Phenotypic nutrient up-take differences in an alley cropping system in semi-arid Machakos, Kenya

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｔｈｅＦｉｆｔｈＦｒａｍｅｗｏｒｋＰｒｏｇｒａｍｍｅｏｆｔｈｅＥｕｒｏｐｅａｎＣｏｍｍｉｓｓｉｏｎ(ＥＣ,1999),ｕｎｄｅｒ“ｔｏｏｌｓｆｏｒｓｕｓｔａｉｎａｂｌｅｄｅｖｅｌｏｐｍｅｎｔ”,ｔｈｅｒｅｗａｓｒｅｃｅｎｔｌｙａｓｐｅｃｉａｌｃａｌｌｆｏｒｐｒｏｐｏｓａｌｓｆｏｒ“Ｔｅｃｈｎｏｌｏｇｉｅｓｆｏｒｓｕｓｔａｉｎａｂｌｅｐｌａｎｔａｎｄａｎｉｍａｌｐｒｏｄｕｃｔｉｏｎ:ｂｕｉｌｄｉｎｇｂｌｏｃｋｓｆｏｒｉｍｐｒｏｖｅｍｅｎｔ(ｆｏｒｓｍａｌｌｓｃａｌｅｏｒｅｎｖｉｒ…     

Competition of the acitive roots of Cassia siamea Lam. and Zea mays L. (cv. Katumani Composite B) in an alley cropping trial in semi-arid Kenya

A study on root competition in alley cropping was carried out in an agroforestry system, involving Cassia siamea Lam. and maize (Zea mays L. cv. Katumani composite B). The existence and intensity of root competition in the top soil as manifested by the distribution of the active roots of cassia and maize, in space and time, was assessed. The root length density of maize was far greater than that of cassia in the upper 10 cm, implying that cassia was not competing with maize for water and/or nutrients at that depth. However, at maize crop tasselling and grain filling stages there was a marked overlap of roots of the two plants at lower depths (20-50 cm). This varied with distance from the cassia hedge in a way that there was a tendency for highest overlap near middle maize rows. This partly explained observed yield differences. Therefore cassia may not be a suitable choice for alley cropping with maize under semi-arid conditions on non-sloping land, unless most of its active roots can be properly managed to absorb resources below the feeding rhizosphere of the active maize roots.     

黄土丘陵沟壑区苜蓿地土壤水分环境效应

根据田间试验资料,分析研究了黄土丘陵沟壑区苜蓿地土壤水分的周年变化规律,并以休闲地和几种一年生作物地作为对照进行对比研究,得出以下主要结论:①雨季降水对苜蓿地土壤水分的补给起着重要的作用,其土壤贮水量动态与年内的降雨周期相吻合,但总体上朝着土壤不断干化的方向发展;②经过一个雨季,苜蓿地的土壤贮水量与平均含水量分别呈不同程度的下降,而休闲地与4月份持平;③相同的降水对不同作物地的补给效果不同,以3m土层计算,苜蓿地的农田蒸散量与谷子、玉米相当,比豆子地高,但要低于高粱地;④长期种植苜蓿引起的深层土壤干化问题必须引起足够的重视,干化土地的水分恢复不是一朝一夕的事情。     

施氮对黄土旱塬区春玉米土壤呼吸和温度敏感性的影响

了解施氮对土壤呼吸和温度敏感性的影响,是研究农田土壤呼吸变化的重要环节,对预测农田土壤呼吸变化具有重要意义.基于中国科学院长武黄土高原农业生态试验站的氮肥管理试验,于2013年4月至2014年9月利用LI-8100系统(LICOR,Lincoln,NE,USA)监测施氮和不施氮条件下旱地春玉米生长季土壤呼吸、温度、水分以及根系生物量的变化,研究施氮条件下生物与非生物因素对土壤呼吸速率和温度敏感性(Q10)的影响.施氮显著提高了生长季土壤的累积呼吸量(P0.05),与不施氮相比,施氮处理累积呼吸量2013年提高了35%,2014年提高了54%.但施氮显著降低了土壤呼吸温度敏感性(P0.05),施氮处理的Q10较对照2013年降低了27%,2014年降低了17%.施氮显著提高了春玉米产量、地上部生物量和根系生物量(P0.05).施氮处理根系生物量较不施氮处理2013年提高了0.32倍,2014年提高了1.23倍.施氮对土壤温度和水分无显著影响,根系生物量是施氮条件下导致土壤呼吸差异的重要生物因素.     

黄土高原人工林土壤水分效应的地带性特征

为提高黄土高原人工植被建设成效,依据天然植被呈地带性分布的规律,对比分析不同地带人工林与天然植被对土壤水分利用的差异。结果表明:不同植被地带的人工林下均存在一定程度的水分亏缺和干化层现象,其严重程度为森林带<森林草原带<典型草原带。森林带的水分条件可满足林木成材对水分的需求,林木采伐后土壤水分可得到很好恢复;森林草原带可满足10龄以下林木生长对水分需求,10龄以上林分的水分亏缺严重,林木采伐后土壤水分恢复进程缓慢;典型草原带不能满足人工林生长对水分需求。在此基础上,提出了与地带性水分条件相适应的人工林草植被建设模式。     

黄土丘陵沟壑区狼牙刺灌木林地的土壤水分动态

在陕北黄土区安塞县纸坊沟小流域,选择不同林龄的狼牙刺地块,对其土壤水分作了动态观测,并以柠条地和撂荒地为对照。分析研究得出如下结论:①在土层足够深的地块上,天然灌木狼牙刺年蒸散量约为590mm,单株平均耗水量约85mm。强烈耗水期是5月中旬至7月底,8月底土壤水分达到最低值,9月份以后开始恢复;②狼牙刺地土壤水分活跃层在0-2.5m之间,土壤水分的消耗强度随深度的增加而下降;③狼牙刺地干层超过10m,比同龄的柠条土壤干层(8m)深,在两个生长季中,干层没有进一步发展。     

Competition between maize and pigeonpea in semi-arid Tanzania: Effect on yields and nutrition of crops

Productivity of maize–pigeonpea cropping systems is dependent on facilitative and competitive interactive effects on resource availability. Controlling these interactions may benefit farmers through increased productivity associated with optimized crop yields. Previous research on maize–pigeonpea culture in Sub-Saharan Africa has focused on yield and soil fertility, but provided inadequate information on the mechanisms of possible interspecific competition. We employed a factorial field experiment to examine yield and nutritional responses of maize and pigeonpea to cropping systems (sole maize, intercropping, and improved fallow), N and P fertilizer additions, and cattle manure additions in Dodoma, Tanzania. The study objectives were to assess competition between crops and to determine how manure or fertilizer inputs may mitigate such interactions to improve yields. Intercropping enhanced maize yield over sole maize only when fertilized, reflecting probable nutrient competition. Improved fallows alone or with fertilizers (1.2–1.6 Mg ha⁻¹) increased maize yields over sole maize (0.6 Mg ha⁻¹). These increases were attributed to pigeonpea facilitation through soil nutrient replenishment, reduced competition associated with sequential cropping arrangements, and added nutrients from fertilization. Combined fertilizer and manure applications also improved maize and pigeonpea yields. Plant nutrient diagnosis indicated primary and secondary P and Ca deficiencies, respectively associated with P-fixation and leaching of cations due to high soil acidity and exchangeable Al. Maize competed strongly in mixture suppressing biomass and grain yields of the unfertilized pigeonpea by 60% and 33%, respectively due to limited soil nutrients and/or moisture. These yield reductions suggest that the intercropped pigeonpea did not recover from competition after maize harvesting that reduced competition. Optimizing yields of both maize and pigeonpea would require the addition of prescribed fertilizer when intercropped, but applications can be reduced by half under the improved fallow system due to alleviating interspecific competition.     

紫色土坡耕地硝酸盐淋失特征

利用具有壤中流测定功能的径流小区的定位观测结合土壤剖面硝酸盐累积的动态分析,研究了紫色土坡地硝酸盐淋失特征.结果表明,紫色土坡地硝酸盐呈旱季累积,雨季淋失的特点,而壤中流是紫色土硝酸盐淋失的主要通道.紫色土为土层浅、土壤下伏透水性极弱的紫色泥页岩,同时夏季降雨丰富,壤中流极为发育,2003～2005年壤中流平均流量为169.7mm,占雨季径流量的52.42%,其中,NO3--N含量持续偏高,2003～2005年平均含量高达14.92mg·L-1.3年平均随壤中流淋失的硝态氮达27.98 kg·hm-2,占年施肥量的10.0%,硝酸盐淋失具有季节与年际间差异,淋失负荷主要受壤中流流量影响.紫色土坡地硝酸盐随壤中流大量淋失不仅造成当地浅层地下水硝酸盐污染,而且将加剧长江三峡库区水环境压力.     

河套灌区土壤水和地下水动态变化及水平衡研究

为探究田间土壤水及地下水在不同作物种植区、不同灌期等情况下的动态变化规律与水平衡特征,以春小麦、玉米、向日葵为典型作物,在河套灌区选取4块2亩的试验田,于2009年4-11月采集田间土壤及地下水样品进行研究.结果表明,不同作物地块间土壤含水率的变化差别主要集中在5-9月的作物生长期.夏灌灌水量不足,土壤含水率呈下降趋势,田间土壤水分变化属于“蒸腾蒸发消耗型”;秋浇期内水量充足,各地块各土层含水率均明显增加,田间土壤水分呈“入渗补给型”.各地块地下水埋深月均变化趋势基本一致,由于优先流的存在,地下水对灌溉降水响应快.本文定量研究了区域土壤水和地下水的变化规律,揭示了灌区水平衡要素间的相互转换关系,可为灌区科学合理的水资源管理提供理论依据.     

Influence of trees on the spatial structure of arbuscular mycorrhizal communities in a temperate tree-based intercropping system

Tree-based intercropping (TBI) is an ecologically sustainable agricultural practice that may promote a more diverse arbuscular mycorrhizal (AM) fungal community compared to conventional systems, but the influence of the dynamics of these systems on AM fungi has not been established. Soil and root samples were collected in the intercropping alleys along transects perpendicular to tree rows occupied by white ash (Fraxinus americana), poplar (Populus deltoids × nigra), Norway spruce (Picea abies), and rows without trees (control). Molecular analysis of the AM fungal community at the TBI site revealed 17 phylotypes belonging to the Glomeraceae. Overall, the AM fungal community in the TBI site was comparable to other conventional agricultural systems; with the majority of phylotypes belonging to Glomus group A. AM fungal phylotype richness and community composition significantly differed among the treatments in the TBI site. AM fungal communities were more diverse in cropping alleys adjacent to trees that associate with AM fungi than trees that do not associate with AM fungi. Norway spruce had a negative influence on the AM fungal community as tree rows and bordering intercropping alleys had a significantly lower phylotype richness and different community composition. These results suggest that to maintain a diverse AM fungal community throughout TBI systems, it may be best to incorporate tree species that associate with AM fungi.     

Nitrous oxide emissions from a maize field during two consecutive growing seasons in the North China Plain

Nitrous oxide (N₂O) emissions from a maize field in the North China Plain (Wangdu County, Hebei Province, China) were investigated using static chambers during two consecutive maize growing seasons in the 2008 and 2009. The N₂O pulse emissions occurred with duration of about 10 days after basal and additional fertilizer applications in the both years. The average N₂O fluxes from the CK (control plot, without crop, fertilization and irrigation), NP (chemical N fertilizer), SN (wheat straw returning plus chemical N fertilizer), OM- 1/2N (chicken manure plus half chemical N fertilizer) and OMN (chicken manure plus chemical N fertilizer) plots in 2008 were 8.51, 72.1, 76.6, 101, 107 ng N/(m²·sec), respectively, and in 2009 were 33.7, 30.0 and 35.0 ng N/(m²·sec) from CK, NP and SN plots, respectively. The emission factors of the applied fertilizer as N₂O-N (EFs) were 3.8% (2008) and 1.1% (2009) for the NP plot, 3.2% (2008) and 1.2% (2009) for the SN plot, and 2.8% and 2.2% in 2008 for the OM-1/2N and OMN plots, respectively. Hydromorphic properties of the investigated soil (with gley) are in favor of denitrification. The large differences of the soil temperature and water-filled pore space (WFPS) between the two maize seasons were suspected to be responsible for the significant yearly variations. Compared with the treatments of NP and SN, chicken manure coupled with compound fertilizer application significantly reduced fertilizer loss rate as N₂O-N.     

西藏高原草原化小嵩草草甸生长季土壤微生物呼吸测定

以西藏当雄县草原化小嵩草草甸生态系统为研究为对象,利用Li6400-09对生长季土壤微生物异养呼吸进行了测定。土壤异养呼吸R(h)动态与土壤温度T()变化趋势一致,尤其与5cm地温相关性最强,说明5cm地温是土壤微生物异养呼吸的主要限制因子。在生长季中土壤异养呼吸与5cm土壤温度呈现不同的函数关系:在降水比较集中的雨季(6～8月),函数关系是Rh=0.106exp0.133T;在降水相对较少的旱季(5月,9～10月),函数关系是Rh=0.18exp0.0833T。在生长季中,雨季土壤日异养呼吸量为2.4g CO₂.m-2,雨季异养呼吸总量为219.6g CO₂.m-2,Q 10为3.8;旱季日异养呼吸量为1.8g CO₂.m-2,呼吸总量为160.2gCO 2.m-2,Q 10值为2.3。结果表明,土壤异养呼吸在降水集中的雨季对土壤温度反应更敏感,在生长季不同时期由于降水格局的影响,土壤水分对土壤微生物异养呼吸对温度的响应有调节作用。2004年生长季(5～10月)土壤异养呼吸总量达379.8gCO₂.m-2。     

Vertical and horizontal movement of phorate and its metabolites in field soil under cropped and uncropped conditions

Vertical and horizontal movement of phorate and its metabolites in field microplots was studied under cropped and uncropped conditions in winter and summer seasons. Phorate bands were placed 2.5 cm below the soil surface and were subject to leaching by irrigation and rain. The crops used were peas, in winter, and maize, in summer. Periodic analyses of samples showed that total phorate residues (TPR) were significantly more mobile under cropped conditions than in fallow conditions in both seasons. The peak concentration depth remained at 7.5 cm throughout most of the experimental period. Irrespective of treatments, downward movement of TPR was greater in winter. Horizontal movement of TPR was greater under cropped conditions in summer. Differences in lateral mobility were insignificant in two seasons under cropped conditions. However, under uncropped conditions, horizontal movement was relatively more in the summer season. TPR persisted in the soil for 120 and 90 days in winter and summer, respectively. The TPR persistence was almost the same in the two crops. Maize and pea plants at harvest had residues below the legal health tolerance limit. Half-life values of TPR in maize and pea plants were 38 and 42 days, respectively.     

Runoff and sediment losses from 27 upland catchments in Southeast Asia: Impact of rapid land use changes and conservation practices

Rapid changes in upland farming systems in Southeast Asia generated predominantly by increased population pressure and ‘market forces’ have resulted in widespread land degradation that has been well documented at the plot scale. Yet, the links between agricultural activities in the uplands and downstream off-site effects remain largely unknown because of the difficulties in transferring results from plots to a larger scale. Many authors have thus pointed out the need for long-term catchment studies. The objective of this paper is to summarize the results obtained by the Management of Soil Erosion Consortium (MSEC) over the last 5 years from 27 catchments in five countries (Indonesia, Laos, Philippines, Thailand, and Vietnam). The purpose of the study was to assess the impacts of cultivation practices on annual runoff and erosion rates. Initial surveys in each catchment included topography, soils and land use. Monitoring included climatic, hydrologic and erosion (total sediment yield including bed load and suspended sediment load) data, land use and crop yields, and farmers’ income. In addition, new land management options were introduced through consultations with farmers and evaluated in terms of runoff and erosion. These included tree plantations, fruit trees, improved fallow with legumes, maize intercropped with legumes, planted fodder, native grass strips and agro-ecological practices (direct sowing and mulch-based conservation agriculture). Regressions analyses showed that runoff during the rainy season, and normalized runoff flow coefficient based on erosive rainfall during the rainy season (rainfall with intensity exceeding 25 mm h⁻¹) increase with the percentage of the catchment covered by maize. Both variables decrease with increasing soil depth, standard deviation of catchment slope (that reflects terrain roughness), and the percentages of the catchment covered by fallow (regular and improved), tree plantations and planted fodder. The best predictors of sediment yield were the surface percentages of maize, Job's tears, cassava and footpaths. The main conclusions generated from this study were: (i) soil erosion is predominantly influenced by land use rather than environmental characteristics not only at the plot scale but also at the catchment scale; (ii) slash-and-burn shifting cultivation with sufficiently long rotations (1 year of cultivation, 8 years of fallow) is too often unjustly blamed for degradation; (iii) in its place, continuous cropping of maize and cassava promotes high rates of soil erosion at the catchment scale; (iv) conservation technologies are efficient in reducing runoff and total sediment yield at the catchment scale; (v) the adoption of improved soil management technologies by upland farmers is not a function of the degree of intensification of their farming system and/or of their incomes. The results suggest that if expansion of maize and cassava into already degraded upland systems were to occur due to increased demand for biofuels, there is a risk of higher runoff and sediment generation. A failure to adopt appropriate land use management strategies will result in further rapid resource degradation with negative impacts to downstream communities.     

Forest soil CO2 fluxes as a function of understory removal and N-fixing species addition

We report on the effects of forest management practices of understory removal and N-fixing species (Cassia alata) addition on soil CO2 fluxes in an Eucalyptus urophylla plantation (EUp), Acacia crassicarpa plantation (ACp), 10-species-mixed plantation (Tp), and 30-species-mixed plantation (THp) using the static chamber method in southern China. Four forest management treatments, including (1) understory removal (UR); (2) C. alata addition (CA); (3) understory removal and replacement with C. alata (UR+CA); and (4) control without any disturbances (CK), were applied in the above four forest plantations with three replications for each treatment. The results showed that soil CO2 fluxes rates remained at a high level during the rainy season (from April to September), followed by a rapid decrease after October reaching a minimum in February. Soil CO2 fluxes were significantly higher (P < 0.01) in EUp (132.6 mg/(m2·hr)) and ACp (139.8 mg/(m2·hr)) than in Tp (94.0 mg/(m2·hr)) and THp (102.9 mg/(m2·hr)). Soil CO2 fluxes in UR and CA were significantly higher (P < 0.01) among the four treatments, with values of 105.7, 120.4, 133.6 and 112.2 mg/(m2·hr) for UR+CA, UR, CA and CK, respectively. Soil CO2 fluxes were positively correlated with soil temperature (P < 0.01), soil moisture (P < 0.01), NO3?-N (P < 0.05), and litterfall (P < 0.01), indicating that all these factors might be important controlling variables for soil CO2 fluxes. This study sheds some light on our understanding of soil CO2 flux dynamics in forest plantations under various management practices.     

生物炭对农田地表反照率及土壤温度与湿度的影响

为了探究生物炭输入后农田地表反照率及土壤温度与土壤湿度的响应,通过田间小区试验,分析生物炭影响下农田地表反照率、土壤温度、土壤湿度的变化情况. 试验共设置3个主处理——CK处理(不施用生物炭)、BC5处理〔生物炭施用量为0.5 kg/(m2·a)〕、BC45处理〔生物炭施用量为4.5 kg/(m2·a)〕,同时每个主处理设置2个副处理——种植作物(以+表示)和未种植作物(以-表示). 结果表明:在有作物覆盖条件下,相对于CK+处理,BC45+、BC5+处理的地表反照率在玉米苗期分别下降23.1%、19.1%(P＜0.05),在玉米拔节期分别下降20.0%、15.1%(P＜0.05),但在玉米抽穗期至成熟期,各处理的地表反照率无明显差异. BC5+、BC45+处理的土壤温度、土壤湿度与CK+处理相比均未见显著改变. 在未种植作物条件下,相对于CK-处理,BC45-、BC5-处理的地表反照率最大降幅分别为26.7%、24.3%(P＜0.05),BC5-处理的土壤湿度增幅为1.7%~3.8%,BC45-处理的土壤温度、土壤湿度无显著变化. 可见,随着玉米冠层结构的发展,生物炭输入降低地表反照率的效应在逐渐减弱甚至消失;生物炭输入对土壤温度、土壤湿度的影响程度与作物覆盖条件以及生物炭施用量有关.      

贵州坡耕地水土保持措施效益研究

对旱坡地水土保持的截流沟措施、横坡种植措施和植物篱措施进行效益研究,结果表明:在裸露耕地上,水土流失十分严重,地表径流达到4 044.4m³/hm²·a、土壤流失高达172.4t/hm²·a,以此速率流失土壤,其耕层(15cm)约在12年后,将被冲刷殆尽。截流沟措施与横坡种植措施相比,可减少地表径流702.6m³ /hm²·a和土壤流失19.2t/hm²·a;但其占地面积大,农作物产量低,收益小。植物篱种植措施与横坡种植相比可减少地表径流345.3m³/hm²·a;土壤流失21.0t/hm²·a。虽然植物篱占据耕地面积,但并不影响农作物产量。植物篱种植下的耕层土壤的酸碱度和质地得到改善,土壤养分含量有所提高,土壤侵蚀速率远低于易风化土壤的成土速率,同时结合人工翻耕,每年平均以17.5cm的速度形成梯坎,以1.1°的速度减缓坡度。该项措施最终可实现坡改梯的目的,实现旱坡地的可持续利用。     

污泥植物处理后对玉米生长及土壤重金属含量的影响

为了探明植物处理后污泥作为肥料施用后对后续作物和土壤的影响,将植物处理后的污泥混于土壤,种植后续作物玉米(Zea mays),测定作物产量以及土壤和作物的重金属含量.结果表明,污泥施用2a后仍有肥效,其玉米生物量显著大于无污泥的对照处理,且单种植物处理后的污泥肥效要优于无植物或套种处理的污泥.施用污泥后的2a内,4季玉米的茎叶和籽粒Zn、Cd、Cu和Pb含量均符合饲料标准;但第3季以后玉米籽粒才可作为食用.施用污泥后土壤重金属含量随时间而下降,Zn的年消失率为32%~35%,Cd为28%~33%,Cu为18%~30%,Pb为15%~23%;施用污泥的土壤重金属年下降率高于对照和化肥处理.污泥施用于土壤2a后,表层土壤全Zn和全Pb含量与对照处理已无明显差异.     

华北平原地下水浅埋区土壤水分动态的时间序列分析

以沧州和衡水实验站为华北平原地下水浅埋区典型区,利用3 a土壤水负压和地下水观测数据,研究了不同年份和土壤质地土壤水分动态。土壤水分数据表明,平水年或丰水年后的枯水年土壤水分从表层到深层为增长型趋势,枯水年为增长-减小-增长趋势;在土壤非均值条件下(沧州),土壤水分具有补给和消耗的季节性变化,而土壤均质条件下(衡水),无明显季节性变化。时间序列分析结果表明,平水年或丰水年沧州实验点土壤浅层(100 cm以上)和深层(100 cm以下)具有明显差异,从上到下土壤水分更加稳定,衡水实验点无明显差异性;枯水年两实验站浅层和深层差异性更小。土壤质地在降水和土壤水以及地下水的响应关系方面具有显著作用。     

影响不同农作物镉富集系数的土壤因素

农作物的Cd富集系数（BCF）受多种因素影响.为明确田间条件下不同农作物的Cd富集系数特征差异及土壤性质对其影响,分别在我国水稻、小麦和玉米主产区不同污染程度的地块上作物收获期采集土壤和作物籽粒点对点样品,研究水稻、小麦、夏玉米和春玉米的Cd富集系数特征及土壤性质对不同农作物的Cd富集系数的影响,并通过多元回归方程建立以上农作物Cd富集系数与土壤性质的定量关系.结果表明,在田间土壤中Cd含量范围为0.15~2.66 mg·kg^-1条件下,水稻、小麦、夏玉米和春玉米Cd富集系数的均值分别为0.915、0.155、0.113和0.102,水稻明显高于小麦和玉米,春玉米的Cd富集系数最低.土壤中的Cd含量与小麦、夏玉米和春玉米的BCF呈极显著负相关;土壤有机质（SOM）与小麦、夏玉米BCF之间的关系呈极显著负相关;土壤pH和阳离子交换量（CEC）对作物BCF也有影响.引入土壤Cd含量、pH、SOM、CEC等因素,建立水稻、小麦、夏玉米和春玉米的Cd富集系数预测方程.水稻、小麦、夏玉米和春玉米的BCF预测方程相关系数分别为0.423^*、0.796^**、0.826^**和0.551^**,均达到显著或极显著水平,可以较好地预测不同土壤条件下不同农作物的BCF值.