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41.
J. Verloop G. J. Hilhorst J. Oenema H. Van Keulen L. B. J. Sebek M. K. Van Ittersum 《Nutrient Cycling in Agroecosystems》2014,98(3):267-280
This paper describes the dynamics of soil N mineralization in the experimental intensive dairy farming system ‘De Marke’ on a dry sandy soil in the Netherlands. We hypothesized that knowledge of the effects of crop rotation on soil N mineralization and of the spatial and temporal variability of soil N mineralization in a farming system can be used to better synchronize N application with crop N requirements, and hence to increase the recovery of applied N and to reduce N losses. Soil N mineralization was recorded continuously in the soil layer 0–0.30 m, from 1992 to 2005, using a sequential in situ coring technique on six observation plots, of which two were located in permanent grassland and four in crop rotations with a 3 year grassland phase and an arable phase of 3 or 5 years, dominated by maize. Average annual soil N mineralization was highest under permanent grassland: 381 kg ha?1 and lowest under ≥3rd years arable crops: 184 kg ha?1. In temporary grassland, soil N mineralization increased in the order: 1st year, 2nd year, 3rd year grassland and in arable crops after grassland mineralization decreased in the order: 1st year, 2nd year, ≥3rd years. Total mineral N input, i.e. the sum of N mineralization and mineral N supply to soil, exceeded crop N requirements in 1st year maize and was lower than the requirements in 1st year temporary grassland. N mineralization in winter, outside the growing season, was 77 kg ha?1 in maize and 60 kg ha?1 in grassland. This points at the importance of a suitable catch crop to reduce the susceptibility to N leaching. Temporal and spatial variability of soil N mineralization was high and could not be related to known field conditions. This limits the extent to which N fertilization can be adjusted to soil N mineralization. Variability increased with the magnitude of soil N mineralization. Hence, situations with high soil N mineralization may be associated with high risks for N losses and to reduce these risks a strong build-up of soil organic N should be avoided. This might be achieved, for instance, by fermenting slurry before application on farmland to enhance the fraction mineral N in slurry at the expense of organic N. 相似文献
42.
Analysis of structural determinants of the stability of thermolysinlike proteases by molecular modelling and site-directed mutagenesis 总被引:1,自引:0,他引:1
Veltman Oene R.; Vriend Gert; Middelhoven Pieter J.; van den Burg Bertus; Venema Gerard; Eijsink Vincent G.H. 《Protein engineering, design & selection : PEDS》1996,9(12):1181-1189
The thermolysin-like protease (TLP) produced by Bacillus stearothermophilusCU21 (TLP-ste) differs at 43 positions from the more thermallystable thermolysin (containing 316 residues in total). Of thesedifferences, 26 were analysed by studying the effect of replacingresidues in TLP-ste by the corresponding residues in thermolysin.Several stabilizing mutations were identified but, remarkably,considerable destabilizing mutational effects were also found.A Tyr-rich three residue insertion in TLP-ste (the only deletional/insertionaldifference between the two enzymes) appeared to make an importantcontribution to the stability of the enzyme. Mutations withlarge effects on stability were all localized in the ßpleatedN-terminal domain of TLP-ste, confirming observations that thisdomain has a lower intrinsic stability than the largely -helicalC-terminal domain. Rigidifying mutations such as Gly58 Alaand Ala69 Pro were among the most stabilizing ones. Apart fromthis observation, the analyses did not reveal general rulesfor stabilizing proteins. Instead, the results highlight theimportance of context in evaluating the stability effects ofmutations. 相似文献
43.
Crop residue,manure and fertilizer in dryland maize under reduced tillage in northern China: II nutrient balances and soil fertility 总被引:1,自引:0,他引:1
Xiaobin Wang Willem B. Hoogmoed Dianxiong Cai Udo D. Perdok Oene Oenema 《Nutrient Cycling in Agroecosystems》2007,79(1):17-34
A long-term experiment was carried out in the dryland of northern China to assess the effects of applications of maize stover,
cattle manure and NP (1:0.44) fertilizer on partial nitrogen (N), phosphorus (P) and potassium (K) balances, extractable soil
N (SEN), P and K, and soil organic matter (SOM) in a spring maize cropping system, under reduced tillage conditions. The experiment
was set-up according to an incomplete, optimal design, with three factors at five levels and 12 treatments, including a control
with two replications. Statistical analyses using multiple regression models showed that the partial N, P and K balances were
strongly influenced by annual variations in the amounts of soil water at seeding (SWS) and growing season rainfall (GSR).
Most treatments had positive P but negative N and K balances. Cumulative P and K balances were reflected in extractable soil
P (P-Olsen) and K (exchangeable K), but the weak relationships indicated that the sorption of P and buffering of K were strong.
Cumulative balances of effective organic carbon (C) were weakly related to soil organic C (SOC) content after 12 years. Negative
C balances were related to decreases in SOC, but positive C balances were not translated into increases in SOC. The analysis
of nutrient balances and soil fertility indices revealed that nutrient inputs in most treatments were far from balanced. It
is concluded that the concepts of ‘ideal soil fertility level’ and ‘response nutrient management’ provide practical guidelines
for improving nutrient management under the variable rainfall conditions of dry land areas in northern China. 相似文献
44.
Compliance with current phosphorus (P) fertilization recommendations would ultimately result in a soil P status of agricultural land in the agronomical optimal range. In practice though there are large variations in soil P status among farms and fields. Our study aimed at increasing the understanding of the cause-effect relationships for these spatial variations in soil P test values. The Northeast Polder in The Netherlands was chosen as study area, because of its characteristics. It was reclaimed from the sea in 1942, has one major soil type (calcareous loam), well-educated farmers, one dominant land use (arable farming) and little pressure to use animal manure. We tested the hypothesis that in this polder mean P status has developed towards the optimal range with a small standard deviation. We analysed available soil P analyses records (>30,000) from the period ~1950?C2004, and conducted a questionnaire about fertilization practices among farmers. The soil P(w) values increased steadily and significantly from the agronomical range ??low?? to ??ample sufficient?? from 1971 to 2004. Variation within and between farms also increased. About 45?% of the farmers appear to aim at a soil P status above the agronomical optimal range, and >70?% of the farmers indicated that they are uncertain whether the obtained increase in soil P(w) status is actually plant available P. In conclusion, our hypothesis was rejected: for farmers in our study area, risk avoidance seems the decisive factor for pursuing a soil P status above the agronomical optimal range. If even well-educated farmers question the official fertilizer recommendations and aim at higher levels of soil P fertility, also other farmers worldwide may continue to aim such supra-optimal soil P status. This is undesirable given the diminishing P resources. Possible solutions could be to define more refined P fertilization recommendations and better and more intensified communication of those recommendations to farmers and their advisers. 相似文献
45.
G. L. Velthof I. E. Hoving J. Dolfing A. Smit P. J. Kuikman O. Oenema 《Nutrient Cycling in Agroecosystems》2010,86(3):401-412
Managed grasslands are occasionally ploughed up and reseeded in order to maintain or increase the sward productivity. It has
been reported that this renovation of grassland is associated with a flush of soil organic nitrogen (N) mineralization and
with a temporary increase in soil mineral N contents. Here, we report on the effects of method and time of grassland renovation
on herbage yield, nitrate (NO3
−) leaching and nitrous oxide (N2O) emission. Field experiments were carried out at three sites (two sandy soils and a clay soil) in the Netherlands for three
years. Renovation of grassland increased the percentage of Perennial ryegrass from 48–70% up to more than 90%. However, averaged
over three years, dry matter yields were higher for the reference (not reseeded) swards (on average 13.6 Mg ha−1 for the highest N application rate) than for the renovated grasslands (12.2–13.1 Mg ha−1 dry matter). Grassland renovation in April did not increase N leaching in comparison to the reference. However, renovation
in September increased the risk of leaching, because mineral N contents in the 0–90 cm were in November on average 46–77 kg N
ha−1 higher than in the reference. Contents of dissolved organic N (DON) in the soil were not affected by renovation. Renovation
increased N2O emissions by a factor of 1.8–3.0 relative to the reference grassland. Emissions of N2O were on average higher after renovation in April (8.2 kg N2O-N ha−1) than in September (5.8 kg N2O-N ha−1). Renovation without ploughing (i.e. only chemically destruction of the sward) resulted in a lower percentage of perennial
ryegrass (60–84%) than with ploughing (>90%). Moreover, N2O emissions were higher after renovation without ploughing than with ploughing. Clearly, farmers need better recommendations
and tools for determining when grassland renovation has beneficial agronomic effects. Losses of N via leaching and N2O emission after renovation can probably not be avoided, but renovation in spring in stead of autumn in combination with ploughing
and proper timing of fertilizer application can minimize N losses. 相似文献
46.
Hans J P Marvin Cornelis F Krechting Eibertus N van Loo Charles H A Snijders Arjen Lommen Oene Dolstra 《Journal of the science of food and agriculture》1996,71(1):111-118
The organic matter (OMD) and cell wall (CWD) digestibility of stalks of 25 different maize samples were determined in an in vitro assay using rumen fluid. The stalk OMD and CWD varied between 62–80% and 44–62%, respectively. The free phenolic acids formed in the liquid phase during fermentation in in vitro incubations were assessed by HPLC and 1H NMR. The following nine phenolic acids could be demonstrated to be present: p -hydroxybenzoic (HBA), p -hydroxyphenylacetic (HPAA), vanillic (VA), syringic (SYRA), 3-(4-hydroxyphenyl)propionic (HPPA), p -coumaric (PCA), ferulic (FA), phenylacetic (PAA) and 3-phenylpropionic (PPA) acids. Large variation was observed among the maize samples for all phenolic acids identified. The most abundant phenolic acids, PPA, PAA and HPAA were present in concentrations ranging from 0·57 to 1·41 mM, 0·32 to 0·46 mM, and 71 to 105 μM, respectively, and were present as free monomeric molecules. HBA concentrations ranged from 6·9 to 21·1 μM and this acid was also present as free molecules. The other phenolic acids could only be observed after NaOH treatment of the liquid phase and were detected in minor amounts (0 to 12 μM). Correlation studies revealed a negative relation between digestibility and NaOH labile esters in the medium (ie PCA, FA, VA and SYRA esters) and a positive relationship between digestibility and PPA and PAA. When path analysis was applied, an inverse effect of PCA esters in the medium on both OMD and CWD ( r =-0·71 and −0·56, respectively) was observed and a high positive effect of PPA acid on CWD ( r =+0·67). Principal component analysis revealed close associations between released phenolic acid esters, neutral detergent fibre, and cell wall esters of PCA and FA. 相似文献
47.
Nitrogen is the most limiting plant nutrient in Vertisols in Kenya. Soil properties, climatic conditions and management factors
as well as fertilizer characteristics can influence fertilizer nitrogen (N) use efficiency by crops. Vertisols, characterized
by low-basic water infiltration rate, are prone to waterlogging under sub-humid and humid conditions. We determined effects
of drainage, N source and time of application on yields, nutrient uptake and utilization efficiencies by maize grown on Vertisols
in sub-humid environments. Treatments comprised two furrows (40 cm and 60 cm deep) and a check (i.e., no furrow), calcium
nitrate to furnish NO3-N, ammonium sulphate to supply NH4-N at 100 kg N ha−1, a control (i.e., no fertilizer N), and fertilizer N application at sowing, 40 days after sowing, and split (i.e., half the
rate at sowing and half 40 days after sowing). A split-plot design was used in which drainage formed the main plots and N
source × time of N application formed the sub-plots. Higher grain and total dry matter yields, harvest index, leaf N content,
uptake of N, P and K, as well as N agronomic (NAE) and recovery (NRE) efficiencies were obtained from drained compared to
undrained plots. The increase ingrain yields as a result of drainage varied from 31 to 45% for control, 35 to 43% for NO3-N, and 16 to 21% for NH4-N treatments. Drainage resulted in total N uptake increases from 50 to 80 kg N ha−1 in control plots, 80 to 130 kg N ha−1 in NO3-N treated plots, and 90 to 130kg N ha−1 in NH4-N treated plots. Ammonium-N source was superior to NO3-N source in terms of higher yields, NAE, and NRE in undrained plots, but the two N sources behaved similarly in drained plots.
Delayed or split NO3-N application gave higher yields, NAE and NRE than when all N was applied at sowing in undrained plots. There was no difference
between 40 cm and 60 cm deep furrows in terms of crop yields and nutrient use efficiencies. Thus, draining excess water with
furrows at least 40 cm deep is essential for successful crop production in these Vertisols under sub-humid conditions.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
48.
The hydrolysis of a polycarbonate/polybutylene terephthalate (PBT) blend (50/50) was investigated by immersing molded samples in water baths between 21 and 98°C. Samples were also placed in a 100°C air circulating oven (dry environment). Changes in impact properties, dynamic mechanical properties, molecular weight, and thermal properties were followed. In 80°C water bath the material was found to embrittle in five to six days, and in circulating air oven at 100°C in less than 90 days. A sharp decline in molecular weight and changes in thermal and mechanical properties were observed. The activation energy for the embrittlement process in water was found to be 22 kcal/ mole. This value is between the activation energy for the hydrolysis of PC and that of PBT. 相似文献
49.
Oene?OenemaEmail author Nicole?Wrage Gerard?L.?Velthof Jan Willem?van?Groenigen Jan?Dolfing Peter?J.?Kuikman 《Nutrient Cycling in Agroecosystems》2005,72(1):51-65
Wastes from animal production systems contribute as much as 30–50% to the global N2O emissions from agriculture, but relatively little attention has been given on improving the accuracy of the estimates and
on developing mitigation options. This paper discusses trends and uncertainties in global N2O emission from animal waste and discusses possible mitigation strategies, on the basis of literature data and results of
simple calculations. Total N2O emissions from animal production systems are estimated at 1.5 Tg. Dung and urine from grazing animals deposited in pastures
(41%), indirect sources (27%), animal wastes in stables and storages (19%), application of animal wastes to land (10%) and
burning of dung (3%) are the five sources distinguished. Most sensitive factors are N excretion per animal head, the emission
factor for grazing animals and that for indirect emissions. Total N2O emissions are related to type and number of animals, N excretion per animal, and the management of animal wastes. Projections
by FAO suggest that animal numbers will increase by 40% between 2000 and 2030. Mean N excretion per animal head will probably
also increase. These trends combined suggest a strong increase in total N2O emission from animal production systems in the near future, which is opposite to the objectives of the Kyoto Protocol. Improving
N use efficiency, combined with anaerobic digestion of animal wastes for bio fuel generation are the most feasible options
for mitigation, but these options seem insufficient to reverse the trend of increasing N2O emission. In conclusion, animal production systems are a major and increasing source of N2O in agriculture. The uncertainties in the emission estimates are large, due to the many complexities involved and the lack
of accurate data, especially about N excretion and the management of animal wastes in practice. Suggestions are made how to
increase the accuracy of the emission estimates and to mitigate N2O emission from animal production systems. 相似文献
50.
Oene Bottema 《Mechanism and Machine Theory》1975,10(1):11-15
If k is the path of a point P of a moving body, three lines are associated to P instantaneously: the tangent t, the principal normal n and the binormal b of k at P. It is well-known that the locus of t is a tetrahedral complex. Recently it was shown by Sticher that the locus of n is a subset of the linear complex L of all normals. In this paper the locus of b is investigated. 相似文献