Estimating Carbon Capture Potential of Fallow Weeds in Rice Cropping Systems

Weeds occurred during the fallow season can well perform the function of carbon(C)capture due to receiving little human disturbance.This study aimed to evaluate the C capture potential of fallow weeds in rice(Oryza sativa L.)cropping systems.A six-region,two-year on-farm investigation and a three-year tillage experiment were conducted to estimate C capture in fallow weeds in rice cropping systems.The on-farm investigation showed that the average mean C capture by fallow weeds across six regions and two years reached 112 g m^(-2).The tillage experiment indicated that no-tillage practices increased C capture by fallow weeds by 80%on average as compared with conventional tillage.The results of this study not only contribute to an understanding of C capture potential of fallow weeds in rice cropping systems,but also provide a reference for including fallow weeds in the estimation of vegetative C sink.

Native Species Composition and Diversity of Valuable Woody Plants Regeneration during Fallow Period in Kamwatta, Moruca, Guyana

An intelligent method of shifting cultivation to regenerate vegetation after a long fallow period is critical information for restoration strategies. The literature review identified that the assessment of woody plant species on abandoned farmland has never been done before in Kamwatta, Moruca Region 1. In addition, more information should be available in indigenous communities and at the national level, including more documentation of the utilization of natural resources by the Warrau community. This study assessed the valuable woody plant species that grew during the fallow periods. Nine farmlands were randomly selected along a 100 m transect, each with varying fallow periods. In order to collect information on the age of farm abandonment, the researcher employed a mixed-methods approach. First, we found how long each farm had been fallow by administering a semi-structured questionnaire. Then, we conducted a flora survey to gain information on the variety and abundance of valuable plants using the age of farm abandonment as a dependent variable. The data analysis included the number of valuable woody trees with a diameter of >10 cm, seedlings and saplings with a diameter of <10 cm, the location of identified trees, and the uses of identified tree species. Microsoft Excel was used to code and analyze the questionnaire, while QGIS, Shannon’s Index of Diversity, and Simple Linear Regression were used to analyze the inventory data. The results showed that the respondents listed 38 valuable woody species, and 79% occurred in the studied area. The field verification revealed that the dominant family in the area was Mimosaceae. Species abundance increased with fallow up to 10 years before declining in the latter years. Plant diversity and abundance had a weak relationship with the age of abandoned farmlands for woody trees, while the seedlings and saplings showed no relationship.

Species diversity,population structure and regeneration of woody species in fallows and mature stands of tropical woodlands of southeast Angola

This study in the dry tropical woodlands of SE Angola in Cuando-Cubango Province assessed the diversity and composition of woody species in fallows compared to those in mature woodlands. We assessed the population structure of the most harvested woody species by calculating size class distribution and evaluated their regeneration potential based on the density of saplings. The vegetation was surveyed in 20 plots of 20 × 50 m(1000 m2). In each plot, we measured the diameter at breast height(DBH) of all woody species with DBH ≥ 5 cm. The saplings were counted, identified and recorded; 718 individuals, corresponding to 34 species in 32 genera and 15 families were recorded. The size class distribution of target woody species showed three different patterns in fallows and mature woodlands. In general,most of the smaller diameter classes had more individuals than the larger ones did, showing that the regeneration may take place. However, in some diameter classes, the absence of larger stems indicated selective logging of larger trees. Few saplings were recorded in the fallows or mature woodlands; fire frequency and intensity is probably the main obstacle for seed germination and seedling survival rates in the studied area.

Modeling habitat suitability and utilization of the last surviving populations of fallow deer(Dama dama Linnaeus,1758)

DüzlerçamıWildlife Reserve Area(WRA)is the last natural habitat of fallow deer(Dama dama)in the world.Fallow deer is native to Turkey,however,its geographical range is currently confined to DüzlerçamıWRA,Antalya.To date,a detailed habitat investigation of fallow deer dis-tribution has not been conducted.This study is vital for the last surviving populations of fallow deer in Turkey.There-fore,we studied the habitat suitability and utilization of fal-low deer in the DüzlerçamıWRA.Vegetation and wildlife inventory was surveyed across a total of 304 sample areas between 2015 and 2017.Plant species were recorded accord-ing to the Braun-Blanquet method and wildlife surveys were based on footprints,feces,and other signs of fallow deer.Classification and regression tree techniques,as well as MAXENT,were used to model vegetation and fallow deer habitat.Topographic position index,terrain ruggedness index,roughness index,elevation,and bedrock formation were also calculated and included in the models.Based on our results,we drafted a habitat protection map for fallow deer.To ensure sustainability of habitats where populations of fallow deer are found in Turkey,we developed recommen-dations such as closuring human access of the 1st-degree Protection Area and reintroduction of the species to other potential habitats.

Divergent responses of tiller and grain yield to fertilization and fallow precipitation:Insights from a 28-year long-term experiment in a semiarid winter wheat system

Tillering is an important phenological stage,which is strongly related to the yield in spike components and final grain yield during winter wheat growth.Precipitation during the fallow season(fallow precipitation)influences tillering in winter wheat on the semi-arid Chinese Loess Plateau.However,little work has been done regarding tiller number changes under various types of fertilization and amounts of fallow precipitation on a long-term scale.Effects of fallow precipitation and fertilization on tiller were investigated in a winter wheat(Triticum aestivum L.)system in a 28-year field study(1990 to 2017)in a semiarid agro-ecosystem.Tiller number,spike number and grain yield were measured in four fertilization conditions:control without fertilizer(CK);mineral nitrogen fertilizer alone(N);mineral phosphorus fertilizer alone(P);mineral nitrogen and phosphorus fertilizer together(NP).Based on the long-term annual fallow precipitation,dry years(mean annual fallow precipitation)were distinguished.Phosphorus fertilization alone significantly increased the mean annual tiller number(23%),and the increase in tiller number was higher in wet years(29%)than in the dry years(17%).However,nitrogen fertilization alone had little effect on mean tiller number,while nitrogen and phosphorus together significantly increased mean annual tiller number(30%),mean tiller number in wet years(45%)and mean tiller number in dry years(17%).Tiller number was significantly and positively correlated with fallow precipitation in dry years for all fertilizer treatments,whereas it was weakly and either positively or negatively correlated with fallow precipitation in wet years depending on the treatment.This study found positive correlations between tiller number and fallow precipitation in the CK and NP treatments,and it found negative correlations between tiller number and fallow precipitation in the treatments with nitrogen fertilization alone or phosphorous fertilization alone in wet years.Understanding the impacts of fallow precipitation and fertilization on tiller development shed light on ways to improve crop production in rain-fed agricultural regions.

Research on Scientifically and Rationally Promoting the Fallow of Cultivated Land under the Strategy of Rural Revitalization

Implementing the rural revitalization strategy is an important decision-making arrangement made by the party s 19th National Congress,and is the general grasp of the work of"agriculture,rural areas and farmers"in the new era.In rural development,the issue of cultivated land is an important way to promote poverty alleviation in the vast rural areas and build a well-off society in an all-round way.In combination with the fact that the current quality of cultivated land resources in China is not high and the basic fertility has been continuously declining caused due to pollution,China must promote a scientific and rational system of arable land fallow to ensure the further development of agricultural modernization in China.In the process of researching the implementation of the arable land fallow system,the problems of land abandonment and"non-agriculturalization"after farmland fallow,the willingness of farmers to fallow and the subsidy for farmland fallow have been discovered.In response to the problems above,corresponding policy recommendations are put forward in order to better promote the process of arable land fallow and poverty alleviation in China.

Comparison of Soil Quality Improvement under Different Fallow Types on Dystric Nitosols Derived from Sand Stone in South Western Nigeria

The project was carried out to determine the effects of different fallow types on soil derived from sand stone of low nutrient status in south western Nigeria. The different fallow types include Leu-caena, elephant grass, guinea grass and secondary forest. Cultivated farm land was used to serve as control for comparison of soil quality improvement. Soil samples were collected in four replicates on each land cover type and analyzed for major physical and chemical parameters. The results show little fertility improvement for base saturation with 1.42 cmol/kg in Leucaena, 1.99 cmol/kg in secondary forest, 1.60 cmol/kg in guinea grass and in Elephant grass. Leucaena resulted to better soil quality than secondary forest especially in surface properties though not significantly different. Elephant grass and guinea grass also resulted to better Nitrogen content. Nitrogen content recorded in Leucaena was high with 0.20% - 0.25%. Guinea grass and elephant grass resulted to better soil quality in terms of nitrogen content [0.20% - 0.25%] than cultivated and secondary forest [0.07% - 0.11%] due to their yearly incorporation in to the soil by ploughing. The values of phosphorus were higher in Leucaena though not significant [6.46 mg/kg]. Low soil properties improvement is attributed to nutrient exploitation in Leucaena and secondary forest after a long period of fallow [20 years] while, nitrogen enrichment in the grasses is attributed to yearly tillage. Over all low to medium soil variability indicates that the soils could be managed as a unit for crop production.

Fertility Reduction in Male Persian Fallow Deer (Dama dama mesopotamica): Inbreeding Detection and Morphometric Parameters Evaluation of Semen

Persian fallow deer (Dama dama mesopotamica) is only found in a few protected and refuges areas in the northwest, north, and southwest of Iran. The aims of this study were analysis of inbreeding and morphometric parameters of semen in male Persian fallow deer to investigate the cause of reduced fertility of this endangered species in Dasht-e-Naz National Refuge, Sari, Iran. The Persian fallow deer semen was collected by an electroejaculator from four adult bucks randomly during the breeding season and from five dehorned and horned deer’s in non-breeding season. Twelve blood samples were taken and mitochondrial DNA was extracted, a non-coding region called d-loop was amplified, sequenced and then were considered for genetic analysis. The Persian fallow deer’s normal and abnormal spermatozoa were similar to that of domestic ruminants but very smaller and difficult to observe at the primary observation. The post-mating season collected ejaculates contained abnormal spermatozoa, debris and secretion of accessory glands in horned bucks and accessory glands secretion free of any spermatozoa in dehorned or early velvet budding bucks. Microscopic evaluation in all four bucks during the mating season showed the mean concentration of 9 × 106 spermatozoa/ml. The mean ± standard deviation of age, testes length and testes width was 4.60 ± 1.52 years, 3.58 ± 0.32 and 1.86 ± 0.09 cm, respectively. The results identified 1120 loci in which 377 were polymorphic. In conclusion, reduced fertility of male Persian fallow deer may be caused by inbreeding of the protected herd in a limited area of Dasht-e-Naz National Refuge.

Extent of Reduction of the Fallow Period and Its Impact on Upland Rice Production in the Nongowa Chiefdom of Kenema District in Eastern Sierra Leone

Slash-and-burn agriculture is the common practice for upland rice intercropping system in Sierra Leone and it has been blamed for the loss of forest vegetation across the country. Shortening of the fallow period in the Eastern region of Sierra Leone has implications on agricultural food production and the persistence of the remaining tropical rainforest. This study was therefore undertaken to assess: 1) the extent of reduction of the fallow period in the Nongowa Chiefdom of Kenema District;2) the causes of reduction in the fallow period;3) farmers’ perception of the relevance of fallow period and the implications of reduction of fallow period on crop production. The study revealed a drastic reduction of the fallow period in the chiefdom with a mean of 3.8 years which falls far below the country mean fallow period of 8.8 years as estimated by FAO. Farmers pointed out that the reduction of the fallow period was as a result of land scarcity due to competing land uses such as large scale commercial agriculture, logging, mining, charcoal burning and expansion of settlements. Farmers agreed that a fallow period of at least 10 years is necessary for upland rice production. Farmers were aware of the impact of reduction of the fallow period on upland rice production and were able to estimate rice yields based on the age of the fallow. Also, farmers have attempted to adapt to the constraints posed by shorter fallow periods by selection of rice varieties to suit the length of the fallow periods.

Visual Analysis of Crop Rotation Fallow Patterns in Recent 5 Years Based on CiteSpace

Based on the"Web of Science Core Collection"(SCIE database),this article used the visualization software CiteSpace to visualize and analyze the crop rotation fallow patterns in the past five years.It analyzed the countries,institutions,keywords and hot topics of related literature to explore their research characteristics and development,and to provide reference for crop rotation fallow research and practice.The research shows that:1)developed countries are the main research force in the field of crop rotation and fallowing,and the connection between the research of each country and each institution is not close;2)research hotspots can be mainly summarized as:crop growth and yield,greenhouse gas emissions and soil health analysis,and the research in this field is constantly refined,combining macro and micro;3)In recent years,there is a big gap between China and foreign countries in the field of crop rotation and fallow research.It is necessary to strengthen the cooperation with research institutions in developed countries in Europe and the United States,and to carry out cross-regional and interdisciplinary research cooperation to improve the quality of papers and scientific research level.

夏闲期耕作下旱地土壤有机碳库与温度和含水量季节变化及关系研究

为明确夏闲期耕作下土壤有机碳(SOC)库与温度和含水量的季节变化及其相互关系,设置夏闲期免耕、翻耕和深松3种耕作处理,分析了黄土高原旱地麦田SOC和易氧化有机碳(POxC)含量的季节变化、土壤含水量和温度的季节变化、以及碳库与温度和含水量变化的关系。结果表明,在冬小麦生育期内,随着生育进程的推进,翻耕和深松处理0~5和5~10 cm土层SOC含量呈先升高后降低的变化趋势,而POxC含量呈“降低—升高—再降低”的变化趋势;土壤质量含水量变化均呈“增加—降低—再增加”的变化趋势,而土壤温度呈先降低后升高的变化趋势。回归分析发现,5~10 cm土层土壤质量含水量与SOC含量呈线性关系(P<0.05),与POxC含量呈二次多项式关系(P<0.05),尤其与免耕和深松处理相比,翻耕处理拟合效果更佳。此外,0~5和5~10 cm土层土壤温度变化与SOC含量无显著相关性,而日最高温度、日平均温度和日最低温度与POxC含量呈显著负相关。综上所述,不同夏闲期耕作下旱地麦田0~10 cm土层POxC含量季节变化与土壤质量含水量和温度变化密切相关,而SOC含量变化对土壤温度变化的敏感性较弱。本研究结果为旱地麦田碳库管理提供了理论依据。

Mapping rice-fallow cropland areas for short-season grain legumes intensification in South Asia using MODIS 250 m time-series data

The goal of this study was to map rainfed and irrigated rice-fallow cropland areas across South Asia,using MODIS 250 m time-series data and identify where the farming system may be intensified by the inclusion of a short-season crop during the fallow period.Rice-fallow cropland areas are those areas where rice is grown during the kharif growing season(June–October),followed by a fallow during the rabi season(November–February).These cropland areas are not suitable for growing rabi-season rice due to their high water needs,but are suitable for a short-season(≤3 months),low water-consuming grain legumes such as chickpea(Cicer arietinum L.),black gram,green gram,and lentils.Intensification(double-cropping)in this manner can improve smallholder farmer’s incomes and soil health via rich nitrogen-fixation legume crops as well as address food security challenges of ballooning populations without having to expand croplands.Several grain legumes,primarily chickpea,are increasingly grown across Asia as a source of income for smallholder farmers and at the same time providing rich and cheap source of protein that can improve the nutritional quality of diets in the region.The suitability of rainfed and irrigated rice-fallow croplands for grain legume cultivation across South Asia were defined by these identifiers:(a)rice crop is grown during the primary(kharif)crop growing season or during the north-west monsoon season(June–October);(b)same croplands are left fallow during the second(rabi)season or during the south-east monsoon season(November–February);and(c)ability to support low water-consuming,short-growing season(≤3 months)grain legumes(chickpea,black gram,green gram,and lentils)during rabi season.Existing irrigated or rainfed crops such as rice or wheat that were grown during kharif were not considered suitable for growing during the rabi season,because the moisture/water demand of these crops is too high.The study established cropland classes based on the every 16-day 250 m normalized difference vegetation index(NDVI)time series for one year(June 2010–May 2011)of Moderate Resolution Imaging Spectroradiometer(MODIS)data,using spectral matching techniques(SMTs),and extensive field knowledge.Map accuracy was evaluated based on independent ground survey data as well as compared with available sub-national level statistics.The producers’and users’accuracies of the cropland fallow classes were between 75%and 82%.The overall accuracy and the kappa coefficient estimated for rice classes were 82%and 0.79,respectively.The analysis estimated approximately 22.3 Mha of suitable rice-fallow areas in South Asia,with 88.3%in India,0.5%in Pakistan,1.1%in Sri Lanka,8.7%in Bangladesh,1.4%in Nepal,and 0.02%in Bhutan.Decision-makers can target these areas for sustainable intensification of short-duration grain legumes.

填闲作物对烤烟生长和温室气体排放的影响

为了解填闲作物对烤烟生长和温室气体排放的影响,本研究以潮土烟田为研究对象,在冬季休闲期分别种植光叶紫花苕(Vicia villosa var.glabrescens)、小黑麦(×Triticale Wittmack)和油菜(Brassica napus),地上部分饲用,残茬还田,分析各处理间填闲作物及烤烟生物学产量、土壤CO_(2)和N_(2)O排放的差异。结果表明:(1)3种填闲作物处理烤烟总生物量和烟叶产量均显著高于对照,其中光叶紫花苕最高、油菜次之;(2)光叶紫花苕-烤烟、小黑麦-烤烟和油菜-烤烟土壤CO_(2)排放量分别略高于、显著高于和显著低于对照,土壤N_(2)O排放量均显著低于对照,其中油菜-烤烟差异最大;(3)烟田土壤CO_(2)的全球增温潜势远大于N_(2)O,光叶紫花苕、小黑麦和油菜处理土壤的全球增温潜势分别是对照的106.1%、116.2%和78.1%。综上所述,黄淮烟区潮土烟田油菜-烤烟种植模式既能提高烤烟收益又可降低烟田土壤的全球增温潜势,光叶紫花苕-烤烟在不显著提高烟田土壤全球增温潜势的同时可更大幅度提高烤烟收益,因此,可因地制宜发展油菜-烤烟或光叶紫花苕-烤烟等种植模式。

中国耕地种植制度遥感探测及其时空特征

[目的]耕地种植制度是农业生产方式的具体体现,其形成受自然资源要素与人类土地利用行为综合影响,反映了“人类-自然”的耦合关系。本研究旨在科学掌握全国耕地种植制度格局,为优化农业生产布局、提高农业生产能力、推动农业可持续性发展提供依据。[方法]结合遥感监测与空间决策树模型等手段,构建适合我国农情的跨年度种植制度探测方法体系,并开展空间格局分析。首先,通过辨析种植强度、复种指数等概念,从长期性、周期性、稳定性等方面,定义种植制度的内涵;其次,构建连续度、频度指标,并利用基于时序遥感的2001—2018年中国复种指数监测结果,结合时间滑动窗口方法,在像元尺度分别计算两个指标的具体值;最后,评估耕地的种植强度与种植制度特征的显著性,利用决策树方法确定种植制度类型,从区域差异、动态规律等方面分析不同区域种植制度的时空异质特征。[结果](1)面积上看,一年一熟所占面积最大,占53.52%,超过耕地总面积的一半;其次是一年两熟,占23.28%,季节性休耕(如两年三熟)与年度休耕分别占12.80%和6.94%。(2)空间上看,一年一熟、一年两熟、季节性休耕与年度休耕的集中分布区分别为东北地区、华北地区、长江以南地区与“镰刀弯”地区。(3)时间上看,动态稳定的种植制度从时间维度上揭示了静态复种指数背后的异质性,例如,2018年复种指数为1的区域,其中75.18%属于一年一熟、6.60%属于一年两熟、8.92%属于季节性休耕、8.02%属于年度休耕。[结论]本研究提出了一种结合时序遥感监测与空间决策树模型的跨年度分类体系,揭示了中国耕地种植制度分区聚集、种植强度南高北低的空间格局,直观展现了松嫩平原、“镰刀弯”等空间聚集区;分析了耕地复种与种植制度的时空差异特征,主要表现在种植制度与年度复种指数的空间不一致性,以及种植制度特有的周期性。研究结果可为合理提高耕地复种强度、推动实施“藏粮于地”战略提供案例支撑。

减量施肥对冬小麦休闲期农田杂草物种多样性及生态化学计量特征的影响

【目的】分析减量施肥对冬小麦休闲期农田杂草物种多样性及生态化学计量特征的影响,旨在为化肥农药“双减”政策产生的生态环境效应科学评价提供参考。【方法】以陕西杨凌曹新庄试验地冬小麦肥料试验为基础,设置不施肥(CK)、减量施肥(氮(N)、磷(P_(2)O_(5))用量分别为165和122 kg/hm^(2))和常规施肥(N、P_(2)O_(5)用量分别为220和160 kg/hm^(2))3个处理,测定不同处理小麦产量及夏季休闲期农田杂草的生物量、株高、盖度、多度、频度、丰富度,以及藜、狗尾草和马唐的有机碳、全氮、全磷含量,计算植物多样性指标及生态化学计量比(C/N、C/P、N/P),研究减量施肥对农田杂草物种多样性及生态化学计量特征的影响。【结果】与对照相比,减量施肥和常规施肥处理均对冬小麦休闲期农田杂草的生物量、株高、盖度、多度、频度有明显影响,冬小麦籽粒产量和杂草生物量增加;施肥处理藜和地锦草的株高和生物量均显著增加,其他农田杂草的株高和生物量总体降低。与对照相比,施肥处理苋的有机碳含量以及藜、狗尾草、马唐和葎草的全氮含量均显著增加,藜、马唐全磷含量显著降低。相较于常规施肥,减量施肥处理狗尾草全磷含量显著降低。与对照相比,减量施肥和常规施肥处理藜、狗尾草和马唐氮磷比和碳磷比总体显著增加,碳氮比显著降低。相对于常规施肥处理,减量施肥处理缓解了藜和马唐氮磷比的增加幅度。与对照相比,施肥处理的Shannon-Wiener多样性指数、Simpson多样性指数和Margalef丰富度指数均显著降低;与减量施肥处理相比,常规施肥处理Pielou均匀度指数与丰富度显著降低。植物β多样性指数表明,常规施肥对小区植物多样性的影响最大。【结论】减量施肥和常规施肥处理冬小麦休闲期农田杂草的物种多样性均明显降低,但减量施肥处理缓解了常规施肥对农田杂草生物多样性和生态化学计量特征的影响。

基于“极化—涓滴”理论的成渝地区双城经济圈休耕地分区研究

研究目的:将“极化—涓滴”理论引入耕地休耕研究,探索成渝地区双城经济圈休耕地分区管制策略与技术方法。研究方法:PSR模型、灰色预测模型、GIS空间分析法。研究结果:(1)研究区耕地利用极化度整体较高,需加强耕地养护。(2)以耕地保有量为休耕规模约束条件,得出目标年可休耕规模共397.66万hm^(2),占研究区耕地总面积的35.11%,呈“中”“东”两大主要集聚区。(3)根据综合休耕指数,将研究区划分为优先休耕区、重点休耕区、有条件休耕区和后备休耕区,针对不同类型区特点制定个性化的休耕模式及实施机制。研究结论:休耕地分区受“极化度”和“休耕规模”双重约束,未来应关注耕地健康状况,在保障粮食安全的基础上,合理规划分区开展休耕。

夏闲期玉米压青对旱地麦田土壤水分周年变化的影响

[目的]揭示旱地麦田土壤水分对夏闲期玉米压青的周年适应变化规律,阐明压青模式对小麦产量提高及优化的水分驱动机制,为旱作压青蓄水技术提供理论参考。[方法]通过晋南旱地麦田夏闲期玉米压青还田试验,采用大区对比方法,以夏闲期免耕处理为对照,研究夏闲期玉米压青模式下麦田土壤周年贮水耗水变化规律,分析了其对后茬小麦产量的影响及水分利用效率。[结果]与免耕模式相比,夏闲期玉米压青处理可显著提高0—200 cm土壤周年贮水量,且对100—200 cm较深层土壤的蓄水能力更强;玉米压青处理0—200 cm土壤周年耗水量及耗水百分比均显著低于免耕处理;与免耕相比,压青处理可提高夏闲期0—200 cm土层盈水量,减少小麦季0—100 cm浅土层的水分耗散量;压青处理小麦穗数、穗粒数显著高于免耕,而千粒重差异较小;压青处理夏闲期0—200 cm土壤对降雨的蓄水效率显著高于免耕;在夏闲期玉米压青还田生物量显著高于免耕处理条件下,小麦季和周年阶段,压青处理生物产量及籽粒产量的降水、水分利用效率均显著高于免耕处理。[结论]在旱地麦田丰水年份,夏闲期玉米压青可显著提高旱地麦田土壤贮水,降低作物周年耗水量,优化小麦产量三要素,蓄水增产。

冬闲盐碱地绿肥种植对淡水淋盐土壤及淋溶液碳氮影响

为探讨绿肥种植对盐碱地淡水淋盐下土壤及淋溶液碳氮含量的影响,于2021年10月至2022年5月设置冬闲(T1)、冬牧70黑麦(T2)和油菜(T3)3个处理进行大田试验,测定土壤及淋溶液有机碳(SOC)、硝态氮(NO_(3)^(-)-N)、铵态氮(NH_(4)^(+)-N)空间分布情况。结果表明,T1、T2、T3处理0~30 cm土层中土壤有机碳分别由淋盐前的6.20,6.58,7.24 g/kg增加到淋盐后的6.48,7.39,8.06 g/kg,增幅分别为4.41%,12.20%,11.23%。淋盐前后0~60 cm土层中T1处理土壤硝态氮含量显著高于T2和T3,淡水淋盐后,0~30 cm土层各处理分别降低42.42%,3.85%,10.84%;60~90 cm土层中减少了1.38%,7.96%,18.11%。淋盐前各土层土壤铵态氮含量不同处理之间无显著差异,淋盐后各土层土壤铵态氮含量均以T2含量最高。综上,淋盐灌溉后,相较于淋盐前各处理不同土层土壤有机碳均呈增加趋势,而土壤氮素则呈明显降低趋势,通过对土壤及淋溶液氮素含量分析发现,淋盐灌溉造成的氮素淋失主要以硝态氮为主。相较于冬闲田,种植油菜绿肥对土壤氮素提高有明显效果,而种植冬牧70绿肥对减少土壤氮素淋失具有最佳效果。

Mapping the spatial and temporal patterns of fallow land in mountainous regions of China

The rapid growth of the global population has resulted in a continuous increase in cropland intensity and a shortening of the fallow period as part of the cropland rotation cycle.Yet,there is a lack of systematic knowledge on the extent of fallow lands,particularly in complex landscapes,such as the mountainous regions of China.To fill this knowledge gap,taking Yuanyang County(YYC),Yunnan Province,China,as a case study,we tested a method to identify the spatial-temporal distribution of fallow land by mapping cropland with Landsat data.The overall accuracy of land cover classification,including cropland,ranged between 90.1%and 95.8%from 1998 to 2019.The average accuracy of fallow plots was 75.7%from 2001 to 2019.The annual fallow rate varied between 8.3%and 54.3%,with an average of 20.7%.Kernel density estimated with the probability density function showed that fallow varied between 5 and 13 blocks per km2,gradually decreasing from the central area to the periphery.Increasing elevation,the low value of regional domestic products,and the increased distance to rural settlements were closely related to the higher proportions of fallow land.The approach presented here can be applied to map fallow land in other regions.