Combining field incubation with nitrogen-15 labelling to examine nitrogen transformations in low to high intensity grassland management systems

 The ¹⁵N isotope dilution method was combined with a field incubation technique to provide simultaneous measurements of gross and net rates of N turnover in three long-term swards: unfertilized (Z) or receiving N either from N fixation as clover (C), or as 200 kg fertilizer N ha^–1 year^–1 (F). Uniform N enrichment of soil microplots was achieved with a multi-point soil injector to measure mineralization/immobilization turnover and nitrification over a 4-day incubation. Net rates of mineralization ranged between 0.6 and 2.9 μg N g^–1 day^–1 and in all three treatments were approximately half the gross rates. Nitrification rates (gross) were between 1.0 and 1.6 μg N g^–1 day^–1. In the F treatment, the turnover of NH₄ ⁺-N and NO₃ ^–-N pools was on a 2- and 4-day cycle, respectively, whereas in the N-limited treatments (C and Z) turnover rates were faster, with the NO₃ ^–-N pools turning over twice as fast as the NH₄ ⁺-N pools. Therefore, available N was recycled more efficiently in the C and Z treatments, whereas in the F treatment a higher N pool size was maintained which would be more vulnerable to leakage. A large proportion of the added ¹⁵N was recovered in the soil microbial biomass (SMB), which represented a 4–5 times larger sink for N than the plant biomass. Although the C treatment had a significantly lower SMB than the grass-only treatments, there were no differences in microbial activity. Gross rates of nitrification increased along the gradient of N input intensity (i.e. Z<C<F), and the addition of a nitrification inhibitor (C₂H₂) tended to increase microbial immobilization, but did not influence plant N uptake. In this study, the value of combining different techniques to verify net rates was demonstrated and the improved methodology for ¹⁵N labelling of soil enabled measurements to be obtained from relatively undisturbed soil under natural field conditions. Received: 25 May 1999     

可溶性硅和杀菌剂对禾谷镰孢活性影响及田间药效试验

以禾谷镰孢菌为研究对象,在室内测定不同浓度可溶性硅和不同杀菌剂及其互配对禾谷镰孢菌生长的影响。结果表明,可溶性硅浓度越大,对禾谷镰孢菌的抑制率越高,1 666.7 mg/L硅处理后对禾谷镰孢菌的抑制率达30.3%。40%咯菌腈·氟唑菌酰羟胺(0.008 mg/L)对禾谷镰孢菌的毒力最强(EC₅₀=0.008 mg/L),可溶性硅与40%咯菌腈·氟唑菌酰羟胺混配可明显降低对禾谷镰孢菌的抑制率,降幅为8.7%～12.87%;可溶性硅与5%香芹酚按不同比例混配对禾谷镰孢菌互作效应不同;可溶性硅与其他四种杀菌剂混配都能促进对禾谷镰孢菌的抑制。田间药效试验表明,除40%咯菌腈·氟唑菌酰羟胺外,其他5种杀菌剂与硅肥混合喷施防效和产量都高于单喷,其中,混合喷施2 000 mg/L可溶性硅肥+25%吡唑醚菌酯防效最好,增产最高。     

High P Availability in Brazilian Cerrado Soils Reduces Nodulation and Grain Yield of Soybean

The aim of this work was to evaluate the effect of phosphorus (P) levels on nodulation and soybean production components in Cerrado soils. The experimental design was randomized in blocks, with five replicates, and four consecutive crop seasons (2013/2014, 2014/2015, 2015/2016, and 2016/2017), being cultivated in the same experimental field area. In the first three crop seasons phosphate fertilization were carried out establishing the treatments of increasing levels of P: 0, 43.6, 87.3, 131.0, and 174.6 kg ha^?1, and an additional level (farm standard) of 42 kg ha^?1. The results of this work refer to the crop season 2016/2017 without different P application, evaluating the influence of content of previous crop seasons. The dry weight of roots, plant population, thousand grains weight, grain yield, nitrogen (N) and P content in leaves, number and dry weight of nodules were evaluated in the reproductive stages (R2 and R8) of soybean. Increasing levels of P in soil provided significant effects on nodulation, morphological components and production of soybean plants. Levels above 40 mg dm^?3 of P available in soil provided a reduction in the number and dry weight of the nodules that are highly correlated to reduction on grain yield.     

农田尺度小麦产量的空间变异研究

以潮土区2007年GPS实时定位的104个采样点小麦产量数据为基础,基于地统计学原理和方法,结合GIS空间分析技术,探讨了小麦产量的空间变异特征,建立了小麦产量的空间变异模型,形成了小麦产量的空间分布图,阐明了影响小麦产量分布不均衡的原因。研究结果表明,潮土区农田地块小麦产量平均值为47.426 g/kg,最高值为64.508 g/kg,最低值为20.163 g/kg,球状模型是本研究小麦产量连续性分布的最佳模型,其块金值/基台值为1.655,表明在变程为171.62 m范围内具有弱的空间变异性,农田地块东南部和南部为小麦产量的高值区,由此向外小麦产量逐渐降低,基本呈圈层分布,说明小麦产量具有一定的渐变性分布规律,其空间变异主要来自施肥、灌溉、管理水平等随机因素的影响。     

基于磁场调制式磁齿轮传动的永磁同步风力发电系统

提出一种基于磁场调制的同心式磁齿轮设计,将其引入风力发电系统代替传统机械齿轮,既解决了风力机与发电机的转速匹配问题,又减小了风电机组的总体积,避免了机械齿轮的振动、噪声及润滑等自身无法避免的问题,从而提高了整个风电系统的效率和工作可靠性.在对磁齿轮谐波磁场进行有限元分析的基础上,以时步有限元法为基础,实现了电动机有限元模型与磁齿轮有限元模型的联合动态仿真.设计了一台传动比为6.75的1 kW磁场调制式磁齿轮(FMMG)样机,搭建了基于FMMG传动的风力发电系统试验平台,发电机反电势计算波形与试验波形的一致性说明了电磁设计与分析结果的正确性.     

Experimental and simulated soil mineral N dynamics for long-term tillage systems in northern France

Soil N mineralization was quantified in two long-term experiments in northern France, in which no-till (NT) and conventional tillage (CT) had been differentiated for 33 years (Site 1) and 12 years (Site 2). Both sites had the same soil type but differed in crop rotation. N mineralization kinetics were assessed in situ in bare soil in both systems for 254 days (Site 1) and 555 days (Site 2) by taking frequent measurements of water and nitrate contents from soil layers and using the LIXIM calculation model. The N mineralization potential was also determined in soil samples incubated under controlled laboratory conditions. Small or non-significant differences in water and nitrate contents between NT and CT were apparent within the soil profiles on both sites. Net mineralization did not differ significantly between sites or tillage treatments. The amount of N mineralized from August 2003 to April 2004 was 67 ± 10 kg N ha⁻¹ on Site 1 and 74 ± 5 kg N ha⁻¹ on Site 2, and 161 ± 6 kg N ha⁻¹ from August 2003 to February 2005 on Site 2. The kinetics of N mineralization versus normalized time (equivalent time at constant temperature of 15 °C and water content at field capacity) were linear during the shorter period (254 days corresponding to 120 normalized days). The slope (N mineralization rate) did not differ significantly between treatments and sites, and the average rate was 0.57 ± 0.05 kg N ha⁻¹ nd⁻¹. The kinetics were non-linear on Site 2 over the longer period (555 days corresponding to 350 normalized days). They could be fitted to an exponential model with a slope at the origin of 0.62 kg N ha⁻¹ nd⁻¹. The N mineralization kinetics obtained in laboratory incubations for 120–150 normalized days were also almost linear with no significant differences between treatments. Assuming that mineralization took place in the ploughed layer (in CT) or over the same soil mass (in NT) they were in good agreement with the kinetics determined in situ on both sites. The calculated water drainage below the sampled profile was slightly greater in NT due to lower evaporation. The calculated leached N was slightly higher in NT than CT on Site 1, but did not differ between treatments on Site 2. It is concluded that N mineralization and leaching in NT and CT were similar, despite large differences in N distribution within the soil profile and a slight difference in organic N stock.     

原料配比对无土复合栽培基质水分参数的影响

为了研究不同原料配合比例对基质水分物理性质的影响,用压力膜法和土柱法测定了18种栽培基质的不同水吸力下的基质持水量及速效水含量,及不同处理的基质容重、总孔隙度、毛管孔隙度、毛管水上升高度、渗透速率等水分物理指标,用单因子及互作逐步回归方法分析了蛭石、河沙及锯末三种原料不同配比对以上水分指标的影响。结果表明原料的组成与配比对无土栽培基质的各项水分参数有密切的相关性,原料配比对水分参数的影响可以用回归方程的形式量化和表达。     

湖北四种典型土壤硫肥效应

选择黄棕壤、红壤、灰潮土和水稻土等湖北省四种主要土壤类型,对油菜和水稻分别进行盆栽和田间硫肥试验。试验结果表明:黄棕壤、红壤和灰潮土三种土壤盆栽油菜施用硫肥后,均能促进油菜的生长发育并增加油菜的干物重,但总体上施石膏的效应比施硫磺要好。水稻土田间水稻硫肥试验后,明显提高了水稻产量,但施硫磺粉的效果要比施石膏好,前者的增产率达到27.44%,后者是14.88%。试验前后土壤有效硫的变化进一步说明施用硫肥可以维持土壤硫素平衡,满足作物营养需求。使用澳大利亚KC l—40方法测定土壤有效硫含量,能反映土壤供硫水平与作物产量的相关性,这对于指导我国农业生产具有重要的意义。     

我国粮食生产的生态服务价值研究

试验研究证明农田生态系统产生生态服务价值,并在此基础上估算出我国农田生态系统因自然生态过程和人类种植业活动过程共同作用,为人类年提供19509.1亿元生态服务和经济产品总价值,其中41.9%是由农田生态系统自然过程提供和产生的,58.1%是由人类种植业活动过程产生的。目前我国统计系统计量的年度种植业总价值中仅计量了人类种植业活动过程产生的经济价值和部分由自然生态过程产生的生态服务价值,得到计量和反映的仅为64.7%,未计量的生态服务价值为35.3%,年达6881.06亿元。由于粮食生产过程中伴随产生的生态服务属公共服务范畴,国家应为粮食生产提供公共财政补贴的额度高限可达5140元/hm2·浕。     

黑龙江省农田土壤蓄水量盈亏值时空变化规律研究

利用黑龙江省33个站点近20年的农田土壤水分田间实测资料，分析得出黑龙江省农田土壤蓄水量盈亏值的时空变化规律：整个生长季全省0～50cm各层土壤蓄水量盈亏状况总体呈现东盈西亏规律。春、秋季东部盈余较大，最大盈余与亏缺之差值较大；夏季不仅呈现东盈西亏规律，且亏缺区域面积增大，程度加重，最大盈余与亏缺之差值缩小。土壤深墒相对稳定。土壤蓄水量盈亏值的垂直变化依据土壤质地的不同而呈现不同规律。