Dynamics of upward and downward N2O and CO2 fluxes in ploughed or no-tilled soils in relation to water-filled pore space, compaction and crop presence

Sharp peaks in nitrous oxide (N₂O) fluxes under no-tillage in wet conditions appear to be related to near surface soil and crop cover conditions. Here we explored some of the factors influencing tillage effects on short-term variations in gas flux so that we could learn about the mechanisms involved. Field investigations revealed that a cumulative emission of 13 kg N₂O–N ha⁻¹ over a 12-week period was possible under no-tillage for spring barley. We investigated how reducing crop cover and changing the structural arrangement of the water-filled pore space (WFPS) by short-term laboratory compaction influenced N₂O and carbon dioxide (CO₂) fluxes in upward and downward directions in core samples from tilled and untilled soil. Increasing the downward flux of N₂O within a soil profile by changing soil or moisture conditions may increase the likelihood of its further reduction to N₂ or dissolution. We took undisturbed cores from 3 to 8 cm depth, equilibrated them to −1 or −6 kPa matric potential, incubated them and measured N₂O and CO₂ fluxes from the upper and lower surfaces in a purpose-designed apparatus before and after compaction in an uniaxial tester. We also measured WFPS, air permeability, bulk density and air-filled porosity before and after compaction. Spring barley was tested in 1999 and winter barley in 2000.Fluxes of N₂O were from 1.5 to 35 times higher from no-tilled than ploughed even where the soil was of similar bulk density. Reduction of the crop cover increased CO₂ flux and could reduce N₂O flux. The effects of structural changes induced by laboratory compaction on the fluxes of N₂O and CO₂ were not influenced greatly by the tillage and crop cover treatments. Fluxes from the upper surfaces of cores (corresponding to 3 cm soil depth, upwards direction) could be up to 100 times greater (N₂O) or 8 times (CO₂) than from the lower surfaces (8 cm depth, downwards direction). These differences between surfaces were greatest when N₂O fluxes were very high in no-tilled soil (4.2 mg N₂O–N m⁻² h⁻¹) as occurred when WFPS exceeded 80% or became blocked with water, an effect that was increased by our compaction treatment. In general N₂O fluxes increased with WFPS. The production and emission of N₂O were strongly influenced by the soil physical environment, the magnitude of the water-filled pore space and continuity of the air-filled pore space in particular, produced in no-till versus plough cultivation.     

Artificial incubation of Great bustard (Otis tarda) eggs

A trial of artificial incubation to great bustard (Otis tarda) egg was conducted from 1995 to 1997. Among the 45 collected eggs, 28 eggs were fertilized and 26 hatched, with fertilizing rate 62.2% and incubation rate 92.85%. The mean incubation-days for great bustard egg was confirmed as 24.4 (21–28 days) with the formula for caculating fresh egg weight (W=KwLB ²) and that for counting the incubated days by parents birds in field (Id=24(w−y)/0.144y). The proper incubation temperature and relative humidity were 36–37.8°C and 50–65%, respectively. The egg weights and egg size average 130.45 g and 77.4±1.42×55.5±0.65 mm respectively. The total weight loss of egg was 18.38±0.646 g, daily weight loss 0.748±0.071 g in the incubation time, with a weight loss rate of 13.6±1.02%. A linear regression equation to discribe the relationship between the egg weight and incubation days, was built,y=130.73−0.619x (x-incubation day,y-egg weight) r=−0.978. Twenty-eight hours were nassassary for great bustard embryo to complete the fledging when the were put in gas room. The mean weight of fledglings was 86.3±3.29 g(n=26). (Responsible Editor: Chai Ruihai)     

我国南方地区典型土壤有机硫矿化速率及供硫潜力研究

利用开放培养技术研究了21个中国南方代表性土壤有机硫矿化动力学。结果表明,182d培养土壤有机硫矿化量（S）为61.86～145.1mg/kg(均值88.56mg/kg),其中22.45%～48.03%(均值32.74%)来自前14d的矿化。14d和182d土壤有机硫矿化量分别占土壤总有机硫1.5%～8.2%(均值3.6%)和6.73%～19.8%(均值10.6%)。实测数据拟合方程发现,土壤有机硫矿化符合一级动力学方程S#-t=S#-0[1-e#+（-kt）]。21个土壤有机硫矿化势（S#-0）为62.76～133mg/kg(均值84.94mg/kg)。试验还发现第四纪红土母质发育的土壤有机硫供硫潜力及速率明显大于花岗岩、砂页岩和紫砂岩母质。     

土壤中掺入不同植物材料对其pH的影响

在低pH的酸性红壤、近中性的黄棕壤和高pH的盐土中加入茶叶、稻草、大豆3种植物茎叶碎末进行室内培养,研究不同植物材料在短期腐解过程中对不同土壤pH的影响。结果表明：经过14d培养后,茶叶轻微降低红壤和盐土的pH,对黄棕壤的pH没有影响;稻草亦显示出类似的趋势;大豆叶可使酸性红壤和中性黄棕壤的pH有一定程度升高,但使盐土的pH有所下降。     

栽培方式及光照条件对叶菜水培效果影响初探

以生菜及小白菜为试材,在简易泡沫槽及管道式水培模式下,探索其水培效果,并进一步在简易管道式水培模式下研究2种光照条件对叶菜生长的影响。结果表明:在同样生长条件下,2种模式水培的叶菜和基质栽培的产量差别并不显著,证实水培生产不影响这2种叶菜的产量;在2种光照条件下,生菜和小白菜都可以正常生长,可以形成一定的商品产量,但相较于200μmol/(m~2·s),100μmol/(m~2·s)光照更适合叶菜的生长,其生长量整体有较大的提升。     

石蛙孵化因子的研究

通过对石蛙蛙卵孵化因子进行研究,发现水中溶氧量、水温和水质是影响蛙卵孵化的主要因子。石蛙孵化要求:溶氧量大于5 m g/L,水温低于28 ℃,水质无污染。     

连续淹水培养条件下土壤氮素的矿化过程

在淹水条件下,采用每隔一定时间取样分析的连续培养方法,研究了土壤有机氮的矿化过程。试验表明,与间歇淋洗相比,连续培养条件下有机氮矿化过程较慢,矿化累积量较少,且达一定程度后明显降低。但该法在反映不同土壤矿化量高低、不同有机质矿化难易、不同土壤对加入有机物的矿化速率与间歇淋洗法有同样功效;两种培养方法３２ｄ的矿化量也有密切线性关系。     

Broodstock spawning and larviculture of whiting (Merlangius merlangus L.) reared in captivity

In recent years, an increasing interest in the farming of marine ‘white’ fish, such as cod, has been observed in the aquaculture industry. One species being considered for aquaculture development is whiting (Merlangius merlangus L.). With little data being available on the domestication of this species, our study aimed to characterize spawning behaviour and rhythmicity in captive broodstock and provide original data on egg incubation, embryonic development and larval rearing. The results observed through video recording showed that spawning mainly occurred at night with active courtship behaviour. Daily egg batches were collected from two separate spawning seasons, with an average fertilization success declining from 77% to 53%. Time to hatch was inversely related to the incubation temperature and occurred after 78 degree‐days (9 days at 8 °C), with emerging larvae ranging in size from 3.3 to 3.46 mm total length and hatch success ranging from 48.3% to 99.9%. In comparison with a clear water environment, a green water regime during the first days of larval rearing significantly improved larval growth and survival. These results are the first to describe spawning activity, early development and larval performances in whiting and are promising for the potential future development of whiting aquaculture.     

Predation by invasive signal crayfish on early life stages of European barbel may be limited

相似文献