Erodibility of agricultural soils on the Loess Plateau of China

Soil erodibility is thought of as the ease with which soil is detached by splash during rainfall or by surface flow. Soil erodibility is an important factor in determining the rate of soil loss. In the universal soil loss equation (USLE) and the revised universal soil loss equation (RUSLE), soil erodibility is represented by an erodibility factor (K). The K factor was defined as the mean rate of soil loss per unit rainfall erosivity index from unit runoff plots. Although high rate of soil loss from the Loess Plateau in China is well known and widely documented, it is remarkable that there is little systematic attempt to develop and validate an erodibility index for soils on the Loess Plateu for erosion prediction. Field experimental data from four sites on the Loess Plateau were analyzed to determine the K factor for USLE/RUSLE and to compare with another erodibility index based on soil loss and runoff commonly used for the region. The data set consists of event erosivity index, runoff, and soil loss for 17 runoff plots with slope ranging from 8.7 to 60.1%. Results indicate that the K factor for USLE/RULSE is more appropriate for agricultural soils on the Loess Plateau than the erodibility index developed locally. Values of the K factor for loessial soils range from 0.0096 to 0.0269 t h/(MJ mm). The spatial distribution of the K value in the study area follows a simple pattern showing high values in areas with low clay content. For the four sites investigated, the K factor was significantly related to the clay content, (K=0.031−0.0013 Cl, r²=0.75), where Cl is the clay content in percent. The measured values of the K factor are systematically lower than the nomograph-based estimates by a factor of 3.3–8.4. This implies that use of the nomograph method to estimate soil erodibility would considerably over-predict the rate of soil loss, and local relationship between soil property and the K factor is required for soil erosion prediction for the region.     

黄土高原土壤养分的损失

The soil nutrient losses due to excessive soil loss on Loess Plateau were studied by means of runoff plots and systematical determination of soil nutrients both in sediments and runoff.The results show that the amounts of nutrient losses depended on the amounts of ersoion sediments.Along with sediment,11-197kg nitrogen/hectare and 9-174kg phosphorus/hectare were lost,accounting for 92.46-99.47 percent of the total amount of nitrogen loss and 99.85-99.99 percent of the total amount of phosphorus loss respectively.The nutrient losses,very small in runoff,were mainly attributed to erosion of a few rainstorms during a year.The nutrient level in sediment was mostly higher than that in the original soil.Planting grass evidently redued the losses of soil nutrients.The N level was lower in runoff than in rainfall so that the N loss from runoff could be made up by rainfall.Fertilizer application to crops raised the nutrient level in runoff.     

Microbial activity and community structure in degraded soils on the Loess Plateau of China

Soil erosion is the main process leading to soil degradation on the Loess Plateau of China. The effects of soil‐erosion intensity (sheet, rill, and gully erosion) and different land use (140 y–old secondary forest site, 16 y–old bare site, 6 y–old succession site, and 43 y–old arable site) on gross and net N mineralization, soil organic‐carbon (SOC) turnover, the size and structure of the soil microbial community (phospholipid fatty acid analysis) were assessed. Erosion intensity in the bare plot increased from top slope (sheet erosion) to down slope (gully erosion). The more severe the soil erosion the stronger was the decline of SOC, total N, and microbial biomass (MB). The MBC/SOC ratio decreased whereas the metabolic quotient (qCO₂) increased. Differences in nutrient turnover in the different erosion zones of the bare plot were not significant. The microbial community changed towards less Gram negative bacteria and relative more fungi in the gully‐erosion zone. In forest soils, qCO₂ and the MBC/SOC ratio demonstrate a higher substrate‐use efficiency of the microbial biomass than in bare soils. Gross N mineralization and gross NH consumption clearly indicated a higher microbial activity in forest than in bare soils. Arable land use shifted the soil microbial community towards a higher relative abundance of fungi and a lower one of actinomycetes. During 6 y of natural succession on former bare plots, soil nutrient content and turnover as well as microbial biomass and structure developed towards forest conditions.     

黄土高原石灰性土壤不同形态磷组分分布特征

以黄土高原自北向南采集的12个0～20 cm耕层土壤为供试土样,采用Tiessen和Moir修正的Hedley土壤有机无机磷分级方法研究了黄土高原石灰性土壤中不同形态磷组分的分布特征。结果表明:供试土壤各形态P总体分布特征为:HCl-P>Residual-P>NaHCO3-Po>NaHCO3-Pi>NaOH-Po>NaOH-Pi>H2O-P,以HCl-P和Residual-P为主,分别占土壤全磷的54.00%～88.96%和0～39.11%。黄土高原土壤磷含量总体分布表现为南高北低。在各土壤类型间,NaOH-Po、Residual-P和全磷平均含量表现为干润砂质新成土<黄土正常新成土<简育干润均腐土<土垫旱耕人为土,自北向南依次增加;H2O-P和HCl-P表现为简育干润均腐土<黄土正常新成土<干润砂质新成土<土垫旱耕人为土,自北向南先降后升,且上升幅度较大。黄土高原土壤全氮与全磷及各形态磷含量相关性均达显著水平,其中与NaOH-Pi、NaOH-Po、HCl-P及全磷含量达到极显著水平。C/N、pH及砂粒与全磷及各形态磷含量呈负相关关系,其中pH与NaHCO3-Po呈显著负相关,与H2O-P、NaHCO3-Pi、NaOH-Pi及HCl-P呈极显著负相关;砂粒与NaHCO3-Pi、Residual-P及全磷呈显著负相关。除NaHCO3-Po、NaOH-Po及Residual-P,CaCO3与其他各形态磷含量具有一定程度负相关。除NaOH-Pi和NaOH-Po外黏粒与其他各形态磷及全磷也具有一定程度负相关。土壤各形态磷组分和有效磷的多元回归分析发现,各形态磷中对有效磷贡献最大的是H2O-P,其次为NaOH-Pi和NaHCO3-Po;土壤各形态磷组分和有效磷逐步回归分析结果,进一步说明H2O-P的有效性最高。     

Carbon mineralization and properties of water-extractable organic carbon in soils of the south Loess Plateau in China

Addition of organic manure over thousands of years has resulted in the development of very fertile soils in parts of the Loess Plateau in Northwest China. This region also suffers from serious soil erosion. For that reason, afforestation of arable soils has taken place. The dynamics of soil organic matter in these soils affected by a very specific management and by land use changes is largely unknown. Therefore, we measured C mineralization in a 35-days incubation experiment and analyzed amounts and properties of water-extractable organic carbon (WEOC) in 12 topsoils of this region. The soils differed in land use (arable vs. forest) and in amounts of added organic manure. Afforestation of arable soils resulted in a distinct stabilization of organic C as indicated by the smallest C mineralization (0.48 mg C g⁻¹ C d⁻¹) and the highest C content (2.3%) of the studied soils. In the soils exposed to intensive crop production without regular addition of organic manure we found the largest C mineralization (0.85 mg C g⁻¹ C d⁻¹) and the lowest contents of organic C (0.9%). Addition of organic manure over a time scale of millennia resulted in high organic C contents (1.8%) and small C mineralization (0.55 mg C g⁻¹ C d⁻¹). The content of WEOC reflected differences in C mineralization between the soils quite well and the two variables correlated significantly. Water-extractable organic C decreased during C mineralization from the soil illustrating its mainly labile character. Carbon mineralization from soils was particularly large in soils with small specific UV absorbance of WEOC. We conclude that amounts and properties of WEOC reflected differences in the stability of soil organic C. Both afforestation of arable land and the long-term addition of organic manure may contribute to C accumulation and stabilization in these soils.     

Soil desiccation in the Loess Plateau of China

Soil desiccation usually takes place below the depth of soil affected by rainfall infiltration (about 1–3 m) with relatively low water content, and is one kind of particular hydrological phenomena in semi-arid and semi-humid regions of the Loess Plateau in China. This desiccation results from the excessive depletion of deep soil water by artificial vegetation and long-term insufficient rainwater supply, which is difficult to disappear with land use change. Due to the influence of global warming during 1950–2000, large-scale vegetation rehabilitation aggravated water scarcity and led to soil desiccation in the deep soil layer in the Loess Plateau. From southeast to northwest, soil desiccation becomes more intensive with lower water content and bigger range in depth due to drier climate and lower water holding capacity. The range of soil desiccation has a close relationship with root distribution of plant, and its intensity varies with the types and ages of vegetation. The climate drought, soil properties and soil water cycle characteristics might be the precondition for the occurrence of soil desiccation, and artificial vegetation with improper type and exorbitant productivity could have accelerated this process in range and intensity. Soil desiccation has obviously negative effects on water cycle in soils, greatly reduces the anti-drought capacity of plants, and heavily influences the growth and natural succession of vegetation. In order to reduce the range, intensity, and negative effects of soil desiccation, proper types of vegetation should be selected according to rainfall and soil water conditions, and the control of vegetation density and productivity should be considered together with soil-water conservation measures.     

黄土高原粗质地土壤剖面水分运动与浅层地下水补给可能性模拟

黄土高原水土流失严重,生态环境脆弱,水资源短缺,地下水对保障区域社会经济发展和维持生态系统平衡具有重要意义,而该区的地下水转化和补给机制尚不明确。为探究黄土高原水蚀风蚀交错区土壤剖面深层水分运动及降水对浅层地下水补给的可能性,利用六道沟小流域分布的粗质地风沙土样地2013—2016年土壤剖面0~600 cm含水量数据,运用HYDRUS-1D模型对各土层水力参数进行反演和验证,并用于模拟样地土壤深剖面0~1 500 cm水分运移过程。结果显示,在平水年2014年(439 mm)和干旱年2015年(371 mm),0~600 cm土壤含水量生长季末与生长季初持平或略有亏缺;降水充沛年2013年(669 mm)和2016年(704 mm)土壤含水量生长季末远高于生长季初,降水入渗深度超过观测深度(600 cm)。深剖面水分运动模拟显示,2014年和2015年剖面含水量变化不明显,水分向深层运移微弱缓慢;但是,2013年和2016年降水可分别入渗运移至1 100 cm和1 200 cm深度,远超过样地上生长的旱柳根系区域,可能补给浅层地下水。在4年模拟期间,平均土壤蒸发为14.87 cm·a-1,平均植物蒸腾为33.70 cm·a-1,土壤水分主要以植物蒸腾形式损耗。在2个丰水年,得益于较充足的降水和粗质地风沙土壤的高入渗率,降水大量转化为土壤水快速向下入渗运移,模拟显示当年生长季末降水最深运移至1 200 cm,至年末已超过模拟深度(1 500 cm),水分继续运移可能补给浅层地下水。相关研究结果为黄土高原水蚀风蚀交错区地下水来源和补给机制提供理论依据。     

黄土高原南部不同减氮模式对春玉米产量及土壤硝态氮残留的影响

【目的】研究了不同减量施氮模式对黄土高原南部春玉米产量、土壤硝态氮残留的影响,提出科学施肥模式,旨在指导当地玉米施肥、保护环境安全。【方法】在黄土高原南部沟壑区农田连续进行了3年的田间试验,供试作物为春玉米,一年一熟,采用半覆膜种植方式。试验设不施氮（CK）;传统施肥模式（Con,施尿素N 200 kg/hm2）;减氮模式Ⅰ（Mod Ⅰ,施尿素N 160 kg/hm2）;减氮模式Ⅱ（Mod Ⅱ,施尿素N 160 kg/hm2和加一定量的硝化抑制剂双氰胺）;减氮模式Ⅲ（Mod Ⅲ,施脲甲醛N 160 kg/hm2）5种处理。调查了玉米产量、收获后土壤硝态氮残留和氮素利用率。【结果】三种减量施氮模式较传统施氮模式施氮量减少20%的情况下,玉米产量连续三年无显著变化（P 0.05）,相差0.1~0.5 t/hm2。与Con相比,Mod Ⅰ、Mod Ⅱ、Mod Ⅲ处理的氮肥农学效率及偏生产力分别增加了20.2%~23.2%和21.9%~23.7%,0-200 cm土层NO3--N的残留量分别减少了90.7、97.3、100.7 kg/hm2,其降幅依次为44.7%、47.9%、49.6%。【结论】连续三年减少20%的施氮量不影响春玉米产量及吸氮量,可提高氮肥的农学效率和偏生产力,显著减少土壤剖面NO3--N残留量。在同一施氮量下,添加硝化抑制剂或施用缓控释肥对硝态氮残留量减少作用不甚明显。     

Spatial scaling of saturated hydraulic conductivity of soils in a small watershed on the Loess Plateau, China

Purpose

Soil saturated hydraulic conductivity (K _S) is a key variable in hydrologic processes, the parameters of which have strong scale-dependency. Knowing the scaling dependency of K _S is important when designing an appropriate sampling strategy.

Materials and methods

Determinations of K _S were made for 4,865 undisturbed soil samples, collected from a grid with cells of 10?×?10?m in the Daye watershed (50?ha) on the Loess Plateau, China. The dataset was ??re-sampled?? to investigate the effect on K _S of scales that differed by two orders of magnitude in terms of spacing and support, and eight scales of extent. The variance, correlation length, and nugget?Csill ratio derived by analysis of the full dataset were taken to be the true values. Apparent values of variance, correlation length, and nugget?Csill ratio were those calculated for each re-sampled data sub-set.

Results and discussion

Comparing the parameter values at different scales showed that apparent variance increased with increasing extent (p?<?0.01), decreased with increasing support (p?<?0.01), but was not significantly affected by spacing (p?=?0.137). Apparent correlation length increased with increasing extent and support (p?<?0.01). As spacing increased below 1.1 times the true correlation length (i.e., below 80?m), the apparent correlation length decreased slightly but, as spacing increased above 80?m, it notably increased. Apparent nugget?Csill ratio decreased with increasing spacing and support (p?<?0.01), and increased with increasing extent (p?<?0.01). The scaling dependency for K _S was in the order of extent > support > spacing for all three parameters, with mean coefficient of determination values of 0.96, 0.88, and 0.53, respectively.

Conclusions

The statistical properties investigated for K _S were found to be scaling-dependent, which would benefit sampling strategy design.     

Tillage erosion,water erosion and soil quality on cultivated terraces near Xifeng in the Loess Plateau,China

This study sought to contribute to the understanding of soil redistribution by tillage on terraces and the extent and causes of within-field variation in soil properties by examining the spatial distributions of soil redistribution rates, derived using caesium-137, and of total nitrogen and total phosphorus concentrations, within a ribbon and a shoulder terrace in a yuan area of the Loess Plateau of China. Additional water erosion rate data were obtained for nine other terraces. Water erosion rates on the ribbon terraces were low (<1 kg m⁻² yr⁻¹), unless slope tangents exceeded 0·1. However, despite the use of animal traction, high rates of tillage erosion were observed (mean 5·5 kg m⁻² yr⁻¹). Soil nitrogen concentrations were related to rates of soil redistribution by tillage on the ribbon terrace examined in detail. In general, higher rates of water erosion (0·5–2·9 kg m⁻² yr⁻¹) and lower rates of tillage erosion (mean 1·4 kg m⁻² yr⁻¹) were evident on the longer shoulder terraces. On the shoulder terrace examined in detail, soil phosphorus concentrations were related to net rates of soil redistribution. A statistically significant regression relationship between water erosion rates and the USLE length and slope factor was used in conjunction with the simulation of tillage erosion rates to evaluate a range of terrace designs. It is suggested that off-site impacts of erosion could be further reduced by ensuring that the slope tangents are kept below 0·06 and lengths below 30 m, especially on the shoulder terraces. Tillage erosion and the systematic redistribution of soil nutrients could be reduced by modification of the contour-cultivation technique to turn soil in opposing directions in alternate years. Copyright © 1999 John Wiley & Sons, Ltd.     

金霉素在不同耕作土壤中的吸附－解吸行为

用批平衡吸附试验研究了金霉素在河南封丘潮土、南京黄棕壤、常熟水稻土和江西鹰潭红壤4种土壤中的吸附行为。结果表明,金霉素的土壤吸附-解吸行为均可用Freundlich模型和Langmuir模型进行良好的线性拟合。其Kf值差异较大,分别为潮土1135Lkg-1,黄棕壤1250Lkg-1,水稻土2618Lkg-1和红壤4315Lkg-1,显示金霉素在4种土壤中的吸附行为存在较大的差异。此外,金霉素在4种土壤上的解吸过程存在明显的滞后现象。研究还表明4种土壤中金霉素的吸附参数Kf值与土壤pH呈显著负相关。     

Evaluation of soil microbial indices along a revegetation chronosequence in grassland soils on the Loess Plateau,Northwest China

There is a growing interest in using soil microbial parameters as indicators of soil quality changes after revegetation of disturbed soils. This study investigated the changes in different soil microbial parameters as well as physico-chemical parameters as affected by vegetation rehabilitation of soil in the Loess plateau of China subjected to natural succession after enclosure. The results showed that the soil nutrients tend to be concentrated in the soil surface layer, especially the soil organic C, total N and alkali extractable N with soil organic C being doubled (up to 20 g kg⁻¹) after 50 years of revegetation. Soil enzyme activities and microbial biomass C (Cmic) and N (Nmic) increased with rehabilitation time up to 23 years. After 23 years, soil Cmic and Nmic and enzyme activities remained stable. Enzyme activities increased rapidly during the early stage of revegetation, about 15–20 years after enclosure. Soil Cmic and Nmic also increased about 20% faster up to 23 years since enclosure in the 0–20-cm soil layer. Soil basal respiration (BR) in the 23 years site was higher than in other sites, indicating high microbial activity in this site. These findings demonstrated significant impacts of natural vegetation succession in overgrazed grassland on the properties of the surface soils, including the soil nutrients, organic matter, soil microbial biomass, respiration, and enzyme activities.     

Simulating site-specific impacts of climate change on soil erosion and surface hydrology in southern Loess Plateau of China

Proper spatial and temporal treatments of climate change scenarios projected by General Circulation Models (GCMs) are critical to accurate assessment of climatic impacts on natural resources and ecosystems. The objective of this study was to evaluate the site-specific impacts of climate change on soil erosion and surface hydrology at the Changwu station of Shaanxi, China using a new spatiotemporal downscaling method. The Water Erosion Prediction Project (WEPP) model and climate change scenarios projected by the U.K. Hadley Centre's GCM (HadCM3) under the A2, B2, and GGa emissions scenarios were used in this study. The monthly precipitation and temperature projections were downloaded for the periods of 1900–1999 and 2010–2039 for the grid box containing the Changwu station. Univariate transfer functions were derived by matching probability distributions between station-measured and GCM-projected monthly precipitation and temperature for the 1950–1999 period. The derived functions were used to spatially downscale the GCM monthly projections of 2010–2039 in the grid box to the Changwu station. The downscaled monthly data were further disaggregated to daily weather series using a stochastic weather generator (CLIGEN). The HadCM3 projected that average annual precipitation during 2010–2039 would increase by 4 to 18% at Changwu and that frequency and intensity of large storms would also increase. Under the conventional tillage, simulated percent increases during 2010–2039, compared with the present climate, would be 49–112% for runoff and 31–167% for soil loss. However, simulated soil losses under the conservation tillage during 2010–2039 would be reduced by 39–51% compared with those under the conventional tillage in the present climate. The considerable reduction in soil loss in the conservation tillage indicates the importance of adopting conservation tillage in the region to control soil erosion under climate change.     

Simulating site-specific impacts of climate change on soil erosion and surface hydrology in southern Loess Plateau of China

Proper spatial and temporal treatments of climate change scenarios projected by General Circulation Models (GCMs) are critical to accurate assessment of climatic impacts on natural resources and ecosystems. The objective of this study was to evaluate the site-specific impacts of climate change on soil erosion and surface hydrology at the Changwu station of Shaanxi, China using a new spatiotemporal downscaling method. The Water Erosion Prediction Project (WEPP) model and climate change scenarios projected by the U.K. Hadley Centre's GCM (HadCM3) under the A2, B2, and GGa emissions scenarios were used in this study. The monthly precipitation and temperature projections were downloaded for the periods of 1900–1999 and 2010–2039 for the grid box containing the Changwu station. Univariate transfer functions were derived by matching probability distributions between station-measured and GCM-projected monthly precipitation and temperature for the 1950–1999 period. The derived functions were used to spatially downscale the GCM monthly projections of 2010–2039 in the grid box to the Changwu station. The downscaled monthly data were further disaggregated to daily weather series using a stochastic weather generator (CLIGEN). The HadCM3 projected that average annual precipitation during 2010–2039 would increase by 4 to 18% at Changwu and that frequency and intensity of large storms would also increase. Under the conventional tillage, simulated percent increases during 2010–2039, compared with the present climate, would be 49–112% for runoff and 31–167% for soil loss. However, simulated soil losses under the conservation tillage during 2010–2039 would be reduced by 39–51% compared with those under the conventional tillage in the present climate. The considerable reduction in soil loss in the conservation tillage indicates the importance of adopting conservation tillage in the region to control soil erosion under climate change.     

黄土高原南部半湿润残塬沟壑区人工纯林土壤性质极化研究

为充分认识黄土高原南部半湿润残塬沟壑区主要人工纯林土壤性质的极化趋势,采用多样地多样点混合取土法,对该区进入后期成熟生长期的油松（Pinus tabulaeformis）、侧柏（Platycladus orientalis）和刺槐（Robinia pseudoacia）等人工纯林,以及相同立地条件下植被充分覆盖、生长旺盛的天然草地（对照）土壤性质进行测定。结果表明：油松林土壤物理性质弱度恶化（极化度Pr为-9．26％）,有偏酸性发展的趋势,中度贫养化（Pr为-11．54％）,部分酶活性中度恶化（Pr为-12．88％）,微生物总数量有所增加;侧柏林土壤物理性质有恶化趋势,pH值保持基本稳定,弱度贫养化（Pr为-8．24％）,部分酶活性尚未发生明显极化,微生物总数量保持基本稳定;刺槐林土壤物理性质呈中度恶化（Pr为-12．74％）,pH值保持基本稳定,中度贫养化（Pr为-12．77％）,部分酶活性弱度恶化（Pr为-8．89％）,微生物总数量保持基本稳定;各种土壤性质的绝对综合极化程度表现为微生物数量组成最为敏感,酸碱性相对变化缓慢。可见,长期生长或多代连栽的人工纯林土壤性质存在极化和退化的危险。     

黄土高原南部人工植被作用下的土壤水分研究

在大量野外调查和室内测定的基础上,研究了黄土高原南部地区丰水年前后不同人工植被下0～6m土壤水分含量。研究表明,年均降雨量600mm左右的正常年份,该区内杨树林、法国梧桐林和中国梧桐林下1.5～4m土层平均含水量约为90g/kg左右,发育了弱的土壤干化层,4～6m土层平均含水量约为120g/kg,水分状况优于上部土层。麦地和草地下0～6m水分状况良好,未出现土壤干化现象。丰水年充足的降水后所有林木下土壤干层消失,水分得到很好的恢复,说明该区并未形成永久性土壤干层,这为该区人工植被的良好生长提供了必要的条件。但目前加速发展的生态建设及经济林业仍会给该区土壤水分良性循环带来威胁,因此应加强人工植被下土壤水分的长期观测,合理引种、适当栽培,在收益的同时保证生态环境的可持续发展。     

Soil desiccation trends after afforestation in the Loess Plateau of China

Journal of Soils and Sediments - Soil moisture is the main factor limiting the growth of vegetation in semiarid areas. A large area of the Loess Plateau has undergone vegetation restoration efforts...     

黄土塬区不同玉米品种间作的竞争力表现

为探明不同玉米品种间作下植株对资源的竞争力变化, 以及竞争对植株生长和产量的影响, 本文利用紧凑型玉米品种"郑单958"和半紧凑型玉米品种"沈单16号", 在两个密度(低密度: 45 000株·hm^-2, 高密度: 75 000株·hm^-2)条件下进行隔行间作田间试验, 测定了不同玉米品种茎叶干物质积累量、株高、穗位高度和根系干物质量及收获期产量和产量构成因素的变化。研究结果表明: 随着生育期的延伸, 玉米茎叶比呈先增加而后逐渐稳定的变化趋势; 茎叶比在营养生长阶段呈明显增长, 灌浆期后间作竞争明显降低了茎叶比; 低密度间作茎叶比有所增加, 高密度间作茎叶比显著降低, "郑单958"表现突出。间作栽培下根冠比随间作密度的增加显著降低, 低密度间作处理之间根冠比差异显著。穗位比、收获指数随间作密度的增加而增加, 穗位比在低密度间作时显著低于单作, 高密度间作时显著增加, "沈单16号"变化较明显; 间作收获指数较单作明显增加, 且随间作密度的增加而增加, "郑单958"变化不稳定, 低密度间作时较单作显著增加, "沈单16号"具有稳定而明显的变化。品种间作竞争可以改变间作种群的产量构成, 穗长和穗粗明显减小, 秃尖长明显缩短。竞争系数具有品种差异, "郑单958"强于"沈单16号"。说明品种间作竞争具有提高玉米产量的能力, 有效利用竞争效应, 有可能实现高效利用资源和发掘玉米增产潜力。     

Efficiency of wheat straw mulching in reducing soil and water losses from three typical soils of the Loess Plateau,China

Mulching the soil surface with a layer of plant residue is considered an effective method of conserving water and soil because it increases water infiltration into the soil, reduces surface runoff and the soil erosion, and reduces flow velocity and the sediment carrying capacity of overland flow. However, application of plant residues increases operational costs and so optimal levels of mulch in order to prevent soil and/or water losses should be used according to the soil type and rainfall and slope conditions. In this study, the effect of wheat straw mulch rate on the total runoff and total soil losses from 60-mm simulated rainstorms was assessed for two intensive rainfalls (90 and 180 mm h⁻¹) on three slope gradients typical conditions on the Loess Plateau of China and elsewhere. For short slopes (1 m), the optimal mulch rate to save water for a silt loam and a loam soil was 0.4 kg m⁻². However, for a clay loam soil the mulch rate of 0.4 kg m⁻² would be optimal only under the 90 mm h⁻¹ rainfall; 0.8 kg m⁻² was required for the 180 mm h⁻¹. In order to save soil, a mulch rate of 0.2 kg m⁻² on the silt loam slopes prevented 60%–80% of the soil losses. For the loam soil, mulch at the rate of 0.4 kg m⁻² was essential in most cases in order to reduce soil losses substantially. For the clay loam, 0.4 kg m⁻² may be optimal under the 90 mm h⁻¹ rain, but 0.8 kg m⁻² may be required for the 180 mm h⁻¹ rainstorm. These optimal values would also need to be considered alongside other factors since the mulch may have value if used elsewhere. Hence doubling the optimal mulch rate for the silt loam soil from 0.2 kg m⁻² or the clay loam soil under 90 mm h⁻¹ rainfall from 0.4 kg m⁻² in order to achieve a further 10% reduction in soil loss needs to be assessed in that context. Therefore, Optimal mulch rate can be an effective approach to virtually reduce costs or to maximize the area that can be treated. Meantime, soil conservationist should be aware that levels of mulch for short slopes might not be suitable for long slopes.