应用Penman Monteith模型估算稻田蒸散的误差分析

通过对Penman Monteith模型（PM模型）进行微分处理,从理论上分析了土壤热通量、储热项、表面层阻力和空气动力学阻力对PM模型模拟稻田蒸散的误差贡献;在此基础上提出储热项修正和稳定度修正建议,并对水稻4个生育期修正后的PM模拟结果与原始模型模拟结果进行比较。分析表明：按照一般量级关系,净辐射、土壤热通量、储热项、表面层阻力、空气动力学阻力误差分别为5%、10%、100%、20%和20%时,对蒸散误差的贡献率分别为26.8%、5.36%、53.6%、11.11%、3.17%。在水稻移栽拔节、拔节抽穗、抽穗灌浆、成熟4个生育期,10cm土层的储热量均大于田间水层的储热量,且土层和水层储热量均随生育期推进而降低。水层储热在前两个生育期对蒸散的影响比后两个生育期大,与原始模拟值相比,前两个生育期仅考虑土壤储热修正后7：00-14：00蒸散降低幅度为0.04～0.073、0.02～0.11mm·h-1,仅考虑水层储热修正后蒸散降低幅度为0.006～0.038、0.003～0.015mm·h-1;仅考虑空气动力学阻力修正后4个生育期的蒸散值平均降低了0.00064、0.0134、0.0055、0.0024mm·h-1。     

Modeling the Temperature Pattern of a Covered Anaerobic Pond with Computational Fluid Dynamics

This paper presents the development of a 3D computational fluid dynamics (CFD) model of a covered deep anaerobic pond treating raw sewage. The model was based on an unsteady-state laminar flow which was solved in accordance with the finite volume method and simulated the hydrodynamic pattern and thermal energy balance of the anaerobic pond throughout a year of operation. The model input included hourly ambient air temperature, monthly soil temperature profile, daily influent wastewater temperature and velocity, which were incorporated through an external routine in C⁺⁺. Numerical simulation was validated by temperature measurements from the experimental pond. The mean relative error and correlation factor out of 164 temperature values of the simulated pond, in comparison with the experimental one, was 9.34% and 0.91, respectively. The average temperature of the simulated pond throughout the experimental period was 18.9 ^°C. The validated 3D thermal model can be used as a tool for assessing and evaluating the impact of various design modifications (changes in construction material, adding insulation, installing a heat exchanger, etc.) on the thermal behaviour of an anaerobic pond, aiming at its average temperature increase which will, in turn, positively affect its organic removal performance. The thermal model presented, is the first stage of a complete anaerobic pond model which will include wastewater quality transport and basic biochemical reaction mechanisms of the anaerobic decomposition process present in an anaerobic pond. The complete anaerobic pond model will be able to predict the effluent COD of the pond.     

Carbon flow into microbial and fungal biomass as a basis for the belowground food web of agroecosystems

The origin and quantity of plant inputs to soil are primary factors controlling the size and structure of the soil microbial community. The present study aimed to elucidate and quantify the carbon (C) flow from both root and shoot litter residues into soil organic, extractable, microbial and fungal C pools. Using the shift in C stable isotope values associated with replacing C3 by C4 plants we followed root- vs. shoot litter-derived C resources into different soil C pools. We established the following treatments: Corn Maize (CM), Fodder Maize (FM), Wheat + maize Litter (WL) and Wheat (W) as reference. The Corn Maize treatment provided root- as well as shoot litter-derived C (without corn cobs) whereas Fodder Maize (FM) provided only root-derived C (aboveground shoot material was removed). Maize shoot litter was applied on the Wheat + maize Litter (WL) plots to trace the incorporation of C4 litter C into soil microorganisms. Soil samples were taken three times per year (summer, autumn, winter) over two growing seasons. Maize-derived C signal was detectable after three to six months in the following pools: soil organic C (C_org), extractable organic C (EOC), microbial biomass (C_mic) and fungal biomass (ergosterol). In spite of the lower amounts of root- than of shoot litter-derived C inputs, similar amounts were incorporated into each of the C pools in the FM and WL treatments, indicating greater importance of the root- than shoot litter-derived resources for the soil microorganisms as a basis for the belowground food web. In the CM plots twice as much maize-derived C was incorporated into the pools. After two years, maize-derived C in the CM treatment contributed 14.1, 24.7, 46.6 and 76.2% to C_org, EOC, C_mic and ergosterol pools, respectively. Fungi incorporated maize-derived C to a greater extent than did total soil microbial biomass.     

Simulating the development of field grown potato (Solanum tuberosum L.)

The simulation of developmental stages is an important part of many crop simulation models because photoassimilates partitioning to different organs varies with plant developmental stage. Developmental models can also help in pest control and fertilizer application programs, in breeding strategies, and in crop harvest programming. There are several models for simulating potato (Solanum tuberosum L.) development. These models have assumptions that are open to criticism, such as the thermal time approach to describe the effect of temperature on potato development, they assume a constant set of cardinal temperatures throughout the crop cycle and they do not take into account the effect of photoperiod on potato development. These assumptions have disadvantages, because they are not completely realistic from a biological viewpoint. The Wang and Engel (WE) model [Wang, E., Engel, T., 1998. Simulation of phenological development of wheat crops. Agric. Syst. 58, 1–24.] seems appropriate to overcome the disadvantages of current potato models, but it has been used to simulate development in annual crops where the reproductive organs are above ground, not in potato. The objective of this study was to adapt the WE model to simulate development of field grown potato. A series of field experiments was carried out at Santa Maria, Rio Grande do Sul State, Brazil, with 15 planting dates: nine in the year of 2003 and six in the year of 2004. The WE model was superior to the thermal time approach for predicting the date of major developmental stages (tuber initiation, beginning of plant senescence, and harvest), with an average root mean square error (RMSE) of 10.4 days, which corresponds to a 28–45% decrease in the RMSE compared with the thermal time methods. Model predictions with the WE model were better for earlier (tuber initiation, RMSE = 3.7 days) than for later developmental stages (harvest, RMSE = 14.0 days).     

Phenological Stage, Plant Biomass, and Drought Stress Affect Microbial Biomass and Enzyme Activities in the Rhizosphere of Enteropogon macrostachyus

Indigenous grasses have been effectively used to rehabilitate degraded African drylands. Despite their success, studies examining their effects on soil bioindicators such as microbial biomass carbon(C) and enzyme activities are scarce. This study elucidates the effects of drought stress and phenological stages of a typical indigenous African grass, Enteropogon macrostachyus, on microbial biomass and enzyme activities(β-glucosidase, cellobiohydrolase, and chitinase) in the rhizosphere soil. Enteropogon macrostachyus was grown under controlled conditions. Drought stress(partial watering) was simulated during the last 10 d of plant growth, and data were compared with those from optimum moisture conditions. The rhizosphere soil was sampled after 40 d(seedling stage), 70 d(elongation stage), and 80 d(simulated drought stress). A high root:shoot ratio at seedling stage compared with elongation and reproduction stages demonstrated that E. macrostachyus invested more on root biomass in early development, to maximise the uptake of nutrients and water. Microbial biomass and enzyme activities increased with root biomass during plant growth. Ten-day drought at reproduction stage increased the microbial biomass and enzyme activities, accompanying a decrease in binding affinity and catalytic efficiency. In conclusion, drought stress controls soil organic matter decomposition and nutrient mobilization, as well as the competition between plant and microorganisms for nutrient uptake.     

Remobilization of iron from primary leaves of bean plants grown at various iron levels

In order to study the effect of different growth rates of the shoot apex, i.e. shoot demand, on the remobilization of iron (Fe) from mature (primary) leaves, bean (Phaseolus vulgaris L.) plants were precultured with 8x10^‐5 M FeEDTA for four days. Thereafter, plants were grown for another six days at various levels of Fe (0.0, 1.0, and 10.0μM FeEDTA), and simultaneously treated with or without shading of one primary leaf. Dry weight increment of the shoot apex decreased with decreased Fe in the nutrient solution. Shading of one primary leaf decreased total dry weight of plants irrespective of Fe supply, but increased the dry weight of the shoot apex of plants supplied without Fe or with only 1.0μM Fe. In these plants, the concentration of chlorophyll and Fe in the shoot apex corresponded with the treatment effects on dry weight of the shoot apex. Shading induced senescence of the shaded leaf, decreased the content of “active Fe”; (extractable in dilute acid), and also enhanced the remobilization of Fe and copper (Cu) from the shaded leaf. The remobilization of Fe from primary leaves was not related to the severity of chlorosis in the shoot apex (the Fe demand of sink tissue), indicating that only a certain fraction of the total Fe in mature leaves can be remobilized.     

滴灌夏玉米土壤水分与蒸散量SIMDualKc模型估算

为研究西北半干旱地区作物蒸腾和土壤蒸发规律,以及土壤蒸发量占蒸散量的比例(简称蒸发占比),开展2 a夏玉米滴灌控水试验,设置正常灌水(W1)、适度水分亏缺(W2)和中度水分亏缺(W3)3个灌水水平.采用W2实测土壤水分数据对SIMDualKc模型进行参数率定,并采用W1和W3实测土壤水分数据对模型进行验证;进一步基于SIMDualKc模型对不同水分供应的土壤水分胁迫系数、土壤蒸发量、植株蒸腾和蒸散量进行定量模拟分析.结果表明,SIMDualKc模型可以较好地模拟西北半干旱区滴灌夏玉米不同水分供应条件下的土壤水分动态变化过程,实测值与模型预测值有较好的一致性(R2＞0.88,RMSE＜5％);夏玉米生长期,模型能较好地估算不同水分供应的土壤水分胁迫系数、土壤蒸发量和植株蒸腾.土壤蒸发主要集中在生育前期,而生育中期较低,后期略微升高.植物蒸腾主要集中在快速生长期和生长中期,整个生育期呈先增大后减小的趋势.蒸散量随着土壤蒸发和植物蒸腾的变化而变化,前期主要受土壤蒸发的影响,快速生长期、生长中期和后期主要受植物蒸腾的影响.Wl～W3处理土壤蒸发量为78.1～100.2 mm,植株蒸腾为221.8～293.3 mm,蒸散量为299.3～383.0 mm,蒸发占比为24.1％～28.7％.研究可为西北半干旱地区制定合理的夏玉米滴灌制度和灌溉决策提供理论依据.     

Macronutrient accumulation dynamics in apple fruits

In this study, we assessed the macronutrient levels of apple fruits cv. “Golden Smoothee” by monitoring their fruit absorption rates (mg fruit^?1 day^?1) and accumulation patterns (mg fruit^?1) throughout fruit development. Nutrient accumulation was a continuous process throughout the growing season, with patterns of absorption rates varying according to the nutrients concerned. Calcium was chiefly absorbed by the fruit during the first developmental stage, while the greatest absorption rates of other macronutrients occurred later in fruit development (from the end of shoot growth until harvest). From these patterns, it would be desirable to reduce the supply natural calcium (Ca) antagonists, such as potassium (K), ammonium (NH⁴⁺), and magnesium (Mg), during the first part of fruit development in order to achieve a good Ca balance with other nutrients and, consequently, an optimum fruit quality. Knowing these nutrient absorption and accumulation patterns is essential for planning optimum nutrient supply and improving their influence on fruit quality.     

Parameter selection and testing the soil nitrogen dynamics model SOILN

Abstract. The SOILN model with a crop growth submodel for grass and cereal crops and the associated soil water and heat model SOIL were selected out of a number of similar models to simulate nitrogen cycling in a soil/crop system. The main parameter values required by the model were selected on the basis of a combination of field experiments and literature sources. Experimental data measured on grassland at Dumfries in the West of Scotland and on arable land at Bush Estate near Edinburgh were used to test the model. Simulated biomass yields and nitrogen contents of harvested biomass were in reasonable agreement with measured values for both grass and cereal crops. There were similar trends in accumulated leached nitrate between the simulations and experiments at the sites. Any discrepancy between simulated and measured nitrate leached appeared to correspond to similar discrepancies between simulated and measured water flow. The comparison between simulated and experimental results suggests that the model with the selected parameter values can simulate nitrogen and carbon cycling both in grassland and in arable land, and make convincing predictions about the effects of varying soil, crop, fertilizer and manure management practices. A basic sensitivity analysis carried out on the parameters determining the biological and biochemical processes showed the model predictions of annual N-leaching are relatively insensitive to all but two of the plant parameters. However, the model predictions of annual N-harvested and dry mass production are sensitive to numerous plant parameters.     

苗期土壤含水率变化对冬小麦根、冠生物量累积动态的影响

为合理进行冬小麦生长过程的适时水分调控，该文对不同生育期土壤含水率对冬小麦根冠影响的试验进行分析。采用的试验包括5种水分处理，即苗期充分供水，其它生育期进行中度胁迫(FB)、重度胁迫(FC)处理和从苗期开始的中度水分胁迫(SB)、重度水分胁迫(SC)处理以及全生育期充分供水的对照处理。试验结果表明：苗期土壤含水率对冬小麦根、冠的生物量，生物量的累积速率产生不同影响，使全生育期内根、冠占植株总量的比例和根冠比发生改变。当苗期水分改变时，生育初期，根、冠均没有明显响应，但到播后16 d，播后20 d，根、冠生物量分别随胁迫程度的增加而减小(FB>SB，FC>SC)；在播后28 d，SB和SC的根系质量累积速率超过对应FB和FC处理，且苗期受胁迫处理的冬小麦在生殖生长阶段所维持的根系大于苗期不受胁迫处理的根系；冠的累积速率则在播后28 d和35 d也出现SB>FB，SC>FC的结果，到播后42 d，SB、SC的冠质量分别超过对应的FB、FC的冠质量。在此过程中，根、冠生物量占总质量的比例发生改变，根表现为SB>FB，SC>FC；冠在营养生长阶段FB>SB，FC>SC，在生殖生长期SB达到最大；相应根冠比改变。     

Effects of drought on the accumulation and redistribution of cadmium in peanuts at different developmental stages

This study aimed to investigate the impact of water deficit on cadmium (Cd) accumulation in peanut plants during different developmental stages. Two contrasting peanut cultivars, Fenghua 1 (high-biomass cultivar) and Silihong (low-biomass cultivar), were grown in a Cd-contaminated arable soil under different water regimes. The two cultivars differed from each other in seed Cd concentrations. Fenghua 1 exhibited lower Cd concentrations in the seeds than Silihong, which is associated with root-to-shoot Cd translocation. Drought plays different roles in the translocation and redistribution of Cd in peanut plants during different developmental stages. At the seedling stage, drought decreased shoot Cd concentrations for both cultivars, whereas at the pod-filling and pod-ripened stages, drought increased shoot Cd concentrations. Similarly, drought stress reduced pod Cd concentrations at the pod-filling stages and increased at the pod-ripened stages. Seed Cd concentrations in mature plants were increased by drought for both cultivars. Seed Cd concentrations were negatively correlated with biomasses of shoots and pods, but positively correlated with Cd concentration in the shoots and pods. Increased seed Cd concentrations under drought stress might result from the concentration effects due to drought induced decrease of plant growth.     

基于生长模拟模型的冬小麦生理过程水份胁迫影响因子效应的定量研究

A deep understanding of crop-water eco-physiological relations is the basis for quantifying plant physiological responses to soil water stress. Pot experiments were conducted to investigate the winter wheat crop-water relations under both drought and waterlogging conditions in two sequential growing seasons from 2000 to 2002, and then the data were used to develop and validate models simulating the responses of winter wheat growth to drought and waterlogging stress. Thee xperiment consisted of four treatments, waterlogging (keep 1 to 2 cm water layer depth above soil surface), control (70%-80% field capacity), light drought (40%-50% field capacity) and severe drought (30%-40% field capacity) with six replicates at five stages in the 2000-2001 growth season. Three soil water content treatments (waterlogging, control and drought) with two replicates were designed in the 2001-2002 growth season. Waterlogging and control treatments are the same as in the 2000-2001 growth season. For the drought treatment, no water was supplied and the soil moisture decreased from field capacity to wilting point. Leaf net photosynthetic rate, transpiration rate, predawn leaf water potential, soil water potential, soil water content and dry matter weight of individual organs were measured. Based on crop-water eco-physiological relations, drought and waterlogging stress factors for winter wheat growth simulation model were put forward. Drought stress factors integrated soil water availability, the sensitivity of different development stages and the difference between physiological processes (such as photosynthesis, transpiration and partitioning). The quantification of waterlogging stress factor considered different crop species, soil water status, waterlogging days and sensitivity at different growth stages. Data sets from the pot experiments revealed favorable performance reliability for the simulation sub-models with the drought and waterlogging stress factors.     

钟模型法建立甘蔗发育期模拟模型

基于作物发育动态理论模型原理及钟模型方法构建甘蔗发育期模拟模型（SDSM,sugarcane development simulation model）,模拟新植蔗和多年宿根蔗不同发育期。利用广西甘蔗主产区（宜州、沙塘、来宾、扶绥、贵港）的甘蔗发育期多年观测资料及同期气象数据,结合甘蔗各发育阶段的三基点温度指标,通过试错法确定甘蔗发育期模拟模型（SDSM）参数,模拟新植蔗、宿根蔗各发育期（播种-出苗、出苗-分蘖、分蘖-茎伸长、茎伸长-工艺成熟)。通过模拟值与实测值对比分析,对模拟效果进行评价。结果表明：模型具有较强的机理性,模型中基本发育函数部分反映了品种的基因特性,模型能够有效模拟甘蔗的发育期。新植蔗各发育阶段NRMSE在5.2%～26.31%,播种-出苗阶段模拟值与实测值相差8.1d,出苗-分蘖相差7.4d,分蘖-茎伸长相差4.6d,茎伸长-工艺成熟相差7.4d;宿根蔗各发育阶段NRMSE在6.52%～21.66%,上一年工艺成熟-发株阶段模拟值与实测值相差8.8d,发株-分蘖相差8.7d,分蘖-茎伸长相差7.5d,茎伸长-工艺成熟相差9.9d。说明模拟值与实测值具有较好的一致性与相关性,模型可以实现对甘蔗发育期的预测。     

冬小麦物候期对土壤水分胁迫的响应机制与模拟

作物模型在农业生产管理和决策中发挥着重要作用,而物候期模拟是作物模型正确模拟作物生长发育和产量形成过程的基础。作物模型模拟物候发育的常用算法一般是基于积温的计算,同时也考虑光周期和春化作用的影响,但是水分胁迫对物候发育的次级影响却较少被考虑在内。该研究以连续2季(2013-2014和2014-2015)的遮雨棚下土柱试验和连续3季(2012-2013、2013-2014和2014-2015)的遮雨棚下大田试验数据和前人研究成果为基础提出了冬小麦物候期对水分胁迫的响应机制理论假设,并以土壤相对有效含水率为水分胁迫指标校正冬小麦物候期水分胁迫响应函数。该研究以2014-2015生长季土柱试验各处理试验数据来建立冬小麦物候期水分胁迫响应函数,确定发育加速点A、发育减速点D和发育停止点S所对应的相对有效含水率值分别为0.30、0.10和0。结果发现拔节期和开花期模拟值和观测值之间的均方根误差(root mean square error,RMSE)分别为0.8和1.7 d,绝对相对误差(absolute relative error,ARE)分别低于0.68%和2.09%。然后用2013-2014生长季土柱试验各处理数据进行验证,结果发现拔节期和开花期模拟值和观测值之间的RMSE分别约为0.9和1.1 d,ARE分别在1.37%和1.68%以下。最后再用3年独立大田试验数据对上述修正后的冬小麦物候期算法进行验证,结果发现开花期和成熟期的模拟值与观测值之间的RMSE分别约为2.4和2.0 d,ARE分别低于4.21%和2.67%;与DSSAT-CERES-Wheat模型的模拟结果进行比较,发现修正算法能反映出水分胁迫对冬小麦物候期造成的差异(有提前也有推迟),而DSSAT-CERES-Wheat模型无法体现这种差异,且开花期和成熟期的模拟值与观测值之间的RMSE分别约为4.0和5.5 d,误差最大分别为8和6 d。这表明校正后的冬小麦物候期算法模拟精度得到了较大提高,能在一定程度上描述和量化水分胁迫对冬小麦物候期的影响机制,可用来模拟不同水分胁迫条件下不同品种冬小麦的物候期。     

Der Einfluß von Bormangel und von mechanischer Zerstörung des Spitzenmeristems auf die Zellteilung bei Sonnenblumen

Influence of boron deficiency and destruction of the apical meristem on the cell division in sunflowers With a severe, nearly absolute boron deficiency metabolism and formation of tissues are so disturbed that the primary symptom of boron deficiency can not be recognized with certainty. Investigations here had to clarify if cutting the tops or destruction of the apical meristem with a red-hot needle will induce symptoms similar to those of boron deficiency or how symoms develop under mild boron deficiency. With the red-hot needle technique, it was possible to obtain cambial enlargement in plants with a normal boron nutrition. Cutting off the tops also, induced an enlargement of the hypocotyl. In this case the enlargement was however due to an enlargement of the cortex by formation of an aerenchymlike tissue. A boron supply near the deficiency level caused development of deficiency symptoms in growing plants (chlorosis, inhibited enlargement of the stem, small deaf' blades, small-celled xylem, malformed and discoloured cell walls and appositions on the young cell walls). As long as the shoot apex displayed growth, enlargement of the cabium did not appear as a rule. This symptom seems to be a secondary symptom of boron deficiency caused by damage to the shoot apex and, thus disturbed auxin metabolism.     

Antioxidant activities and metal acquisition in mycorrhizal plants growing in a heavy-metal multicontaminated soil amended with treated lignocellulosic agrowaste

The plant growth, nutrient acquisition, metal translocation and antioxidant activities [ascorbate peroxidase (APX), glutatione reductase (GR), superoxide dismutase (SOD) and catalase (CAT)] were measured in plants growing in a heavy-metal (HM) multicontaminated soil inoculated with selected autochthonous microorganisms [arbuscular mycorrhizal (AM) fungus and/or plant growth promoting bacteria (PGPB)] and/or amended with an Aspergillus niger-treated agrowaste. The treated agrowaste on its own increased root growth by 296% and shoot growth by 504% compared with non-treated control plants. Both chemical and biological treatments, particularly when combined, enhanced plant shoot and root development. The stimulation effect on plant biomass was concomitant with increased AM colonization, P and K assimilation, and reduced metal translocation from soil to plant shoot. The treated residue, particularly through interactions with AM inoculation, produced the expected bioremediation effect, leading to enhanced plant development and successful rehabilitation of contaminated soil. The enhancement of CAT, APX and GR activities caused by AM inoculation suggests that AM colonization helped plants to limit oxidative damage to biomolecules in response to metal stress. The response of the plant's antioxidant activities to the amendment appears to be related to enhanced plant biomass production. The application of amendments and/or microbial inoculations to enhance plant growth and reduce metal translocation in multicontaminated soil could be a promising strategy for remediating HM pollution.     

Nitrogen Uptake,Leaf Nitrogen Concentration,and Growth of Saskatoons in Response to Soil Nitrogen Fertility

ABSTRACT

Nutrient requirements of the saskatoon (Amelanchier alnifolia: Rosaceae), a relatively new horticultural crop on the Canadian prairies, are unknown. In this study, two-year old saskatoon plants of the cultivar ‘Smoky’ were grown in a greenhouse in pots under four different soil nitrogen (N) regimes (20, 40, 60, and 80 mg N L^?1). Half the plants were harvested after one growing season. After a five-month period of dormancy, the remaining plants were grown for a second growing season under the same soil N regimes. At harvest, plant growth, dry weight biomass, and leaf N concentration were measured, and soil N uptake was calculated. In both years, leaf N concentration and plant N uptake were strongly positively correlated (first year r = 0.93; second year r = 0.95) and increased linearly with an increase in soil N. Stem diameter and new shoot growth increased in both years of the study in response to additional N. The soil N treatments had no significant effect on plant biomass during the first growing season. In the second year, stem, root, total shoot and total plant biomass increased with increasing soil N.     

Chloride depth in soil and uptake by soybean

Abstract

Soybean [Glycine max.(L.) Merr.] yield reductions due to chloride (Cl) toxicity, as a result of KCl application, have been recognized. A field study was conducted to determine whether Cl uptake by soybean could be minimized by incorporating Cl deeper in the soil profile and to predict the most probable depth of Cl after surface application by a weather‐based model. Essex, a Cl‐susceptible soybean cultivar, was grown on a Mexico silt loam (fine montmorillonitic, mesic Udollic Ochraqualfs) with Cl incorporated at depths of 0–15, 30–45, or 60–75 cm and analyzed for Cl through the growing season. Chloride applied at the 0 to 15‐cm depth significantly increased Cl concentrations in soybean leaves, stems, and roots, especially, in early stages of growth. Chloride concentration was higher in roots > stems > leaves. There was no significant increase in Cl uptake when Cl was applied below 30 cm in the soil. Chloride added to the surface of reformed soil profiles moved with the water front as the soil was wetted. In the field, Cl added to the soil surface in May was uniformly distributed throughout the profile by mid‐September. The weather‐based model, under Missouri conditions, predicts a 9 out of 10 chance that Cl added in the fall would move below a depth of 50 cm by June. Results suggest that the risk of Cl toxicity to soybean can be minimized by applying fertilizers containing Cl far enough in advance to insure a soil wet‐dry cycle prior to soybean planting.     

Phosphorus acquisition and wheat growth are influenced by shoot phosphorus status and soil phosphorus distribution in a split‐root system

Root proliferation and greater uptake per unit of root in the nutrient‐rich zones are often considered to be compensatory responses. This study aimed to examine the influence of plant phosphorus (P) status and P distribution in the root zone on root P acquisition and root and shoot growth of wheat (Triticum aestivum L.) in a split‐root soil culture. One compartment (A) was supplied with either 4 or 14 mg P (kg soil)^–1, whereas the adjoining compartment (B) had 4 mg P kg^–1 with a vertical high‐P strip (44 mg kg^–1) at 90–110 mm from the plant. Three weeks after growing in the split‐root system, plants with 4 mg P kg^–1 (low‐P plants) started to show stimulatory root growth in the high‐P strip. Two weeks later, root dry weight and length density in the high‐P strip were significantly greater for the low‐P plants than for the plants with 14 mg P (kg soil)^–1. However, after 8 weeks of growth in the split‐root system, the two P treatments of compartment A had similar root growth in the high‐P strip of compartment B. The study also showed that shoot P concentrations in the low‐P plants were 0.6–0.8 mg g^–1 compared with 1.7–1.9 mg g^–1 in the 14 mg P kg^–1 plants after 3 and 5 weeks of growth, but were similar (1.1–1.4 mg g^–1) between the two plants by week 8. The low‐P plants had lower root P concentration in both compartments than those with 14 mg P kg^–1 throughout the three harvests. The findings may indicate that root proliferation and P acquisition under heterogeneous conditions are influenced by shoot P status (internal) and soil P distribution (external). There were no differences in the total root and shoot dry weight between the two P treatments at weeks 3 and 5 because enhanced root growth and P uptake in the high‐P strip by the low‐P plants were compensated by reduced root growth elsewhere. In contrast, total plant growth and total root and shoot P contents were greater in the 14 mg P kg^–1 soil than in the low‐P soil at week 8. The two P treatments did not affect the ratio of root to shoot dry weight with time. The results suggest that root proliferation and greater P uptake in the P‐enriched zone may meet the demand for P by P‐deficient plants only for a limited period of time.