Field evaluation of sand-ditch water harvesting technique in Jordan

Water harvesting is viable alternatives for rainfed agricultural production in semiarid lands. A field experiment was conducted to evaluate the efficiency of a relatively new water harvesting technique, called sand ditch, for moisture and soil conservation. Twelve field plots of 10 m × 2 m were constructed in two adjacent fields having silt loam soils but varied in soil depth, 0.75 m and 2 m, and slope of 10% and 12%. A 130 L barrel was installed at the downslope end of the plots to collect water and sediments at the end of each rainstorm along the rainy season. Three types of treatments were used in duplicates (12 plots in total); sand-ditch plots in which a ditch of 2-m long, 1 m wide and 0.8 m deep was constructed in the middle of plots across the slope (2 in each field), two compacted plots and two plots covered with plastic mulch in addition to four control plots, 2 in each field. The total amount of runoff, sediment concentration, total infiltration and sediment loss for the experimental plots were measured or calculated after each storm during the winter season 2004/2005. Experimental results showed that sand-ditch technique significantly reduced runoff and sediment loss and increased infiltration and soil moisture compared to control or compacted plots. The overall average runoff and sediment reductions in the sand-ditch plots were 46% and 61% compared to control plots. Sediment losses from compacted plots were about 2.2 and 6 folds higher than control and sand-ditch plots, respectively making soil compaction unsuitable technique for rainfall harvesting under the current experimental and climatic conditions. Construction of sand ditch also increased the dry matter yield of native grass by an average of 62% and 40% in the two experimental fields compared to control.     

Summer cover crop impacts on soil percolation and nitrogen leaching from a winter corn field

The impacts of a leguminous summer cover crop (sunn hemp; Crotalaria juncea) on nitrogen leaching from a corn (Zea mays L.) field was evaluated by direct measurements of soil water content and nitrogen balance components, complemented by direct and inverse modeling as an exploratory tool to better understand water flow and nitrogen balances in the soil. Water and nitrogen inputs and outputs were measured during winter corn production in an experimental field located in the south Miami-Dade basin in southern Florida (USA). Data from the last two seasons (2001-2002 and 2002-2003) of a 4-year study are presented. The field was divided into six 0.13 ha plots. One-half of the plots were rotated with sunn hemp (CC plots) during the summer while the remaining plots were kept fallow (NC plots). Sweet corn management was uniform on all plots and followed grower recommended practices. A numerical model (WAVE) for describing water and agrochemical movement in the soil was used to simulate water and nitrogen balances in both types of plots during the corn seasons. The hydrodynamic component of WAVE was calibrated with soil water data collected continuously at three depths, which resulted in accurate soil water content predictions (coefficients of efficiency of 0.85 and 0.91 for CC and NC plots, respectively). Measured components of the nitrogen balance (corn yields, estimated nitrogen uptake, and soil organic nitrogen) were used to positively assess the quality of the nitrogen simulation results. Results of the modeled water balance indicate that using sunn hemp as a cover crop improved the soil physical conditions (increase in soil water retention) and subsequently enhanced actual crop evapotranspiration and reduced soil drainage. However, nitrogen simulation results suggest that, although corn nitrogen uptake and yields were slightly higher in the CC plots than in the NC plots, there were net increases of soil N content that resulted in increased N leaching to the shallow aquifer. Therefore, the use of sunn hemp as cover crop should be coupled with reductions in N fertilizer applied to the winter crop to account for the net increase in soil N content.     

Evaluation of the DRAINMOD-N II model for predicting nitrogen losses in a loamy sand under cultivation in south-east Sweden

The DRAINMOD-N II model (version 6.0) was evaluated for a cold region in south-east Sweden. The model was field-tested using four periods between 2002 and 2004 of climate, soil, hydrology and water quality data from three experimental plots, planted to a winter wheat-sugarbeet-barley-barley crop rotation and managed using conventional and controlled drainage. DRAINMOD-N II was calibrated using data from a conventional drainage plot, while data sets from two controlled drainage plots were used for model validation. The model was statistically evaluated by comparing simulated and measured drain flows and nitrate-nitrogen (NO₃-N) losses in subsurface drains. Soil mineral nitrogen (N) content was used to evaluate simulated N dynamics. Observed and predicted NO₃-N losses in subsurface drains were in satisfactory agreement. The mean absolute error (MAE) in predicting NO₃-N drainage losses was 0.16 kg N ha⁻¹ for the calibration plot and 0.21 and 0.30 kg N ha⁻¹ for the two validation plots. For the simulation period, the modelling efficiency (E) was 0.89 for the calibration plot and 0.49 and 0.55 for the validation plots. The overall index of agreement (d) was 0.98 for the calibration plot and 0.79 and 0.80 for the validation plots. These results show that DRAINMOD-N II is applicable for predicting NO₃-N losses from drained soil under cold conditions in south-east Sweden.     

The effect of partial wetting of the root zone on yield and water use efficiency in a drip-and sprinkler-irrigated mature grapefruit grove

Summary The effect of partial wetting of the root zone on yield and water use efficiency in a drip- and sprinkler-irrigated mature grapefruit grove was tested in a long-term experiment from 1976 to 1979. Three different percentages of the surface soil areas ( 30%, 40% and 70%) were wetted by the use of single and double drip laterals and sprinklers, respectively. Irrigation frequencies were 3 and 7 days for the drip treatments and 14 and 21 days for the sprinkler-irrigated plots.Two amounts of water, 80% and 100% of the total seasonal water application as previously determined from the soil moisture depletion data (ca. 630 and 800 mm), were applied at the different irrigation intervals for the drip- and sprinkler-irrigated treatments during the irrigation season (April–November). Soil moisture and salinity patterns were determined by the neutron scattering method and by gravimetric sampling. The partition of water extraction from the wet and dry zones in the drip-irrigated treatments was determined. About 86% of the total amount of water depletion was from the wet zone and 14% from the dry zone. Percolation losses in the irrigated treatments receiving 80% of the total seasonal water application decreased as compared with the 100% irrigated plots. Salts accumulated during the irrigation season were leached out by the winter rainfall.The effect of the reduction of irrigation application amount, first introduced in 1976, on the grapefruit yield was cumulative. The average yield (for the three years 1977, 1978, 1979) in the 80%, drip-irrigated plots at 3-day intervals, was 89 t/ha, compared with 98 t/ha in the 100% irrigated plots. The average yields obtained in the sprinkler and trickle irrigation treatments receiving 100% of the water application was 84 t/ha and 100 t/ha, respectively. Yield reductions in the plots receiving reduced water application of 80% were 11% for the drip treatments and 13% for the sprinkler treatment; the extent of the yield reduction varied according to the time interval between irrigations. The fruit quality was up to the required standards in all treatments. Water use efficiency was greater in the drip-irrigated plots than in the sprinkled ones, and also greater in the plots given the reduced water applications (80% of the maximum seasonal amount of the irrigation water applied), as compared with plots receiving the full amount of irrigation.Contribution from the Agricultural Research Organization, The Volcani Center, P.O.B. 6, Bet Dagan 50–250, Israel. No. 175-E, 1981 series     

Effects of moling and cultivation on soil-water and runoff from a drained clay soil

Flow regimes of water draining from replicated mole drained and undrained plots under different cultivation systems were examined in a 10-year study. In 9 out of 10 years, winter cereals were grown with all residues removed by burning. One crop of oil-seed rape was sown in 1985. A 2 year uniformity trial at the start of the experiment, when all plots were tine cultivated, showed that a cultivation pan exerted an important influence on soil-drainage and water movement. Once removed, effective subsurface drainage increased the depth to the water-table by an average of 215 mm over the winter, with up to 90% of the flow occurring through the mole drains. Following the imposition of differential cultivations in 1980, no discernible change in runoff was observed on plots under ploughing compared to the previous tine cultivations. In contrast, direct drilling caused higher surface runoff than ploughing due to surface compaction, although better subsoil structure development led to more rapid vertical movement of water, and especially in the years following mole drainage an increased peak drain-flow of up to 30%. Although drainage decreased the overall flood risk by as much as 16% in a 10 year return period event, cultivations were of considerable importance and direct drilling increased peak runoff by at least 70% from both drained and undrained plots.     

Use of multiple regression analysis to estimate average corn yields using selected soils and climatic data

A systematic method for predicting corn yields was developed using research plots, selected soil properties and climatic data. :Multiple regression analyses were employed to generate coefficients for the relative contributions of selected soil properties and climatic data from five experimental research plots located in New York State. Yield data were collected from 2 to 19 years, along with climatic data. The soils at each of the plots were mapped, described, sampled, characterized, classified and interpreted. Linear equations, with coefficients generated from the multiple regression analyses, were developed from 43 years of corn data at five research plots. The predictive linear equation was tested at an independent experimental plot with 19 years ofactual corn yield data. The resulting linear relationship between actual and estimated corn yields had an r² of 0·52. The model did, however, predict an average corn yield (for 19 years) within 194 kg ha⁻¹ (3 %) of the actual average corn yield. The equations have the potential to predict the average 20-year crop yields under high management for all soil map units in New York State.     

Simulation of nitrate-N movement in southern Ontario,Canada with DRAINMOD-N

DRAINMOD-N, a mathematical model to predict nitrate-N concentrations in surface runoff and drain outflows from subsurface-drained farmlands, has been tested against field data collected in southern Ontario. The data was collected in a corn field from 16 conventional drainage and subirrigation plots in Woodslee, Ontario, from 1992 to 1994. The model performance was evaluated by comparing the observed and simulated nitrate-N concentrations in surface runoff and drain outflows. A precise calculation of water-table depth is an essential prerequisite for a model to obtain a proper prediction of nitrate-N movement. For the simulation of water-table depth, the lowest root mean square error and the highest correlation coefficient of linear regression were 173 mm and 0.51 for the subirrigation plots; and 178 mm and 0.84 for the subsurface drainage plots. Therefore, the performance of DRAINMOD-N for soil hydrologic simulations was satisfactory and it could be used for assessing nitrogen fate and transport. For the simulation of nitrate-N losses in the subirrigation plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.74 kg/ha and 0.98 for surface runoff; and 6.53 kg/ha and 0.91 for drain outflow. For the simulation in the subsurface drainage plots, the lowest root mean square error and the highest correlation coefficient of linear regression were 0.70 kg/ha and 0.96 for surface runoff; and 6.91 kg/ha and 0.92 for drain outflow. The results show that DRAINMOD-N can perform satisfactory simulation of soil hydrology and nitrate-N losses in surface runoff under various water-table management practices. The model can, therefore, be used to evaluate different water pollution scenarios and help in the development and testing of various pollution control strategies for fields in cold weather such as that in southern Canada.     

基于地块面积和形状的土地整治机械旋耕效率研究

为量化不同面积与形状的地块机械耕作效率差异,科学评价土地整治在机械旋耕效率提升方面的潜力,设计一套标准田块,选取69.83kW东方红LX950型拖拉机配套旋耕机进行耕作,工作宽幅为200cm,采用田间实验法对不同面积梯度和形状的地块进行机械旋耕效率测算,并在此基础上,基于区域尺度建立地块面积、形状与机械旋耕效率的耦合关系及函数模型,修正后得到区域尺度机械旋耕效率。结果表明：地块形状的规则程度影响机械旋耕效率,形状越规整,机械旋耕效率越高。在相同的面积梯度上,矩形地块机械旋耕效率最高,梯形地块次之,直角三角形地块最低。随着地块面积的增大,机械旋耕效率不断增加,当地块面积达到一定程度时,机械旋耕效率趋于稳定。当地块面积超过7000m2时,机械旋耕效率基本保持不变,矩形、梯形地块机械旋耕效率较高,维持在0.25s/m2,其他形状地块机械旋耕效率较低,维持在0.30s/m2左右。案例区地块单元水平的机械旋耕效率为0.27s/m2。其中,中低效地块单元数量最少,占比7.10%;高效地块单元数量最多,占比58.24%。案例区西部机械旋耕效率大于东部,主要由于东部区域土地细碎化程度高于西部区域,地块单元面积较小,形状也不尽规则,从而极大地降低了区域机械旋耕效率。实验结果表明,面积大于7000m2地块是大型机械化耕作的适宜耕作规模,地块面积与形状规则程度均影响机械旋耕效率,土地整治工程在扩大地块面积的同时也需保证地块形状的规则化程度。     

Can shelterbelts improve sprinkler irrigation performance under windy semi arid conditions?

Field experiments were performed to study the effect that wind shelterbelts has on irrigation uniformity of hand move sprinkler irrigation system located in northwest Kenya. Catch can tests were performed to evaluate the distribution of applied water using coefficient of uniformity and distribution uniformity for plots with shelterbelt and without shelterbelt scenarios. Three medium pressure twin nozzle sprinkler head types were tested to determine their water distribution uniformity at varying wind speed and working pressure and obtained results were statistically analysed. The analysis was used to ascertain the performance of the medium pressure sprinklers under varying wind conditions for the two scenarios. Results indicate that uniformity is improved by wind for wind speeds below 1.4?m/s. Analysis of data from sheltered and unsheltered plots showed a significant difference of uniformity parameters on sheltering with coefficient of uniformity for sheltered plots averaging 84?% compared to 74?% for unsheltered plots. Results indicate that the coefficient of uniformity values were higher than the distribution uniformity values although both had a strong linear relationship with a coefficient of determination above 0.96 in both scenarios. It is concluded that shelterbelts improve sprinkler irrigation performance under windy conditions.     

Irrigation and drainage needs of transplanted rice in diked rice fields of rainfed medium lands

An experiment was conducted in diked rice fields with various weir heights (6 cm to 30 cm at an interval of 4 cm) for three consecutive years in the sub-humid climate of eastern India. The results reveal that about 56.75% and 99.5% of the seasonal rainfall can be stored in 6 cm and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen loss in runoff water from rice fields ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots). The available K loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Keeping in mind the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of the Bhubaneswar region during the Kharif (rainy) season. A lumped water balance model for diked rice field was developed and used for the present investigation. The computed values of runoff obtained from the simulation model are in close agreement with the observed values obtained in an experiment using higher weir heights (22 cm and above). The temporal distribution of runoff and irrigation requirement at fortnight intervals reveal that highest irrigation requirement is found during the first half of November followed by the second half of October and the first half of October. Rice fields up to a weir height of 18 cm produced about 20% of the total runoff in each of the first three fortnights. A gradual reduction in runoff was observed in the remaining fortnights. The least runoff was noticed in the month of November (during the first fortnight).     

沙棘引种试验地选择与布局

沙棘引种试验地一般包括场圃区和三荒地（荒山、荒滩、荒沙）两种类型。场圃区主要用于初选试验和区域性试验,三荒地主要用于生产性试验。试验地以能代表当地自然条件、交通方便为主要选择因素。国外优良沙棘品种引进后,应在“三北”10余个项目区分别做好试验地的规划,并编制指导生产实践的种植计划书,才能使整个引种过程付诸于实施。     

Soil surface water repellency induced by treated wastewater irrigation: physico-chemical characterization and quantification

Irrigation with treated wastewater (TWW) is commonly practiced in Israel to relieve freshwater (FW) shortages. We hypothesized that the organic matter (OM) originating from TWW irrigation alters the physico-chemical properties of the soil, induces water repellency in the soil’s top layer, and consequently alters water distribution in the soil profile. In measurements taken in an avocado orchard on a clayey soil, water repellency was found in TWW-irrigated plots. In addition, smaller wetted surface areas were recorded around the drippers in comparison with FW drippers. Drier zone below soil surface was observed in TWW-emitting drippers. OM extraction from the different plots exhibited differences in quantity and quality of organic substances between TWW- and FW-irrigated soils, with a higher quantity of hydrophobic substances in the TWW-irrigated soil extract.     

The agronomic and economic benefits of fertilizer and mulch use in highland banana systems in Uganda

Banana is the most important food crop in Uganda. However, there has been a decline in productivity, attributed to declining soil fertility, drought, pests and diseases and crop management factors. This study aimed to explore the possibility of increasing yields through the use of fertilizer and mulch, and to evaluate the benefits of these inputs across the major banana producing regions in Uganda. This study was carried out in 179 smallholder plots in Central, South, Southwest and East Uganda in 2006/7. Half of the plots were ‘demonstration plots’ of an agricultural development project, while the other half were neighboring farmer plots that acted as ‘control’. Demonstration plots received mineral fertilizer (100% of plots), averaging 71 N, 8 P, 32 K kg ha⁻¹ yr⁻¹ and external mulch from grass and crop residues (64% of plots), whereas control plots received no mineral fertilizer and little external mulch (26% of plots). Demonstration plots had significantly (P ? 0.05) higher yields than control plot in Central, South and Southwest, but average yield increases varied from 4.8 t ha⁻¹ yr⁻¹ (Southwest) to 8.0 (Central), and 10.0 (South). Average weevil corm damage (3%) and nematode-induced root necrosis (7%) was low and similar for both plot types, so yield increases could only be explained by the use of fertilizer and mulch. The highest demonstration plot yield increases were observed where fertilizer addressed key nutrient deficiencies identified using the compositional nutrient diagnosis approach. Farm gate bunch prices declined from 0.17 (Central Uganda) to 0.07 USD kg⁻¹ (Southwest Uganda). Consequently, average marginal rate of return (MRR) of fertilizer and mulch use ranged from 0.1 (Southwest) to 5.8 (Central). The technologies were likely to be acceptable to farmers (MRR ? 1.00) up to 160 km away from the capital. Fertilizer use is likely to be acceptable in all regions (MRR = 0.7-9.4) if local fertilizer prices of 2006/7 (average USD 0.56 kg⁻¹ of fertilizer) declined by 50%. Doubling of fertilizer prices is likely to make fertilizer use unacceptable beyond 100 km away from the capital. The study concludes that there is scope for increased input use in banana systems in Uganda, but that regional variations in crop response, input/output prices, and price fluctuations have to be taken into account.     

Water use and plant response in two rice irrigation methods

Pin-Point (PP) irrigation is being used by rice producers in the southern US to suppress red rice (Oryza sativa), the major weed in rice production. In PP irrigation, germinated seed is dropped into the floodwater. After 24 h the field is drained, remains moist for 3 to 5 days, then reflooded until near harvest. Little is known about water use of the PP method in comparison to the conventional Flush-Flood (FF) method in which germinated seed is also dropped into the floodwater and the field is drained after 24 h, similar to PP, or the field is drill-seeded, flooded and drained, but permanent flood is delayed for 30 to 35 days. During this 30 to 35 days non-flood period, flushing (periodic irrigation) is used to maintain seedling contact with the soil and prevent water stress. Water use of PP and FF irrigated rice was studied during 1994 and 1995 growing seasons near Beaumont, TX. Three plots were subjected to the PP irrigation technique and three to the FF method. A flow meter measured irrigation water applied, and lysimeters measured evapotranspiration, transpiration, and evaporation. The FF method required an average of 113 mm more irrigation water than the PP method, due to flushing of FF plots during the non-flood period. Evapotranspiration (ET) was higher for PP plots during the period when FF plots were dry. During the flood period, ET in FF plots was higher than in PP plots in 1994, due to mainly a lower leaf area index and a more open canopy which led to greater evaporation from the water surface. No differences in ET were found in 1995. Stomatal conductance was lower in FF plots during the non-flood period, indicating some degree of water stress. Irrigation method did not affect yield, but the PP method reduced time to 100% heading by 5 to 7 days. These results suggest that the PP method can be useful not only to suppress red rice, but also to save water and produce an earlier maturing crop. Early maturity is particularly important in areas where ratoon cropping is practiced.     

LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey

This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6-day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6-day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots significantly increased yield. However, there was no significant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use efficiency (IWUE) and water use efficiency (WUE) were found as 0.813 and 0.741 kg/m³ in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey.     

Rainwater,soil and nutrient conservation in rainfed rice lands in Eastern India

In rainfed rice ecosystem, conservation of rainwater to maximum extent can reduce the supplemental irrigation water requirement of the crop and drainage need of the catchment. The results of 3 years of experimental study on the above stated aspects in diked rice fields with various weir heights (6–30 cm at an interval of 4 cm) revealed that about 56.75% and 99.5% of the rainfall can be stored in 6 and 30 cm weir height plots, respectively. Sediment losses of 347.8 kg/ha and 3.3 kg/ha have been recorded in runoff water coming out of 6 cm and 30 cm weir height plots, respectively in a cropping season. Similarly, total Kjeldahl nitrogen (TKN) loss in runoff water from rice field ranged from 4.23 kg/ha (6 cm weir height plots) to 0.17 kg/ha (26 cm weir height plots) and available potassium loss ranged from 2.20 kg/ha (6 cm weir height plots) to 0.04 kg/ha (30 cm weir height plots). Conservation of rainwater in rice fields with various weir heights could not create any significant impact on grain yield differences, leaf area index and other biometric characters. Irrigation requirement of 18 cm and above weir height plots was found to be half of the requirement of 6 cm weir height plots. Keeping in view the aspects of conserving rainwater, sediment and nutrient and minimizing irrigation requirement, 22–26 cm of dike height is considered to be suitable for rice fields of Bhubaneswar region.     

黄土堆积体植物篱减沙效益与泥沙颗粒分形特征研究

为探究植物篱措施对工程堆积体边坡的减流减沙效益及其对侵蚀泥沙颗粒分形维数的影响,以堆积体未防护边坡为对照,以不同放水流量对不同坡度堆积体植物篱防护边坡进行了放水冲刷试验。结果表明:与对照相比,植物篱边坡初始产流时间滞后100~500 s,其产流率、产沙率整体均较小,产流率在时间尺度上表现为间歇性波动上升;植物篱减流效率在4%~60%之间,减沙效率范围在15%~50%之间,减流减沙效率均随坡度和放水流量的增加呈幂函数形式减小;各处理侵蚀泥沙颗粒中粉粒均占主导地位,黏粒次之,砂粒含量最少。与对照小区相比,植物篱防护边坡侵蚀泥沙砂粒体积分数降低,黏粒和粉粒体积分数升高;黏粒富集率增加,砂粒富集率减小,泥沙颗粒分形维数增大。分形维数与黏粒和砂粒体积分数之间均呈极显著线性相关,侵蚀泥沙颗粒分形维数主要由黏粒体积分数决定。     

Runoff and soil loss from an oxisol in Southeastern Nigeria under various management practices

Water infiltration, runoff and soil loss were investigated in an oxisol in Southeastern Nigeria under six management practices. The infiltration rates ranged from 235 mm h^?2 to 947 mm h^?1. Annual runoff and soil loss of up to 204 mm and 55 t/ha, respectively, were recorded in the bare fallow plots, whereas in the mulched maize plots the values were as low as 12 mm and 0.9 t/ha, respectively. No runoff or soil loss was recorded under three vegetative covers tested. Surface crusting was noted to be the major cause of the runoff and soil loss.     

基于DBSCAN和BP_Adaboost的农机作业地块划分方法

农业机械(农机)在多个地块作业,费用和效率有时需按地块统计,现有的农机监控系统仅能记录农机定位信息和作业状态信息,难以实现地块的自动精准划分。本文通过研究轨迹点属性特征,分析作业地块数量不确定性和轨迹点分布规律,采用基于密度聚类方法(Density-based spatial clustering of applications with noise, DBSCAN)和分类器集成算法(BP＿Adaboost)结合的方法划分地块。根据DBSCAN算法对农机轨迹点多数有效、识别错误集中的特点,结合BP＿Adaboost算法挖掘多维度信息关联、容错能力强、分类效果好等优势,先利用DBSCAN得到初步的轨迹点状态类别,再利用BP＿Adaboost算法建立训练模型对农机轨迹点状态精准识别,根据时间序列和类别标记划分地块。本文方法既解决了只依靠阈值和经纬度信息聚类不准确的问题,也减少了大量样本标记工作。利用该方法轨迹点状态识别准确率达96.75%,地块划分准确率为97.74%。     

覆盖措施对红壤丘陵区花生生理状况的影响

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