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841.
《Communications in Soil Science and Plant Analysis》2012,43(6):475-486
Abstract Samples of four soils having a wide range of volume weights (0.65, 1.02, 1.25, 1.62 g/cm3) were either weighed or measured by volume and extracted with: (a) the Bray P1 extractant, (b) the Mehlich double acid extractant for P, K, Ca, Mg, Mn, Zn and (c) neutral N NH4OAc for K, Ca, Mg all at a soil/extracting solution ratio of 1:10. The soil test results were recorded on a volume basis in mg/dm3 and on a weight basis in mg/kg. The test values for all macronutrients obtained with all extractants decreased, relative to a constant volume, with increasing VW of soil when analyzed and expressed on a weight basis. Results based on the use of a volume sample (scooped) but calculated on an assumed weight of soil changed the values in direct ratio of 1/assumed VW. The use of an assumed VW has no justification, since uniform soil test results can be obtained when expressed on a volume basis by either using a scooped sample of known volume or a weighed sample followed by multiplication with the VW of each soil. 相似文献
842.
首先分析了现阶段中国农业院校提高农业科技成果转化效率的现实意义,在此基础上以中国H农业大学为例,深入研究了中国农业院校在农业科技成果转化工作中存在的问题,并针对性地提出了解决对策。 相似文献
843.
844.
以农林类高校女研究生就业困境问题为切入点,对当前农林类高校女研究生就业的现状进行了分析,并探讨了就业困境的原因,同时结合农林类高校女研究生就业的实际情况,并借鉴欧美促进女性就业的策略,提出了相关建议和措施。 相似文献
845.
Emissions of N2O were measured following addition of 15N‐labelled residues of tropical plant species [Vigna unguiculata (cowpea), Mucuna pruriens and Leucaena leucocephala] to a Ferric Luvisol from Ghana at a rate of 100 mg N/kg soil under controlled environment conditions. Residues were also applied in different ratio combinations with inorganic N fertilizer, at a total rate of 100 mg N/kg soil. N2O emissions were increased after addition of residues, and further increased with combined (ratio) applications of residues and inorganic N fertilizer. However, 15N‐N2O production was low and short‐lived in all treatments, suggesting that most of the measured N2O‐N was derived from the applied fertilizer or native soil mineral N pools. There was no consistent trend in magnitude of emissions with increasing proportion of inorganic fertilizer in the application. The positive interactive effect between residue‐ and fertilizer‐N sources was most pronounced in the 25:75 Leucaena:fertilizer and cowpea:fertilizer treatments where 1082 and 1130 mg N2O‐N/g residue were emitted over 30 days. N2O (loge) emission from all residue amended treatments was positively correlated with the residue C:N ratio, and negatively correlated with residue polyphenol content, polyphenol:N ratio and (lignin + polyphenol):N ratio, indicating the role of residue chemical composition in regulating emissions even when combined with inorganic fertilizer. The positive interactive effect in our treatments suggests that it is unlikely that combined applications of residues and inorganic fertilizer can lower N2O emissions unless the residue is of very low quality promoting strong immobilisation of soil mineral N. 相似文献
846.
对海南多个景观水体的水生植物进行调查研究,并采用浮床栽培技术对多种植物进行水培试验,结果植株在污染水体培养的植物长势和景观效果优于自来水体,富贵竹、闭鞘姜、黄花蔺等植物在浮床栽培技术中具有较高的观赏价值,可运用于热带地区水体景观中。 相似文献
847.
R. P. O. Schulte R. Fealy R. E. Creamer W. Towers T. Harty R. J. A. Jones 《Soil Use and Management》2012,28(4):580-589
The Less Favoured Area (LFA) scheme is a major element of the EU Rural Development Policy, aimed at supporting farming in areas with natural handicaps or low soil productivity. It has been in place since 1975 and accounts for 14% of total Community funding. In 2003, the European Court of Auditors recommended that the socio‐economic criteria on which the current scheme is based be replaced by biophysical criteria. Reviews of the proposals suggest that in Atlantic climates of Northwest Europe, the new criteria do not delineate adequately areas where agricultural productivity is constrained by the biophysical environment and that such areas are instead demarcated by the occurrence of excess soil moisture conditions. In this paper, we review the impact of excess soil moisture conditions on the sustainability of farming systems and their role in constraining strategic and tactical farm management practices. In particular, we review the scientific evidence on the impact of excess soil moisture conditions on herbage growth, herbage utilization, farm operations and environmental sustainability. On the basis of this, we propose an additional biophysical criterion for the new delineation of LFAs, namely the length of time that soil water is in excess of field capacity (‘field capacity days’). While there is no clear threshold for field capacity days above which agricultural sustainability is acutely constrained, the evidence reviewed in this paper suggests that the sustainability of intensive livestock farming and tillage systems is particularly challenging in scenarios where the 80 percentile of field capacity days exceeds 220–230 days. 相似文献
848.
《Communications in Soil Science and Plant Analysis》2012,43(19):2330-2339
This study evaluates the effect of soil particle size (SPS) on the measurement of exchangeable sodium (Na) (EXC-Na) by near-infrared reflectance (NIR) spectroscopy. Three hundred thirty-two (n = 332) top soil samples (0–10 cm) were taken from different locations across Uruguay, analyzed by EXC-Na using emission spectrometry, and scanned in reflectance using a NIR spectrophotometer (1100–2500 nm). Partial least squares (PLS) and principal component regression (PCR) models between reference chemical data and NIR data were developed using cross validation (leaving one out). The coefficient of determination in calibration (R2) and the root mean square of the standard error of cross validation (RMSECV) for EXC-Na concentration were 0.44 (RMSECV: 0.12 mg kg–1) for soil with small particle size (SPS-0.053) and 0.77 (RMSECV: 0.09 mg kg–1) for soils with particle sizes greater than 0.212 mm (SPS-0.212), using the NIR region after second derivative as mathematical transformation. The R2 and RMSECV for EXC-Na concentration using PCR were 0.54 (RMSECV: 0.07 mg kg–1) and 0.80 (RMSECV: 0.03 mg kg–1) for SPS-0.053 and SPS-0.212 samples, respectively. 相似文献
849.
《Communications in Soil Science and Plant Analysis》2012,43(2):220-230
Different relationships between soil-test methods results have been reported in several agricultural regions. Differences in the same soil-test procedure (e.g., soil/solution ratio) exist between soil-testing laboratories from different agricultural regions. Our objectives were to (1) determine the effect of soil/solution ratio on the amount of phosphorus removed by Bray 1 and Mehlich 3 methods, (2) compare the amounts of phosphorus removed by Bray 1 and Mehlich 3 in Mollisols from the Pampean region, and (3) determine whether soil/solution ratio affects the relationship between Bray 1 and Mehlich 3. Soil phosphorus availability was determined with two extractants (Bray 1 and Mehlich 3), using two soil/solution ratios (1:10 and 1:8, wt/v) in 72 soils (noncalcareous, loess-derived Molisolls) from the Pampean region. The amount of phosphorus removed was 20–24% greater when using 1:10 than 1:8 (wt/v) soil/solution ratio. This effect was significantly greater in Bray 1 than in Mehlich 3 (p = 0.04). When compared using the same soil/solution ratio, Mehlich 3 removed 4 to 8% more phosphorus than Bray 1. The soil/solution ratio used in the comparison affected the relationship between both extractants. The difference between extractants was slightly greater with a soil/solution ratio of 1:8 than of 1:10 (p = 0.03). Our results showed that even when using the same method, changes in the procedure (like soil/solution ratio) may cause different soil-test results and also differences in the relationship between two extracting solutions. Therefore, reported relationships between two methods are only valid for the soils and region where the relationship was developed and should not be extrapolated to other regions, even with similar soils. 相似文献
850.
对海南多个景观水体的水生植物进行调查研究,并采用浮床栽培技术对多种植物进行水培试验,结果植株在污染水体培养的植物长势和景观效果优于自来水体,富贵竹、闭鞘姜、黄花蔺等植物在浮床栽培技术中具有较高的观赏价值,可运用于热带地区水体景观中。 相似文献