A model of nitrogen efficiency in contrasting grass-based dairy systems

Nitrogen (N) efficiency is one of the key drivers of environmentally and economically sustainable agricultural production systems. An N balance model was developed, evaluated, and validated to assess N use efficiency and N surplus and to predict N losses from contrasting grass-based dairy production systems in Ireland. Data from a 5-yr study were used to evaluate and validate the model. Grass-based and high-concentrate production systems combined with 3 divergent strains of Holstein-Friesian (HF) dairy cows—high-production North American (HP), high-durability North American (HD), and New Zealand (NZ)—were evaluated. As concentrate input increased, N surplus per hectare increased and N use efficiency per hectare decreased (23 and 10%, respectively). When the N required to rear replacement animals to maintain the production system was considered, the N surplus of the HP genetic strain was greater (156 kg of N/cow) than that of the HD (140 kg of N/cow) or the NZ (128 kg of N/cow). The model estimated N leaching of 8.1 mg of NO₃-N/L, similar to that measured by others at the same site. The model creates awareness of methods and indicators available to assess the most suitable and environmentally sustainable grass based dairy production systems.     

始兴烟区旱地烤烟氮素利用及生态经济适宜施氮量

为解决氮肥施用不合理引起的氮肥利用率低及环境恶化等问题,以烤烟品种K326为材料,研究了不同施氮水平对烤烟氮素利用率及经济性状的影响。结果表明,适当增施氮肥有利于提高烤烟产量及产值,以195 kg/hm²(N3)处理产量最高,150 kg/hm²(N2)处理产值最大。随着施氮水平的增加烤烟的氮肥偏生产力(NPFP)、氮肥吸收利用率(NRE)逐渐减小,烟叶生产效率(NTPE)、氮肥生理利用率(NPE)、氮肥农学利用率(NAE)先增加后减小,施氮水平为150 kg/hm²(N2)时,NTPE、NPE、NAE最大,此时烤烟的氮肥利用率最高。通过环境经济学的 Coase 原理和边际收益分析,综合烟叶产量、经济和生态效益,当前始兴烟区旱地烤烟适宜氮肥用量为115.10~162.13kg/hm²,相应的产量为2381.42~2677.72 kg/hm²。     

Effects of dietary crude protein concentration on late-lactation dairy cow performance and indicators of nitrogen utilization

The objectives of this study were to measure performance responses and to evaluate indictors of N utilization in late-lactation cows fed diets with incremental reductions in crude protein (CP) concentration. Holstein cows (n = 128; 224 ± 54 d in milk) were stratified by parity and days pregnant (86 ± 25 d) and randomly assigned to 1 of 16 pens in a randomized complete block design. For 3 wk, all cows received a covariate diet containing 16.9% CP [dry matter (DM) basis]. For the subsequent 12 wk, pens were randomly assigned to 1 of 4 treatments that contained 16.2, 14.4, 13.1, or 11.8% CP (DM basis). Diets were offered once daily and contained 32.5% corn silage, 32.5% alfalfa silage, 13.5% high-moisture corn, and 21.5% concentrate mix. A reduction in dietary CP was achieved by replacing soybean meal with soy hulls in the concentrate mix (DM basis). Dry matter intake, milk urea N (MUN; mg/dL), and the yield of milk urea N (g/d) decreased linearly with dietary CP. Compared with a 16.2% CP diet, a 14.4% CP diet did not alter milk yield throughout the study, but the 13.1 and 11.8% CP diets reduced milk yield after 4 and 1 wk, respectively. Furthermore, milk protein percentage was reduced for all dietary CP less than 16.2%, but this negative effect was temporary and disappeared after 7 wk for the 14.4% CP diet. In contrast, MUN adjusted to a new steady state within 1 wk for all dietary treatments. Modeling quadratic responses with a plateau led to predictions of no reduction in fat- and protein-corrected milk (32.6 kg/d) and yields of fat (1.31 kg/d), lactose (1.49 kg/d), and true protein (1.12 kg/d) until dietary CP decreased below 15.5, 15.3, 15.9, and 16.2%, respectively. In this study, MUN and the yield of MUN were highly correlated with N intake, milk protein yield, and fat- and protein-corrected milk. Surprisingly, N use efficiency (milk protein N/intake N) was not correlated with any variables related to N utilization and reached an apparent upper limit of approximately 30%. Although this observation may be associated with feeding diets deficient in metabolizable protein, late-lactation cows in this study adjusted to low dietary CP concentration better than anticipated as milk production was 2.6, 3.6, 6.4, and 8.0 kg/d higher than National Research Council (2001)-predicted metabolizable protein-allowable milk for dietary CP of 16.2, 14.4, 13.1, and 11.8%, respectively.     

控释肥对烤烟光合特性和产质量与氮钾利用率的影响

为了寻求研制优质、高效、环保的烟草控释肥料所需的参考依据,采用田间试验研究了控释肥和烟草专用复合肥对烤烟光合特性、产量与质量及氮钾利用率的影响。结果表明:(1)当施氮量由90 kg/hm²提高到150 kg/hm²时,烤烟产量和产值均显著增加,上等烟比例和均价略有下降,各叶位烤后烟叶全钾含量提高或显著提高,烟碱含量显著提高,总糖与还原糖含量显著下降;(2)与烟草专用复合肥相比,控释肥可提高烤烟旺长期以后的叶片叶绿素含量,提高旺长期烟叶净光合速率、气孔导度、胞间CO₂浓度,但对蒸腾速率无明显影响;(3)与烟草专用复合肥比较,控释肥能使烤烟产量提高3%~7%,产值提高9%~16%,各叶位烤后烟叶全钾含量提高或显著提高,烟碱含量变化不明显,总糖与还原糖含量降低。(4)控释肥有利于提高烤烟氮肥、钾肥利用率,在施氮90 kg/hm²和150 kg/hm²条件下氮肥利用率分别提高21.1和8.7个百分点,施钾180 kg/hm²和300 kg/hm²条件下钾肥利用率分别提高9.4和8.6个百分点。可见,控释肥可改善烤烟中后期光合特性,增加产量与产值,改善烤后烟叶品质,提高氮钾利用率。     

The effects of rumen nitrogen balance on nutrient intake,nitrogen partitioning,and microbial protein synthesis in lactating dairy cows offered different dietary protein sources

The aim was to study the effects of rumen N balance (RNB), dietary protein source, and their interaction on feed intake, N partitioning, and rumen microbial crude protein (MCP) synthesis in lactating dairy cows. Twenty-four lactating Holstein cows were included in a replicated 4 × 4 Latin square experimental design comprising four 20-d periods, each with 12 d of adaptation to the experimental diets and 8 d of sampling. The dietary treatments followed a 2 × 2 factorial arrangement (i.e., 4 treatments) with 2 main protein sources [faba bean grain (FB) and SoyPass (SP; Beweka Kraftfutterwerk GmbH, Heilbronn, Germany)] offered at 2 dietary RNB levels each [0 g/kg of dry matter, DM (RNB0) and ?3.2 g/kg of DM (RNB?)]. The RNB was calculated as the difference between dietary crude protein (CP) intake and the rumen outflow of undegraded feed CP and MCP and divided by 6.25. Composition of concentrate mixtures was adjusted to create diets with desired RNB levels. Each of these protein sources supplied ≥35% of total dietary CP. Both diets for each protein source were isoenergetic but differed in CP concentrations. The DM intake (kg/d) was lower for RNB? than for RNB0 in diets containing FB, whereas no differences were seen between the RNB levels for SP diets. The RNB? decreased N intake and urinary N excretion but increased milk N use efficiency in both FB and SP diets, with greater differences between the RNB levels for FB diets than for SP diets. Similarly, duodenal MCP synthesis (g/kg of digestible organic matter intake) estimated from purine derivatives in the urine was lower for RNB? than for RNB0 in FB diets but similar between the RNB levels in diets containing SP. Low RNB of approximately ?65 g/d (approximately ?3.2 g/kg of DM) in diets reduced feed intake, N balance, and performance in high-yielding dairy cows with possibly more pronounced effects in diets containing rapidly degradable protein sources.     

施氮量与基追比例对烟叶品质及氮肥利用率的影响

通过3年的田间试验,研究了不同施氮量和基追比例对烟叶化学成分、感官质量及氮肥利用率等的影响。结果表明,降低施氮量增加了烟叶的总糖、还原糖含量和糖碱比,降低了总植物碱、总氮、钾含量及钾氯比,改善了烟叶感官质量;降低施氮量显著降低了氮素积累量、来自肥料和土壤的氮量,显著提高了氮肥利用率。相同施氮量,随追肥比例增加,2009和2012年度烟叶的总糖、还原糖含量及糖碱比先增加后降低,总植物碱、总氮含量先降低后增加;2010年烟叶总糖、还原糖含量及糖碱比降低,总植物碱和总氮含量提高。2009、2010年度感官质量分别以追肥比例为70%和50%的处理最佳;2012年度高施氮量以追肥比例为70%处理最佳,低施氮量以50%处理最好。增加追肥比例显著提高了氮肥利用率。通过3年研究发现,施氮量从90 kg/hm²降至45~60 kg/hm²,追肥比例增至50%~70%可改善烟叶感官质量及提高氮肥利用率。     

多相增效磷/氮在制浆造纸废水处理中的应用

为了改善制浆造纸废水处理系统营养盐氮磷投加量大、劳动强度高、吸收率低、加药泵与输送管道易堵塞等问题,在污水处理生化系统中投加营养多相增效磷有效替代磷酸二铵,投加营养多相增效氮有效替代尿素。试验结果表明:采用北京某公司的多相增效磷和多相增效氮替代磷酸二铵和尿素作为污水处理系统营养补充剂,可促进好氧系统微生物活性增加,污泥沉降效果进一步改善,CODC r去除效果更好,处理成本明显下降,同时减轻劳动人员的工作强度。     

Starch and dextrose at 2 levels of rumen-degradable protein in iso-nitrogenous diets: Effects on lactation performance,ruminal measurements,methane emission,digestibility, and nitrogen balance of dairy cows

Our objectives were to determine the effects of readily rumen-available carbohydrate source (refined starch vs. dextrose), the level of rumen-degradable protein (RDP), and their interaction on lactation performance, ruminal measurements, enteric methane (CH₄) emission, nutrient digestibility, and nitrogen (N) balance in lactating dairy cows. Eighteen mid-lactation multiparous Holstein cows were used in this split-plot study. The main plots were created by randomly assigning 9 cows to diets of 11 or 9% RDP obtained by altering the percentage of soybean meal, expeller soybean meal, and blood meal in the diet. All diets included 16.4% crude protein. In the subplots, the effects of 0:10, 5:5, and 10:0 refined starch:dextrose ratio (% of dietary dry matter) were determined in three 3 × 3 Latin squares by randomly assigning the 9 cows in each RDP level into squares. Each period lasted 4 wk, with the last 2 wk allotted for sample collection. Carbohydrate source × RDP level interaction tended to influence dry matter intake (DMI), the concentration of urinary N, and urinary urea-N. Replacing refined starch with dextrose increased DMI, the molar percentage of ruminal butyrate and valerate, daily CH₄ production (g/d), and fecal N and decreased the molar percentage of ruminal branched-chain volatile fatty acids, feed efficiency (fat- and protein-corrected milk/DMI), and N use efficiency (milk N/intake N) but did not influence nutrient digestibility. Enteric CH₄ production was negatively related to the molar percentage of ruminal propionate but positively related to the molar percentage of ruminal butyrate. Treatments did not influence milk production responses, but cows fed 9% RDP diets had lower ruminal ammonia concentration (7.2 vs. 12.3 mg/dL) and tended to excrete less urinary purine derivatives (428 vs. 493 mmol/d) compared with cows fed 11% RDP diets, suggesting lower ruminal synthesis of microbial protein. Reducing the level of RDP in iso-nitrogenous diets had no effect on nutrient apparent total-tract digestibility, manure excretion and composition, N balance, and CH₄ production. In this study, treatments did not affect yield (20.0 g of CH₄/kg of DMI) or intensity (13.1 g of CH₄/kg of fat- and protein-corrected milk), but methane production (g of CH₄/d) was 7.0% lower and N use efficiency (conversion of intake N into milk protein) was 7.8% higher for cows fed a diet of 28.1% starch and 4.6% water-soluble carbohydrate compared with diets with lower starch and higher water-soluble carbohydrate contents.