Ex-ante economic analysis of alternative mulch-based management systems for sustainable plantain production in Southeastern Nigeria

Due to rapid loss of soil fertility in traditional cropping systems and subsequent yield decline, plantain fields in Southeastern Nigeria are usually reverted to fallow after three years. This study investigates the potential of mulch-based systems for long term plantain production: alley cropping with Dactyladenia barteri and natural bush, and a cut-and-carry technique with Pennisetum purpureum. Model results simulate yields decline observed under traditional cropping systems due to a decrease in soil fertility. The adoption of mulch-based technologies is conditioned by capital availability. However, when adequate capital is available, mulch-based systems are quite profitable. Under baseline conditions, the alley cropping system with natural bush outperforms the other two improved technologies with a 154% and 72% increase in net returns over continuous and shifting traditional systems, respectively. The traditional system had the worst performance without fertilizer use. A sensitivity analysis shows that the increase in net return due to fertilizer in the alley cropping and traditional systems is at least 25%. This analysis indicates that credit programs that reach small farmers and land reform that gives them secure title are essential to widespread adoption of mulch-based plantain systems.     

国外主要作物模型研究进展与存在问题

作物模型作为大田试验研究方法的补充,已经得到越来越广泛的应用,其在栽培育种、田间管理、产量预测、灾害评估以及农业技术推广等过程中都发挥了重要作用。介绍了荷兰、美国、澳大利亚等主要作物模型研究国家作物模型的开发与应用现状,并对各国目前应用较为广泛的主要模型进行了详细分析,指出作物模型发展至今存在的问题,以期为我国作物模型的开发和应用提供指导。     

黄土高原水蚀风蚀交错带煤田开发区小流域植被恢复模式

该文以陕北神木县六道沟小流域为研究区,应用参与性农户评估方法（PRA）调查煤田开发对流域居民收入和流域可持续发展的影响,分析流域内主要植被的生长和土壤水分状况,探讨陕北特大型煤田开发基地的生态恢复模式,为煤田可持续开发提供科学依据。调查表明,煤田开发明显改变了流域内农民的收入结构和数量,工农收入比由1.4∶1（1993年）变为26.5∶1（2007年）,人均收入由830.0元增加为9 340.0元,增加了约10倍;收入的增加提高了流域农民对退耕还林（草）政策的认知度,高达95%的群众对退耕还林还草政策持肯定态度;流域内的土地利用方式有了明显变化,表现为种植业用地显著下降,由原来的31.3%下降为21.5%,而畜牧业用地（包括荒草地）从39.6%增加为52.4%,原因是煤田开发让大部分劳动力投入到煤矿生产中,部分耕地特别是坡耕地荒废,成为荒草地。流域内小叶杨人工乔木林85%以上林木生长老化、衰败,树高平均仅4～6 m,形成典型的低效、低产林,林地土壤水分亏损严重,0～50 cm土层含水量仅有3.85%;流域10年生人工柠条灌木林郁闭度只有0.2,并且深层土壤水分被过渡利用,200～600 cm层次平均含水量仅有4.1%;10年生人工紫花苜蓿草地土壤水分消耗也较显著,但程度明显低于人工柠条林地,且紫花苜蓿的存在促进了天然草本群落的演替。研究认为,在煤炭资源枯竭之前,进行有效的草本植被恢复,建立以草本植物为主体、草灌结合、具有高效生态效益和一定经济效益、有利于促进流域次生地带性植被自然生长的人工植物群落是流域有效的植被恢复模式。因此,保证流域形成具有一定郁闭度的优质放牧草原群落,在煤炭资源枯竭之后,流域经济可以顺利地由资源消耗型经济转为以放牧业为支柱产业的循环经济,实现流域的可持续发展。      

西安市水土流失空间分布特征与管控空间划分

城镇规模的快速发展是引发城市水土流失的关键因素。以西安市为研究区域,计算了各区县土壤侵蚀面积并进行了强度等级划分,分析了水土流失在空间上的分布特征并进行预测,识别出需要重点监管的区域。结果表明:西安市年均土壤侵蚀量为278.49万t,年均土壤侵蚀模数为176.74 t/(km^2·a),微度侵蚀和轻度侵蚀占总侵蚀面积的99.76%,中度侵蚀以上面积仅占0.24%;未来情景下西安市各区域土壤侵蚀模数主要分布在0~200 t/(km^2·a),其中建成区和发展区土壤侵蚀面积分别为65.37,302.19 km^2;水土流失空间管控与重点区域主要分布在高陵区、鄠邑区、长安区和临潼区等地区。随着城市建设与发展的完善,西安市重点管控区的面积也在发生变化。     

Soil type-dependent effects of drying-wetting sequences on aggregates and their associated OC and N

Evaluating the impacts of drying-wetting (DW) cycles on soil aggregates and their associated organic carbon (OC) and nitrogen (N) is crucial to understand the OC and N cycles. Soils are likely subjected to DW cycles with different sequences depending on seasons or in agroecosystems. However, studies on how DW sequences influence OC and N dynamics within aggregates, and whether this effect is dependent on soil type, are relatively limited. Herein, two DW sequences, i.e., drying-wetting-drying-wetting (2DW) and wetting-drying-wetting-drying (2WD) treatments were designed, and a consistent wetting (CW) was set as a control to assess the effects of DW sequences. Four soils (Entisol, Ultisol, Anthrosol and Mollisol) varying in texture and OC content were used. The aggregate size distribution, the OC, total N (TN), readily oxidizable OC (ROOC) and mineral N (Min-N) content in aggregates were determined. Results showed that 2DW treatment increased but 2WD treatment decreased the large aggregates of Entisol and Ultisol, while 2DW and 2WD treatments synchronously increased the large aggregates of Anthrosol but decreased them of Mollisol. Two DW treatments increased the OC in each aggregate of Entisol, Anthrosol and Mollisol but decreased them of Ultisol. The 2DW didn't affect but 2WD treatment decreased ROOC in 1–2 mm aggregates of Entisol and <0.25 mm aggregates of Ultisol and Mollisol. The 2DW and 2WD treatments minimally affected TN but potentially influenced Min-N in aggregates. The 2DW and 2WD treatments both decreased the Min-N in each aggregate size class of Entisol and Mollisol, while 2DW increased but 2WD treatment decreased Min-N in each aggregate of Ultisol and Anthrosol. These results indicated that the varied effects of DW sequences and the interactive effects of soil type with DW sequences on aggregate turnover and OC and N cycling should be reconsidered to provide more precisive evidences for global C and N cycles under the scenario of future climate changes.     

Community structure of prokaryotes and their functional potential in subsoils is more affected by spatial heterogeneity than by temporal variations

Spatial and temporal dynamics of microbial community structure and function in subsoils have been rarely studied in the past. In this paper we present data on how bacterial communities as well as selected functional groups of microbes change in the rhizosphere, the drilosphere, and in bulk soil over time in topsoil as well as in subsoil. We show that the overall richness of bacteria and abundance of nitrifiers and denitrifiers decreases in bulk soil with soil depth. However, these effects were not or to a much lower degree observed in the rhizosphere and the drilosphere. Temporal fluctuations contributed by far less than spatial factors to the dynamics of bacterial communities and abundance of nitrifiers and denitrifiers in all compartments independent from the soil depth.     

杨凌地区冬小麦-夏玉米水分供需适配性分析

采用1984—2015年气象观测站逐日气温、降水等资料,计算冬小麦-夏玉米各生育期阶段的需水量和有效降水,采用趋势分析及数理统计方法分析近32 a陕西杨凌示范区冬小麦和夏玉米生育期的降水特征,并结合作物需水特征分析其水分供需的适配性。结果表明:冬小麦和夏玉米生育期的有效降水都表现出不稳定性,除个别年份外,大多年份降水不能满足作物的需水要求。冬小麦播种~返青阶段有效降水量仅为18.9 mm,需水量在126.5 mm左右;返青~拔节阶段有效降水13.5 mm,且变异系数达130%,而需水量为81.2 mm;拔节~孕穗阶段有效降水为37.6 mm,但小麦在此阶段需水量达206.6 mm;根据小麦生理需水规律,一般年份在冬前灌水45~50 mm,拔节期灌水50 mm左右,孕穗期视情况而定。夏玉米播种~出苗阶段有效降水变异系数最大,其次是拔节~抽雄阶段,各生育阶段有效降水均表现出不稳定性。出苗~抽雄阶段平均有效降水量为126.8 mm,此阶段玉米需水量为157.2 mm;玉米抽雄~灌浆阶段平均有效降水73.9 mm,而需水量为166.6 mm;根据玉米生理需水规律,一般年份可在夏玉米大喇叭口期灌水50 mm左右,抽雄灌浆期灌水60 mm。     

Impacts of horizontal resolution and downscaling on the USLE LS factor for different terrains

Slope length and slope steepness are critical topographic factors (L and S) in the Universal Soil Loss Equation (USLE) and Chinese Soil Loss Equation (CSLE) for soil erosion modelling. Both slope length and slope gradient are potentially sensitive to spatial resolution when calculated in a GIS framework. The resolution effect on the LS factor and approaches suitable for improving the LS factor at a coarse resolution have not been well identified. To address this problem, the LS factor at 5-m and 30-m resolution in twenty-four watersheds with various terrains was estimated. And a downscale model based on matching of the lower resolution LS cumulative frequency curves to a higher resolution (“Histogram Matching” method) was tested for its potential to improve LS factor estimation accuracy. In the larger relief mountainous area, compared to 5-m resolution, the 30-m resolution generated LS was generally overestimated by more than 20% and in lower relief areas underestimated by more than 15%. This bias is less than 10% in medium relief areas. The downscale model improved LS factor estimates compared to the 30-m resolution estimate by more than 10% when comparing frequency distribution curves and more than 20% in mean values in larger relief areas. The downscale model worked well in all regions except for the low relief areas, which intuitively are the low soil erosion potential areas. The results of this research help quantify the uncertainty in soil erosion estimates and may ultimately help to improve the assessment of soil erosion through its impact on LS factor estimates, especially at regional and global scales.     

Feasibility of magnetite powder as an erosion tracer for main soils across China

Purpose

This study aimed to explore the potential feasibility of magnetite powder as an erosion tracer for national-scale soil erosion monitoring in China.

Materials and methods

This study evaluated the effectiveness of silt-sized magnetite powder, a magnetic erosion tracer, in four representative erodible soils in China with distinct textures (from sandy loam to silty clay). The χ_lf values of different magnetic tracer-tagged aggregate size ranges (>?0.05 mm) were similar based on dry aggregate analysis.

Results and discussion

Simulated long-term leaching tests showed that the tracer had low mobility in soil profiles. The simultaneous separation of the tracer and tested soils under surface flow scouring conditions indicates that the tracer exhibited good bonding ability with different soils.

Conclusions

These findings indicate that magnetite powder is suitable for erosion monitoring in China. This method may be extended to other regions over the world.