半干旱区柠条植物篱水分再分配格局研究

通过对黄土高原丘陵沟壑区26年生柠条植物篱不同部位(带间、带前、带内、带后)土壤水分的2年监测,对比分析了柠条植物篱不同部位土壤水分的分布特征及其动态,探讨了柠条植物篱对降水的再分配效应。结果表明:带状柠条植物篱内不同部位间土壤水分物理性质有明显的不同,其中,带内部位土壤密度(0.99 g·cm-3)、非毛管孔隙度(8.77%)、毛管持水量(58.89%)等均优于带间、带前、带后,土壤更为疏松,透水保水性能更良,而带前更加黏性化;随着土壤深度的增加,各部位土壤含水量均表现出逐层降低的趋势,依次为0~20 cm(25.51%±2.28%)40~60 cm(12.96%±1.34%)60~80 cm(10.03%±0.59%)80~100 cm(9.16%±0.81%)100~120 cm(8.76%±1.00%),但越接近表层,带前、带内部位土壤水分含量的优势更明显。根据对土壤水分的有序聚类分析,将柠条植物篱土壤层次划分为弱利用层、利用层和调节层3层,其中,带内的土壤水分利用层(20~120 cm)大于带前、带后(20~60 cm)和带间(40~60 cm),与柠条对土壤水分的主要利用层次相一致,带内的土壤水分调节层在120 cm以下,较带间(80 cm以下)和带前、带后(60 cm以下)均深,反映了带状植物篱带前、带内土壤含水率提高而带后表层土壤含水率降低的分异特征。     

等高绿篱-坡地农业复合系统土壤CO_2排放特征

基于2008年12月初至翌年6月初绿篱-冬小麦复合系统土壤CO2全生长季的观测,研究了绿篱复合种植及其枝叶不同还田(移出/AR、翻施/AI和表施/AC)方式下土壤CO2的排放特征。结果表明,整个冬小麦生长期间,各处理土壤CO2排放具有相似的季节变化趋势,小麦生长旺盛期明显高于越冬期和成熟期。绿篱复合种植及其枝叶还田显著影响土壤CO2排放,与作物单作(CK)处理相比,AR处理土壤CO2平均排放通量降低了9.07%,而AI和AC处理分别增加了35.70%和8.42%。土壤温度、作物生长及土壤微生物生物量碳是影响土壤CO2排放的主要因素。土壤CO2排放通量与土壤温度呈显著或极显著指数正相关,其中与10 cm处土壤温度的相关性最高;同时,土壤CO2排放与0~5 cm土层微生物生物量碳含量及小麦地下生物量均呈显著线性相关;土壤水分对土壤CO2排放的影响居于次要地位。     

Food-crop-based production systems as sustainable alternatives for Imperata grasslands?

Purely annual crop-based production systems have limited scope to be sustainable under upland conditions prone to infestation by Imperata cylindrica if animal or mechanical tillage is not available. Farmers who must rely on manual cultivation of grassland soils can achieve some success in suppressing Imperata for a number of years using intensive relay and intercropping systems that maintain a dense soil cover throughout the year, especially where leguminous cover crops are included in the crop cycle. However, labour investment increases and returns to labour tend to decrease in successive years as weed pressure intensifies and soil quality declines.Continuous crop production has been sustained in many Imperata-infested areas where farmers have access to animal or tractor draft power. Imperata control is not a major problem in such situations. Draft power drastically reduces the labour requirements in weed control. Sustained crop production is then dependent more solely upon soil fertility management. Mixed farming systems that include cattle may also benefit from manure application to the cropped area, and the use of non-cropped fallow areas for grazing. In extensive systems where Imperata infestation is tolerated, cassava or sugarcane are often the crops with the longest period of viable production as the land degrades.On sloping Imperata lands, conservation farming practices are necessary to sustain annual cropping. Pruned tree hedgerows have often been recommended for these situations. On soils that are not strongly acidic they may consistently improve yields. But labour is the scarcest resource on small farms and tree-pruning is usually too labour-intensive to be practical. Buffer strip systems that provide excellent soil conservation but minimize labour have proven much more popular with farmers. Prominent among these are natural vegetative strips, or strips of introduced fodder grasses.The value of Imperata to restore soil fertility is low, particularly compared with woody secondary growth or Compositae species such as Chromolaena odorata or Tithonia diversifolia. Therefore, fallow-rotation systems where farmers can intervene to shift the fallow vegetation toward such naturally-occurring species, or can manage introduced cover crop species such as Mucuna utilis cv. cochinchinensis, enable substantial gains in yields and sustainability. Tree fallows are used successfully to achieve sustained cropping by some upland communities. A variation of this is rotational hedgerow intercropping, where a period of cropping is followed by one or more years of tree growth to generate nutrient-rich biomass, rehabilitate the soil, and suppress Imperata. These options, which suit farmers in quite resource-poor situations, should receive more attention.     

Productivity of hedgerow shrubs and maize under alleycropping and block planting systems in semiarid Kenya

A field experiment was conducted for eight cropping seasons from 1988 to 1991 in semiarid Machakos, Kenya, to compare the productivity of shrubs and crops in intercropping (alleycropping) versus block (sole) planting systems. The study, conducted in a split-plot experiment with three replications, consisted of two tree species (Leucaena leucocephala andSenna siamea syn.Cassia siamea) in the main-plots and combinations of two planting systems (alleycropping and block planting of the shrubs and maize) with five different ratios of land allocation for the shrub and crop (1000, 1585, 2080, 2575, and 0100) in sub-plots. Thus, a sole maize and a sole tree were included in the subplot treatments. The spacing between hedgerows of shrubs in intercropping was 6.7, 5, and 4 m, respectively, corresponding to 15, 20, and 25% land allocation to shrubs. The trees were pruned to 0.5 m height four times a year. Intercropped hedgerows of senna and leucaena produced 10% and 24% more biomass than their respective block planting systems. On average, leucaena produced more biomass than senna. Maize alleycropped with leucaena yielded 16% less grain than sole-crop maize, whereas senna intercropping caused hardly any maize-yield reduction. Compared with the respective sole-crop systems, leucaena intercropping did not affect land equivalent ratio (LER), whereas LER increased by 28% with senna intercropping. The different tree:crop land occupancy ratios did not affect the production of either the component species or of the total system, except that LER declined with incrreased spacing between hedgerows. It is concluded that in semiarid highlands of Kenya, leucaena and crops should better be grown in sole blocks, not in alleycropping. In the case of slow-growing species such as senna, intercropping is worthwhile to consider only if the additional labour needed does not pose a serious problem for management, and the species has fodder value.     

Influence of root pruning and cutting interval ofLeucaena hedgerows on performance of alley croppedrabi sorghum

The influence of root pruning and cutting interval ofLeucaena hedgerows on alley croppedrabi sorghum was investigated. Paired (60 cm)Leucaena hedgerows spaced 6.6 m wide were subject to either root pruning, using a country plough during mid-kharif season, or no root pruning. The cutting frequency ofLeucaena hedgerows ranged from one month to six months during therabi cropping period. The effect on soil moisture, crop growth, yield and yield components ofrabi sorghum was examined.Root pruning ofLeucaena hedgerows increased grain and stover yields of the alley croppedrabi sorghum by 33 and 17%, respectively, over root not pruned hedgerows. Similarly, shorter cutting intervals (one and two months) increased crop yields as compared with longer cutting intervals (three and six months). The growth (height and dry matter) of the crop was similarly influenced. Soil moisture studies indicated that the competition between crop and hedgerows was considerably reduced by the root pruning. The results clearly showed that the competition between hedgerows and arable crop can be reduced considerably by root pruning and frequent cutting (at one to two months interval) of the hedgerows.     

Soil nitrogen dynamics in alley cropping and no-till systems on ultisols of the Georgia Piedmont, USA

On highly-weathered Ultisols of the Georgia (USA) Piedmont, a combination of no-till agriculture and alley cropping presents an option for rapidly increasing soil nitrogen availability while restoring long-term soil fertility. Three years after the establishment of Albizia julibrissin hedgerows and no-till agriculture trials, we measured inorganic soil nitrogen (NO₃ ^-–N and NH₄ ^-–N) and net nitrogen mineralization during a 4-month field study and a 14-day laboratory study . We also measured the influence of tree leaf amendments on grain sorghum production and N uptake. Soil nitrate increased four-fold within two weeks of adding Albizia leaf mulch. Soil ammonium did not increase as rapidly nor to the same extent after tree mulch addition. Averaged over the 4-month study, soil nitrate and ammonium were 2.8 and 1.4 times higher in the alley-cropped than in the treeless no-till plots. Net nitrification and mineralization were no higher in the alley cropping plots, during either field or laboratory incubations. Tree mulch additions enhanced crop biomass production and N uptake 2 to 3.5 times under both high and low soil moisture conditions. Our study demonstrates the dramatic short-term impacts of Albizia mulch addition on plant available nitrogen. Combined with no-till practices, alley cropping with Albizia hedges offers Piedmont farmers an option for reducing reliance upon chemical N fertilizer while improving soil organic matter levels. This revised version was published online in August 2006 with corrections to the Cover Date.     

Conservation farming practices for small reservoir watersheds: a case study from Sri Lanka

Traditional agricultural villages in the dry zone of Sri Lanka are minor watersheds where small earth bank reservoirs provide water for irrigation and domestic purposes. The farmers practise rainfed farming on a shifting basis called chena in the reservoir catchments, which are being degraded due to soil erosion. The consequent sedimentation in reservoirs has reduced the extent of irrigation, and the total farming system has lost its ecological balance and economic sustenance. The present study aimed at identifying suitable farming methods for reservoir catchments in order to prevent further deterioration.The investigation was carried out on plot basis to assess soil loss and runoff from forest, scrub and cultivated lands as well as from four other types of farming lands namely plough-farming, bund-farming and two conservation farming practices: strip mulch and graded hedgerow farming. In graded hedgerow farming hedgerow trees are planted across the slope with a mild gradient of 0.4–0.5%. The study was carried out in a reservoir watershed at Maha Illuppallama, Sri Lanka during 1989/90 major rainy season.Results indicated that the two conservation farming practices generate 33–34% annual runoff while replenishing soil moisture of the watershed. Soil loss data showed that the conservation farming practices provide more than 80% protection against soil erosion while bunding can provide only 40% protection compared to existing shifting cultivation practices.     

Models of Steep Cultivated Slop Land Returning Forest

Slop land resource is an important part of land resource in China and its utilization and conservation deeply affect the stability of environment. It will playan important role on soil land water conservation and improvement of mountain area eco-environment for cultivated slop land to be returned to forest for instance: agroforestry method, contour hedgerow technique, plant barrier, terraced field and so on up till now. The models of agroforestry and terraced field are use extensile, but comparing with other methods of slop land utilization, contour hedgerow technique cost is less and its effect in soil water conservation and soil fertility sustaining is terrific. So it is necessary to be applied and popularized.     

香根草植物篱护坡反季节施工技术

 在萍莲319国道改建工程中运用香根草(Vetiveriazizanioides)植物篱护坡反季节施工技术,在石块砾石区下边坡,香根草成活率达90%,在煤土堆积下边坡,香根草成活率达94%。表明香根草植物篱技术在江西萍乡10—11月反季节应用非常成功,证明了香根草等高植物篱技术防护公路边坡的有效性,也说明在极劣地利用香根草进行生态恢复,一年四季皆可取得成功。这为香根草等高植物篱技术的广泛运用和推广提供了新的施工方法。     

四川紫色土丘陵区不同植物篱物种对农田地表甲虫群落结构的影响

2005-2007年的冬小麦和夏玉米生长季节,在四川省土壤肥料研究所资阳试验站的1号试验地(坡度20°)和2号试验地(坡度12°)利用陷阱法调查了香根草(1号地)、紫穗槐(1号地)、蓑草(2号地)和苜蓿(2号地)4种植物篱物种作为半自然生境对地表甲虫的活动密度(种群密度和活动性的参数)和科丰富度的影响.结果表明,植物篱带地表甲虫的活动密度在小麦生长季节与对照裸地或临近农田之间差异不明显,在玉米生长季节明显低于对照裸地或临近农田.植物篱带地表甲虫的科丰富度在小麦生长季节和玉米生长季节与对照裸地之间差异均不明显.在小麦和玉米生长季节,植物篱带的出现均没有明显提高农田地表甲虫的活动密度和科丰富度.以上结果表明,有助于保持水土的植物篱由于宽度较窄、植被结构简单,导致对提高农田生态系统地表甲虫的物种多样性作用不明显.