Maximum Rooting Depth Research Articles

Rooting Characteristics and Associated Drought Resistance of Zoysiagrasses

AbstractDeclining availability of water for landscape irrigation has increased the need for drought‐resistant turfgrasses. Though drought‐resistance mechanisms are known to include deep rooting in some plants, little is known concerning zoysiagrass rooting characteristics. This study was conducted to determine if differences in rooting parameters exist among zoysiagrasses, and if they are associated with drought resistance. Twentyfive zoysiagrasses cultivars and species [Zoysia japonica Steud., Z. matrella (L.) Merr., and Z. japonica Steud. ✕ Z. tenuifolia Willd. ex Trin.] were studied in polyethylene tubes in a glasshouse. Differences were observed for average maximum root depth (AMRD), total root weight, and root numbers and weights at increasing 100‐mm depth increments. Average maximum root depth was positively correlated with total root weight and root number and weight at increasing 100–ram depth increments. Grasses with superior AMRD, total root weight, and root numbers at deeper profile depths (300–500 mm) included QT2047, El Toro, DALZ8512, TC5018, Meyer, DALZ8514, and DALZ8516. In a previously reported field experiment, 11 of the 25 zoysiagrasses were rated for percent of plot area covered by green turfgrass (an indicator of drought resistance) under three levels of irrigation (0, 35, and 100% of turfgrass evapotranspiration [ET]). Average maximum root depth, total root weight, and root numbers at 200‐, 300‐, and 400‐mm depths in polyethylene root tubes were positively correlated with percent green plot cover in the field under deficit irrigation (0 and 35% ET), indicating that rooting depth, weight, and branching at lower depths are important droughtresistance mechanisms in zoysiagrasses.

A method of modeling vertical fluid flow and solute transport in a GIS context

An irrigated agricultural area of 2350 ha in the San Joaquin Valley of California was used for assessing regional-scale vertical flow and solute transport. The study area was sufficiently large to show variability in salt-loading to the groundwater due to cropping and irrigation efficiency. A geographic information system (GIS) was used to store and manipulate a variety of data required for vertical transport modeling of water flow in the field area. Measured data included crop and irrigation schedules, daily evapotranspiration, soil type maps, and field sampling for determination of physical properties such as the saturation percentage and the gravimetric water content. A data classification scheme was developed consisting of four basic types of variables: (1) local variables for point data; (2) spatial variables for data having a constant value within a restricted domain such as an individual quarter-section; (3) derived variables being those selected based on a discrete value of another parameter (e.g. maximum root depth depends on the discrete variable, crop type), and (4) regional variables exhibiting a constant value over the entire study area. Each specific variable was classified utilizing the classification scheme and a relational database was created for all the data. From the data included in this database, calculations of fluid and solute transport were made at selected locations by a capacity-based, one-dimensional transport model. The results of a calculation were incorporated into the database for further manipulation and representation. A sample calculation was run for 315 locations within the field area to determine the spatial variation of salt-loading to the groundwater.

A Wet Excavation Method for Root/Shoot Studies of Pearl Millet on the Sandy Soils of the Sahel

SUMMARYRoot/shoot relations of two cultivars of pearl millet (Pennisetum glaucum) were studied on a sandy soil at Sadore in Niger using a wet excavation method. For the first 10 days after emergence (DAE), the length of the seminal root showed an exponential growth rate while plant height increased more or less linearly. The maximum rooting depth for millet was 168 cm and the maximum number of root axes and primary laterals, 172 per plant. Root length continued to increase up to 75 DAE, the maximum length exceeding 5000 cm per plant. The proportion of total day matter accumulated in the roots decreased from 30% in the early stages to less than 20% by maturity. The wet excavation method is a promising technique for the rapid removal of intact root systems of pearl millet from the sandy soils of the Sahel.

Comparison of water extraction models for grain sorghum under continuous soil drying

The aim of this study was to compare three contrasting models of water extraction, by comparing predictions of the models with water extraction observed under continuous soil drying from seven crops of grain sorghum in the field. Sensitivity of the model predictions to variation in evaporative demand, and soil and root characteristics were also assessed. The datasets covered soil types ranging from 68 to 252 mm of total extractable soil water (TESW), and levels of mean evaporative demand ranging from 1.8 to 4.9 mm d −1 . The first model was based on the simple function relating daily relative transpiration rate (RTR), the ratio of transpiration to demand, to the fraction of extractable water (FESW) in the maximum root zone of 200 cm, where RTR declined from 1.0 to zero as FESW fell from 0.3 to zero. The second model was the same as the first, except that RTR depended on FESW in the current root zone, where the current root zone was assumed to increase by 3 cm d −1 from emergence to reach 200 cm at anthesis. The third, more complicated model calculated daily transpiration as the lesser of potential extraction and transpirational demand, with potential uptake calculated in each soil layer from root-soil diffusivity and simulated root length density. Inputs of transpirational demand and extractable soil water contents were the same for all models. All models gave good predictions of the observed pattern of RTR and cumulative extraction in the seven crops studied, despite the differences in the level of detail specified within the models. The results indicated that in most situations, RTR will decline once FESW in the maximum rooting depth reaches around 0.3. Sensitivity analysis revealed that this threshold will change substantially where crops are growing on a low TESW soil under high demand, or on a high TESW soil under low demand. Of the soil and root characteristics assessed, the threshold FESW at which RTR declined was most sensitive to the downward rate of root front penetration, rather than the density of rooting or the root-soil diffusivity. This study confirms the robustness and validity of the simple relationship between RTR and extractable soil water currently used in many crop growth models. Use of the more detailed model showed under which situations the form of this relationship is likely to change.

Root growth of maize cultivars under field conditions as studied by the core and minirhizotron method and relationships to shoot growth

AbstractIn a 2‐year field study conducted on a Gleyic Luvisol in Stuttgart‐Hohenheim, root growth of one experimental and nine commercial maize cultivars was studied. According to the core method, roots of all cultivars penetrated the soil down to a depth of 150 cm indicating that no differences in maximum rooting depth existed. However, significant differences among the cultivars were found in root‐length densities (RLD) at silking in 1987 (1988) the ranges being 3.07–4.41 (2.88 – 4.43), 1.21 – 2.14 (1.14 – 1.75), 0.24 – 0.68 (0.24 – 0.56), and 0.05 – 0.12 (0.05 – 0.13) cm cm−3 in the various 30 cm layers down to 120 cm depth. In both years of the study vegetative yield was positively correlated with RLD in the 60 – 90 cm layer, whereas relationships between shoot traits and total root length were not consistent between the years. Differences between cultivars in root growth as identified by the core method could be confirmed by minirhizotron observations only at early stages of plant development. Quantitative comparisons between both methods showed that minirhizotron observations resulted in (a) an underestimation of root density (RD) in the topsoil and (b) the description of a linear decline of RD with depth below 30 cm whereas RLD in the soil cores decreased exponentially with depth. When RD at 7.5 and 15 cm profile depth were excluded from analysis, significant positive relationships between In RLD in soil cores and RD assessed with the minirhizotrons were calculated for different stages of plant development. However, the slope of the regression lines varied considerably between calibration dates indicating that one calibration is not sufficient to estimate RLD from minirhizotron observations.

Root Growth Simulation Model under Specified Environment

Sound irrigation management models require the information of root‐depth development with time in order to determine the active zone of soil reservoir. Development indicates rate of change. Sigmoidal as well as exponential root‐depth‐development models as a function of time, soil, crop, and management practices are developed. The models require as input data the maximum rooting depth to be achieved under a particular set of soil, crop, and management practices as well as the days until the root depth attains a maximum value. A comparison was made between experimental observations of a wheat crop and the estimates derived from several previously developed root‐growth models and the models developed in this study. The results clearly indicate that both of the developed models had a high degree of accuracy, which was comparable with or better than other reported empirical root‐growth models.

Changes in root growth within successive wheat crops in a cropping cycle using minimum and conventional tillage

The aim was to describe, through a cropping cycle of four years of successive wheat, root growth following different times of sowing using minimum or conventional tillage in the central west of New South Wales. The hypothesis was that, due to transient differences in soil structure at sowing, early growth of roots would be retarded under minimum tillage, but that eventually root growth would be better under minimum tillage than under conventional cultivation because of long-term changes in soil structure and infiltration characteristics. Minimum tillage did cause total root length to be less in the seedling stage in the first three years, whereas root length was the same in later growth in the early years, and greater under minimum tillage than under conventional cultivation in the later two years of the cropping cycle. Tillage, time of sowing or cultivar did not affect the relative distribution of roots with depth; treatments also did not affect maximum root depth, which increased during the development of each crop to an asymptote of only 75 cm. Minimum tillage resulted in higher rates of water infiltration to the soil at the end of the cropping cycle, and in higher soil water and greater crop water use during the cycle; minimum tillage did not result in statistically higher grain-yields compared with conventional cultivation. Relatively low grain-yields and low water-use efficiencies, particularly in years of above-average rainfall, implied over-riding constraints probably associated with poor soil structure, on crop performance.

Dynamics of seasonal recharge beneath a semiarid vegetation on the gnangara mound, Western Australia

AbstractTo estimate seasonal changes in recharge to the underlying sandy aquifer, the soil water dynamics of the unsaturated zone was monitored down to a depth of 20 m over a period of three years (1985 to 1987). The measurements were made by a neutron probe at eight locations beneath a native vegetation in a semiarid region, Western Australia, receiving precipitation of 775 mm yr−1. A relatively simple method, based on the analyses of sequentially measured soil water profiles involving utilization of zero flux plane in the unsaturated zone, is presented and used to compute seasonal recharge rates.Drainage fluxes (recharge rates) below two specified depths were estimated. These were: R1 (water flux at a depth of 10 m, just below the maximum rooting depth) and R2 (water flux at a depth of 18 m, just above the water table). These two estimates were significantly different both on a seasonal and annual basis, but their cumulative values for the three year period were very similar. While the annual precipitation varied from 525 to 850 mm yr−1, the corresponding spatially averaged R1 varied from 34 to 149 mm yr−1, and R2 varied from 65 to 80 mm yr−1. A significant difference in recharge between the upslope and downslope positions on a hillslope was ascribed to differences in vegetation density of the understorey and differences in hydraulic properties of subsoils.For the three year period, the average R1 and R2 were 13 per cent and 10 per cent of the precipitation respectively. These values compare favourably with a long‐term estimate based on an environmental tracer technique.

Development of a trickle irrigation scheduling model

A trickle irrigation scheduling model was developed based on a water balance approach to water flow, with each increasing soil depth represented by an increasing size ellipsoid. During an irrigation the wetting front and volume of water to fill each ellipsoid is determined. The water is distributed into cubes that form each ellipsoid and the size of the cubes is input information for the model. Cubes are used to approximate the ellipsoid shape to be able to model one-dimensional water flow from rainfall. Evaporation losses are accounted for from each surface cube. Rainfall fills the surface cubes, with excess rainfall passing into the cube below each surface cube. Transpiration is extracted from each cube, based on a potential transpiration and available moisture in the rooting volume. Deep drainage is the water that passes below the ellipsoid to a depth equal to the maximum rooting depth of the crop. Lettuce yield and the water balance of a lettuce crop grown during the summer of 1984 at Lalamilo, Hawaii were simulated for different irrigation amounts and the results compared to a field experiment using a gradient irrigation design. The model simulated within 2% the seasonal evapotranspiration of lettuce grown under six irrigation treatments that resulted in measured seasonal evapotranspiration ranging from 72 to 178 mm.

Effects of Establishment Method on Root Form of Lodgepole Pine and Sitka Spruce and on the Production of Adventitious Roots

Root systems of lodgepole pine and Sitka spruce were measured 15 years after establishment from bare-rooted transplants and direct sowing on a ploughed peat site. On one sample the root systems were divided into eight sectors in plan view for dry weight analysis and measurements were made on branching frequency. On another sample the five largest lateral roots on the Sitka spruce were dissected and sectioned to find whether they originated from the original root system or adventitiously from the stem. Root system form was considerably influenced by the ploughing, with the largest part of the dry weight contained in sectors which included the plough ridge. Although both species were affected to the same degree by the ploughing, statistical analysis showed that the distribution of root weight was more symmetric in the spruce than in the pine. Rooting depth, which was limited by waterlogging, was greater in pine than in spruce, and the development of a taproot from the seedling radical in the direct sown trees did not influence maximum rooting depth. The frequency of major root branches and the incidence of branches arising from injury were similar in all treatments. In the spruce, most of the transplants had major roots of adventitious origin, but adventitious roots were uncommon in the direct sown trees. In the transplants adventitious roots were most frequent (74–84 per cent) in the two largest of the five main roots and least abundant (10 per cent) in the two smallest. The size class distribution of the five main roots was less even in the transplants than in the sown trees, with greater allocation to the largest roots.

ROOTING CHARACTERISTICS OF CORN, SOYBEANS AND BARLEY AS A FUNCTION OF AVAILABLE WATER AND SOIL PHYSICAL CHARACTERISTICS

Root densities of field-grown corn, soybeans and barley were measured as functions of depth in four soils of different textures for 1 yr, and root depths were monitored for 2 additional years. General relationships were established between root depth, available soil water and soil texture. Maximum root depths were found to be inversely related to available water within the limits imposed by crop rooting habits and soil physical characteristics. Roots continued to develop during the reproductive growth phase and maximum root densities were found about the time of physiological maturity. Root distribution with depth was described for each crop on each soil using a modified exponential equation with an extinction coefficient specific to crop, growth stage and soil. Reasonable estimates of root distribution can be predicted from root density in the top layer using a crop-specific extinction coefficient in this modified exponential equation. Key words: Maximum root density, root distribution, rooting depth, nonlinear fitting

Compaction by forestry equipment and effects on coniferous seedling growth on four soils in the Alberta foothills

Soils developed on four parent materials (glaciolacustrine clay, clay loam till, coarse fluvial, and loamy eolian) in west-central Alberta were examined to determine residual effects of logging and use of site-preparation equipment upon soil bulk density. These studies were conducted on sites that were logged during the previous 24 years. Compaction was evident on all soils except those of the Summit association, which were dominantly Brunisolic Gray Luvisols developed on cobbly fluvial deposits of Tertiary age. Compaction was greatest on soils of the Marlboro association, which were dominantly Brunisolic Gray Luvisols developed on clay loam till. Soil bulk density values on the clear-cuts had recovered to those of the controls at comparable depth at ages ranging from 0 (Summit) to 17–21 years (Marlboro). Lodgepole pine and white spruce seedlings were grown on the four soils compacted in the laboratory to three bulk densities approximating the following field conditions: (1) those observed or expected immediately following logging and site preparation; (2) those observed 5–10 years after logging and site preparation; and (3) undisturbed control. In most cases, significant reduction in nine expressions of seedling growth (maximum root depth, maximum root depth in soil core, total weight, shoot weight, root weight, stem diameter, shoot height, seedling survival, and shoot weight: root weight ratio) was observed with increased bulk density.

THE ANATOMICAL CHARACTERISTICS OF ROOTS AND PLANT RESPONSE TO SOIL FLOODING

SUMMARYNinety‐one plant species from wetland (WL), intermediate (INT) and non‐wetland (NWL) habitats were grown in flooded and drained soils and responses to flooding were assessed in relation to root anatomy and fractional root porosity (FRP).Flooding response and tolerance were related to FRP. Rooting depth increased with FRP in accordance with diffusion model predictions and emphasized the ventilating efficiency of aerenchyma. Major determinants of FRP were cortical cell configurations, closeness of cell packing, the relative proportions of configuration types, porous: non‐porous tissue ratios, aerenchyma development and the type and degree of secondary growth. A classification of cortical types based on cell and aerenchyma patterns is presented.Aerenchyma, both schizogenous and lysigenous, developed preferentially where pre‐aerenchymatous cortical cell configurations (in TS) were radial and particularly, cubic and radial typical of WL and INT species. Aerenchyma rarely formed from hexagonal non‐radial arrays which occur chiefly in NWL and in the outer cortical zones of WL and INT plants. The ventilating potential in non‐aerenchymatous tissue was shown to be greater for cubic (fractional porosity, FP, max. 0–2146) than for hexagonal arrays (FP max. 0˙0931); closer packing greatly accentuated the differences. It is suggested that cubic: hexagonal zonal ratios in roots may reflect a balance between respiratory and mechanical needs.In a majority of WL and INT species, shoot weights were unaffected by or increased with flooding and maximum rooting depths usually much exceeded 50 mm. Cubic packing raised the FRPs, as did aerenchyma which was often much greater under flooding. In the dicotyledonous species, a suppression of secondary growth in some, and a highly porous phelloderm in others, helped maintain high FRP. A minority of species were anatomically and responsively similar to NWL plants; survival under flooding was attributed to shallow rooting.Under flooding, the FRP of almost all NWL species was < 0˙055 due to hexagonal packing, a lack of aerenchyma and, in dicotyledonous plants, secondary growth with scanty phelloderm. Shoot weights were reduced in 50% of cases, rooting depths were <50 mm, and some species died. Some species were exceptional in having cubic and radial packings; a lack of aerenchyma was associated with continuing meristematic activity in the primary cortex.

Root systems of selected plant species in mesic mountain fynbos in the Jonkershoek Valley, south-western Cape Province

Twenty-five individuals of 10 species of fynbos plants were harvested 26 years after fire at a mountain fynbos site. The species included shrubs up to 4 m tall, geophytes and other herbaceous plants. The total mass, canopy area and height were determined for shoots. Root systems were excavated by washing away soil around the roots, with water. The mean root:shoot phytomass ratios were lower (0,2) for dominant re-seeding shrubs than for resprouting shrubs (2,3). Herbaceous species (all resprouters) had a mean root:shoot phytomass ratio of 1,5. Roots were concentrated in the upper soil. Sixty-seven percent of the root phytomass was found in the top 0,1 m of soil. The maximum rooting depth ranged from 0,1 m for some herbaceous species to > 3,5 m for deep-rooted shrubs. Fine roots (< 5 mm) contributed at least 59% of the root length and were also concentrated in the upper soil. The root classification scheme of Cannon (1949) was successfully applied to the study, and three primary and two adventitious root types were identified. The rooting patterns of fynbos plants were compared to data from other fynbos areas and to other mediterranean-type shrublands. Dominant fynbos shrubs with deep roots reproduce from seed following fire. Root phytomass can be reduced by 50% following fire in fynbos, while root phytomass remains largely unaffected by fire in Australian heathlands. Vyf-en-twintig individuee van 10 fynbos-plantspesies was 26-jaar na ’n brand in bergfynbos ontgin. Die spesies het struike (tot 4 m hoog), bolplante en ander kruidagtige plante ingesluit. Die totale massa, die oppervlakte van die kroondak en die hoogte was vir bo-grondse dele bepaal. Wortelsisteme was ontgin deur die grond om die wortels met water weg te spoel. Die gemiddelde wortel:loot-biomassaverhoudings was laer (0,2) in die dominante struike wat deur middel van saad verjong, in vergelyking met struike wat na ’n brand spruit (2,3). Kruidagtige spesies (almal spruitende plante) het ’n gemiddelde wortel:loot-biomassaverhouding van 1,5 gehad. Wortels was in die bogrond gekonsentreer. Die grootste gedeelte (67%) van die wortel-biomassa het in die boonste 0,1 m van die grond voorgekom. Die maksimum wortel-diepte het tussen 0,1 m vir sekere kruidagtige spesies, en > 3,5 m vir sekere struike gewissel. Fyn wortels (< 5 mm) het ten minste 59% van die wortellengte bygedra, en was ook in die bogrond gekonsentreer. Die wortelklassifikasieskema van Cannon (1949) was suksesvol op die studie toegepas. Drie primêre en twee bywortel-tipes was uitgeken. Die bewortelingspatrone van fynbos-plante is met die van ander fynbos-areas en met die van mediterreense struikveld-soorte vergelyk. Dominante fynbos-struike met diep wortelsisteme verjong deur middel van saad na brand. Wortel biomassa kan met tot 50% gereduseer word na brand, terwyl wortel-biomassa in Australiese heideveld grootliks onveranderd bly na brand.

Subsoil conditions and maximum rooting depths of commercial pea crops grown in Canterbury, New Zealand

Abstract In order to use the water balance approach to schedule irrigation, estimates of crop maximum rooting depths (Zmax) are needed. Published guidelines for irrigation scheduling have suggested that Zmax for peas can be taken as 80 cm. The objectives of this research were firstly to ascertain how accurate the 80 cm estimate of Zmax was for a number of commercial pea crops in Canterbury, and secondly to identify the factors most likely to have limited Zmax for these crops. Values of Zmax for process pea crops at harvest were estimated at ten Canterbury sites during the 1983 – 84 growing season. Soil texture, pH, and dry bulk density were also recorded along with a root disease index, plant population, shoot dry matter, and pea yield. Zmax values for the different sites varied between 40 and 75 cm, with few values exceeding 60 cm. Root penetration to depth did not appear to be much affected by root diseases or subsoil acidity. Rather, subsoil compaction seemed to be responsible for the poor root penetra...

PREEXISTING CHANNELS AND SOYBEAN ROOTING PATTERNS

We used a trench-profile method to study soybean (Glycine max (L.) Merr.) root distribution and vertical channel patterns in Flanagan (Aquic Argiudoll) silt loam. Root distribution was quantified as the number of first-order lateral roots, the depths at which tap and first-order lateral roots encountered burrows, and the maximum rooting depth where white, young roots with growing tips occurred. In this work, we called all round vertical channels in the soil burrows, not attempting to determine whether they had been made by worms, insects, or roots. Numbers per unit area and diameters of burrows were measured at 20-cm-depth increments from 10 to 130 cm. The first-order lateral roots occurred in the top 30 cm of the soil, and most roots encountered burrows at 30 to 45 cm below the surface. If a taproot failed to encounter a burrow at this level, the root tip died. Once in a burrow, the root grew downward within the channel to the point at which the burrow ended. The number of burrows with diameters greater than 1.5 mm increased with increasing depth from the surface to about 40 cm, then decreased, with very few burrows below a depth of 130 cm. Under sod, the same trend in distribution was observed, but with more burrows below 50 cm than were seen under soybeans. The number of burrows at a depth of 30 cm ranged from 500 to 1400 m−2. The maximum total cross-sectional area of burrows at the 30-cm depth was about 0.007 m2 m−2 of soil surface. The numbers of burrows, with the tendency of roots to grow in these burrows, suggest that burrows have a profound effect upon the shape of the root system, as well as upon rapid gas and water movement.

Root characteristics of some temperate legume species and varieties on deep, free-draining entisols

We report experiments comparing several legumes with the aim of distinguishing genotypic from environmental differences in those root parameters which influence water use and nutrition. Temperate crop and pasture legumes were grown on three xeric psamment soils at latitude 29�S. in Western Australia to evaluate the relative root characteristics of different species. Sites had 428, 298 and 155 mm rainfall in the (winter) growing season. Maximum root depth was significantly different (P &lt; 0.001) between genotypes, but non-significant between sites. Genetic control for maximum root depth is thus implied. This has significance for water use and plant production of these low water-storage sandy soils. Lupinus spp. extended their roots to an average 190 cm, Pisum sativum L. to only 65 cm, Triticum aestivum L. to 113 cm. The pasture species ranged from Vicia benghalensis L. (75 cm) and Trifolium spp. (69 cm) to Medicago spp. which averaged 92 cm. Lupins and wheat had less than 50% of their total root length (cm-1) in the top 20 cm, whereas other species all had over 70% of roots in that layer. Pasture legumes with high root density in that layer tend to dry sandy topsoils frequently, reducing nutrient availability and hence vegetative growth. Root density averaged only 0.045 for lupins, compared with 1.0 cm-2 for clovers. All total root lengths were low at maturity, compared with more favorable environments. Nevertheless, they were calculated to be adequate for water and mobile nutrient extraction from these sandy soils.

Effects of solar radiation on growth of cassava (Manihot esculenta crantz.). II. Fibrous root length

Effects of solar radiation on the growth of fibrous roots of cassava cv. M Aus 7 were examined by growing plants without shading (control) and under shade cloths which reduced input to 78% and 32% respectively of full solar radiation. Plants were at two different stages of growth when shading treatments were imposed. The experimental results indicate that cassava can develop fibrous root systems rapidly and extensively. Within 50 days of planting, root length density in the 0-20 cm soil layer was 1.6 cm cm-3 and by 84 days it had increased to 3.6 cm cm-3. Maximum root depth also increased from 60-80 cm at 29 days after planting to 100-120 cm by day 50 and beyond 120 cm by day 72. Estimated total fibrous root length per m2 ground area to a depth of 120 cm was 32 km m-2 and 23 km m-2 at the end of the experiment for the two crops, 133 days old and 84 days old, respectively. Shading the plants for 35 days reduced the rate of increase in root length density and hence decreased total root length in the two crops. Reduction in solar input to 32% resulted in a 50% reduction in elongation rate of fibrous roots. Reduction to 78% resulted in a similar reduction in elongation rate when plants were at tuber bulking stage, but much less reduction when plants were at the tuber initiation stage. The results indicate that under limited carbohydrate supply shoot was a stronger sink than both fibrous roots and tubers. At tuber initiation stage tuber was a weaker sink than fibrous roots, but at bulking stage it was about equal to fibrous roots.

Root Development of Winter Wheat as Related to Tillage Practice in Western Nebraska1

AbstractTillage practices can influence crop root development. Root distributions were determined for wheat (Triticum aestivum L.) grown in a wheat‐fallow rotation during the 1977–1978 winter wheat crop year on an Alliance silt loam (Aridic Argiustoll). The fallow tillage treatments were plow, subtillage, and chemical (no tillage). Each tillage treatment was split into subplots for N application of 0 or 45 kg/ha.Rooting density was determined by washing the roots in soil cores 7.6 cm in diam by 15 cm long extracted to depths of 90, 105, and 120 cm on 28 Mar., 2 May, and 8 June 1978, respectively. After root length was determined, roots were dried and weighed. Soil penetration resistance was determined with depth in the soil by inserting a penetrometer horizontally 4 cm into the soil at vertical intervals of 10 cm from the surface.Root weight was greatest for the chemical treatment (46 mg/dm3) and least for the subtillage treatment (26 mg/dm3). Approximately 62% of the total root mass was in the upper 30 cm of soil with maximum rooting depth greater than 120 cm for all treatments by 8 June 1978. Root development was limited by the alluvial horizon at a depth of about 25 to 40 cm. Visual observations also showed some root resistance by tillage shear plane at 10 cm. Nitrogen fertilization did not significantly change the rooting pattern; however, the N‐by‐tillage interaction for root weight was significant at the second sampling date—the subtillage treatment showed a positive response to added N, while chemical and plow treatments showed a negative response. Wheat yields were not significantly influenced by fallow tillage or N. This indicated that root development occurring above and below the resistant layer was sufficient to supply the plant with its water and mineral needs.

Responses of soybeans to two row spacings and two soil water levels. II. Water use, root growth and plant water status

Soybeans ( Glycine max (L.) Merr.) grown in rows narrower than 0.5 m often outyield those grown at the more traditional 1.0-m row spacings. Limited research also has indicated that narrow-row plants produce a greater root length per ha. The present research was concluded to determine if an improved plant water status associated with this greater root length was the reason that narrow-row soybeans often outyield wide-row soybeans. Soybeans were planted in 0.25- and 1.0-m row spacings and a population of 160000 plants per ha established. Half of the experimental area was irrigated when the soil water content in the 0.15- to 0.30-m layer was reduced below 0.20 m 3 m −3 and half was rainfed during the season. Irrigation increased the midday leaf water potentials at both row spacings. However, the fact that irrigation did not produce a yield increase suggests that severe water stress did not occur in the nonirrigated plants, despite a 200 mm soil water depletion. All treatments produced a similar maximum root depth (1.8 m) but the narrow-row treatments produced 49% more roots per unit land area and 52% more roots per unit leaf area. Despite the difference in rooting densities, there were no consistant differences between the nonirrigated treatments in water use over time or depth, plant water potentials or soil temperatures. We concluded that the observed differences between row spacings in biomass accumulation and seed yield were caused by differences in radiation interception and not by improved plant water relations associated with the greater root length densities of the narrow-row plants.