Access tube location within a simulated potato crop and the measurement of soil moisture with a neutron probe

Laboratory calibrations simulating different locations of access tubes in a potato crop, examined the possible influence of the water content of tubers on measurements of soil moisture made with a neutron probe. It was concluded that even when access tubes were located within the row, the presence of tubers did not significantly affect estimates of soil moisture made with the neutron probe.     

Growth of crop roots in relation to soil moisture extraction

Growth of the roots of sugar beet, potato and barley in the field was observed through glass panels and related to changes in soil moisture measured by a neutron probe during 1969–71. The depth of observed root growth was generally related to, but 10–15 cm deeper than, the maximum depth of soil-moisture extraction. On average of three years, sugar beet, potato and barley used water from the top 23, 33 and 45 cm soil respectively by the beginning of June, and from the top 70, 68 and > 100 cm soil by the end of June. Maximum soil drying in each horizon gave an in situ measure of available water capacity, and showed that sugar beet and barley eventually extracted similar amounts of water from each horizon, but potatoes extracted less, especially from below 60 cm. Between 30 and 100 cm deep, the in situ available water capacity (per 10 cm soil) progressively decreased from 16 to 10, 15 to 5 and 16 to 8 mm under sugar beet, potato and barley respectively. The calculated soil-moisture deficit (potential evapotranspiration minus rainfall) and measured soil moisture deficit were not related early in the growing period before the crops established much leaf cover.     

Effects of water potential on the infection of potato tubers by Streptomyces scabies in soil

When soil was maintained at a mean water potential (Slatyer & Taylor, 1960) of the order of -80 J kg^-1 at 25 cm depth throughout the growing period, much infection of potato tubers by Streptomyces scabies occurred, but when soil was irrigated to maintain it at potentials greater than - 13 J kg^-1 at 10 cm depth infection was negligible. Until about 5 weeks after initiation, tubers were very susceptible to infection; irrigation during this period reduced scab considerably, but subsequent irrigation reduced it only slightly. At the low water potential, actinomycete populations on lenticels were high and bacterial populations low; these effects were reversed at the high water potential. Since also actinomycetes were more frequently isolated in the absence than in the presence of bacteria it was deduced that there was an interaction between these two groups. It is suggested that irrigation may decrease the population of S. scabies in tuber lenticels by increasing populations of bacteria antagonistic to it.     

Seasonal Migration of Meloidogyne chitwoodi and its Role in Potato Production

Seasonal vertical migration of Meloidogyne chitwoodi through soil and its impact on potato production in Washington and Oregon was studied. Nematode eggs and second-stage juveniles (J2) were placed at various depths (0-180 cm) in tubes filled with soil and buried vertically or in holes dug in potato fields. Tubes were removed at intervals over a 12-month period and soil was bioassayed on tomato roots. Upward migration began in the spring after water had percolated through the tubes. Nematodes were detected in the top 5 cm of tubes within 1-2 months of burial, depending on depth of placement. Potatoes were grown in field plots for 4 or 5 months before the tubers were evaluated for infection. One hundred eggs and J2 per gram soil placed at 60 and 90 cm caused significant tuber damage at the Washington and Oregon sites, respectively. At the Washington site, inoculum placed at 90, 120, and 150 cm caused potato root infection without serious impact on tuber quality, but inoculum diluted 2-8 times and placed at 90 cm did not cause root or tuber infection. Nematode migration was dependent on soil texture; 9 days after placement at the bottoms of tubes, J2 had moved up 55 cm in sandy loam soil (Oregon) but only 15 cm in silt loam (Washington). Thus, the importance of M. chitwoodi which occur deep in a soil profile may depend on soil texture, population density, and length of the growing season.     

Effects of biological soil crusts on profile distribution of soil water,organic carbon and total nitrogen in Mu Us Sandland,China

Aims Biological soil crusts (BSCs) can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems. Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer. Thus, little is known about effects of BSCs on properties throughout the soil profile. In the current study, we assessed the effects of BSCs on the distribution of soil water content (SW), soil organic carbon content (SOC) and soil total nitrogen content (STN) throughout the soil profile as well as the influence of water conditions on the effects of BSCs.Methods In a field investigation in Mu Us Sandland, North China, soil samples were taken from plots with and without BSCs on 13 and 28 September 2006, respectively. On the two sampling dates, average soil gravimetric water content was 3.83% (±1.29%) and 5.08% (±0.89%), respectively, which were regarded as low and high water conditions. Soil samples were collected every 5 cm to a depth of 60 cm, and SW, SOC and STN were measured in the laboratory.Important findings (i) BSCs affected profile distribution of SW, SOC and STN. In addition, water conditions within the plots significantly modified BSCs' effects on the profile distribution of SW, but marginally affected the effects on SOC and STN. (ii) Under high water conditions, SW in the surface soil layer (0–10 cm) was higher in soils with BSCs compared to those without BSCs, while the opposite was true in the deep soil layer (30–55 cm). (iii) Under low water conditions, SW was lower with BSCs compared with no BSCs in near-surface (5–20 cm) and deep (25–40 cm) soil layers. (iv) BSCs affected SOC and STN only in the surface soil layer (0–5 cm) and were modified by plot water conditions.     

The effects of soil moisture at the time potato tubers are forming on the incidence of common scab (Streptomyces scabies)

Two complementary field experiments at Rothamsted in 1965, with the potato variety Majestic, related the incidence of common scab (Streptomyces scabies) to rainfall, soil moisture and time of tuber formation. In plots where the soil was maintained at field capacity (less than 10 cm. Hg moisture tension) by watering, tubers had little or no scab; infection increased in amount on plots allowed to dry to 30 cm., 50 cm. or more Hg moisture tension during late June. The time tubers formed was varied by planting sprouted (chitted) and non-sprouted seed tubers, and tuber development and scab incidence were observed on sample plants lifted at frequent intervals from unwatered plots. Scab lesions were first seen on 12 July when the distribution of lesions on the surface of tubers was affected by size of tuber both within and between the different seed-tuber treatments. These differences were correlated with estimates of tuber size on 28 June, the beginning of the first dry period. Tubers 1.0 cm. or more in diameter on 28 June had few or no lesions at the stolon attachment (heel) end of tubers on 12 July, whereas tubers smaller than this on 28 June had many lesions in this region on 12 July. The larger the tuber was on 28 June, the greater was the area free from scab lesions on 12 July.     

The effect of soil depth and exposure to winter conditions on survival of the potato tuberworm,Phthorimaea operculella

The potato tuberworm, Phthorimaea operculella Zeller (Lepidoptera: Gelechiidae), is an important pest of solanaceous crops including potato [Solanum tuberosum L. (Solanaceae)]. Recent evidence of survival of the pest in the Columbia Basin of Oregon and Washington, USA, is surprising as potato tuberworm is most commonly a pest in tropical and subtropical regions. Potato tuberworm was studied in a manipulative experiment to determine how stage (egg, larva, and pupa) and soil depth affected the potential for winter survival. In early January 2007, eggs, tubers infested with larvae, and pupae were placed in the soil at 6, 10, and 20 cm depths, or left on the soil surface. Each potato tuberworm life stage was sampled at 7–17‐day intervals for 90 days and survival was estimated at each time period. Eggs survived up to 54 days with the greatest survival observed at 6‐cm soil depth and the lowest survival on the soil surface. However, egg survival was significantly reduced after 1 month of exposure to winter conditions. Larvae were able to survive up to 30 days with the greatest survival observed at 20‐cm soil depth. Tubers at the surface and buried at 6 cm were frozen; thus, no larval survival was recorded. The pupal stage showed a greater tolerance to winter conditions than the egg or larval stages, surviving up to 91 days of exposure. These results suggest that the pupal stage is probably the stage most likely to survive winter conditions in the northwestern USA.     

Effect of sediment depth and sediment type on the survival of Vallisneria americana Michx grown from tubers

Sedimentation resulting from storms may have been one of the reasons for the elimination of submersed aquatic vegetation from the tidal Potomac River in the late 1930's. Laboratory studies were conducted to investigate the effects of different depths of overlying sediment and composition of sediment on the survival of Vallisneria americana Michx (wildcelery) grown from tubers. Survival of plants grown from tubers decreased significantly with increasing sediment depth. Survival of tubers declined from 90% or more when buried in 10 cm to no survival in greater than 25 cm of sediment. Survival with depth in sand was significantly lower than in silty clay.Field investigation determined that the majority of tubers in Vallisneria beds are distributed between 10 and 20 cm in depth in silty clay and between 5 and 15 cm in depth in sand. Based on the field distribution of tubers and on the percent survival of plants growing from tubers at each depth in the laboratory experiment, we suggest that the deposition of 10 cm or more of sediment by severe storms such as occurred in the 1930s could contribute to the loss of vegetation in the tidal Potomac River.     

Competition in tree row agroforestry systems. 3. Soil water distribution and dynamics

The purpose of this study was to test the hypothesis that soil water content would vary spatially with distance from a tree row and that the effect would differ according to tree species. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare soil water distribution and dynamics in a maize monoculture with that under maize (Zea mays L.) intercropped with a 3-year-old tree row of Grevillea robusta A. Cunn. Ex R. Br. (grevillea) and hedgerow of Senna spectabilis DC. (senna). Soil water content was measured at weekly intervals during one cropping season using a neutron probe. Measurements were made from 20 cm to a depth of 225 cm at distances of 75, 150, 300 and 525 cm from the tree rows. The amount of water stored was greater under the sole maize crop than the agroforestry systems, especially the grevillea-maize system. Stored soil water in the grevillea-maize system increased with increasing distance from the tree row but in the senna-maize system, it decreased between 75 and 300 cm from the hedgerow. Soil water content increased least and more slowly early in the season in the grevillea-maize system, and drying was also evident as the frequency of rain declined. Soil water content at the end of the cropping season was similar to that at the start of the season in the grevillea-maize system, but about 50 and 80 mm greater in the senna-maize and sole maize systems, respectively. The seasonal water balance showed there was 140 mm of drainage from the sole maize system. A similar amount was lost from the agroforestry systems (about 160 mm in the grevillea-maize system and 145 mm in the senna-maize system) through drainage or tree uptake. The possible benefits of reduced soil evaporation and crop transpiration close to a tree row were not evident in the grevillea-maize system, but appeared to greatly compensate for water uptake losses in the senna-maize system. Grevillea, managed as a tree row, reduced stored soil water to a greater extent than senna, managed as a hedgerow.     

宁南旱区耕作覆盖对马铃薯产量及土壤水热特征的影响

为探究耕作覆盖对土壤水热及旱作马铃薯产量的影响,连续2年在宁南旱区不同耕作深度结合覆盖模式下开展了研究工作。结果表明: 耕作深度、覆盖材料对马铃薯播种期0～100 cm土层土壤贮水量有极显著影响,而二者交互作用无显著影响;2019年土壤贮水量以深松30 cm覆盖地膜处理最高,2020年以深松40 cm覆盖秸秆处理较高,分别较翻耕15 cm不覆盖处理(对照)显著提高16.9%和33.4%;耕作深度、覆盖材料可显著影响马铃薯关键生育期土壤贮水量;同一耕作深度下土壤贮水量以秸秆、地膜覆盖处理效果较好,同一覆盖材料下以深松30～40 cm处理最佳。覆盖材料、耕作深度与覆盖材料二者交互作用对播种-现蕾期0～25 cm土层土壤有效积温影响显著;同一耕作深度下覆盖地膜处理土壤有效积温平均较不覆盖处理显著增加9.3%,而覆盖秸秆处理较不覆盖处理显著降低18.7%;2019和2020年各处理全生育期土壤有效积温分别以深松30 cm和深松40 cm覆盖地膜处理最高。2019年马铃薯总产量和经济效益以深松30 cm覆盖秸秆处理较高,分别较对照显著提高84.6%和107.9%;2020年以深松40 cm覆盖秸秆处理最佳,分别较对照显著提高81.7%和105.7%。耕作深度、覆盖材料对作物水热利用效率均有显著影响,水分利用效率以深松30～40 cm覆盖秸秆处理较高,而积温利用效率不同耕作深度结合秸秆覆盖各处理均较翻对照显著提高。相关分析表明,块茎形成期的土壤水分和有效积温对马铃薯总产量的形成至关重要,而全生育期土壤水分对总产量的影响高于土壤有效积温。可见,深松30～40 cm覆盖秸秆处理可改善土壤水热状况,实现马铃薯增产增收和水热资源的高效利用,在宁南半干旱区马铃薯生产中有一定的应用推广价值。     

Control of potato cyst nematode (Globodera rostochiensis) by nematicides and a resistant potato cultivar at four sites in Scotland

The control of potato cyst nematode (Globodera rostochiensis) by the oxime-carbamates aldicarb and oxamyl was tested in four fields in Scotland. Dazomet was tested in three of these fields and carbofuran in one. In untreated plots in the three most heavily infested fields Maris Piper (resistant) yielded better than Pentland Crown (non-resistant). All nematicides increased the yields of both potato cultivars but had a greater effect on the yield of Pentland Crown. Dazomet increased yields of tubers most. Heavy nematode infestation reduced yield of tubers more in a sandy soil than in two sandy loams. In a field with few potato cyst nematodes nematicides did not significantly affect tuber yields. Although the nematicides greatly increased yields, they were not completely effective in controlling potato cyst nematodes. In treated plots in the lightly infested field, there were more nematode eggs following a crop of Pentland Crown than before. In contrast, Maris Piper markedly decreased post-cropping populations and except at one site, where dazomet further decreased nematode numbers, combining nematicides with the resistant cultivar failed to decrease nematode numbers further. Nematicides decreased the numbers of larvae invading potato roots by up to 95%, oxamyl at 5–6 kg/ha being consistently the best treatment.     

Effects of biuret content in urea and nitrogen source on the yield and composition of potato tubers

Summary Pot and field experiments were conducted at Simla and Daurala to investigate the effect of biuret content of urea and N source on the yield and composition of potato tubers. Soil application of urea containing biuret upto 1.0 per cent did not affect the yield. However, in foliar application of urea detrimental effect of biuret was recorded even at 0.5 per cent. In foliar application of urea, the removal of N, P, and K by tubers was reduced with increasing levels of biuret. In slightly acidic soil of Simla, performance of calcium ammonium nitrate and urea was at par with respect to potato yield, whereas in alkaline soil of Daurala, urea was comparatively inferior. In both soil types, the apparent recovery of N by tubers was higher with calcium ammonium nitrate than with urea. The efficaciousness of urea was increased by applying half of its dose to soil at planting and the other half as foliar sprays.     

Growth Promotion of Fluorescent Pseudomonads and Control of Potato Common Scab in Field Soil with Non-antibiotic Actinomycete-biofertilizer

Field studies on the control of potato common scab were done with non-antibiotic Actinomycete biofertilizer, which was manufactured from swine feces with coprophilous actinomycetes and acidified to pH 5.0 with sulfuric acid. The field soil at pH 5.0 was mixed with 0.56 kg of the acidified biofertilizer per subplot (1.0 x 1.2 m) to a depth of the 15 cm. The scab severity, in terms of the percent coverage of the total surface area of potato tubers, was 10.7%, in the control, while the lesions were slight in the biofertilizer subplot, scab severity being only 2.30/0, and the potato production was increased 3 times with the biofertilizer. The viable counts of Streptomyces scabies in the biofertilizer subplot decreased to 1 × 10³ per gram soil from 5 × 10⁵ by 12 weeks, while the inhabitant fluorescent pseudomonads increased to 2.4 × 10⁷ per gram soil from 3 × 10⁴, and the increased fluorescent pseudomonads were antagonistic to the pathogenic strains.     

Field and glasshouse experiments on the control of potato mop-top virus

Field observations during 3 yr on a stock of potato cv. Red Craigs Royal partially infected with potato mop-top virus (PMTV) confirmed that the virus was passed by an infected mother plant to only a proportion of its progeny tubers, and showed that in this cultivar symptomless plants gave rise only to symptomless progeny. The elimination of PMTV from stocks can therefore be greatly accelerated by removing symptom-bearing plants. Infected potato tubers were not freed from PMTV by treating them at 37 °C for up to 8 wk. Treating ‘seed’ tubers bearing powdery scabs that contain PMTV-carrying resting spores of Spongospora subterranea with formaldehyde or organo-mercurial fungicide greatly decreased PMTV establishment when the tubers were planted in previously uninfective soil, but fumigation with 2-aminobutane was ineffective. Decreasing the pH of infective soil to 5-0 by applying sulphur greatly decreased the infection of potato cv. Arran Pilot with PMTV and S. subterranea in field experiments, but this treatment did not eliminate either; when the pH of treated soil was raised the transmission of PMTV resumed. Treating infective soil with a range of fungicides greatly decreased the infection of Nicotiana debneyi bait seedlings in glasshouse experiments but only calomel at 75 kg/ha controlled spread of PMTV and 5. subterranea to potato in field experiments. In other field experiments, applying zinc frit, zinc sulphate or zinc oxide to infective soil greatly decreased the spread of both to potato. The amount of zinc required increased with increase in clay content of the soil. However, treatment with zinc compounds did not eliminate PMTV-carrying vectors from soil, and when treated soil was diluted with autoclaved soil many of the bait seedlings planted in the mixture became infected. The zinc frit was phytotoxic because of its boron content but zinc sulphate and zinc oxide caused little or no decrease in tuber yield. The zinc content of potato tubers was increased but not doubled in zinc-treated plots, and during the first year after treatment the zinc content of topsoil decreased greatly. The zinc content of ryegrass grown after potatoes was greater than of potato tubers but did not reach a level considered dangerous to livestock. Treatment of soil with sulphur, zinc oxide or calomel may be useful for small plots used in the early stages of propagation of virus-tested potato clones where there is risk of infection with PMTV.     

Fibrous carrot root responses to irrigation and compaction of sandy and organic soils

Field experiments were performed in Southern Finland on fine sand and organic soil in 1990 and 1991 to study carrot roots. Fall ploughed land was loosened by rotary harrowing to a depth of 20 cm or compacted under moist conditions to a depth of 25–30 cm by three passes of adjacent wheel tracks with a tractor weighing 3 Mg, in April were contiguously applied across the plot before seed bed preparation. Sprinkler irrigation (30 mm) was applied to fine sand when moisture in the 0–15 cm range of soil depth was 50% of plant-available water capacity. For root sampling, polyvinyl chloride (PVC) cylinders (30 × 60 cm) were installed in the rows of experimental plots after sowing, and removed at harvest. Six carrot plants were grown in each of in these soil colums in situ in the field.Fine root length and width were quantified by image analysis. Root length density (RLD) per plant was 0.2–1.0 cm cm^-3 in the 0–30 cm range. The fibrous root system of one carrot had total root lengths of 130–150 m in loose fine sand and 180–200 m in compacted fine sand. More roots were observed in irrigated than non-irrigated soils. In the 0–50 cm range of organic soil, 230–250 m of root length were removed from loosened organic soils and 240–300 m from compacted soils. Specific root surface area (surface area divided by dry root weight) of a carrot fibrous root system averaged 1500–2000 cm² g^-1. Root length to weight ratios of 250–350 m g^-1 effectively compare with the ratios of other species.Fibrous root growth was stimulated by soil compaction or irrigation to a depth of 30 cm, in both the fine sand and organic soils, suggesting better soil water supply in compacted than in loosened soils. Soil compaction increased root diameters more in fine sand than it did in organic soil. Most of the root length in loosened soils (fine sand 90%, organic soil 80%) and compacted soils (fine sand 80%, organic soil 75%) was composed of roots with diameters of approximately 0.15 mm. With respect to dry weight, length, surface area and volume of the fibrous root system, all the measurements gave significant resposes to irrigation and soil compaction. Total root volumes in the 0–50 cm of soil were 4.3 cm³ and 9.8 cm³ in loosened fine sand and organic soils, respectively, and 6.7 cm³ and 13.4 cm³ in compacted sand and organic soils, respectively. In fine sand, irrigation increased the volume from 4.8 to 6.3 cm³.     

Probability of Globodera rostochiensis Spread on Equipment and Potato Tubers

The probability of spreading cysts of Globodera rostochiensis on farming equipment and potato tubers was investigated in naturally infested field plots. The number of cysts recovered from soil that adhered to equipment differed significantly between different pieces of equipment. These differences were related to initial nematode density and, in most cases, to the volume of soil that adhered to the equipment. At an initial density of 0.04 egg/cm³ of soil, significantly more cysts were recovered from a potato digger than from a potato hiller, cultivator, or plow. At an initial density of 0.90 egg/cm³ of soil, significantly more cysts were recovered from the plow than from the other equipment. Although the population density was 22 times greater, only 10 times more cysts adhered 3 to equipment used in soil with a density of 0.90 egg/cm³ of soil than when used in soil infested at 0.04 egg/cm³. The number of potato tuber samples (4.5 kg) that contained cysts with viable eggs was positively correlated with the initial densities of G. rostochiensis in soil in which they were produced. The percentage of tuber samples with cysts containing viable eggs was 10-12% for tubers harvested from soil with densities less than 1 egg/cm³ and 30-76% for tubers harvested from soil with densities greater than 4 eggs/cm³ of soil.     

二级水灌溉对土壤及马铃薯块茎中大肠菌群数量的影响

采用多管发酵法检测二级水灌溉对马铃薯种植土壤中大肠菌群数量,结果表明:充分灌溉后的土壤中大肠菌群的数量均高于分根交替灌的土壤;地下滴灌的土壤中大肠菌群数量高于沟灌土壤的大肠菌群数量;二级水经加氯消毒后,土壤中大肠菌群数量明显下降。同样采用多管发酵法检测马铃薯块茎,结果发现:采用加氯消毒后的二级水灌溉的小区E和F中生长的马铃薯,其块茎组织中大肠菌群数量低于其他小区,采用地下滴灌灌溉的小区I和J所种植出的马铃薯块茎中大肠菌群的数量高于采用沟灌灌溉的小区K和L。结果表明:马铃薯块茎中大肠菌群的数量与其生境中大肠菌群的数量有密切关系。     

Root Growth of Susceptible and Resistant Potato Cultivars and Population Dynamics of Globodera rostochiensis in the Field

Globodera rostochiensis population densities and potato root growth were measured in field plots of one susceptible and two resistant potato cultivars. Root growth and nematode densities were estimated from soil samples taken at three depths between plants within the rows, three depths 22.5 cm from the rows, and at two depths midway between rows (furrows). Four weeks after plant emergence (AE), nematode densities in the rows had declined 68% in plots of the susceptible cultivar and up to 75% in plots of both resistant cultivars. Significant decline in nematode densities in the furrows 4 weeks AE occurred only in plots of the susceptible cultivar. Total decline in nematode density in fallow soil was 50%, whereas in plots of the resistant cultivars, decline was more than 70% in the rows and more than 50% in the furrows. Nematode densities increased in the rows of the susceptible cultivar but declined in the furrows. We conclude that G. rostochiensis decline or increase is correlated with host resistance and the amount of roots present at any particular site.     

The effect of granular nematicide incorporation depth and potato planting depth on potatoes grown in land infested with the potato cyst nematodes Globodera rostochiensis and G. pallida

Field experiments at Harper Adams, Shropshire and Wisbech, Cambridgeshire investigated the effect of nematicide incorporation and seed tuber planting depth on the yield of the potato (Solamum tuberosum L.) cultivars Estima and Maris Piper and the population control of the potato cyst nematodes Globodera rostochiensis Woll. (Skarbilovich) and G. pallida (Stone). The nematicide fosthiazate was applied at 3 kg^?1 ha and either not incorporated, or incorporated to 20 cm or 35 cm. Potatoes were mechanically planted to three depths; approximately 10 cm, 15 cm and 25 cm. Incorporation to 20 cm with tubers planted at a depth of 10 cm or 15 cm, reduced root invasion compared with the other treatments. Incorporating nematicide to 20 cm also gave consistently higher ware yields and better nematode control than the other incorporation methods, which were not significantly different to the control. However, ware yield and nematode multiplication rate were not significantly affected by planting depth.     

华北低丘山区果药复合系统种间水分利用策略

了解林农复合系统的种间水分关系至关重要.该文通过稳定氘同位素研究了华北低丘山区核桃(Juglans regia)-菘蓝(Isatis tinctoria)/决明(Senna tora)复合系统各组分的水分来源, 试图明确该果药复合系统的种间水分利用策略, 为该区林农配置模式的选择提供理论依据.研究结果表明: 果药复合系统的土壤含水量明显高于单作菘蓝和单作决明地块, 在2012年,2013年上半年比单作菘蓝高26.74%和7.93%, 在下半年比单作决明高17.39%和13.65%.在果药复合系统内部, 土壤含水量以核桃树行中间位置的最低,树行北侧和树下最高.在各个土层深度, 单作系统的土壤水氢稳定同位素比率(δD值)均比复合系统的高.在菘蓝生长时期的春旱期, 复合系统中核桃的大部分水分来源于30-80 cm深层土壤水, 表明此时期核桃表层根系活性不高; 而决明生长时期正值雨季, 此时核桃优先利用雨水补充的0-30 cm浅层土壤水,表层根系活性增强.在任何生长时期, 菘蓝和决明85%以上的水分都来自浅层土壤水.在菘蓝苗期, 其根系尚未扎入深层土壤中, 单作菘蓝的水分完全来源于浅层土壤, 而在2012年间作菘蓝却有5.7%的水分来自于深层土壤, 在更为干旱的2013年该比例上升到9.7%, 该结果证实了核桃在旱季存在"水力提升"作用, 供浅根系作物吸收利用, 并且越干旱, 该水力提升作用越强.在华北低丘山区核桃-菘蓝/决明复合系统中, 深根性核桃改善了复合系统的土壤水分状况, 在旱季主要利用深层土壤水以避开与浅层作物的水分竞争,并能将深层土壤水提升至浅层土壤供菘蓝吸收利用, 核桃与两种药材表现为水分互利关系, 因而该模式适合在该地区发展.