Tolerance of eastern gamagrass to excess aluminum in acid soil and nutrient solution

Eastern gamagrass, Tripsacum dactyloides L., has been reported to tolerate a wide variety of soil conditions, including drought, flooding, and acidity, but its specific tolerance to aluminum (Al) has not been tested. One strain of this species, PMK Select Lot 94 SFG‐1, was tested for its tolerance to excess Al in an acid, Al‐toxic Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) and in nutrient solutions containing Al. Roots were able to penetrate unfertilized Tatum subsoil at pH levels as low as 4.1–4.2 (1:1 soil‐water), at Al saturations of 64 to 77% of CEC, and to tolerate Al concentrations in nutrient solution that would be lethal for many crop plants. For example, with 4 mg Al L^‐1 and a final solution pH of 4.67, shoot and root dry weights were 75 and 76%, respectively, of those with no Al. Even with 24 mg Al L^‐1 and a final solution pH of 4.13, shoot and root dry weights were 45 and 46%, respectively, of those for the no Al check treatment. Hence, this strain of gamagrass shows promise for use on soils having acidic, Al‐toxic subsoil layers that act as root barriers and predispose plants to injury by drought. Roots of gamagrass are also reported to penetrate hard clay pans and to create root channels for subsequent crops that lack this ability. Current studies indicate that the strain tested was susceptible to a chlorosis resembling iron (Fe) deficiency when grown in a Jiffy Mix potting mixture or with excess Al in nutrient solutions. Hence, gamagrass is tentatively being classified as a calcifuge [Al tolerant‐Fe‐inefficient]. In the current experiment, considerable plant to plant variability was noted regarding susceptibility to this chlorosis factor and to a purpling symptom resembling phosphorus (P) deficiency. Results indicate that an exhaustive screening of gamagrass populations could identify strains that are more suitable for specific soil situations.     

Critical soil bulk density and strength for pea seedling root growth as related to other soil factors

Bulk density and soil strength are two major soil physical factors affecting root growth of pea seedlings. This study was conducted to determine the influence of soil texture, organic carbon content and water content on critical bulk density and strength. Soil from the plough layer (PL) and beneath the sub-soil (SUB) was used. By soil packing and adjusting the water content between 30% and 100% of field water capacity (FWC) a wide range of bulk density (1.3–1.7 Mg m⁻³) and strength (0.24–6.66 MPa) were obtained. Pea (Pisum sativum L.) was grown in the packed cores of 100 cm³ for 72 h at 20°C. Regression models were developed to explain root growth in terms of bulk density, soil strength, silt and clay (<60 μm) content, organic carbon, and water content. The regression curve of root growth as a function of soil strength showed that 40% of maximum root length can be regarded as an indicator of very poor root growth. By substituting this value into the root growth equations we calculated a critical bulk density and strength in terms of fraction<60 μm, organic carbon percentage and water content. The values of critical bulk density in both layers and of critical soil strength in the sub-soil increased with a decreasing content of fraction<60 μm. Irrespective of fraction<60 μm content, the critical bulk density and strength decreased as soil water content decreased. Critical soil strength was more sensitive than critical bulk density to changes in fraction<60 μm content and water content. This study provides data and a method for predicting critical bulk density and soil strength in relation to other soil properties for pea seedling root growth.     

密植条件下玉米冠根生长抑制的因果关系

密植条件下玉米地上部及根系生长均受到抑制。以澄海3719(DH3719)为材料,通过种植密度×施氮量2因素4处理田间试验,研究了密植条件下玉米地上部及根系生长受抑制的因果关系。结果表明,高密度群体具有较高的叶面积指数(LAI),但拔节期后单株叶面积、冠根干物重、茎粗、总根长及含氮量均小于低密度种植的植株,生长受到抑制。叶面积与根长的消长变化趋势相同,各生育期不同处理植株的冠根比没有明显差异。吐丝期剪去穗位叶以上连续两个叶片或切去地上部最上层节根均减少了植株体内的氮素累积。尽管剪叶使根系生物量的减少远远低于切根的影响,但剪叶造成植株含氮量的减少多于切根的影响。综合结果表明,密植引起地上部生长空间竞争加剧,使地上部生长受到抑制,从而影响根系生长。     

Soil bulk density corrections for providing a better relationship with root growth in gravelly soil

Abstract

Bulk density of a Tifton (Plinthitic Paleudult; fine loamy, siliceous, thermic) soil containing 5.8 to 11.0% of the sample weight as pebbles was 0.06–0.12 g/cc lower when corrections were made for presence of pebbles or concretions. A method for determining the bulk density of the soil matrix between pebbles or concretions is outlined. After adjustment, the bulk density at which root penetration was inhibited in this soil closely approximated that for soils which do not contain concretions. The proposed procedure reflects more nearly how bulk density changes where plant roots are growing than previously published procedures do.     

Soybean seedling root growth as influenced by soil texture,matric suction and bulk density

Abstract

Laboratory experiments were conducted under controlled conditions to determine the effect of five matric suctions (0.05, 0.10, 0.30, 1.00 and 3.00 bars) and three bulk densities (1.10, 1.30 and 1.50 g.cm^?3) on the moisture content, penetrometer resistance and soybean (Glycine max L.) root growth in six different soil textural groups (sand, silt, clay and their combinations).

The different textural groups were compacted in PVC pipes 4.4 cm ID and 10 cm long and placed in pressure cells to obtain the desired matric suction. After equilibrium five pregerminated soybean seedlings were fixed on the soil surface. At the end of 48 hours root elongation was measured.

There was an increase in root growth in all the textural groups at all the bulk densities when the matric suction was increased from 0.05 to 0.30 bar. There was however a gradual decrease in root growth as the matric suction increased from 0.30 to 3.0 bars. The reduction in root growth at low and high matric suctions was related to moisture content, change in soil resistance and redox status of the soil system.

The measured penetrometer resistance values were directly related to the level of compaction, soil matric suction and also were dependent upon the texture. Close relationships were recorded between redox potentials and soil matric suction.     

猪粪对红壤铝毒的缓解效应

利用盆栽实验研究了施用猪粪和石灰对红壤铝毒的缓解效应。结果表明 ,在对照土壤 (pH 4.2)上生长的小麦遭受铝毒害明显 ,出苗后 36d全部枯死 ,施用石灰和猪粪能不同程度地缓解铝毒害。施用猪粪和石灰都可以提高土壤pH ,降低交换性铝含量。与单施石灰相比 ,石灰猪粪混施可以提高土壤 pH ,降低交换性铝含量 ,增加小麦叶绿素含量、光合速率和地上部干物重。与单施猪粪相比 ,石灰猪粪混施使小麦地上部K、Mg和P含量减少。     

土壤容重对土壤物理性状和小麦生长的影响

以黑土和白浆土为试材 ,进行筒栽试验 .结果表明 ,适宜小麦生长的容重范围分别为 1 .1 5～1 .3 0 g/cm3和 0 .9～ 1 .0 5g/cm3.     

4种土壤调理剂改良红壤铝毒害的效果研究

在温室条件下,采用植物盆栽试验,研究4种土壤调理剂不同施用量对酸性红壤铝毒害的缓解效果。结果表明,4种土壤调理剂均显著降低土壤中交换性铝含量及毒害性铝含量,显著提高玉米株高、生物量;各处理土壤中交换性铝含量与玉米株高及生物量之间呈显著相关性。牡蛎壳、白云石、钾长石、麦饭石4种土壤调理剂0.2%的施用量土壤交换性铝分别比对照下降了63.8%、70.5%、53.0%、12.3%;0.4%的施用量土壤交换性铝分别比对照下降了90.5%、92.0%、80.5%、23.4%。土壤中交换性铝、毒害性铝的含量随着4种土壤调理剂的施用量增加而降低,土壤中毒害性铝含量由低到高依次为白云石、牡蛎壳、钾长石、麦饭石。     

有机物料对酸性红壤铝毒的缓解效应

利用盆栽试验研究了施用不等量稻草对酸性红壤旱耕地铝毒的缓解效应。结果表明,添加不等量的秸秆碳(C)后,土壤pH值显著提高,土壤交换性铝和吸附态羟基铝的含量则明显降低,土壤有机络合态铝的含量也呈增加趋势。添加铝盐并不影响秸秆碳对降低土壤交换性铝和吸附态羟基铝含量的作用。在本研究中,土壤pH值与土壤交换性铝和土壤吸附态羟基铝均呈显著负相关,方程分别为y=-2193.9x+11545,R2=0.9798**,y=-655.34x+9748,R2=0.7837**。土壤交换性铝和吸附态羟基铝与玉米主根长,地上部磷、钾含量均呈显著负相关,是抑制玉米吸收养分的主要限制因素,土壤吸附态羟基铝是次于交换性铝的又一活性较大的铝化合物。     

The effect of soil liming on shoot development, root growth, and cluster root activity of white lupin

 The effects of a limed soil upon root and shoot growth of white lupin (Lupinus albus L.) were investigated using soil tubes and pots. After 75 days in the soil tubes, the combined taproot and lateral root dry weight in limed soil (2.5% CaO w/w) was significantly less than in neutral pH soil (by 57%). However, the dry weight and numbers of cluster roots remained comparable between the treatments, demonstrating for the first time that the cluster roots respond differently to the rest of the root system. Cluster roots accounted for 17% of the total root biomass in neutral soil, increasing significantly to over 30% in limed soil. When grown for 43 days in pots containing soil with different additions of lime (0.5–2.5% CaO w/w), soil citrate concentrations were higher than in the neutral pH soil treatment in all except the 2.5% lime treatment, in which they were lower. In both experiments, shoot dry weights were lower in the presence of the limed soil compared with those in the neutral pH soil. Although a reduction in shoot dry weight was not apparent at 21 days in the limed-soil tubes, the initiation of fewer mainstem leaf primordia indicated a slower shoot development than occurred in the neutral soil. Plants grown in the limed-soil tubes showed leaf yellowing and some chlorosis within 9 days. At the final harvest, the shoot phosphorus and manganese concentrations were significantly lower in plants grown in limed soil compared with those in the neutral pH soil, whereas the concentration of calcium was higher. Received: 11 October 1999     

Role of water stress in differential aluminum tolerance of two barley cultivars grown in an acid soil

Two cultivars of barley (Hordeum vulgare L.), Al‐sensitive ‘Dayton’ and Al‐tolerant ‘Kearney’, were grown under controlled environmental conditions to determine the influence of Al stress and water stress imposed separately and in combination with one another. Plants were grown for 4 weeks in polyethylene‐lined, waxed cartons containing 1 kg of acid, Al‐toxic, Tatum subsoil (clayey, mixed, thermic, Typic Hapludult) at high (pH 4.7) or low (pH 6.6) Al stress. During the final 2 weeks they were also subjected to low (‐20 to ‐40 kPa) or high (‐60 to ‐80 kPa) water stress. Under low water stress, little difference in the growth or appearance of the two cultivars was found, even in the presence of low Al stress (pH 6.6). When high water stress treatment was superimposed on low Al stress treatment, however, significant differences between the two cultivars in biomass production, leaf enlargement, and tillering resulted. When high water stress was combined with high Al stress (pH 4.7), these differences in vegetative growth were further magnified. Thus, drought exacerbates the stress effects of Al toxicity in plants and may account for a significant portion of the reduction in yield commonly observed in acid soils under field conditions and formerly attributed to Al toxicity alone. By increasing soil moisture level, the growth suppressive effect of Al toxicity was significantly reduced.     

Role of water stress in differential aluminum tolerance of six sunflower cultivars grown in an acid soil

Six cultivars of sunflower (Helianthus annuus L.), were screened under controlled environmental conditions for tolerance to Al stress and water stress imposed separately and in combination with one another. Plants were grown for 4 weeks in waxed cartons containing 1 kg of acid, Al‐toxic Tatum, subsoil (clayey, mixed, thermic, Typic Hapludult) at high (pH 4.3) or low (pH 6.3) Al stress. During the final 2 weeks they were also subjected to low (‐20 to ‐40 kPa) or high (‐60 to ‐80 kPa) water stress. Plant growth responses and symptoms of Al toxicity suggested that a wide range of cultivar sensitivity existed. ‘Manchurian’, ‘S‐212’, ‘S‐254’, and ‘S‐265’ were relatively tolerant to Al toxicity while cultlvars ‘Romania HS‐52’ and ‘RM‐52’ were extremely sensitive. Under high Al stress and high water stress, chloroplasts in cells from the Al‐sensitive cultivar ‘Romania HS‐52’ were smaller and contained less starch than chloroplasts from the Al‐tolerant cultivar ‘Manchurian’. Furthermore, the smaller chloroplasts tended to have fewer grana stacks per unit area than did the chloroplasts from tolerant plants. These differences were not apparent when the Al‐sensitive cultivar was grown either in the absence of Al or water stress. In general, Al‐sensitive cultivars of sunflower were more tolerant to water stress than were Al‐tolerant cultivars. Increasing the soil moisture level reduced Al toxicity in Al‐sensitive cultivars. Similarly, decreasing Al stress partially overcame the detrimental effects of high water stress. Hence, Al stress and water stress are interrelated factors which must be considered in the characterization and breeding of plants for better adaptation to acid soils.     

The effect of tillage intensity on soil structure and winter wheat root/shoot growth

Despite a vast amount of data on the effect of tillage on crop productivity, surprisingly there is little detailed information available on the influence on below and aboveground crop growth dynamics. Such information is essential for developing sustainable cropping systems. The objective of this study was to investigate the effect of tillage intensity on crop growth dynamics and soil structure. A tillage experiment was established in autumn 2002 on two Danish sandy loams (Foulum and Flakkebjerg) in a cereal‐based crop rotation. The tillage systems included in this study were direct drilling (D), harrowing 8–10 cm (H_8‐10), and ploughing (P). A single‐disc drill was used in the H_8‐10 and D treatments and a traditional seed drill in the P treatment. Measurements were carried out in 2004–05 and 2005–06 and winter wheat was grown in both years (first and second year winter wheat). Shoot and root growth was followed during the growing seasons using spectral reflectance and mini‐rhizotron measurements, respectively. A range of soil physical properties were measured. We found decreased early season shoot and root growth with decreasing tillage intensity. Differences diminished later in the growing season, although significant treatment effects were observed throughout the growing season for the second year winter wheat. The formerly ploughed layer in the D and H_8‐10 treatments was noticeably compacted as indicated by increases in both penetration resistance and bulk density. Nitrate leaching increased with decreasing tillage intensity for the first year winter wheat at Foulum. In general ploughing resulted in the highest grain yields. This study highlights the important interaction between soil structure and crop growth dynamics.     

山东省褐土土壤容重对玉米生长发育及产量形成的影响

以郑单958为材料,采用盆栽试验,以原状土壤不打破犁底层为对照(CK),设置容重1.2、1.3、1.4、1.5、1.6 g/cm3共6个处理水平,探索了山东省褐土不同土壤容重条件下玉米生长发育和产量差异。结果表明:随着土壤容重增加,玉米株高、茎粗、单株叶面积、总根量、植株干物质累积和籽粒产量总体呈现减少趋势,且容重越大,降幅越显著。土壤容重1.5 g/cm3时,玉米生长发育受到明显抑制,土壤容重由1.2 g/cm3增加到1.6g/cm3,玉米株高、茎粗、单株叶面积分别降低15.7%、12.6%、28.7%,且玉米生长中后期叶片衰老速率加剧;玉米根条数、根长、根干重、根冠比、植株干重分别降低17.9%、47.0%、36.8%、20.1%、20.7%,容重增加对根系生长的影响明显高于地上部。与CK相比,容重1.2~1.6 g/cm3各处理的穗粒重分别增加11.1%、18.0%、4.6%、-4.5%、-14.6%。因此,适当降低有效耕层内土壤紧实度,可促进玉米根系生长和干物质积累,提高单株生产能力。     

Effects of traffic on soil aeration, bulk density and growth of spring barley

This paper reports the results of field experiments on several different soils to quantify the effects of different numbers of passes of vehicular traffic on soil aeration status (measured in terms of oxygen diffusion rate, ODR and redox potential, Eh), soil bulk density and development of spring barley. In a further series of field experiments, the effects of single and dual wheels were compared and the effectiveness of a soil loosener operating behind the wheels was evaluated. Additionally, some microplot experiments are reported in which a range of known values of soil bulk density were produced and the effects on soil aeration and development of spring barley were evaluated. It is shown that repeated wheeling, even by a tractor of only about 2 tonnes weight, can produce soil conditions in which aeration can be limiting for crop growth. The use of dual wheels resulted in lower values of soil bulk density and associated greater soil aeration. The loosener alleviated the compaction produced by wheels and also improved soil aeration. For a sandy loam soil, greatest root growth and crop yield occurred at a bulk density of 1.43 Mg m⁻³. Soil aeration as a component of soil physical quality is discussed.     

Effect of soil potassium availability on soybean root and shoot growth under unrestrained rooting conditions 1

The development of soybean (Glycine max (L.) Merr.) root systems was Investigated in two greenhouse pot experiments utilizing a modified cage technique. One soil at two levels of K availability was used to observe the effect of soil K fertility level on root weight and root length in 3 cm depth Increments to 24 cm. Experiments were terminated prior to restraint of root growth by the containers. Shoot mineral accumulation and dry matter partitioning between root and shoot components were Investigated.

High K plants were shorter and had a greater root:shoot mass ratio than low K plants. A trend for greater root dry matter production in soil layers below 12 cm under high K conditions was observed. There were no differences in root length between the treatments at any depth. Tissue K content was greater in the high K treatments and this Increase was equivalents offset by decreased tissue Mg concentrations. The taller low K plants had a greater leaf area and a lower specific leaf weight, resulting in part from decreased starch content. Daily evapotranspirational water losses per pot tended to be greater under the low K availability regime. This Information led to the speculation that under low K conditions, the soybean plant may increase K accumulation by promoting transpirational water use, aiding soil K acquisition by mass flow and diffusion. Tissue carbohydrate analyses suggest greater translocation of photosynthate out of the leaf in the low K plants for use in root absorption metabolism, rather than for production of increased root dry matter and/or increased root length.     

Soybean root growth in relation to ionic composition in magnesium-amended acid subsoils: Implications on root citrate ameliorating aluminum constraints

Abstract

Hydroponic studies with soybean (Glycine max [L.] Merr.) have shown that µmol L^?1 additions of Mg²⁺ were as effective in ameliorating Al rhizotoxicity as additions of Ca²⁺in the mmol L^?1 concentration range. The objectives of this study were to assess the ameliorative effects of Mg on soybean root growth in acidic subsoils and to relate the soil solution ionic compositions to soybean root growth. Roots of soybean cultivar Plant Introduction 416937 extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoils from the Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic) series. The three Mg treatments consisted of native equilibrium soil solution concentrations in each soil (50 or 100 µmol L^?1) and MgCl₂ additions to achieve 150 and 300 µmol L^?1 Mg (Mg150 and Mg300, respectively) in the soil solutions. Root elongations into Mg-treated subsoils were compared with a CaCO₃ treatment limed to achieve a soil pH value of 6. Subsoil root growth responses to the Mg treatments were less than for the lime treatments. Root length relative to the limed treatments for all subsoils (RRL) was poorly related to the activity of the soil solution Al species (Al³⁺ and Al-hydroxyl species) and Mg²⁺. However, the RRL values were more closely related to the parameters associated with soil solution Ca activity, including (Ca²⁺), (Al³⁺)/(Ca²⁺) and (Al³⁺)/([Ca²⁺] + [Mg²⁺]), suggesting that Ca could be a primary factor ameliorating Al and H⁺ rhizotoxicity in these subsoils. Increased tolerance to Al rhizotoxicity of soybean by micromolar Mg additions to hydroponic solutions, inducing citrate secretion from roots to externally complex toxic Al, may be less important in acid subsoils with low native Ca levels.     

Rice and common bean growth and nutrient concentration as influenced by aluminum on an acid lowland soil

Aluminum (Al) toxicity is a major limiting factor for crop production in many acid soils in Brazil. Two greenhouse experiments were conducted to evaluate response of rice (Oryza saliva L.) and common bean (Phaseolus vulgaris L.) to Al levels on a Low Humic Gley acid soil. The Al levels created by liming were: 0,0.03, 0.10, 0.23, 1.03, and 3.83 cmol_c kg^‐1 of soil. Rice dry matter and grain yield were significantly improved (P<0.05) with increasing Al levels in the soil solution. However, common bean dry matter as well as grain yield were significantly (P<0.01) decreased with increasing Al levels. At 3.83 cmol_c Al kg^‐1 of soil, bean did not produce any dry matter or grain yield. On an average, Al decreased nutrient concentrations in the tops of rice plant except zinc (Zn) and manganese (Mn), but in bean crop almost all the nutrients concentrations were increased with increasing Al levels. Rice showed tolerance to Al toxicity, whereas, common bean was susceptible to toxicity of this element. For successful intensive crops production lime application will be necessary in Varzea soils especially for legume production.     

Hydrogen and aluminum inhibition of soybean root extension from limed soil into acid subsurface solutions

Soybean [Glycine max (L.) Merr. cv. ‘Ransom'] root elongation under varying concentrations of solution hydrogen (H) and aluminum (Al) was investigated in a vertical split‐root system. Roots extending from a limed and fertilized soil compartment grew for 12 days into a subsurface compartment with solutions adjusted to either different pH values from 3.7 to 5.5 or a factorial combination of pH (4.0,4.6, and 5.2) and Al (0,7.5, 15, and 30 μM) levels. Ionic forms of Al were estimated with GEOCHEM and solution Al was determined with ferron. Boron (B) (18.5 μM) and zinc (Zn) (0.5 μM) were supplied to all solution treatments, in addition to 2000 μM Ca, after preliminary studies at pH 5.2 without Al indicated that their omission inhibited length of tap roots and their laterals in the subsurface compartment. Both H⁺ and Al inhibited the length of lateral roots more than tap roots. Lateral roots failed to develop on tap roots at pH<4.3 or in treatments with 30 μM Al. Relative tap root length (RRL) among treatments receiving Al correlated with Al as measured by reaction with ferron for 30s. Ferron‐reactive Al was correlated to GEOCHEM‐predicted Al³⁺ activity (r=0.99). A 50% reduction in RRL occurred with either 2.1 μM Al³⁺ activity or 4.9 uM ferron‐reactive Al. The absence of shoot and soil‐root biomass differences among solution treatments in the split‐root system indicated that differences in root growth in the subsurface compartment were not directly confounded with differences in top growth.