Evaluation of two N cycle models for the prediction of N mineralization from grassland soils in the UK

Abstract. The ability of two nitrogen cycle models, of contrasting complexity, to predict N mineralization from a range of grassland soils in the UK, was evaluated. These were NCYCLE, a simple mass balance model of the N cycle in UK grasslands, and CENTURY, a more complex model simulating long-term C, N, P & S dynamics in grassland ecosystems. The models were tested using field measurements of net N mineralization from a range of grassland soils (differing in soil type, history & management practice), obtained over a 2 year period using a soil core incubation technique. This method was considered to measure the total net release of mineral N from the soil organic matter over a specified time, including N which may have been recycled several times. NCYCLE consistently under-estimated mineralization rates at all sites. By contrast, there was some correlation between CENTURY predictions of net N mineralization and field measurements. This may have reflected the different abilities of the two models to simulate N recycling. Neither model, however, was able to predict adequately the effect of cultivation and reseeding on net N mineralization.     

Nitrogen uptake by ryegrass from organic wastes applied to a sandy loam soil

Sandy‐textured Mediterranean soils are invariably depleted in organic matter and supply only small amounts of N to crops. To compensate for these deficiencies, we tested the N supply from six organic wastes applied to a Cambic Arenosol in pots growing ryegrass. The results showed that the behaviour of the wastes in supplying N to a ryegrass crop grown in this soil can be predicted by observing their performance in laboratory aerobic incubations. The N made available during these incubations fitted well to a one‐pool kinetic model.     

试论含氯化肥的合理施用

根据氯对作物和土壤的影响,表明南方可以在各种作物的耐氯极限内施用含氯化肥,并需配合施用石灰和含钙磷肥;而北方旱区,特别是西北地区合理施用含氯化肥应根据每茬作物吸收带走的氯量,确定一个轮作周期内施用含氯化肥的量,保持土壤氯素的平衡,不致使土壤盐渍化。氯化铵可以就近施用,缺钾作物也能以含氯钾肥予以补充。此即本文所述氮素平衡施肥原理。     

Response of Mustard to Ethrel Spray and Basal and Foliar Application of Nitrogen

In a field trial conducted during 1992–93 and 1993–94, the effect of basal (B) nitrogen (N) (45 and 60 kg N ha⁻¹) and foliar application (F) of water (W) or 10 kg N ha⁻¹ and 400 or 600 ppm ethrel (E) (2-Chloro ethyl phosphonic acid) at 70 days after sowing was studied on leaf area index and dry mass at 90 days and pod number per plant, seeds per pod, 1000 seed weight, seed yield, oil content and oil vield at harvest of mustard ( Brassica juncea L. Czern & Coss.) cv. T-59. Recommended basal (B) application of 90 kg N ha (BN₉₀) was used as control. On the basis of 2 year data it was found that basal application of 60 kg N and foliar spray of 10 kg N ha ⁻¹ and 600 ppm ethrel gave higher values for growth and yield characteristics and enhanced seed yield and oil yield by 12.5 and 14.8%, respectively over control BN_90.     

欧式木窗专用推台铣主轴动平衡方法研究

介绍了普及型欧式木窗专用推台铣床的作用及其特性，阐述了欧式木窗推台铣床主轴的平衡理论基础．指出了该机械系统的动平衡方法，并通过试验做出了分析。     

Growth performance, energy, and nitrogen balance of weanling pigs fed a cereal-based diet supplemented with Chinese rhubarb

Forty Swiss Large White piglets of 4 weeks of age were used to determine the effect of dietary Chinese rhubarb on growth performance, as well as on energy and nitrogen metabolism by means of indirect respiration calorimetry studies. A cereal-based diet, supplemented with four different dosages of Chinese rhubarb (0.0%, 0.25%, 0.5%, 1%), was offered ad libitum to the piglets. Gaseous exchange was measured, and urine, faeces, and blood samples were taken. The addition of 0.25% dietary rhubarb increased feed intake (+32%) and daily weight gain (+67%) compared to the diet containing the greatest amount of rhubarb (1%). The piglets fed diet supplemented with 0.25% rhubarb digested and metabolised more energy and nitrogen relative to the animals of treatment 1%. As a consequence, the same group (0.25%) converted more energy and nitrogen into body protein than piglets receiving diet supplemented with 1% rhubarb. However, compared to the control group, the addition of 0.25% rhubarb to the diet resulted in not significantly alter growth performance, energy, and nitrogen metabolism of the animals.Blood parameters were not affected by the rhubarb supplementation. The dose-responding effect of Chinese rhubarb was reflected by the dry matter content of faecal samples. According to the laxative effect of higher doses of rhubarb, the addition of 1% rhubarb to the diet reduced dry matter content of faeces. This effect was well visible in practice, although not relevant in statistical terms. The addition of 0.5% dietary rhubarb had no relevant effect on growth performance or on energy and nitrogen metabolism of treated animals.     

京郊保护地秋季番茄的氮素供应及利用

研究了氮素供应水平对保护地番茄产量、养分吸收和氮素利用的影响。结果表明,氮素供应量(N)为225kg·hm~(-2)时番茄的产量最高,但随着施氮量的增加,番茄产量反而有所下降。增施氮肥对番茄地上部N、P、K的吸收没有明显的影响。在京郊传统生产条件下,保护地番茄生产相对合适的氮素供应水平(播前根层起始土壤无机氮含量+化学氮素用量)为510 kg·hm~(-2),但如果考虑番茄生长期间土壤氮素的矿化作用,番茄生产的氮素供应水平应为584kg·hm~(-2)。     

金昌水资源特点及供需平衡研究

本文通过建立金昌市人口与牲畜增长规律 ,第二、三产业的GDP增长率规律数学模型 ,计算出在长时间序列中的用水量持续增长状况及根据金昌市农业节水技术和城市生态规划 ,得到农业、生态用水量规划数据。根据水量平衡原理 ,分析了金昌市未来水量供需平衡问题 ,对指导金昌水资源利用 ,具有一定的现实意义。     

小叶锦鸡儿根瘤固氮活性的动态变化

对多年生小叶锦鸡儿不同生育期根瘤固氮能力、不同树龄小叶锦鸡儿根瘤固氮能力进行调查,结果表明:开花期固氮酶活性最高,此时土壤含氮量和植株含氮量最高;新瘤多发生于果后营养期,植株生物量的峰值出现在结实期;二年生和五年生植株的根瘤固氮能力强于三年、四年生植株,随生长年限的延长,植株生物量逐渐增大,含氮量呈小幅度下降趋势。     

中国荷斯坦牛部分乳房结构特性对泌乳性能的影响

本研究对规模化场奶牛乳房结构部分性状进行评价和测定,旨在分析其影响因素及其与泌乳性能的关系。现场评价和测定我国北方6个规模化奶牛场荷斯坦牛的乳房均衡(2 030条)、乳头长度(1 551条)和乳头位置评分(分前、后乳头,2 839条),使用SAS 9.2 GLM过程采用固定效应模型分析影响上述3个乳房性状的因素,同时分析3个单项性状对校正日产奶量和体细胞评分的影响。结果表明:场和胎次对3个乳房性状影响极显著(P0.01);前、后乳头位置和后乳头长度对校正日产奶量有显著影响(P0.05),校正日产奶量与前乳头位置评分值呈正比,与后乳头位置评分值呈反比;前乳头位置和长度对体细胞评分有显著影响(P0.05),体细胞评分随前乳头位置评分的增大而减小;5~5.5 cm的乳头长度对于校正日产奶量和体细胞评分都最佳。本研究结果为通过乳房性状选择、淘汰并提高奶牛的生产性能、乳房健康提供了参考。