Subsoil Root Research Articles

Radiation Environment of Mangrove Pneumatophores in Brackish Water.

The pneumatophores of Avicennia and Sonneratia species photosynthesize and the photosynthetically generated O2 is used for the respiration in the roots in subsoil. To understand the radiation environment of the pneumatophores, we measured solar radiation on the vertical surface (Rv) in the water with dye films. The Rv averaged over the daytime at a depth of 30 cm was similar to the light compensation points in the pneumatophores. From this result, it can be supposed that the photosynthesis nearly compensated the respiration at a depth of 30 cm and supplied O2 to the roots in subsoil at shallower places, even when the pneumatophores were submerged in the daytime.

The history and possible causes of forest decline in central Europe, with particular attention to the German situation

The elasticity (nutrient storage, litter decomposition, bioturbation of soil) and diversity of central European forest ecosystems has been reduced by centuries of overutilization. Since the middle of the nineteenth century, their development has been influenced by silvicultural measures, as well as by the deposition of acids and nutrients, especially nitrogen from anthropogenic sources, i.e., by a mixture of stabilizing and destabilizing external influences. During recent decades, most forest soils have been acidified by acid deposition resulting in low levels of nutrient cations and negative alkalinity in the soil solution. Widespread acute acidification of soil in the rooting zone is indicated by extremely high manganese (Mn) contents in leaves (fingerprint). Soil acidification has caused drastic losses of fine roots in subsoil, indicated by denuded structural root systems where adventitious fine root complexes exist only sporadically. Research at the organ (leaf, fine root, mycorrhiza) and cellular levels has provided much information on the effects of air pollutants and soil acidification on leaves and roots. There are considerable uncertainties, however, as to how changes in the status of leaves or roots are processed within the tree and ecosystem from one level of hierarchy to the next on an increasing spatial and time scale, and how these lead to decline symptoms like crown thinning, stand opening (as a consequence of dieback or perturbations), and changes in species composition (soil biota, ground vegetation, tree regeneration). At the tree level, nutrient imbalances (due to cation losses from soil, changes in the acid/base status of the soil, proton buffering in leaves, and N deposition), as well as disturbances in the transport system of assimilates and water, are suspected of causing the decline symptoms. Information on the filtering mechanisms at various hierarchical levels, especially in the case of a break in the hierarchy, is missing. The null hypothesis (no effects of air pollutants on forest ecosystems) can be considered to be falsified. Forest ecosystems are in transition. The current state of knowledge is not sufficient to define precisely the final state that will be reached, given continuously changing environmental conditions and human impacts. The hypothesis, however, of large-scale forest dieback in the near future is not backed by data and can be discarded.Key words: forest ecosystem, process hierarchy, air pollution, deposition, acidity, nitrogen.

Above- and below-ground biomass and fine roots of 4-year-old hybrids of Populustrichocarpa × Populusdeltoides and parental species in short-rotation culture

Mean annual aboveground leafless biomass production averaged 14.8, 11.4, and 24.3 Mg•ha−1•year−1 at harvest at 4 years of age for Populustrichocarpa Torr. & Gray, Populusdeltoides Marsh., and P. trichocarpa × P. deltoides hybrids, respectively. These trees were planted at 1 × 1 m spacing on a medium- to coarse-textured alluvial soil in western Washington. Branches accounted for 13.2–20.3% of the aboveground weight. Total weight of stumps and coarse roots at harvest varied from 12.3 to 29.6 Mg•ha−1, or 22–33% of the weight of aboveground leafless biomass. Small and fine roots sampled to a depth of 3.17 m using soil cores amounted to an additional 6.6–11 Mg•ha−1 of roots. Stumps and all roots as a ratio of aboveground biomass (root/shoot ratio) ranged from 0.34 to 0.42, with hybrids accounting for the entire range of values present. Mass of the fine roots (less than 0.5 mm diameter) ranged from 4.0 to 6.5 Mg•ha−1, or an average of 6.8% of the aboveground biomass. The smallest of the fine roots measured 0.06 mm in diameter. Specific root length of fine roots averaged 50.7 m•g−1 for P. deltoides, 42 m•g−1 for P. trichocarpa, and 30–47 m•g−1 for hybrids. Total length of fine roots to a depth of 3.17 m ranged from 179 000 to 284 000 km•ha−1. Density of fine roots by length per unit soil volume was greatest at the surface with the range of means for clones in the top 0.18 m being 2.4–6.3 cm•cm−3; at 1.0–3.17 m soil depth, density was 0.02–0.6 cm•cm−3. For two of the hybrid clones, the density of fine roots at the soil surface was half that of the other clones. The distribution of fine roots in the stratified soil profile was correlated with soil depth, Kjeldahl N, and organic matter, with the latter two parameters showing the highest coefficients of determination (0.73 and 0.71, respectively). In the more sandy but layered subsoil (0.36–3.17 m depth), soil depth, Kjeldahl N, and sand content were most strongly correlated with fine root density, with depth and sand content giving the highest coefficients of determination (0.32 and 0.31, respectively). Roots in sandy subsoil were coarser and much less branched than in adjacent finer textured layers.

Alleviation of soil constraints to crop growth in the upland Alfisols and associated soil groups of the West African Sudan savannah by tied ridges

The climate of the West African Sudan savannah (annual rainfall of 600–900 mm and a monomodal rainy season of 3–4 months) is characterized by frequent long- and short-term droughts. Crop growth in the Alfisols and associated soil groups is further constrained by soil compaction, low soil fertility, high soil temperatures, low soil water retention and available water holding capacity, and low water infiltration rate. Tied ridges, ridges with earthen bunds constructed at right angles to the self-same ridges at intervals of 1–4 m, can alleviate or circumvent the above constraints, and can conserve rainfall received on-site. Water runoff with tied ridging ranges from 0 to 15% of seasonal rainfall, whereas with either open ridging or flat planting 20–45% of seasonal rainfall is lost as runoff. Soil water content is, therefore, greater with tied ridging. Tied ridging also reduces surface bulk density, maintains soil fertility by reducing losses of soil nutrients in surface runoff and improves soil water retention and available water holding capacity. The water infiltration rate in furrows of tied ridged plots is lower than that with flat planting or open ridging. With tied ridging, however, rainwater is retained on site by the ‘ties’, whereas with open ridging or flat planting it is lost as runoff. Tied ridging increases depth of rooting and subsoil root density in maize ( Zea mays), millet ( Pennisetum americanum) and cotton ( Gossypium hirsutum) in both wet and dry years, and in cowpea ( Vigna unguiculata) in dry years. Root growth of bambara groundnut ( Vigna subterranea) is unaffected by tied ridging. Cowpea subsoil root growth is not significantly affected by tied ridging in wet years although root proliferation occurs in the topsoil because of the high sensitivity of cowpea to transient waterlogging. Vegetative growth and dry matter production of maize, millet, cotton, bambara groundnut, cowpea, groundnut ( Arachis hypogaea) and sorghum ( Sorghum bicolor) are increased by tied ridging in both wet and dry years. Grain yields of maize, millet and sorghum are increased by tied ridging, as is lint production of cotton. Cowpea grain yield is increased only in dry years. Grain yields of bambara groundnut are not significantly affected by tied ridging. Yield responses of groundnut to tied ridges are variable. Growth and yield inhibition may occur in waterlogging-sensitive crops such as cowpea and cotton during wet years. In general, greatest yield and growth increases from tied ridging occur in drought-sensitive cereal crop species and cultivars. Furthermore, strong and positive responses to tied ridges may be obtained consistently over a long period of time only in upland environments where long- and short-term droughts are frequent, soil compaction and temperatures are high, and available water-holding capacity and water infiltration rates are low.

Decreases over seven years in subsoil nitrate in a Vertisol with grain sorghum and grass

Subsoil chemical properties and root distributions were measured over seven years under annual grain sorghum (Sorghum bicolor) cropping with crop residue retention and zero tillage and under perennial Rhodes grass (Chloris gayana). The site, in the semi-arid subtropics of eastern central Queensland, was a Vertisol with alkaline topsoil and acid, strongly sodic subsoil. Nitrate had accumulated between 0.6 and 2.8 m during cropping for the preceding 16 years. The hypothesis that some of this residual nitrate would be depleted by the grass but not by the sorghum was tested during the experiment.

Subsoil Thickness Effects On Yield and Soil Water When Reclaiming Sodic Minespoil

AbstractMinespoil sodicity has the potential to limit plant growth and impede reclamation success on surface‐mined land. A joint government/coal industry experiment was established near Highvale, AB, to determine suitable subsoil thicknesses (0, 55, 95, 135, 185, and 345 cm underlying 15 cm topsoil) for reclaiming sodic minespoil and maximizing production of an annual barley (Hordeum vulgare L.) cereal crop or a perennial alfalfa‐smooth bromegrass (Medicago sativa L., Bromus inermis Leyss.) forage mixture. Barley and forage yields were lower on the 0‐cm subsoil treatment than all other treatments. Yields for both crops increased as subsoil thickness increased to 55 cm. There was a consistent trend toward optimum yields on the 95‐cm subsoil treatment, but the difference between 55 and 95 cm was not significant. The replacement of 55 to 95 cm subsoil plus 15 cm topsoil appeared sufficient to restore post‐mine productivity to the potential achieved on surrounding agricultural land. Root depth under the forage mixture increased as total soil thickness increased, while increases under the cereal were not generally significant. The average effective root zone extended to about 85 cm under barley and 185 cm under alfalfa‐smooth bromegrass. Average seasonal soil water within the effective subsoil root zone generally increased under barley and decreased under alfalfa‐smooth bromegrass over time. Lower consumptive use of available soil water and a shallower effective root zone under barley contributed to accumulations of soil water above the subsoil/minespoil interface. Perennial forages appeared to be more effective in reducing soil water accumulations above the interface and promoting reclamation success of sodic minespoil.

Wheat seedling responses to soil acidity and implications for subsoil rooting

Abstract The ability of roots of acid soil tolerant and intolerant wheat (Triticum aestivum L.) genotypes to grow into and extract water from subsoil acid environments was investigated. The method used to test this minimized the complicating influence of another effect of acidity, interference with uptake and utilization of nutrients. Root growth by 4‐day‐old seedlings estimates plant ability to explore acid subsoils. Root lengths were measured in eight wheat cultivars exhibiting varied tolerance to an acid soil treated with five levels of Ca(OH)2. Length of the longest root per plant was an indicator of plant response, and decreased linearly with soil solution Al concentration. The cultivars were ranked in order of tolerance from lowest to highest by root length (cm) in the zero lime treatment (434 μM Al in soil solution): Hart 1.8, Arthur 2.0, Wampum 4.0, Caldwell 5.5, Logan 6.3, Edwall 7.3, Titan 8.0, and Yecorra Rojo 8.2. Acid‐tolerant Yecorra Rojo was able to extract 2 to 4 times more water than acid...

Acid‐Subsoil Amelioration: II. Gypsum Effects on Growth and Subsoil Chemical Properties

AbstractIn many highly weathered soils crop exploitation of subsoil moisture reserves is severely curtailed by toxic levels of Al. Since vertical movement of lime is usually extremely slow in such soils, specialized mechanical and/or chemical procedures are required to overcome the problem. A field experiment with maize (Zea mays L.) on a strongly acidic Plinthic Paleudult examined the effects of surface‐incorporated gypsum on yield, root development, and profile chemical properties for four cropping seasons. The effects of gypsum (10 Mg ha−1) were time dependent, but by the fourth season had resulted in a cumulative grain yield gain of 3.4 Mg ha−1. Progressive depressions in the level of exchangeable Al were accompanied by increases in subsoil Ca, Mg, and SO4‐S. Water pH increased markedly in the zone of maximum SO4‐sorption/precipitation, but pH determined in KCl remained unchanged. By the fourth season the effects of gypsum on subsoil root development were striking. These results indicate that surface incorporation of gypsum is an economically viable approach to subsoil amelioration on soils such as that studied here.

The effects of lime and phosphorus on the function of wheat roots in acid top soils and subsoils

Two wheat varieties with differing aluminium tolerance were grown in pots of acid soil. Liming did not change significantly the amounts of chemically extractable P and K, but caused improved vegetative growth, increased inflow of P and K and reduced uptake of Al. Without lime, roots had a higher content and concentration of P than shoots; liming reversed this. Without lime the sensitive variety with a shorter root length had an Al inflow ten times that of the tolerant one: tolerance involves a mechanism for exlcuding Al. The inflow of P per unit inflow of Al (mol ratio) without lime was three times greater for the tolerant variety which therefore has more P to counteract the effects of Al. The same varieties were grown in two-layer soil columns, with a low P status and a limed topsoil and acid subsoil. Liming the subsoil improved plant growth but this was still restricted by low P availability. Addition of P to the topsoil caused good growth regardless of subsoil acidity: root growth increased in both layers and P (labelled with32P) taken up from the topsoil was translocated to roots in the subsoil. This P inactivated root Al and allowed the roots to grow and take up more P from the acid subsoil with however a reduction in inflow. The sensitive variety was affected more by the acid subsoil and low P availability, had a similar ability to translocate P to subsoil roots but could not attain the growth rate of the tolerant wheat even with P and lime.

Relationships of Dense Tillage Pans, Soil Properties, and Subsoiling To Tobacco Root Growth

AbstractDeep tillage with subsoilers can fracture tillage pans and increase root development in some soils, but little is known about the precise soil conditions for which subsoiling works best. This study evaluated relationships of soil physical properties, chemical properties, and subsoiling to root distributions in 10 Ultisols. Five sites had dense tillage pans in their E‐B horizons with bulk densities (ρb) ≥1.66 Mg m−3. At each location flue‐cured tobacco (Nicotiana tabacum L.) was grown in subsoiled and nonsubsoiled (moldboard plow/disk) tillage treatments. At approximately 100 d from transplanting, root distributions were described by the trench‐profile method. Soil properties evaluated included bulk density, texture, ped mean weight‐diameter, cone index (CI), Ca and Al saturation ratios, base saturation, and pH. Subsoiling significantly increased the proportion of roots below the E‐B horizon (0.15 m below the Ap), in three of the five sites with E‐B ρb's ≥1.66 Mg m−3, while it had no significant effect on proportion of roots below the E‐B horizon in any of the five sites whose E‐B ρb's were <1.66 Mg−3. A regression analysis showed that ρb of the E‐B horizon, B horizon sand content, and cummulative rainfall accounted for 96% of the observed variation in subsoil root development for the nonsubsoiled treatment across the 10 sites. Soil chemical properties had little effect on variation in subsoil root development across sites.

Effect of Gypsum and Deep‐rooting Perennials on Subsoil Mechanical Impedance

AbstractSubsoil root growth in highly weathered southeastern soils is limited because of poor chemical conditions and high soil strength. Surface‐applied gypsum can leach into the subsoil and amend the chemical properties of these soils. The objective of this study was to determine if gypsum also had a physical effect. Mechanical impedance was measured using a tractor‐mounted penetrometer that gave values of cone index (CI) in gypsum‐treated and nontreated plots of several ongoing experiments. Cone index was lower in the gypsum‐treated plots where alfalfa (Medicago sativa L.) or peach trees [Prunus persica (L.) Batsch] had grown for several years, but there was no reduction in CI in fallow plots treated with gypsum. Samples from the alfalfa plots treated with gypsum had larger stable soil aggregates than samples taken from nontreated plots. We conclude that gypsum amendment increases subsoil root activity, which in turn reduces subsoil mechanical impedance.

Influence of Tillage on Nutrient Uptake and Yield of Corn1

AbstractThough it appears that the surface accumulation of soil nutrients and the shallower distribution of roots is not detrimental to crop growth and yield under no‐tillage management, supportive data with respect to nutrient uptake are scarce. A field plot study was conducted over 3 yr utilizing four tillage treatments: (i) conventional tillage (moldboard plow); (ii) no‐tillage (coulter); (iii) no‐tillage with shallow (10 to 15 cm) in‐row chisel; and (iv) no‐tillage with deep (30 to 45 cm) in‐row chisel. The objective was to determine the influence of tillage on nutrient uptake and yield of corn by: (i) measuring changes in distribution of soil nutrients; (ii) determining the nutrient status of corn plants; (iii) measuring rubidium (Rb) uptake by corn plants when Rb was placed at various row positions and depths in the soil profile; and (iv) measuring grain yields. No‐tillage treatments resulted in a redistribution and concentration of soil nutrients at the soil surface, compared with conventional tillage. However, the nutrient status of plants grown under no‐tillage management was equal or superior to those grown by conventional tillage. Furthermore, the activity of roots and the extraction of water and nutrients, as evidenced by Rb uptake, was greater for no‐tillage compared with conventional tillage. No‐tillage, whether in‐row chisel was included or not, resulted in larger plants and greater grain yields. No evidence was obtained that would support deeper placement of nutrients or in‐row chisel operations to improve subsoil rooting under no‐tillage.

INFLUENCE OF SUBSOIL ACIDITY ON ROOT DEVELOPMENT AND CROP GROWTH IN SOILS OF ALBERTA AND NORTHEASTERN BRITISH COLUMBIA

Experiments were conducted in the field and greenhouse with soils of Alberta and northeastern British Columbia to determine the influence of subsoil acidity on acid-sensitive crops. Experiments involved liming of only the topsoil, liming of both topsoil and subsoil, and measuring the aboveground crop yield and the yield of roots in the topsoil and subsoil. In both field and greenhouse, subsoil acidity reduced the yields of top growth and subsoil root pernetration for both barley and alfalfa. The reductions in yield of top growth and roots in the subsoils were correlated closely with the amount of Al (extractable in 0.02 M CaCl2) in the unlimed subsoil. Lowering the soil temperature did not reduce root growth more in acid soils than in limed soil. There were five field experiments, and in the three of these which had subsoils high in extractable Al, the limed subsoils had less moisture at the time of harvest than the unlimed subsoils. The damage to crops caused by subsoil acidity was eliminated by deep liming or in one case by large applications of P to the subsoil or topsoil. These methods of correcting subsoil acidity would not be economically feasible on a field scale. A preliminary field survey was conducted to delineate agricultural areas where subsoil acidity (based on soil pH and extractable Al content) is a significant problem. The largest areas were found in northwestern Alberta and northeastern British Columbia. Key words: Aluminum toxicity, subsoil acidity, liming, temperature, phosphorus, barley

CALCIUM DEFICIENCY IN CLAYEY B HORIZONS OF SAVANNA OXISOLS

ABSTRACT The restriction of crop root growth in Cerrado (savanna) Oxisols often reduces yields because the volume of soil explored by the roots is insufficient to supply enough water during dry periods that occur in the rainy season. A recent soil survey of the 580 000 hectares of the Federal District in Central Brazil shows a number of profiles that have clayey B21 horizons within 50 centimeters of the surface with very low levels of exchangeable calcium + magnesium (0.2 milliequivalents per 100 grams or less) and no exchangeable aluminum. The hypothesis that root penetration in such subsoils is limited by lack of calcium, rather than by aluminum toxicity, is supported by the results of simple and inexpensive tests showing that the addition of 0.10 to 0.15 meq/100 g calcium as chloride, phosphate, or carbonate effectively normalized seedling root growth, which, in the absence of such additions, stopped within a few days. The addition of magnesium carbonate, however, did not improve root growth. To test whether the leaching of calcium salts might ameliorate the calcium deficiency in the subsoil, samples were taken from an experiment that had received about 2500 kg/ha calcium as limestone and ordinary superphosphate at installation 2 years previous. Compared with root growth in samples from adjacent virgin soil, these soils showed improved root growth to as deep as 75 cm, thus suggesting that fertilizer management can have a beneficial effect on subsoil rooting in such soils.

Economic and Agronomic Impacts of Varied Philosophies of Soil Testing1

AbstractPhilosophical differences exist in the interpretation and recommendations made from soil test values acquired by different organizations that provide advice to farmers on fertilizer use. It was the objective of this study to evaluate the economic and agronomic impacts of these varied philosophies with particular reference to concepts of cation ratio, nutrient maintenance, and nutrient sufficiency level. Field experiments were conducted during 1973–1980 on four major soils of Nebraska comparing yields of corn (Zea mays L.) grown with fertilizer treatments as recommended by five soil testing laboratories operating in the state. The 29 field comparisons revealed no real yield differences despite wide variation in number, rate, and cost of nutrients applied. Since soil test levels are increasing or at least holding steady with the “nutrient sufficiency” approach to soil testing, we find no economic or agronomic basis for the “balance” or “maintenance” concepts on these representative soils of the western Corn Belt. Not to be overlooked are environmental implications nor the waste of energy and resources from any approach responsible for excessive fertilizer use. It is recognized that reserves of available nutrients in the deep subsoils and underlying soil‐forming materials in this region have a substantial bearing on soil test calibration and that different calibrations may exist with less favorable subsoil rooting conditions.

Effects of Soil Compaction on Subsoil Root Penetration and Physical Properties of Three Soils in Louisiana1

SynopsisArtificial soil compaction resulted in increased bulk density and decreased noncapillary porosity and water permeability. Root penetration into artificially packed cylinders of soil decreased as soil compaction was increased.