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41.
42.
《Communications in Soil Science and Plant Analysis》2012,43(2):123-132
In this study, soil physical properties were evaluated in the top 40 cm of cleared forestland that had been subjected to continuous cultivation for 7 years to ascertain selected crop or crop combinations that influenced the soil physical properties the most. There was no significant effect of crop treatment on particle‐size distributions over 6 years of cultivation. In year 7, clay values were significantly (p = 0.05) greater in plots grown with solely cassava (SC) and solely maize (SM) than in the plots grown with solely pigeon pea (SP). The soil depth effects over the 7 years were significant on the clay content. The mean values of bulk density, pore‐size distribution, and hydraulic conductivity obtained from each plot fluctuated over the years. The bulk density values in 1998 ranged from 1.29 to 1.43 g cm3, but from 1999 to 2004, the range was from 1.12 to 1.40 g cm3. Thus, bulk density generally decreased when compared with their respective values in 1998. The greatest decrease of ≈ 22% was in 2000. More than 70% of the macroporosity values were significantly less than their respective values in 1998. The greatest decease of 72% was obtained from SM plots in 2001. All the microporosity were significantly more than the 1998 values. All the increases were >100% of the original values. These increases were reflected in the variations of total and saturated hydraulic conductivity (Ks) values. However, in 2004, Ks values decreased in the plots grown to C + P, SP, and SM. Generally, the C + M + P mixture appeared to be the most consistent in improving micro‐ and total porosities and Ks among the crop treatments. 相似文献
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A study was carried out to determine the effects of different tillage and plant residue management practices on different soil moisture and shrink-swell properties of a Vertisol (very fine, semctitic, thermic, chromic Haploxerert (with less than 1 % slope). The core samples were collected in July (after harvesting of lentil) and in November (after planting of wheat) 1993. The two tillage methods were moldboard (T1) and chisel (T2). The two plant residue incorporation dates were in August (R1) and in October (R2). Results indicated that T2 tends to give higher water holding capacity and available moisture than T1. Immediate incorporation of plant residue (R1) tends to increase the bulk density and to decrease soil specific volume and void ratio when compared to late incorporation treatment (R2). In general, the two tillage treatments tend to decrease moisture availability, shrinkage characteristics, soil specific volume, and void ratio. They also tend to increase the soil shrinkage (subsidence and cracks volume) and bulk density. Chisel plough is recommended in Vertisols, if it is to be used before the rainfall. 相似文献
45.
Improving the soil environment for seedling emergence and plant growth is possible using a good tillage system. From March 1993 until June 1994, the effect of tillage system and plant residue incorporation practices on the bulk density and the soil strength of the surface layer of a vertisol (very fine, smectitic, thermic, chromic Haploxerert), on a less than 1 % slope, was investigated. The two tillage methods were moldboard (T1) and chisel (T2). The two plant residue incorporation dates were in August (R1) and in October (R2). Results indicated that R1 gave significantly higher bulk density than R2, while the different tillage treatments had no significant effect. Soil strength was significantly lower under T1 and R2 than under the other treatments. 相似文献
46.
下部烟叶烘烤工艺研究 总被引:2,自引:0,他引:2
对下部烟叶烘烤研究结果表明,在38℃使底棚烟叶变黄6成,然后升温到41℃完成变黄,再以2小时1℃的速度升温定色,能有效地保证和提高烟叶的内在和外观品质 相似文献
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48.
将竹帘胶合板的"冷进冷出"工艺改造成"热进热出"工艺,关键技术是降低热压温度,而一种中温固化型的酚醛树脂是实现该技术的主要条件.选取树脂反应终点的粘度、甲醛、氢氧化钠与苯酚的摩尔比、促进剂加量4个主要因素,以每个因素三个不同水平进行正交试验,合成各种不同配方的胶粘剂,然后进行竹帘胶合板的压制.通过对制品耐沸水性和耐老化性的检验,确定适合中温固化酚醛树脂的最佳工艺参数为:胶粘剂反应终点的粘度为1.08 Pa·s,甲醛、氢氧化钠与苯酚的摩尔比分别为1.75和0.30,促进剂加量为苯酚质量的4%.按这组参数合成的酚醛树脂胶粘剂可以在105~115℃的中温条件下实现快速和完全固化. 相似文献
49.
Atmospheric lead and cadmium deposition in bulk precipitation and throughfall was investigated at four forests in the Kanto
district, Japan, to assess the impact of human activities on the environmental health of forests. Annual lead and cadmium
depositions in bulk precipitation ranged from 8.9 to 25.7 g ha−1 year−1 and from 0.77 to 1.30 g ha−1 year−1, respectively. Lead and cadmium deposition increased in the summer at every forest due to large amounts of rainfall. At one
of the forests, the depositions were also high in the winter due to heavy snowfall. These depositions were similar to recent
depositions observed at other rural and urban sites in Japan and several forests in Europe and North America after 1990. These
results indicate that although anthropogenic lead and cadmium are deposited at these rates over wide areas, depositions are
still higher than in remote areas. 相似文献
50.
以棉籽油及油脚为原料,经由甲酯化、异构化、聚合及酰胺化等反应,合成了汽车涂料固化剂,探讨了聚合反应的机理,并进行了应用性研究。试验表明,由棉籽油合成的聚酰胺,可以作为汽车电泳涂料固化剂,具有较为广阔的应用前景。 相似文献