Maximum Rooting Depth Research Articles

Developing a water and nitrogen management model for greenhouse vegetable production in China: Sensitivity analysis and evaluation

Excessive water and fertilizer inputs have led to a series of environmental problems in vegetable production areas in China. Identifying the fates of water and nutrients is crucial to develop best management strategies in intensive vegetable production systems. The objectives of this study were to (i) develop a scientific water and nitrogen (N) management tool for intensive greenhouse vegetable production in China, and (ii) evaluate the model performance in the simulating the fate of water and N, and vegetable growth under different water and N management practices in China. A vegetable growth component was added to the field soil-crop system model WHCNS (soil Water Heat Carbon Nitrogen Simulator), named WHCNS_Veg. Parameters for the model were estimated and a sensitivity analysis was conducted by coupling the model with the model-independent parameter estimation program (PEST). Data used to test the model came from two years of cucumber and tomato experiments with various water and N combinations in Shandong province, China. The results of sensitivity analysis showed that the soil hydraulic parameters and vegetable genetic parameters had a relatively higher sensitivity compared with those of N transformation parameters. The saturated soil water content had the highest sensitivity among soil hydraulic parameters, and the total available accumulated temperature, crop coefficient and maximum root depth had higher sensitivity for both vegetable crops. Among the N transformation parameters, the parameters related to nitrification had the highest sensitivity. The automatic optimization algorithm performed well in adjusting soil hydraulic parameters, vegetable genetic parameters and N transformation parameters. The normalized root mean square error for soil water content, soil nitrate concentration, marketable fresh yield and vegetable N uptake were 5.7%, 28.0%, 2.7% and 8.3%, respectively, and indices of agreement were 0.727, 0.730, 0.997 and 0.832, respectively. The results indicated that the WHCNS_Veg model has great potential to simulate and analyze water and N fates, and vegetable growth for the intensive greenhouse vegetable production in China.

Maize and soybean root front velocity and maximum depth in Iowa, USA

Quantitative measurements of root traits can improve our understanding of how crops respond to soil and weather conditions, but such data are rare. Our objective was to quantify maximum root depth and root front velocity (RFV) for maize (Zea mays) and soybean (Glycine max) crops across a range of growing conditions in the Midwest USA. Two sets of root measurements were taken every 10–15days: in the crop row (in-row) and between two crop rows (center-row) across six Iowa sites having different management practices such as planting dates and drainage systems, totaling 20 replicated experimental treatments. Temporal root data were best described by linear segmental functions. Maize RFV was 0.62±0.2cmd−1 until the 5th leaf stage when it increased to 3.12±0.03cmd−1 until maximum depth occurred at the 18th leaf stage (860°Cd after planting). Similar to maize, soybean RFV was 1.19±0.4cmd−1 until the 3rd node when it increased to 3.31±0.5cmd−1 until maximum root depth occurred at the 13th node (813.6°C d after planting). The maximum root depth was similar between crops (P>0.05) and ranged from 120 to 157cm across 18 experimental treatments, and 89–90cm in two experimental treatments. Root depth did not exceed the average water table (two weeks prior to start grain filling) and there was a significant relationship between maximum root depth and water table depth (R2=0.61; P=0.001). Current models of root dynamics rely on temperature as the main control on root growth; our results provide strong support for this relationship (R2>0.76; P<0.001), but suggest that water table depth should also be considered, particularly in conditions such as the Midwest USA where excess water routinely limits crop production. These results can assist crop model calibration and improvements as well as agronomic assessments and plant breeding efforts in this region.

Global sensitivity analysis of the AquaCrop model for winter wheat under different water treatments based on the extended Fourier amplitude sensitivity test

Sensitivity analysis (SA) is an effective tool for studying crop models; it is an important link in model localization and plays an important role in crop model calibration and application. The objectives were to (i) determine influential and non-influential parameters with respect to above ground biomass (AGB), canopy cover (CC), and grain yield of winter wheat in the Beijing area based on the AquaCrop model under different water treatments (rainfall, normal irrigation, and over-irrigation); and (ii) generate an AquaCrop model that can be used in the Beijing area by setting non-influential parameters to fixed values and adjusting influential parameters according to the SA results. In this study, field experiments were conducted during the 2012–2013, 2013–2014, and 2014–2015 winter wheat growing seasons at the National Precision Agriculture Demonstration Research Base in Beijing, China. The extended Fourier amplitude sensitivity test (EFAST) method was used to perform SA of the AquaCrop model using 42 crop parameters, in order to verify the SA results, data from the 2013–2014 growing season were used to calibrate the AquaCrop model, and data from 2012–2013 and 2014–2015 growing seasons were validated. For AGB and yield of winter wheat, the total order sensitivity analysis had more sensitive parameters than the first order sensitivity analysis. For the AGB time-series, parameter sensitivity was changed under different water treatments; in comparison with the non-stressful conditions (normal irrigation and over-irrigation), there were more sensitive parameters under water stress (rainfall), while root development parameters were more sensitive. For CC with time-series and yield, there were more sensitive parameters under water stress than under no water stress. Two parameters sets were selected to calibrate the AquaCrop model, one group of parameters were under water stress, and the others were under no water stress, there were two more sensitive parameters (growing degree-days (GDD) from sowing to the maximum rooting depth (root) and the maximum effective rooting depth (rtx)) under water stress than under no water stress. The results showed that there was higher accuracy under water stress than under no water stress. This study provides guidelines for AquaCrop model calibration and application in Beijing, China, as well providing guidance to simplify the AquaCrop model and improve its precision, especially when many parameters are used.

Root-system characteristics of plantation-grown Populus tomentosa adapted to seasonal fluctuation in the groundwater table

Populus tomentosa developed a deep root system, wide-spreading and dense lateral roots, and structural roots exploring both deep and shallow soil resources to adapt to intense seasonal groundwater table fluctuation. To elucidate the root-system characteristics of P. tomentosa adapting to seasonal fluctuation in the groundwater table, coarse-root architecture and fine-root morphology were investigated in a P. tomentosa plantation under groundwater table fluctuation with an average annual amplitude of 363 cm. Three stands of different ages and planting densities were selected for root sampling, comprising 34 structural roots for assessment of root architecture, ten stumps for measurement of rooting depth and spread distance, and 2106 soil blocks (to 150 cm depth) for analysis of fine-root distribution. The average rooting depth of these stands was 200 cm (maximum root depth 270 cm), indicating that P. tomentosa can be phreatophytic. In 4- and 7-year-old stands, the average lateral root spread distances were 437 and 535 cm, respectively. About 23% of the root area density was distributed in the top-most 20 cm soil, which might help P. tomentosa to intercept rainwater efficiently and absorb shallow soil water resources when the uptake function of deep roots was inhibited by flooding. Some horizontal, inclined, and vertical structural roots were capable of exploring both deep and shallow soil layers. In conclusion, a deep root system, wide-spreading and dense lateral roots in shallow soil layers, and development of some structural roots exploring both deep and shallow soil resources may be the three coordinate rooting adaption strategies that permit P. tomentosa to thrive in sites subject to large fluctuation in the groundwater table.

Classification of Zoysiagrass Genotypes on Rooting Capacity and Associated Performance during Drought

Characterization of rooting capacity in the greenhouse is a routine screening procedure for assessing a plant's ability to cope with drought stress. However, an association between rooting capacity in the greenhouse and turf performance in the field during drought is not always found. The objectives of the study were (i) to classify zoysiagrass (Zoysia spp.) rooting characteristics under well‐watered conditions in the greenhouse, (ii) to compare zoysiagrass performance under drought conditions in the field, and (iii) to relate the results from the greenhouse to the drought responses in the field. The greenhouse study included 17 zoysiagrass genotypes grown in clear acrylic tubes. Root morphological traits and dry weight at different depths (0–30, 30–60, 60–90, and 90–120 cm) were evaluated. Visual responses of zoysiagrass to field dry down were evaluated, and total turf performance index (TTPI) was used to rank the genotypes. Genotypes with higher root length density and root dry weight at 30 to 120 cm, deeper maximum root depth, and lower fraction of surface root length in the greenhouse study were better performers (high TTPI) in the field dry down study and included ‘UF 182’, ‘Emerald’, ‘JaMur’, and ‘Palisades’. The correlation between the greenhouse study and the field dry down study suggests that improvement of drought resistance may be achieved by screening for root traits in the greenhouse.

Implementation and Application of a Root Growth Module in HYDRUS

Core Ideas A HYDRUS module was implemented to model root growth as a function of environmental stresses. Simulations were compared with experimental data for temperature stress effects on root growth. Temperature‐dependent root growth parameters were fitted to experimental data using DREAM. A sensitivity analysis of model parameters revealed key parameters of the modeling approach. A root growth module was adapted and implemented into the HYDRUS software packages to model root growth as a function of different environmental stresses. The model assumes that various environmental factors, as well as soil hydraulic properties, can influence root development under suboptimal conditions. The implementation of growth and stress functions in the HYDRUS software opens the opportunity to derive parameters of these functions from laboratory or field experimental data using inverse modeling. One of the most important environmental factors influencing root growth is soil temperature. The effects of temperature in the root growth module was the first part of the newly developed HYDRUS add‐on to be validated by comparing modeling results with measured rooting depths in an aeroponic experimental system with bell pepper (Capsicum annuum L.). The experiment was conducted at root zone temperatures of 7, 17, and 27°C. Inverse optimization was used to estimate a single set of parameters that was found to well reproduce measured time series of rooting depths for all temperature treatments. A sensitivity analysis showed that parameters such as the maximum rooting depth and cardinal temperatures had only a small impact on the model output and can thus be specified using values from the literature without significantly increasing prediction uncertainties. On the other hand, parameters that define the growth rate or the shape of the temperature stress function had a high influence. The root growth module that considers temperature stress only slightly increased the complexity of the standard HYDRUS models.

Interference of allelopathic rice with penoxsulam-resistant barnyardgrass.

Despite increasing knowledge of allelopathic rice interference with barnyardgrass, relatively little is known about its action on herbicide-resistant barnyardgrass. The incidence of herbicide-resistant barnyardgrass is escalating in paddy fields. Knowledge of the interference of allelopathic rice with herbicide-resistant barnyardgrass and the potential mechanisms involved is warranted. Penoxsulam-resistant and -susceptible barnyardgrass biotypes were identified and segregated from a putative penoxsulam-resistant population occurring in paddy fields in China. Allelopathic rice inhibited the growth of barnyardgrass roots more than shoots, regardless of biotype. In particular, there was a stronger inhibition for resistant barnyardgrass than for susceptible barnyardgrass. Allelopathic rice significantly reduced total root length, total root area, maximum root amplitude and maximum root depth in barnyardgrass. Furthermore, the rice allelochemicals tricin and momilactone B inhibited the growth of both resistant and susceptible barnyardgrass. Compared with root contact, root segregation significantly increased inhibition of barnyardgrass with an increase in rice allelochemicals. Root exudates from barnyardgrass induced the production of rice allelochemicals, but the effect of susceptible barnyardgrass was much stronger than that of resistant barnyardgrass. Allelopathic rice can interfere with the growth of penoxsulam-resistant barnyardgrass through allelochemical-mediated root interactions. This type of allelopathic interference may provide a non-herbicidal alternative for herbicide-resistant weed management in paddy systems. © 2017 Society of Chemical Industry.

Comparison of soil amendments for reforestation with a native multipurpose tree under semiarid climate: Root and root tuber response of Spondias tuberosa

The Caatinga biome, characterized by a species-rich seasonally dry tropical forest, but highly disturbed covers most of Brazil's Northeast. Endemic to this biome is the multipurpose tree Spondias tuberosa Arr., which forms numerous root tubers to resist drought stress. In order to develop improved soil management for reforestation with S. tuberosa the response of its root system to different soil amendments was studied with 52 seedlings, using goat manure, clay substrate, biochar as soil amendments, and mineral fertilizer. The default root architecture of three-year-old S. tuberosa and the relation between soil physical parameters and fine root dry matter (≤2mm), root length density, root tuber volume, root tuber fresh weight, and shoot-root ratio were analyzed.Seedlings still formed a tap root with a maximum rooting depth of 63cm and a maximum horizontal extent of 35cm, developing 2–4 root tubers per seedling. Fine root dry matter in 3000cm3 soil samples differed significantly, ranging from 0.23g in the control to 0.03g in the treatment combining manure with biochar and mineral fertilizer. According to the orthogonal contrast, manure was the pivotal soil amendment affecting fine root dry matter negatively. Simultaneously, manure application led to increased soil water content compared to treatments without . The shoot-root ratio increased by 32% compared to the control, when S. tuberosa was grown in wet soils. Root tuber growth was significantly enhanced by manure addition. This effect is attributed to a reduction of soil bulk density as root tuber volume exhibited a negative correlation with soil bulk density. There was no statistical relationship between root tuber volume and seedling survival during the field experiment. Compared with the control, neither clay, biochar nor solely mineral fertilization significantly affected root growth.Soil management focused on improving water availability is suspected of hampering fine root growth of S. tuberosa seedlings, whereas reducing soil bulk density enables better root tuber development and could, therefore, be a promising measure to increase S. tuberosa drought resistance in the long term for more successful reforestation. Disregarding its negative impact on fine root growth, we assume manure is the most promising amendment among the tested treatments, due to its positive effect on root tuber growth.

Interference of allelopathic rice with paddy weeds at the root level

Despite increasing knowledge of the involvement of allelopathy in negative interactions among plants, relatively little is known about its action at the root level. This study aims to enhance understanding of interactions of roots between a crop and associated weeds via allelopathy. Based on a series of experiments with window rhizoboxes and root segregation methods, we examined root placement patterns and root interactions between allelopathic rice and major paddy weeds Cyperus difformis, Echinochloa crus-galli, Eclipta prostrata, Leptochloa chinensis and Oryza sativa (weedy rice). Allelopathic rice inhibited growth of paddy weed roots more than shoots regardless of species. Furthermore, allelopathic rice significantly reduced total root length, total root area, maximum root width and maximum root depth of paddy weeds, while the weeds adjusted horizontal and vertical placement of their roots in response to the presence of allelopathic rice. With the exception of O.sativa (weedy rice), root growth of weeds avoided expanding towards allelopathic rice. Compared with root contact, root segregation significantly increased inhibition of E.crus-galli, E.prostrata and L.chinensis through an increase in rice allelochemicals. In particular, their root exudates induced production of rice allelochemicals. However, similar results were not observed in C.difformis and O.sativa (weedy rice) with either root segregation or root exudate application. The results demonstrate that allelopathic rice interferes with paddy weeds by altering root placement patterns and root interactions. This is the first case of a root behavioural strategy in crop-weed allelopathic interaction.

Study on the Standards of Proper Effective Rooting Depth for Upland Crops

The study was performed to determine effective soil depth with crop type. Lysimeters, filled with three types of soils (sandy loam, loam and clay loam), were used. Effective soil depths for 25 cm, 50 cm, 75 cm, and 100 cm were considered for each soil. Six crops were investigated for plant height and yield, and rooting depths: Chinese cabbage, maize, lettuce, potato, red pepper, and soybean. Experiment was conducted at the National Institute of Agricultural Sciences in Suwon from 2012 to 2014. Effective rooting depth including 70% of root ranged from 19 cm to 29 cm for Chinese cabbage, from 24 cm to 38 cm for maize, from 17 cm to 24 cm for lettuce, from 27 cm to 32 cm for soybean, and around 50 cm and 30 cm for potato and red pepper. The maximum depth was 60 cm for soybean, 50 cm for Chinese cabbage, lettuce, and potato, and 75 cm for maize and red pepper. Each crop showed high yield in the treatment with soil depth over maximum rooting depth under all soils.Effective and maximum rooting depths under the treatment with soil depth above 100 cm.

Root development and whole-tree allometry of juvenile trees of five seed lots of Pinus radiata D.Don: implications for forest establishment on erosion-prone terrain, East Coast region, North Island, New Zealand

Establishment of exotic forest on erosion-prone pastoral hill country in the East Coast region of New Zealand escalated following a major cyclonic storm in 1988. Pinus radiata D.Don is the predominant species used for erosion control. It has been suggested that planting densities could be reduced if faster growing P. radiata seedlings and cuttings from genetically improved seed lots were used. A field-based trial was established to measure and compare annual growth rates between P. radiata seed lots (GF 16 and GF 19 seedlings and cuttings grown from GF 23 seed) used during the period of early forest establishment (1960s onwards) in this region and genetically improved seed lots (GF 27 seedlings and GF 28 cuttings) developed at a later date. Over a 4-year period, the above-ground parameters (diameter at breast height, root collar diameter, tree height and canopy diameter) were measured before whole trees (canopy and root systems) were destructively sampled. Root collar diameter (over bark) was most highly correlated with tree height, with r 2 ranging between 0.95 and 0.98 for all the seed lots, and all regressions were highly significant (P < 0.001). In any year of the trial, there were no differences among seed lots with respect to root collar diameter, total above-ground biomass or total below-ground biomass. By year 4, mean below-ground biomass comprised 17% of total biomass. There was no consistently significant difference among seed lots in the distribution of total below-ground biomass or root length with distance from the root bole, relative to depth, or in either their maximum lateral root spread or maximum root depth until year 4 when GF16S and GF27S had a greater (P = 0.05) maximum root spread than GF28C while the latter had developed a significantly greater (P = 0.05) proportion of its root biomass and root length within the top 0.5 m of the soil profile. The root cross-sectional area of vertical roots increased significantly with age but decreased with depth. Root orientation formed a ‘bilateral fan-shaped’ architecture. The absence of consistently significant differences among seed lots suggests that during the early 4 year post-establishment period, no one seed lot would provide earlier soil reinforcement or result in a superior level of slope stability than would any of the other seed lots trialled. Thus, irrespective of seed lot preferences, any reduction in the current recommended planting density for erosion-prone hill country would further increase the period of vulnerability and risk of young plantings to damage by storm-initiated landslides.

Response of maize root growth to irrigation and nitrogen management strategies in semi-arid loamy sandy soil

Strategies to promote dense, deep root systems are important for the efficient use of water and nitrogen fertilisers in subtropical loamy sandy soil. This study assessed the effect of interactions between irrigation method (drip and furrow), irrigation level (full and reduced), and nitrogen fertiliser type (quick-release and slow-release) on root growth of maize (Zea mays L.) and the associated effect on grain yield, aboveground biomass and leaf area index. Factorial field experiments on semi-arid loamy sandy soil in Mozambique was carried out in four cropping periods (two in the hot-wet season, two in the cold-dry season). The response to the management factors at three growing stages of coarse (≥0.7mm diameter) and fine (<0.7mm diameter) root density (RD) (two cropping periods) and maximum rooting depth (four cropping periods) were measured in situ by modified profile wall method. The interactions between management factors did not explain the variation in maize RD or maximum rooting depth. However, seasonal variation between the cropping periods affected the distribution of coarse RD. Drip irrigation gave 33–153% higher coarse RD and 26–55% higher fine RD than furrow irrigation in deeper layers (16–64cm), whereas furrow irrigation gave 21–40% higher coarse RD than drip at a shallow depth (0–16cm). Irrigation level had little effect on RD, whereas slow-release fertilisation resulted in overall higher RD, aboveground biomass and grain yield than quick-release fertilisation in the cold-dry season. RD or maximum rooting depth showed few significant correlations with grain yield, biomass and leaf area index, respectively, but higher RD generally tended to result in higher yield. Overall, drip irrigation combined with reduced irrigation and slow-release N fertiliser appeared to be the most promising strategy to promote maize rooting and increase yield, especially in the cold-dry season.

Paleosols can promote root growth of recent vegetation – a case study from the sandy soil–sediment sequence Rakt, the Netherlands

Abstract. Soil studies commonly comprise the uppermost meter for tracing, e.g., soil development. However, the maximum rooting depth of various plants significantly exceeds this depth. We hypothesized that deeper parts of the soil, soil parent material and especially paleosols provide beneficial conditions in terms of, e.g., nutrient contents, thus supporting their utilization and exploitation by deep roots. We aimed to decipher the different phases of soil formation in Dutch drift sands and cover sands. The study site is located at Bedafse Bergen (southeastern Netherlands) in a 200-year-old oak stand. A recent Podzol developed on drift sand covering a Plaggic Anthrosol that was piled up on a relict Podzol on Late Glacial eolian cover sand. Root-free soil and sediment samples, collected in 10–15 cm depth increments, were subjected to a multi-proxy physical and geochemical approach. The Plaggic Anthrosol revealed low bulk density and high phosphorous and organic carbon contents, whereas the relict Podzol was characterized by high iron and aluminum contents. Frequencies of fine (diameter ≤ 2 mm) and medium roots (2–5 mm) were determined on horizontal levels and the profile wall for a detailed pseudo-three-dimensional insight. On horizontal levels, living roots were most abundant in the uppermost part of the relict Podzol with ca. 4450 and 220 m−2, significantly exceeding topsoil root abundances. Roots of oak trees thus benefited from the favorable growth conditions in the nutrient-rich Plaggic Anthrosol, whereas increased compactness and high aluminum contents of the relict Podzol caused a strong decrease of roots. The approach demonstrated the benefit of comprehensive root investigation to support interpretation of soil profiles, as fine roots can be significantly underestimated when quantified at the profile wall. The possible rooting of soil parent material and paleosols long after their burial confirmed recent studies on the potential influence of rooting to overprint sediment–(paleo)soil sequences of various ages, sedimentary and climatic settings. Potential consequences of deep rooting for terrestrial deep carbon stocks, located to a relevant part in paleosols, remain largely unknown and require further investigation.

Toward Marker-assisted Breeding for Root Architecture Traits in Southern Highbush Blueberry

Root growth and root system architecture (RSA) are affected by edaphic and genetic factors and they can impact plant growth and farm profitability. Southern highbush blueberries [SHBs (Vaccinium corymbosum hybrids)] develop shallow, fibrous root systems, and exhibit a preference for acidic soils where water and ammonium are readily available. The amendments used to create these soil conditions negatively affect the profitability of SHB plantations. Hence, breeding for RSA traits has been suggested as an alternative to soil amendments. Vaccinium arboreum is a wild species that is used in SHB breeding. V. arboreum exhibits greater drought tolerance and broader soil pH adaptation than SHB, and—according to anecdotal evidence—it develops deep, taproot-like root systems. The present study constitutes the first in-depth study of the RSA of Vaccinium species with the intention of facilitating breeding for RSA traits. Root systems were studied in rhizotron-grown seedling families. In separate experiments, we tested the effect that growth substrate and family pedigree can have on root growth and RSA. Subsequently, a genotyping by sequence approach was used to develop single nucleotide polymorphism (SNP) markers that could be used along with the phenotyping method to investigate the heritability of RSA traits and look for marker-trait associations. We found that RSA is affected by growth substrate and family pedigree. In addition, we found that V. arboreum exhibited greater maximum root depth and a lower percentage of roots in the top 8 cm of soil than SHB, and interspecific hybrids generally exhibited intermediate phenotypes. Also, we found that RSA traits exhibit moderate to low heritability and genetic correlations among them. Finally, we found 59 marker-trait associations. Among these markers, 37 were found to be located in exons, and 16 of them were annotated based on protein homology with entries in National Center for Biotechnology Information (NCBI) GenBank. Altogether, the present study provides tools that can be used to breed for root architecture traits in SHB.

Does earlier sowing of winter wheat improve root growth and N uptake?

Nitrate leaching from agricultural land is a major environmental concern. Earlier sowing of winter wheat (Triticum aestivum L.) could be a tool to reduce nitrate leaching loss, as deeper root penetration and increased biomass production might increase the N uptake during autumn. Quantitative estimates of the effect of sowing time are needed.A two-year field experiment was conducted on sandy loam soils. During the season, the effects of early, normal and late winter wheat sowing were studied on root development and soil nitrogen to 2.3m soil depth. Root depth and density were studied by means of minirhizotrons and effects on aboveground biomass and nitrogen uptake were measured.Advancing sowing time increased the root depth by the onset of winter in December by up to 18mm day−1 of earlier sowing and the rooting depth increased up to 0.7m, reaching up to 0.9m average maximum root depth. The total root density was 9–16 times higher in early than in late sown wheat. Root depth penetration rates estimated from November (late autumn) until anthesis in June were 0.9–1.2mm°C day−1 and no significant differences were observed between the sowing treatments.In November, soil N reductions of early sown wheat compared to normal and late sown wheat were on average 20kg nitrate N ha−1.Sowing time affected root growth, aboveground growth and N relations during the entire growth season, though it had little effect on yield. Sowing time affected root depth throughout the season. Late sown wheat continued to increase its root depth after anthesis and reached up to 1.5m average maximum root depth, but it never reached the root depth of early and normal sown wheat reaching up to 1.8 and 2.0m average maximum root depth, respectively.The results show that earlier sowing can be an important tool to reduce the amount of soil N during autumn and winter and hence the potential leaching. In addition, it will improve the root growth of the wheat during its main growing season. However, promoting earlier sowing may interact with other agronomic factors.

Modification of transient state analytical model under different saline groundwater depths, irrigation water salinities and deficit irrigation for quinoa

Salinization of soil is primarily caused by capillary rise from saline shallow groundwater or application of saline irrigation water. In this investigation, the transient state analytical model was modified to predict water uptake from saline shallow groundwater, actual crop evapotranspiration, soil water content, dry matter, seed yield and soil salinity under different saline groundwater depths, irrigation water salinities and deficit irrigation for quinoa. Considering the effect of salinity on soil saturated hydraulic conductivity and maximum root depth in presence of shallow saline groundwater, the model resulted in good agreement between the measured and predicted saline groundwater uptake, soil salinity increase at different groundwater depths (300-800 mm) and water salinity (10-40 dS m -1 ). Therefore, the modified model is applicable for quinoa yield and soil salinity prediction and it could be a valuable tool for soil salinity management in presence of shallow saline groundwater. Furthermore, prediction of quinoa yield by the modified model can be used for better irrigation water salinity management under different saline groundwater depths, irrigation water salinities and deficit irrigation.

Environmental and physiological effects on grouping of drought-tolerant and susceptible rice varieties related to rice (Oryza sativa) root hydraulics under drought.

Background and Aims Root hydraulic limitations (i.e. intra-plant restrictions to water movement) may be related to crop performance under drought, and groupings in the hydraulic function of drought-tolerant and drought-susceptible rice (Oryza sativa) varieties have been previously reported. This study aimed to better understand the environmental and physiological relationships with rice root hydraulics under drought. Methods Xylem sap bleeding rates in the field (gsap g-1shoot) were measured on seasonal and diurnal time frames, during which time environmental conditions were monitored and physiological measurements were conducted. Complementary experiments on the effects of vapour pressure deficit (VPD) on root hydraulic conductivity and on transpiration rates of de-rooted tillers were conducted in growth chambers. Key Results The diurnal effects on bleeding rate were more closely related to irradiance than VPD, and VPD effects on root hydraulic conductivity measured on 21-day-old plants were due to effects on plant growth including root surface area, maximum root depth and root:shoot ratio. Leaf osmotic potential was related to the grouping of drought-tolerant and drought-susceptible varieties in rice root hydraulics, and these groupings were independent of differences in phenology. Low single-tiller bleeding rates were observed under high evapo-transpirational demand, higher bleeding rates were observed at more negative leaf osmotic potentials in drought-susceptible varieties, and drought-tolerant and susceptible varieties differed in the VPD-induced increase in transpiration rates of de-rooted tillers. Low root suberin amounts in some of the drought-susceptible varieties may have resulted in higher ion transport, as evidenced by higher sap K+ concentration and higher bleeding rates in those varieties. Conclusions These results provide evidence of the environmental effects on shoots that can influence root hydraulics. The consistent groupings of drought-tolerant and susceptible varieties suggest that traits affecting plant osmotic status may regulate root hydraulic response to drought in rice.

The effect of different evapotranspiration methods on portraying soil water dynamics and ET partitioning in a semi-arid environment in Northwest China

Abstract. Different methods for assessing evapotranspiration (ET) can significantly affect the performance of land surface models in portraying soil water dynamics and ET partitioning. An accurate understanding of the impact a method has is crucial to determining the effectiveness of an irrigation scheme. Two ET methods are discussed: one is based on reference crop evapotranspiration (ET0) theory, uses leaf area index (LAI) for partitioning into soil evaporation and transpiration, and is denoted as the ETind method; the other is a one-step calculation of actual soil evaporation and potential transpiration by incorporating canopy minimum resistance and actual soil resistance into the Penman–Monteith model, and is denoted as the ETdir method. In this study, a soil water model, considering the coupled transfer of water, vapor, and heat in the soil, was used to investigate how different ET methods could affect the calculation of the soil water dynamics and ET partitioning in a crop field. Results indicate that for two different ET methods this model varied concerning the simulation of soil water content and crop evapotranspiration components, but the simulation of soil temperature agreed well with lysimeter observations, considering aerodynamic and surface resistance terms improved the ETdir method regarding simulating soil evaporation, especially after irrigation. Furthermore, the results of different crop growth scenarios indicate that the uncertainty in LAI played an important role in estimating the relative transpiration and evaporation fraction. The impact of maximum rooting depth and root growth rate on calculating ET components might increase in drying soil. The influence of maximum rooting depth was larger late in the growing season, while the influence of root growth rate dominated early in the growing season.

Validation of root growth simulation models for cotton crop grown under specified environment

The cotton root growth was observed through vertical soil column studies. The maximum root depth of 175cm was attained at 180 DAS. However, rooting depth of 148 cm could be obtained at 120 DAS only. It was observed that major part of total root length was concentrated within 30cm up to 80 DAS and within 60cm up to maturity. The root depth data were fitted to models such as Rasmussen and Hanks (1978), Hanks and Hill (1980), Reuss (1980) Fereres et al. (1981), Borg and Grimes (1986) Schouwenaars (1988), and Subbaiah and Rao (1994), by regression analysis. Among these, the model of Rasmussen & Hanks was found the best fitted, followed by Hanks and Hill, Subbaiah and Rao, Borg and Grimes, Fereres et al., Reuss and Schouwenaars.

Bluejoint Is an Effective Bio-Barrier Species on Mine Covers.

Covers with capillary barrier effects (CCBE) are used to prevent acid mine drainage from mine wastes in the short term. However, the long-term efficiency of CCBE can be affected by trees because their roots may reduce the ability of covers to limit oxygen migration and also physically damage the CCBE. Two plant species that are native to boreal Canada, bluejoint () and sheep laurel (, were selected as bio-barrier species (BBS) to test if they reduce the growth and root system architecture of trees established on mine covers (balsam poplar [], willow [ spp], and black spruce []). The experiment was established in 2008 on a mine tailings impoundment located in northwestern Quebec, Canada. Trees were measured for height, diameter, and biomass. Coarse roots were excavated from the plots and digitized in three dimensions. Compared with the control (no BBS), bluejoint strongly decreased tree height and diameter increment, biomass, maximum root depth and radial extension, total root length and volume, and number of second- and third-order tree roots. Height and diameter increment, biomass, maximum root depth and volume, and number of second-order roots of balsam poplar increased with sheep laurel compared with control conditions, whereas willow showed no response to this treatment. Most characteristics of black spruce (except root-to-shoot ratio and number of second-order roots) improved in the presence of sheep laurel compared with the control. Thus, bluejoint was a more efficient BBS than sheep laurel. Bio-barriers comprised of bluejoint can be used as a countermeasure for controlling tree invasion of CCBE.