全文获取类型
收费全文 | 66篇 |
免费 | 5篇 |
国内免费 | 2篇 |
专业分类
林业 | 53篇 |
农学 | 2篇 |
10篇 | |
综合类 | 4篇 |
畜牧兽医 | 1篇 |
植物保护 | 3篇 |
出版年
2021年 | 1篇 |
2017年 | 1篇 |
2016年 | 1篇 |
2013年 | 4篇 |
2012年 | 2篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 4篇 |
2005年 | 3篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
排序方式: 共有73条查询结果,搜索用时 62 毫秒
11.
12.
13.
The variation in P uptake and use efficiency and N accumulation by Gliricidia sepium (N2-fixing tree), Senna siamea and S. spectabilis (leguminous non-N2-fixing trees) were examined in the field at Fashola (savanna zone), southwestern Nigeria, using four P rates, 0, 20, 40 and 80 kg P ha-1. Growth of G. sepium and S. spectabilis responded to P application at 24 weeks after planting (WAP) and average yield increases of 58% and 145% were observed by the application of 40 kg P ha-1 for the two species, respectively. Such a P response was not found in S. siamea at 24 WAP and for any of the species at 48 WAP. G. sepium accumulated more P (on average 162%) than S. siamea and S. spectabilis at 24 WAP and had greater root length and a higher percentage of mycorrhizal infection. However, at 48 WAP S. siamea had 2.5 times more P than G. sepium. Differences in the physiological P use efficiency (PPUE) between G. sepium and the non-N2-fixing trees were significant at the 0 P level, being higher for S. siamea (average, 0.61 g shoot mg-1 P) than for G. sepium (0.27 g shoot mg-1 P). G. sepium had a consistently lower atom % 15N than S. spectabilis, while that of S. siamea for most of the time did not differ from that of G. sepium. The reference plant affected N2 fixation extimates, with negative values and a higher variability (CV 60%) associated with S. siamea than with S. spectabilis (CV<20%). Consequently, S. spectabilis was selected as a better reference plant for measuring N2 fixation in G. sepium. G. sepium fixed on average 35% and 54% of its N at 24 and 48 WAP, respectively. Except at the lowest P rate, percentage and amount of N fixed were not generally enhanced by P application. 相似文献
14.
Farming systems that minimize the rate of soil degradation and optimize food crop yields are needed to sustain soil productivity
on sloping, acid, infertile soils in the humid tropics. Research was conducted on two Oxisols with slopes ranging from 22
to 30% to evaluate the performance of several contour hedgerow systems, with and without the addition of 60 kg N ha−1 per
crop, on rice (Oryza sativa) and maize (Zea mays L.) production. Contour hedgerows were double rows of the tree legume Gliricidia
sepium (G); Gliricidia and the native grass Paspalum conjugatum (GPas); Gliricidia and an exotic fodder grass Penisetum purpureum
(GPen); double rows of Penisetum (Pen); and a conventional open field (C) farming system without hedgerows. Gliricidia prunings
and all crop residues were applied to the soil surface in the alleys, but Penisetum was harvested. Food crop yields in all
hedgerow treatments tended to be less than the Control for the first two years, presumably due to the displacement of land
planted to the food crop. In the third and the fourth years, the rice and maize yields of Treatments G and GPas exceeded the
Control, most consistently when N was not applied. Penisetum reduced food crop yields regardless of N application presumably
due to nutrient removal in the fodder. The results indicate that Gliricidia in a contour hedgerow increases food crop yield
on strongly acid Oxisols by recycling nutrients and partially supplementing the N demand by the food crops.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
Spice crops agroforestry systems in the East Usambara Mountains,Tanzania: growth analysis 总被引:1,自引:0,他引:1
A scarcity of cultivation land calls for more intensive and productive land use in the East Usambara Mountains in NE Tanzania.
Spice crops could generate cash in higher parts of the mountains, but the present cultivation methods are depleting the valuable
forest resources. The trial was established at the end of 2000 to find out how the two popular cash crops, cardamom (Elettaria cardamomum (L.) Maton.) and black pepper (Piper nigrum L.), normally grown under the natural forest, will produce in intensive agroforestry system with two multipurpose farm trees,
Grevillea robusta A.Cunn. and nitrogen fixing Gliricidia sepium Jacq. Results from 6 years showed that cardamom produced better with grevillea than in natural forest; 5.5 times more in
the fourth year than the average in the area. The Land Equivalent Ratios for black pepper and cardamom showed that pepper
intercropped with grevillea produced 3.9 times more than in monoculture whereas cardamom intercropped with grevillea and pepper
produced 2.3 times more than in monoculture. Gliricidia improved the nitrogen and organic matter content of the soil over
the levels found in natural forest. Soil acidity was, however, preventing the plants from using the available mineral nutrients
more effectively. 相似文献
16.
云南干热河谷旱坡地南洋樱植物篱水土保持效益研究 总被引:2,自引:0,他引:2
对云南元谋干热河谷旱坡地水土流失和土壤退化严重的地区,引进豆科速生树种南洋樱,以30 cm×40 cm株行距、品字形双行等高栽植快速形成植物围篱。结果表明,南洋樱植物篱在元谋干热河谷旱坡地生长良好,并且在种植3年间,治理区径流发生次数明显减少,年径流模数减少了29.13×104m3/km2,减少率76.90%;土壤年退化减少12 986.8 t/km2,减少率76.02%。研究区降水量与径流量间者的相关系数由建植篱前的显著相关变为不显著;有机质和钾流失减少量高达3 111.64 kg/hm2和3276.57 kg/hm2。南洋樱植物篱在控制旱坡地水土流失、减少土壤侵蚀和改善土壤养分等效益显著。 相似文献
17.
Modelling daily root interactions for water in a tropical shrub and grass alley cropping system 总被引:2,自引:0,他引:2
A two-dimensional physically-based model for the daily simulation of root competition for water in an alley cropping system associating Gliricidia sepium with Digitaria decumbens is developed. This paper deals with the impact of root distribution on soil water partitioning. By adapting existing principles of root water uptake modelling for pure crops, the model accounts simultaneously for the sink terms of each species in a defined soil domain. Soil-root water transport functions are solved at the level of discrete volumes of soil; each of them are characterized by the inherent soil physical properties, root length density, soil-root distances, and the calculated sink terms of each species. The above ground boundary conditions, such as transpiration and soil evaporation, were managed by simple equations found from the literature or provided by experimental measurements. Running the model with two contrasting observed root maps, an evaluation was carried out over a 10-day period following a rainfall event. With both root maps, the simulated soil water potential profiles at the row, at 0.75 m and 1.50 m from the row did not differ significantly, and were in good agreement with the measurements. However, although water was not limiting during this period, the simulated cumulative water absorption profiles of G. sepium and D. decumbens contrasted markedly, and matched their observed root distribution. This model, although still under further development, forms the basis for development of an above and below ground coupled model to simulate plant interactions for water in intercrops or agroforestry.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
18.
Turnover of nitrogen-rich root nodules follows the pruning of legume trees, forming a potentially important yet little studied
way of N release to the soil. The effects of soil moisture, herbivory by soil mesofauna and microbial decomposition on the
disappearance rate of woody legume nodules was studied in two tree/grass forage production associations. Litter bags containing
nodules of Erythrina variegata L. (Papilionoideae: Phaseoleae) were incubated for four weeks in grass-covered alleys between Gliricidia sepium (Jacq.) Walp. (Papilionoideae: Robinieae) hedgerows, established on a deep alluvial Oxisol under a humid tropical climate
and on a shallow Vertisol under a subhumid tropical climate in Guadeloupe, French Antilles. Soil moisture was regulated by
irrigating or covering small plots from natural rainfall. Fine nylon mesh bags were used to study the rate of microbial decomposition,
and open-ended perforated cylinders were used to estimate nodule herbivory. The chemical traits, especially the lignin: nitrogen
ratio, of E. variegata and G. sepium nodules were similar (lignin: N 1.70 and 1.55, respectively), and suggest that the results are probably also applicable to
the G. sepium nodules in the associations. Both soil moisture and decomposing agent (microbes or mesofauna) had a significant effect on
the nodule disappearance rate, but soil type did not have any apparent effect. The nodule half-life varied from three to seven
days under different treatments. The N release rate from the nodules was high, with N half-life varying from three to five
days. Herbivory accounted for ca. 10% of total mass and N loss from nodules during the four-week field incubation period,
but its importance increased towards the end of the incubation, especially in Vertisol, after the most easily decomposable
part of the nodules had decayed. After pruning, the nodule N is released to soil more rapidly than from mulch.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
19.
Bakach Dikand Kadiata 《Journal of plant nutrition》2013,36(4):677-688
Nutrients released from tree prunings sustain alley cropping. Potassium (K) uptake and utilization efficiency were monitored over 16 months in Gliricidia sepium, Leucaena leucocephala, and Albizia lebbeck. Tree interspecific variation arose in biomass yields and K nutrition. Tissue potassium concentration narrowed within 0.68–1.15% and varied little among tree parts and species over time. Potassium accumulation increased steadily with tree age and significant differences among trees occurred at all ages. Gliricidia sepium had a higher yield than the others over the first 8 months, after which the uptake pattern declined drastically to become the lowest at harvest. Differential K partitioning within trees occurred as K in leaves, stems, and roots amounted to 18, 35, and 47% in Albizia; 28, 25, and 47% in Gliricidia; and 27, 42, and 31% in Leucaena, respectively. Higher K allocation into Leucaena stems and its low partitioning into Albizia leaves were drawbacks for alley cropping. Potassium utilization efficiency decreased inversely to biomass yield and K uptake over time. It differed significantly among trees with Albizia being the most efficient. Low K returns from tree prunings in alley cropping could be due to its uptake potential and partitioning impairment in each species. 相似文献
20.
The water dynamics of cropping systems containing mixtures of Gliricidia sepium (Jacq.) Walp trees with maize (Zea mays L.) and/or pigeonpea (Cajanus cajan L.) were examined during three consecutive cropping seasons. The trees were pruned before and during each cropping season, but were left unpruned after harvesting the maize; prunings were returned to the cropping area in all agroforestry systems to provide green leaf manure. The hypothesis was that regular severe pruning of the trees would minimise competition with crops for soil moisture and enhance their growth by providing additional nutrients. Neutron probe measurements were used to determine spatial and temporal changes in soil moisture content during the 1997/98, 1998/99 and 1999/00 cropping seasons for various cropping systems. These included gliricidia intercropped with maize, with and without pigeonpea, a maize + pigeonpea intercrop, sole maize, sole pigeonpea and sole gliricidia. Soil water content was measured to a depth of 150 cm in all treatments at 4–6 week intervals during the main cropping season and less frequently at other times. Competition for water was apparently not a critical factor in determining crop performance as rainfall exceeded potential evaporation during the cropping season in all years. The distribution of water in the soil profile was generally comparable in all cropping systems, implying there was no spatial complementarity in water abstraction by tree and crop roots. However, available soil water content at the beginning of the cropping season was generally lower in the tree-based systems, suggesting that the trees continued to deplete available soil water during the dry season. The results show that, under rainfall conditions typical of southern Malawi, the soil profile contains sufficient stored water during the dry season (ca. 75–125 mm) to support the growth of gliricidia and pigeonpea, and that gliricidia trees pruned before and during the cropping season did not deleteriously compete for water with associated crops. Water use efficiency also appeared to be higher in the tree-based systems than in the sole maize and maize + pigeonpea treatments, subject to the proviso that the calculations were based on changes in soil water content rather than absolute measurements of water uptake by the trees and crops. 相似文献