin. Additionally, two ampicillin/cefotaxime/ levofloxacin-resistant isolates, one vancomycin-resistant isolate and one ampicillin/cefotaxime-resistant isolate were identified. This study concludes high prevalence of S. agalactiae from subclinical mastitis carrying virulence genes and mainly belonging to Serotype Ia and ST103. [ABSTRACT FROM AUTHOR]

To understand the mechanisms affecting water balance partitioning during fallow on drylands could improve the fallow management practices in arable land ecosystems. A three-year field experiment was conducted to evaluate the effects of field management regimes on water balance partitioning and fallow efficiency during the fallow periods under a winter wheat (Triticum aestivum L.) fallow system on the Loess Plateau, China. The fallow management regimes tested were: (i) conventional practice, (ii) catch cropping, and (iii) no tillage with wheat straw mulching. A process-oriented ecosystem model (CoupModel) was calibrated with field measurements and then used to generate comparative simulations of the water balance partitioning. The simulations indicated that mulching increased the soil water storage change by 38-71 mm during the three fallow periods, thus resulting in higher fallow efficiency by 9-12%, and decreased soil evaporation by 22-72 mm, compared with the conventional practice. Furthermore, water reached deeper horizons, resulting in 7 mm deep percolation in a wet year under mulching but not under conventional practice or catch cropping. The simulation results also showed that the catch cropping decreased the soil water storage change by 13-21 mm, although it lowered soil evaporation by 11-51 mm, and altogether reduced the fallow efficiency by 3-9%, compared to conventional practice. On the Loess Plateau of China mulching proved to be a sound measure for ensuring certain fallow efficiency and possibly benefit to the water cycle, while catch cropping negatively partitioned the water balance. The catch cropping under mulching might be another management regime to be considered. [ABSTRACT FROM AUTHOR]

labile organic pools, soluble organic matter and soil microbial biomass are sensitive to changes in soil management and therefore good indicators of soil quality. Effects of a 17-year long-term fertilization on soil microbial biomass C (SMBC) and N (SMBN), soluble organic C, and soluble organic N during the maize growing season were evaluated in a loess soil (Eum-Orthic Anthrosol) in northwest China. The fertilization treatments included no fertilizer (CK), inorganic N, P, and K fertilizer (NPK), cattle manure plus NPK fertilizer (MNPK), and straw plus NPK fertilizer (SNPK). Our results showed that C storage in the 0-20 cm soil layer was 28% to 81% higher in the fertilized treatments compared to the unfertilized treatment. In the 0-10 cm soil layer, SMBC and SMBN in the three fertilized treatments were higher than in the unfertilized treatment on all sampling dates, while microbial biomass C and N in the 0−10 cm soil layers were the highest at grain filling. In the same soil layer, soil-soluble organic C generally decreased in the order MNPK > SNPK > NPK > CK, while soluble organic N was the highest in the MNPK followed by the SNPK treatment. There was no significant difference in soluble organic N in the NPK and CK treatments throughout most of the maize growing season. Changes in soluble organic N occurred along the growing season and were more significant than those for soluble organic C. Soluble organic N was the highest at grain filling and the lowest at harvest. Overall, our results indicated that microbial biomass and soluble organic N in the surface soil were generally the highest at grain filling when maize growth was most vigorous. Significant positive relationships were found between soluble organic C and SMBC and between soluble organic N and SMBN. [ABSTRACT FROM AUTHOR]

Microbial biomass phosphorus (MBP) and its relationships with other biological and chemical properties were studied on loess soil with an 11-year long-term fertilization experiment. The results indicated that inorganic fertilizers (F) improved soil microbial biomass carbon (MBC), nitrogen (MBN), and MBP levels and F plus maize stalk (SNPK) improved MBC and MBN. Manuring markedly increased soil MBC, MBN, and MBP levels. Fertilization decreased the ratios of MBC/MBN, MBC/MBP, and MBN/MBP. Microbial biomass phosphorus was positively and linearly correlated with MBC, MBN, organic carbon (SOC), total phosphorus (TP), water-soluble P, and Olsen P but negatively correlated with soil pH. Microbial biomass phosphorus constituted 2% of TP on control (CK) and inorganic fertilizer treatments and 12% on manure plots. Microbial biomass phosphorus to Olsen P ratios were 50% on CK, F, and SNPK and 80% on manure treatments. Measurements of MBP in soil containing high Olsen P were subject to analytical problems of unknown reasons. [ABSTRACT FROM AUTHOR]

Wheat, rice, and maize collectively provide the bulk of energy and protein to the human diet worldwide. Over the last seven decades, China increased 5.8-fold the aggregated production of the three cereals, but further gains are required to meet the predicted demand of 776 Mt. by 2030. Here, we report the rate of genetic gain in yield of 0.65% year-1 for wheat between 1937 and 2012, 0.69% year-1 for rice between 1934 and 2011, and 0.77% year-1 for maize between 1950 and 2014 in China. National farm yield in the same periods increased 1.38% year-1 for wheat, 1.15% year-1 for rice and 1.32% year-1 for maize. Hence, genetic improvement (G) accounted for 47%-60% of the increase in farm yield, with improved management (M) and G × M interaction accounting for the balance. The absolute rate of genetic gain (kg ha-1 year-1) was proportional to environmental potential. Genetic gain in nitrogen utilization efficiency (yield per unit nitrogen uptake) was significant for all three crops and was achieved at the expense in grain N concentration that decreased at 0.19% year-1 in rice and 0.47% year-1 in maize. To guarantee future food security and environmental sustainability, breeding and agronomic efforts need to increase the rate of gain in yield and revert the declining trends in grain protein by improving nitrogen uptake and nitrogen harvest index. [ABSTRACT FROM AUTHOR]

This study assessed changes in nitrogen (N) and phosphorus (P) uptake and partitioning in response to selection for yield in milestone varieties of Chinese winter wheat (Triticum aestivum L.). We established a factorial trial combining 11 nutrient–water regimes with three (2013–14) and five (2014–15) varieties released from 1970 to 2005. Grain yield increased at a rate of 0.46% year–1, with no apparent increase in the uptake of nutrients. Nitrogen harvest index did not change, and P harvest index increased at a rate of 0.15% year–1. Consequently, yield per unit N uptake and yield per unit P uptake increased at similar rates (0.4% year–1) at the expense of nutrient concentration in grain, which declined at a rate of 0.47% year–1 for N and 0.31% year–1 for P. No trends in N nutrition index were found. Selection for yield in wheat increased the yield per unit nutrient uptake at the expense of grain nutrient concentration. Further gains in yield need to be matched by increasing N uptake to maintain grain protein. Dilution of P in grain needs to be considered in terms of the putatively undesirable role of phytate for human nutrition, and the need for P reserves in seed for crop establishment. [ABSTRACT FROM AUTHOR]

Improving N use efficiency (NUE) and reducing the negative impact of N fertilization on the environment are essential for sustaining agricultural production in many intensive farming regions around the world. The objective of this research was to investigate the effect of various fertilization regimes on yield, N uptake, and NUE by maize (Zea mays L.) in long-term (15-yr) experiments performed at four sites (Changping, Zhengzhou, Yangling, and Qiyang) in China. Eight treatments were examined: unfertilized control (CK); inorganic fertilizer (manufactured source) N, N and P, N and K, and N, P, and K; inorganic N, P, and K with manure (NPKM); 1.5′ the rate of NPKM (1.5NPKM); and N, P, and K with maize stover returned (NPKS). Compared with inorganic fertilization, mixed inorganic and manure fertilization (NPKM and 1.5NPKM) resulted in more stable and significantly higher yield and NUE as well as increases in soil nutrient storage at all sites, with the most significant improvement in the acid soil (pH = 5.7) at Qiyang. Phosphorous was identified as one of the most important limiting factors in maize NUE because the NUE at all four sites increased from about 20 to 45% by increasing the available P in the soil. Higher NUEs (up to 70%) were observed mostly from the continuous manure applications. We conclude that manure and P applications are the most important and effective nutrient management strategies for both the acid and alkaline soils in this study for maize production in China. [ABSTRACT FROM AUTHOR]

The critical value of soil Olsen-P is the point above which the probability of crop yield response to fertilizer P is small or nil. Determining this critical value is fundamental when making appropriate P fertilizer recommendations. In this study, the critical values were determined for continuous maize ( Zea mays L.)-winter wheat ( Triticum aestivum L.) cropping systems from a 15-year field experiment across three sites in China using linear-linear, linear-plateau and Mitscherlich models. The mean critical values for maize using the three models ranged from 12.1 to 17.3 mg P kg−1 (average 15.3 mg P kg−1) and for winter wheat from 12.5 to 19.0 mg P kg−1 (average 16.3 mg P kg−1) among study sites. The mean critical value for maize was approximately 7% lower than that for winter wheat across all sites based on the three models. Critical values identified by the Mitscherlich model were 1.4 to 2.1 times those from linear-linear and 1.3 to 1.9 times of those from linear-plateau and were crop and site dependent. There was a significant negative correlation ( P < 0.05) between the mean critical value from the three models and the observed P uptake by either maize or wheat. Our study shows that the critical values can vary with sites, crops and models used, and thus caution should be taken when selecting the most appropriate one when making P fertilizer recommendations for agronomic return and to minimize chances of negative environment impact from overfertilization. [ABSTRACT FROM AUTHOR]