Maximum Root Length Density Research Articles

Subsoiling depth affects the morphological and physiological traits of roots in film-mulched and drip-irrigated cotton

Subsoil compaction is increasingly a problem. Subsoiling breaks up the soil, removes compaction, and improves root growth. However, it is unclear whether subsoiling depth affects root growth and physiological functioning of film-mulched and drip-irrigated cotton, which has a shallow root system (< 60 cm). A 2-year experiment (2019–2020) was performed under field conditions (soil texture was sandy loam from 0 to 40 cm and clay loam from 40 to 60 cm) to determine the morphological and physiological traits of the root system at different subsoiling depths: no subsoiling (NS, control) and subsoiling to 30 (S30), 40 (S40), and 50 (S50) cm. The root/shoot ratios were significantly higher for the S30 and S40 treatments than for the control (p < 0.05). The dry matter levels over the 2 years were 24.2% higher in S40 plants than in controls and 20.7% higher than in the others subsoiling treatments. The average 2-year yields (676.9 g m–2) were 24.3%, 11.9%, and 1.4% higher in S40 plants than in controls, S30, and S50 plants. At different soil depths of 0–60 cm, the average 2-year root length density (RLD) of all subsoiling treatments was 0.5 cm cm−3 in the top 20 cm of soil, 14.0% higher than that from 20 to 40 cm and 344.2% higher than that from 40 to 60 cm. However, RLDs of the NS and S30 treatments were highest at 0–20 cm, while S40 and S50 maximum RLDs were in the 20–40 cm layers. The RLD, average diameter of roots, and surface area density of roots were significantly higher in the S40 and S50 treatments than in the S30 and NS treatments (p < 0.05). Compared to NS, subsoiling reduced the levels of malondialdehyde and abscisic acid in roots; improved superoxide dismutase, peroxidase, and catalase activities in roots, and increased the levels of gibberellic acid and indole-3-acetic acid in roots. Our results provide evidence that could help optimize subsoiling depth in film mulching and drip-irrigated cotton in Xinjiang.

Effects of plant morphology on root–soil hydraulic interactions ofSchefflera heptaphylla

Root water uptake induces additional soil suction by soil water extraction. However, induced soil suction restricts root water uptake when beyond a threshold (st) and tends to stop water uptake at a limiting suction (sl). This process is called root–soil hydraulic interactions, whose relationship with plant morphology (e.g., plant height, leaf area, and root length) is unclear. This study aims to investigate the effects of plant morphology on response of the sink term (water uptake intensity; WUI) to soil suction for Schefflera heptaphylla. Laboratory tests were conducted on 26 individuals in five different height groups. A new empirical model was derived to consider effects of plant morphology on root water uptake distribution in the full soil suction range. The locations of maximum root length density (RLD) and WUI for taller individuals were relatively deeper and farther from centreline. Before soil suction reached st, water uptake length ability (WULA) remained at a maximum level, positively related to LR ratio (ratio between leaf area, LA, and root length, RL), but less affected by plant height. For taller plants, the decreasing rate of stwith LR ratio was larger, while the decreasing rate of WULA with soil suction beyond stappeared smaller. slappeared independent of height, LA, and RL.

Optimum water and nitrogen supply regulates root distribution and produces high grain yields in spring wheat (Triticum aestivum L.) under permanent raised bed tillage in arid northwest China

Shortages in water, energy and human resources, low water productivity, soil degradation, and environmental pollution in northwestern China are compelling farmers to develop and adopt sustainable conservation technologies. While the effect of permanent raised beds with furrow irrigation (PRBF) on soil fertility, crop yields and water use efficiency under different soil and climatic conditions has been studied extensively, few experiments have investigated the regulation of irrigation and nitrogen (N). A two-year field experiment, conducted in arid northwestern China, assessed the effects of nitrogen and irrigation rates on grain yield, root growth, root distribution, soil nitrate-nitrogen (NO3–-N) distribution, and water and N use efficiencies in spring wheat under PRBF tillage. The experiment followed a completely randomized split-plot design with three irrigation amounts—one-third conventional irrigated [1200 m3 ha–1 (I0.33)], two-thirds conventional irrigated [2400 m3 ha–1 (I0.67)], and conventional irrigated [3600 m3 ha–1 (I1.0)]—as the main-plot treatments, and four nitrogen levels—unfertilized [0 kg ha–1 N (N0)], one-third conventional unfertilized [90 kg ha–1 N (N0.33)], two-thirds conventional unfertilized [180 kg ha–1 N (N0.67)], and conventional fertilized [270 kg ha–1 N (N1.0)]—as the sub-plot treatments.We identified a significant interaction between irrigation and N application rate. The response of root length density (RLD) and its distribution to the N treatments also depended on the irrigation amount. When conventionally irrigated (3600 m3 ha–1), N fertilizer was the main factor limiting spring wheat root growth; N application at 270 kg ha–1 produced the highest RLD values (1.273 and 1.374 cm cm–3) in 2014 and 2015, respectively. At lesser irrigation amounts (1200 and 2400 m3 ha–1), N fertilizer had little effect, with the contribution of water more important to spring wheat root growth; N application at 180 kg ha–1 produced maximum RLD values (1.335 and 1.545 cm cm–3) in the 2400 m3 ha–1 irrigation treatment in 2014 and 2015, respectively, and N application at 90 kg ha–1 produced maximum RLD values (1.042 and 1.163 cm cm–3) in the 1200 m3 ha–1 irrigation treatment in 2014 and 2015, respectively. The I0.67N0.67 treatment produced the highest yields (5022 and 6124 kg ha–1) and RLD values (1.223 and 1.554 cm cm–3) in 2014 and 2015, respectively, and the same treatment had a relatively wide distribution of RLD at 20–60 cm. The NO3–-N concentration from 0 to 120 cm increased with N fertilization and decreased with irrigation amount. The results showed that the I0.67N0.67 treatment, with one-third less N and irrigation water than traditional rates (I1.0N1.0), produced equivalent grain yields, had relatively low N losses, and had the highest 20–60 cm root distribution. In the PRBF irrigation system, the I0.67N0.67 treatment appears to be the most promising strategy for producing a high percentage of roots in deep soil layers and increasing grain yields, and water and N use efficiencies.

Stand establishment, root development and yield of winter wheat as affected by tillage and straw mulch in the water deficit hilly region of southwestern China

Good crop stand establishment and root system development are essential for optimum grain yield of dryland wheat (Triticum aestivum L.). At present, little is known about the effect of tillage and straw mulch on the root system of wheat under dryland areas in southwestern China. The aim of this study was to evaluate the effect of three tillage treatments (no-till, NT; rotary till, RT; conventional till, CT) and two crop residue management practices (straw mulch, ML; non-straw mulch, NML) on stand establishment, root growth and grain yield of wheat. NT resulted in lower soil cover thickness for the wheat seed, higher number of uncovered seeds, lower percentage of seedling-less ridges and lower tiller density compared to RT and CT; ML resulted in higher tiller density compared to NML. Straw mulching resulted in more soil water content and root length density (RLD) at most of the growth stages and soil depths. The maximum RLD, root surface area density and root dry matter density were obtained under NT. In the topmost 10 cm soil layer, higher RLD values were found under NT than those under RT and CT. There were no significant differences in the yield or yield components of wheat among the tillage treatments in 2011–2012, but NT resulted in a significant higher yield compared to RT and CT in 2012–2013. Grain yield was significantly higher in ML compared to in NML. A strong relationship was observed between the water-use efficiency and the grain yield. Both NT and ML proved beneficial for wheat in term of maintaining higher tiller density, better soil water status and root growth, leading to a higher grain yield and enhanced water-use efficiency, especially in a low rainfall year.

Modelling potassium uptake by wheat

A model has been used to simulate potassium (K) uptake by wheat in a pot culture experiment. Three soils from India, namely Alfisol, Inceptisol and Vertisol, were differentially K exhausted by Sudan grass (Surghum vulgare var. Sudanensis) for a period of 280 days and were used to simulate potassium uptake by wheat (Triticum aestivum) and also to predict the amounts of K released or fixed during cropping. Except in Alfisol all the predicted values of K uptake closely agreed with that of measured values. When predicted K uptake values were plotted against the observed values, r 2 values were found to be 0.927, 0.828 and 0.721 in Inceptisol, Alfisol, and Vertisol, respectively. There is a close relationship between observed and predicted values of K uptake as evident from the high r 2 values, but in case of Alfisol and Vertisol the model has over-predicted K uptake, which perhaps was due to over prediction of K release from non-exchangeable form. The model has been validated and has been applied to simulate response towards fertilizer application at different available K. It was showing that maximum response occurs at a particular value of available K, which shifts towards higher value as release threshold level (RTL) increases. Predicted K uptake was most sensitive to changes in root parameters such as root length density (RLD) and maximum influx rate (Vmax), since changes in the time at which maximum root length density was attained (RLD-B) and the decay constant of Vmax (Vmax-B) gave the greatest changes in K uptake in almost all the soils except highly exhausted Alfisol in which predicted potassium uptake was more sensitive to changes in RLD-B and intercept (c) than to root uptake kinetics, as described by Michaelis-Menten constant (Km) and Vmax. The predicted potassium uptake was least sensitive to changes in rate constants of release and fixation and fixation threshold level in Inceptisol and Vertisol, but was sensitive to release threshold level and rate constant of release in Alfisol.

Three‐Dimensional Electrical Resistivity Tomography to Monitor Root Zone Water Dynamics

Knowledge of soil moisture dynamics and its spatial variability is essential to improve our understanding of root water uptake and soil moisture redistribution at the local scale and the field scale. We investigated the potential and limitations of electrical resistivity tomography (ERT) to measure three‐dimensional soil moisture changes and variability in a large, undisturbed, cropped soil column and examined the interactions between soil and root system. Our analysis sustained the value of ERT as a tool to monitor and quantify water contents and water content changes in the soil, as long as the root biomass does not influence the observed resistivity. This is shown using a global water mass balance and a local validation using time domain reflectometry (TDR) probes. The observed soil moisture variability was rather high compared to values reported in the literature for bare soil. The measured water depletion rate, being the result of combined effects of root water uptake and soil water redistribution, was compared with the evaporative demand and root length densities. We observed a gradual downward movement of the maximum water depletion rate combined with periods of redistribution when there was less transpiration. Finally, the maximum root length density was observed at −70 cm depth, pointing out that root architecture can strongly depend on soil characteristics and states.

Efeito da fertilização azotada na dinâmica de enraizamento e na produção comercial de cebola de dias médios no alentejo

Intermediate-day onions (cv. Gilmar) rooting patterns, soil availability NO3-, leaf N concentration and commercial yield were evaluated in a field trial where four nitrogen fertilizer rates (0, 37, 74 and 111 kg N ha-1) were applied into four split applications, following a randomized block design with four replications. Root length, soil availability NO3-, and leaf N concentration were evaluated at four dates during growing season (33, 57, 96 and 127 days after planting). Root length density (cm cm-3) at different sampling dates, locations (under the bulb and at 4 cm from the plant row) and depths was not affected by nitrogen level. For all sampling dates about 65 to 100 % of the root length was concentrated in the top 10 cm of the soil profile, under the bulb and the maximum root length density was 1.88 cm cm-3. The maximum rooting depth ranged from 20 and 30 cm, not exceeding 10 cm in depth, up to 32 days after planting. Under the conditions of the experiment, results recommend an application of 30 kg ha-1 of nitrogen at planting and an increasing of the amount of nitrogen applied (16.2% of total N applied) at bulb initiation. Marketable onion yield increased with the level of nitrogen but the production obtained with the application of 74 kg ha-1 (5.12 kg m-2) and 111 kg N ha-1 (6.59 kg m-2) did not differ significantly.

Root length density and soil water distribution in drip-irrigated olive orchards in Argentina under arid conditions

Several studies have evaluated many above-ground aspects of olive production, but essential root system characteristics have been little examined. The objective of our study was to evaluate root length density (RLD) and root distribution relative to soil water content in three commercial orchards (north-west Argentina). Depending on the orchard, the different drip emitter arrangements included either: (1) emitters spaced continuously at 1-m intervals along the drip line (CE-4; 4 emitters per tree); (2) 4 emitters per tree spaced at 1-m intervals, but with a space of 2 m between emitters of neighbouring trees (E-4); or (3) 2 emitters per tree with 4 m between emitters of neighbouring trees (E-2). All of the orchards included either var. Manzanilla fina or Manzanilla reina trees (5–8 years old) growing in sandy soils, although the specific characteristics of each orchard differed. Root length density values (2.5–3.5 cm/cm3) in the upper soil depth (0–0.5 m) were fairly uniform along the drip line in the continuous emitter (CE-4) orchard. In contrast, roots were more concentrated in the E-4 and E-2 orchards, in some cases with maximum RLD values of up to 7 cm/cm3. Approximately 70% of the root system was located in the upper 0.5 m of soil depth, and most of the roots were within 0.5 m of the drip line. For each of the three orchards, significant linear relationships between soil water content and RLD were detected based on 42 sampling positions that included various distances from the trunk and soil depths. Values of RLD averaged over the entire rooting zone and total tree root length per leaf area for the three orchards were estimated to range from 0.19 to 0.48 cm/cm3 and from 1.8 to 3.5 km/m2, respectively. These results should reduce the uncertainty associated with the magnitude of RLD values under drip irrigation as intensively managed olive orchards continue to expand in established and new growing regions.

Growth and nutrient uptake by cotton roots under field conditions1

The relationship between nutrient uptake and root growth of cotton (Gossypium hirsutum L.) was studied under field conditions. This basic information could be beneficial when making best management decisions concerning the time of application and placement of fertilizer. A field study was conducted in North Alabama on a fertile Dewey silt loam (clayey, kaolinitic, thermic Typic Paleudult). Aboveground whole plants were harvested at approximately 10‐day intervals beginning at 211 cumulative heat units (CHU) after planting (37 days after planting: 4‐true leaves). Root length of harvested plants was also measured by depth and distance from the plant. Maximum root length was obtained at 1174 CHU (117 days after planting), while dry matter continued to increase until a maximum was obtained at 1317 CHU (128 days after planting). Maximum root length density of 1.60 cm cm3 was obtained in the surface 0–15 cm layer in the in‐row position at 912 CHU (99 days after planting). After first bloom approximately 70% of the cotton root system was in the surface 30 cm of soil. Average daily influx of S per m of root length increased with plant age until 1317 CHU (near cut‐out), after which influx declined. Nitrogen (N), calcium (Ca), and iron (Fe) influx peaked very early in the season (291–469 CHU) followed by a general decrease with plant age. Maximum daily influx of potassium (K), phosphorus (P), magnesium (Mg), copper (Cu), manganese (Mn), and zinc (Zn) per meter of root occurred at approximately peak‐bloom (764–912 CHU, 87–99 days after planting) and decreased with plant age. Copper, Fe, Mn, and Zn influx rates were ∼ 1000 times lower as compared to the other nutrients.

Comparison of minirhizotrons and the soil-water-depletion method to determine maize and soybean root length and depth

Root length density of maize ( Zea mays L.) and soybean [ Glycine max (L.) Merr.], measured with minirhizotrons, was compared with soil-water depletion, measured with neutron probes, to determine whether the soil-water-depletion method could indicate root length density and root depth in a stratified soil. The study was carried out in southeast Kansas, USA, on a Parsons silt loam soil (Mollic Albaqualf fine, mixed, thermic) overlying clay (a claypan). Measurements were taken during two dry periods, one in 1983 and one in 1984, to a depth of 1.35 m for soil water and to a depth of 1.15 m for root length density. At the beginning of the dry period, average soil water content for both crops throughout the profile was 0.47 m 3 m −3 in 1983 and 0.42 m 3 m −3 in 1984. During both dry periods, roots died back in the surface soil because the silt loam dried out; it was drier than the clay. The claypan inhibited root growth. In the clay, roots of both crops increased in root length density in the water year (1983) or decreased in root length density in the drier year (1984). In both years, the depth of maximum water depletion in the soil profile for maize (0.45 m in 1983, 0.90 m in 1984) corresponded well with the depth of maximum root length density measured with minirhizotrons (0.50 m in 1983, 0.80 m in 1984). The depths of maximum depletion for soybean (0.15 m and 0.30 m in 1983, and 0.60 m in 1984) also corresponded relatively well with the zones of maximum root length density (0.15 and 0.50 m in 1983, and 0.40 m in 1984). Depth of rooting was not evident from the soil-water measurements. Root length densities for both crops were low (less than about 1000 and 300 mm −3 for maize and soybean, respectively) at bottom depths of the profile.

Tillage-induced differences in the growth and distribution of wheat-roots

Root growth and distribution of wheat under different tillage practices was studied in a 4-year-old tillage experimental site at Cowra, N.S.W. Tillage affected root density as well as distribution. Up to 98 days after sowing, root length density was lower (P &lt; 0.05) in the 0.05-0.10 m layer of the direct-drilled soil than the conventionally cultivated soil. Poor root growth found in direct-drilled soils, which was significantly related to the poor shoot growth, was not caused by soil physical conditions, viz. higher bulk density and soil strength. Rather, biological factors were involved because fumigation completely eliminated the poor shoot growth and significantly increased root length density of the direct drilled soils. Compared to a compaction treatment, roots grown under direct drilling, in addition to having lower density, also had impaired function. Under conventional cultivation, significantly lower root length density was found in the surface soil layer (0-0.05 m) and maximum root length density was found in the 0-05-0.10 m layer. Fumigation did not change the root distribution pattern. This tillage-induced difference in root distribution reflected less favourable surface soil conditions as a result of cultivation, e.g. seedbed slumping, compared to the soil under direct drilling.

Effects of soil type on soybean crop water use in weighing lysimeters

Different soils are known to affect the amount and distribution of both available water and roots. Optimising irrigation water use, especially when shallow water-tables are present requires accurate knowledge of the root zone dynamics. This study was conducted to determine the effect of two soil types on root growth, soil water extraction patterns, and contributions of a water-table to crop evaporation (E). Two weighing lysimeters (L1 and L2) with undisturbed blocks of soil were used. The soil in L1 had higher hydraulic conductivity and lower bulk density than that in L2. Well watered conditions were maintained by irrigation for the first 110 days from sowing (DFS). Root length density (RLD) was calculated from observations made in clear acrylic tubes installed into the sides of the lysimeters. Volumetric soil water contents were measured with a neutron probe. A water-table (EC = 0.01 S m-1) was established 1 m below the soil surface 18 DFS. RLD values were greater in L1 than L2 at any depth. In L1, maximum RLD values (3 × 104 m m-3) were measured immediately above the water-table at physiological maturity (133 DFS). In L2, maximum RLD values (1.5 × 104 m m-3) were measured at 0.42 m on 120 DFS and few roots were present above the water-table. From 71 to 74 DFS, 55 and 64% of E was extracted from above 0.2 m for L1 and L2, respectively. In L2, extraction was essentially limited to the upper 0.4 m, while L1 extraction was to 0.8 m depth. Around 100 DFS the water-table contributed 29% (L1) and 7% (L2) of the water evaporated. This proportion increased rapidly as the upper soil layers dried following the last substantial irrigation 106 DFS. Over the whole season the water-table contributed 24% in L1 and 6.5% in L2 of total E.

Soybeans root distribution under wet soil culture on a red-brown earth

Root distribution of soybean was determined under wet soil culture on two Red-Brown earths in S.E. Australia. In general there was a parabolic distribution of roots with low root length densities in the furrow (saturated soil zone) and centre of the bed (dry zone). Maximum root length density (20 cm cm−3) occurred at the base of the plants, approximately 300 mm from the furrow under wet soil culture. Roots were confined to the wet aerated zone which was determined by the permeability of the soil.