Active root distribution pattern of <Emphasis Type="Italic">Hevea brasiliensis</Emphasis> determined by radioassay of latex serum

The active root distribution pattern of mature rubber (Hevea brasiliensis Muell. Arg.) up to a lateral distance of 250 cm from the tree and to a soil depth of 90 cm was studied in an oxisol by employing ³²P soil injection technique in Kerala, the state which accounts for 83% of rubber cultivation in India. The trees were aged 18 years and grown at a spacing of 4.9 × 4.9 m. The extent of absorption of applied ³²P by the tree from various placements was assessed by radio assay of leaf and latex serum. Latex serum registered higher counts and variability was less compared to leaf indicating the suitability of latex serum as a potential source for radio assay for ³²P studies in rubber. The results revealed that rubber is a surface feeder with 55% of the root activity confining to the top 10 cm of soil layer. Root activity declined with increasing depths and the concentration of physiologically active roots at 90 cm depth was only 6%. A more or less uniform distribution of root activity was noticed with respect to lateral distance indicating more extensive spread of lateral roots. Concentration of physiologically active roots in the surface layer suggests the possibility for competition under intercropped situation in mature plantations.     

Biomass distribution in 40-year-old trees of Japanese black pine

Measurements were carried out to survey the quantity of above- and below-ground biomass and its distribution of five Japanese black pines (Pinus thunbergii Parl.) growing on a sandy soil. The roots, divided into diameter groups, were surveyed using two methods—soil coring and excavation. Average dry weight of total biomass of the trees was 176,185 g. Roots represented 13.2%, below-ground stump 6.5%, stem 70.4% and branches with needles 9.9% of total biomass. Roots made up about two thirds and stump one third of below-ground biomass. Total length of below-ground biomass (except roots with diameter < 0.1 cm) was 479.1 m/tree. Roots with diameter of 0.1–0.2 cm represented only 0.7% of below-ground biomass, however as much as 49.9% of their total length. Roots with diameter over 10.0 cm constituted as much as 21.6% of below-ground biomass, however were only 0.3% of its total length. Root systems had well developed tap roots to maximal depth of 231 cm. The results indicated that mass and length of roots with diameter 0.5–2.0 cm had a close correlation with branch mass. Mass and length of roots with diameter 2.0–10.0 cm closely correlated to stem mass. Stem mass, root mass and root length closely correlated to DBH. A rather low correlation was found between DBH and mass of branches and below-ground stump. DBH was a suitable variable for predicting total biomass.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 2. Competition for water

A study was carried out in an alley cropping system in the Eastern Maize Belt of the United States with the objective of quantifying the competition for water between trees (black walnut (Juglans nigra L.) and red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial and temporal variation in soil moisture, tree and maize rooting patterns, tree and maize water uptake, and maize leaf area expansion were determined in three treatments; barrier (polyethylene root barriers separating maize and tree roots), trench (trenching without a polyethylene barrier), and no barrier (control). Significant temporal variation in soil moisture was observed in both black walnut and red oak alley cropping systems. The barrier and trench treatments resulted in higher soil moisture in the maize alley and lower soil moisture in the tree row than the no barrier treatment. Uptake of water by maize was higher in the barrier than the no barrier treatment. However, tree water uptake was higher in the no barrier treatment than in the barrier treatment because tree roots utilized water from the maize alley. Maize leaf area was negatively impacted by water stress in the no barrier treatment. Quantification of rooting patterns revealed that maize and tree roots were concentrated in the top 30 cm soil layer where water fluctuations were greatest. The barrier and trench treatments successfully eliminated the belowground root competition between trees and maize and resulted in greater leaf area and higher grain yields than the no barrier treatment. Thus, competition for water rather than competition for light seems to be critical in defining the productivity and sustainability of this alley cropping system.This revised version was published online in November 2005 with corrections to the Cover Date.     

Agroforestry in the Bolivian Altiplano: evaluation of tree species and greenhouse growth of wheat on soils treated with tree leaves

Severe environmental problems encountered in the highlands of Bolivia may be remedied through the adoption of agroforestry systems, never before studied adequately in this region. As a first step, seven tree species were tested for growth, survival and health at two elevations in the Bolivian altiplano. Species responded variably with Buddleja coriacea Remy., Pinus radiata D. Don. and Eucalyptus globulus Labill. (at the higher elevation) and E. globulus, Baccharis spp., Robinia pseudoacacia L. and B. coriacea (at the lower elevation), displaying high survival, growth and health. In a related greenhouse study, grain yields of wheat planted in soils amended with incorporated foliage of B. coriacea, P. radiata and E. globulus increased three-fold (0.3 g·plant⁻¹ to >1.0 g·plant⁻¹) over grain yields in unamended soils (B. coriacea > P. radiata = E. globulus). Grain nitrogen (mg·plant⁻¹) increased equally in soils amended with P. radiata and B. coriacea foliage (18 mg N⋅plant⁻¹ to 20 mg·plant⁻¹) but decreased in soils amended with foliage of E. globulus (18 g·plant⁻¹ to 9 g·plant⁻¹). This revised version was published online in June 2006 with corrections to the Cover Date.     

Estimation of phenotypic variability in symbiotic nitrogen fixation ability of common bean under drought stress using 15N natural abundance in grain

Common bean (Phaseolus vulgaris L.) is the most important food legume, cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. The main objectives of this study were to: (i) test and validate the use of ¹⁵N natural abundance in grain to quantify phenotypic differences in SNF ability for its implementation in breeding programs of common bean with bush growth habit aiming to improve SNF, and (ii) quantify phenotypic differences in SNF under drought to identify superior genotypes that could serve as parents. Field studies were conducted at CIAT-Palmira, Colombia using a set of 36 bean genotypes belonging to the Middle American gene pool for evaluation in two seasons with two levels of water supply (irrigated and drought stress). We used ¹⁵N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. Our results showed positive and significant correlation between nitrogen derived from the atmosphere (%Ndfa) estimated using shoot tissue at mid-pod filling and %Ndfa estimated using grain tissue at harvest. Both methods showed phenotypic variability in SNF ability under both drought and irrigated conditions and a significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) could be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified four bean lines (RCB 593, SEA 15, NCB 226 and BFS 29) that combine greater SNF ability with greater grain yield under drought stress and these could serve as potential parents to further improve SNF ability of common bean.     

雷竹笋用林覆盖措施对土壤养分的影响

以砻糠为覆盖材料,试验研究了雷竹林不同覆盖次数对林地土壤养分的影响。结果表明:覆盖措施减少了林地土壤的水解氮和速效磷含量,减少幅度随着覆盖次数的增加而增大,土壤速效钾含量却呈现相反的变化趋势,覆盖次数越多土壤钾素积累越多;覆盖增加了土壤有机质含量和土壤阳离子交换量,土壤保肥性增强;覆盖改善了土壤的物理性质,土壤容重减小,保水、通气性增强;多次覆盖使土壤的酸性减弱,pH值增大,表层土壤酸性强度减弱,pH值增高趋势因施肥和覆盖年限而异。因此,建议改变林地经营模式或者采用间隔带状覆盖的形式降低土壤劣变现象的出现。     

MJS水泥土的试桩成桩效果分析

以南京地铁7号线中胜站全断面承压含水砂层MJS加固下穿既有运营10号线车站工程为背景,基于试桩芯样对MJS水泥土试桩成桩效果进行研究,研究不同桩型、不同水泥掺入比、不同地层下各部位MJS水泥土试桩的成桩效果(加固范围、成桩质量、抗压强度、弹性模量、水泥含量),并与室内MJS水泥土强度数据比较.结果表明:全圆桩整体成桩效...     

小兴安岭北坡森林土壤有机碳储量时空分布格局

通过对2010—2012年小兴安岭北坡森林土壤有机碳密度、碳储量的调查、测算、分析,对小兴安岭北坡森林土壤有机碳储量时空分布格局进行了研究,结果表明：各类型土壤有机碳密度大小顺序为沼泽土〉暗棕壤〉黑土〉草甸土〉白浆土,各土壤类型有机碳密度与年均降水量之间除暗棕壤（P=-0.900,0.01〈ɑ〈0.05）外,均无显著相关性,说明降水量对土壤有机碳密度影响不大;处于寒温带的爱辉区和孙吴县与处于温带季风气候区的4个地区之间土壤有机碳密度未发现普遍规律;土壤碳储量分布规律为暗棕壤〉白浆土〉沼泽土〉草甸土〉黑土。2010—2012年,小兴安岭北坡森林土壤有机碳储量整体呈先减后增趋势,这主要与森林经营导致的森林面积改变有关。     

白桦次生林4个林龄0～30cm土层水源涵养功能比较

以小兴安岭地区白桦次生林4个林龄为研究对象,对其凋落物持水量、土壤贮水性能、土壤特性等进行研究.试验表明：4个林龄凋落物的蓄积量和最大持水量是70 a为最低,40 a为最大;土壤非毛管孔隙度在各林龄间变化呈波动性,30 a白桦次生林0～30 cm土层非毛管孔隙最小,不利于水分下渗,40 a白桦次生林0～ 30 cm土层非毛管孔隙最大,有利于降水的下渗,土壤水源涵养功能大小排序为40 a（3 276.820 t·hm-2）＜30 a（3 434.626 t·hm-2）＜50 a（3 525.015 t·hm-2）＜70 a（3 629.445 t·hm-2）.     

The Sustainability of Quinoa Production in Southern Bolivia: from Misrepresentations to Questionable Solutions. Comments on Jacobsen (2011, J. Agron. Crop Sci. 197: 390–399)

Reviewing the situation of quinoa production in southern Bolivia, Jacobsen (2011, J. Agron. Crop Sci. 197: 390) argues that the booming export market has a negative effect on the environment and on the home consumption of quinoa, thereby leading to an environmental disaster in the region. In view of the scarcity of scientific knowledge on the rapid social and environmental dynamics in the region, we consider that Jacobsen’s review misrepresents the situation of quinoa production in southern Bolivia. Specifically, we argue that (i) the data presented by Jacobsen (2011, J. Agron. Crop Sci. 197: 390) do not support any drop in quinoa crop yield supposed to reflect soil degradation and (ii) his demonstration regarding home consumption of quinoa is ill‐founded from both a nutritional and a cultural point of view. We suggest that the diffusion of the arguments exposed by Jacobsen (2011, J. Agron. Crop Sci. 197: 390), because of their flaws, might have strong negative impacts on those concerned with sustainable food production and fair‐trade with developing countries. We conclude that, rather than reinforced agro‐technical controls on local farmers, the rising competition in the international quinoa market requires a shift towards an ethical economy and ethical research cooperation with quinoa producers.