Does Soil Strength Play a Role in Wheat Yield Losses Caused by Soil Drying?

Shoot growth in wheat is sensitive to high soil strength, but as high strength and drying tend to occur together it has proved difficult to separate the effects of water stress and mechanical impedance. The results of two field experiments in 2003 and 2004, where soil strength was manipulated by compaction and irrigation, demonstrated that the yield of wheat (Triticum aestivum L.) was sensitive to physical stress in the root zone. We obtained linear relationships between yield and soil strength and between yield and accumulated soil moisture data (accumulation analogous to thermal time), with similar slopes for both seasons. We were unable to detect root-sourced signals of xylem-sap ABA concentration, despite changes in stomatal conductance. When mechanical impedance and matric potential were varied independently in controlled environments, the growth of wheat was sensitive to mechanical impedance, but not to small changes in matric potential. While the response of stomatal conductance to soil drying in the field could be interpreted as evidence of hydraulic signalling, we suggest that the role of high soil strength, in limiting growth rates on moderately dry soil, requires further research.     

Analyses of the effects of potato cyst nematodes (Globodera pallida) on growth, physiology and yield of potato cultivars in field plots at three levels of soil compaction

Field experiments were carried out in 1991 and 1992 on sandy soil highly infested with the potato cyst nematode Globodera pallida. Half the trial area was fumigated with nematicide to establish two levels of nematode density. Three levels of soil compaction were made by different combinations of artificial compaction and rotary cultivation. Two potato cultivars were used in 1991 and four in 1992. Both high nematode density and soil compaction caused severe yield losses, of all cultivars except cv. Elles which was tolerant of nematode attack. The effects of the two stress factors were generally additive. Analysis of the yield loss showed that nematodes mainly reduced cumulative interception of light while compaction mainly reduced the efficiency with which intercepted light was used to produce biomass. This indicates that nematodes and compaction affect growth via different damage mechanisms. Nematodes reduced light interception by accelerating leaf senescence, by decreasing the specific leaf area and indirectly by reducing overall crop growth rate. Partitioning of biomass between leaves, stems and tubers was not affected by nematode infestation but compaction decreased partitioning to leaves early in the growing season while increasing it during later growth stages. The effects of nematodes and compaction on root length dynamics and nutrient uptake were also additive. This suggests that the commonly observed variation in yield loss caused by nematodes on different soil types is not related to differences in root system expansion between soils of various strength. Cv. Elles, which showed tolerance of nematodes by relatively low yield losses in both experiments, was characterised by high root length density and thick roots. These characteristics did not confer tolerance of soil compaction, since compaction affected root lengths and tuber yields equally in all cultivars. In the first experiment only, high nematode density led to decreased root lengths and lower plant nutrient concentrations. The yield loss which occurred in the second experiment was attributed to the effects of nematodes on other aspects of plant physiology.     

Toxicity of Cadmium and nickel in the context of applied activated carbon biochar for improvement in soil fertility

Toxicity induced by heavy metals deteriorates soil fertility status. It also adversely affects the growth and yield of crops. These heavy metals become part of the food chain when crops are cultivated in areas where heavy metals are beyond threshold limits. Cadmium (Cd) and nickel (Ni) are considered the most notorious ones among different heavy metals. The high water solubility of Cd made it a potential toxin for plants and their consumers. Accumulation of Ni in plants, leaves, and fruits also deteriorates their quality and causes cancer in humans when such a Ni-contaminated diet is used regularly. Both Cd and Ni also compete with essential nutrients of plants, making the fertility status of soil poor. To overcome this problem, the use of activated carbon biochar can play a milestone role. In the recent past application of activated carbon biochar is gaining more and more attention. Biochar sorb the Cd and Ni and releases essential micronutrients that are part of its structure. Many micropores and high cation exchange capacity make it the most acceptable organic amendment to improve soil fertility and immobilize Cd and Ni. In addition to improving water and nutrients, soil better microbial proliferation enhances the soil rhizosphere ecosystem and nutrient cycling. This review has covered Cd and Ni harmful effects on crop yield and their immobilization by activated carbon biochar. The focus was made to elaborate on the positive effects of biochar on crop yield and soil health.     

Exploring the interacting effect of soil texture and bulk density on root system development in tomato (Solanum lycopersicum L.)

Knowledge of the responses of root systems in horizoned heterogeneous soil is vital to optimise uptake of water and nutrients to maximise crop productivity. We explored the interacting effects of soil bulk density and texture on the development of root systems in tomato.Two main techniques were employed, X-ray micro-Computed Tomography (μCT), to provide non-destructive, three-dimensional (3D) images of root systems in situ and destructive root washing followed by WinRHIZO^® scanning. Solanum lycopersicum L. cv. Ailsa Craig plants were grown in soil columns for 10 days to measure the effect of soil compaction on selected root traits. Treatments included bulk density (1.2–1.6 Mg m⁻³), soil texture (loamy sand and clay loam) and the effects of layering.The effect of bulk density on root growth was greatest 3 days after transplanting (DAT) in both soil types. The effect of soil texture was not apparent at this stage, but was significant at 10 DAT for most root and shoot variables. The influence of bulk density differed between soil types as increasing compaction promoted plant growth in clay loam but retarded root growth in loamy sand.We observed that at 3 DAT root growth is primarily influenced by bulk density but by 10 DAT a switch in the processes regulating root growth occurs and the texture of the soil becomes very influential. Future investigations of root growth must consider soil physical properties individually and at specific time points, as their importance changes as the root system becomes established. Here we have demonstrated both positive and negative impacts across a wide range of bulk density treatments in different soil textures on root growth. This illustrates the importance of understanding the complex nature of root–soil interactions, especially for agricultural practices such as seedbed preparation.     

Effect of soil compaction on growth, yield and light interception of selected crops

The response of spring barley (Hordeum vulgare, cvs Carnival and Atem), faba beans (Vicia faba, cv. Maris Bead), sugar beet (Beta vulgaris, cv. Monoire), forage maize (Zea mays, cv. Leader), forage peas (Pisum sativum, cv. Poneka) and white turnip (Brassica campestris, cv. Barkant) to topsoil compaction was investigated in a three year trial. Soil compaction was induced by tractor wheeling after crop sowing. Compaction reduced leaf area and dry matter accumulation in all crops in every season. Yield of barley was reduced by 29%, 27% and 40% in 1984, 1986 and 1987 respectively. Yield of maize, peas and turnip decreased by 33%, 14% and 13% in 1986 and 25%, 16% and 19% in 1987. Yields of beans and sugar beet were decreased by 34% and 35% respectively in 1984. Light interception was decreased in all crops in all three years of study but, with the exception of maize in 1987, the efficiency of conversion of radiant energy to dry matter was not significantly affected by soil compaction. It is concluded that reduced dry matter production and yield due to soil compaction was more a consequence of reduced light interception because of restricted leaf area development rather than as a result of an impaired ability of crops to utilise intercepted radiant energy.     

Indicator based assessment of the soil compaction risk at arable sites using the model REPRO

Soil compaction impairs all essential soil functions, which are crucial for the lives of humans, animals, plants and soil organisms. In order to secure the various soil functions, soil compaction must be avoided. One successful method of preventing soil compaction could be based on the precautionary principle, and mathematical modelling might be used to support farmers or consultants when making decisions about husbandry operations. This paper presents a model which calculates an indicator and assesses the risk of soil compaction on arable land based on site-specific data including information on soil, weather and specific husbandry. The first step is to estimate the soil strength in response to soil stress for a topsoil (20 cm) and a subsoil (35 cm) layer. The estimations of these parameters take into account changes in soil moisture throughout the year. Soil strength compared with soil stress is used to calculate the indicator Soil Compaction Index (SCI) for each time the machinery passes over the soil. The results from the separate passes are then integrated for a comprehensive assessment of the risk of soil compaction at farm level. The model was validated in numerous trials. It was found that the calculated SCI was a good reflection of the actual change in soil structure. The model is already being applied on arable farms in Germany. As an example presented in this paper, the calculations for the subsoil at these farms result in low to medium compaction risks.     

Omics of root-to-shoot signaling under salt stress and water deficit

Maximizing crop yield depends on the leaves receiving an optimal supply of water, mineral nutrients, small organic molecules, proteins, and hormones from the root system via the xylem. Soil drying and salinization alter these xylem fluxes, and modern omics techniques offer unparalleled opportunities to understand the complexity of these responses. Although absolute xylem concentrations of any constituent depend on the genotype and xylem sap sampling methodology, analysis of the relative changes in concentrations has revealed some conserved behavior. Typically, these stresses increase xylem concentrations of the plant hormone abscisic acid (ABA) that limits crop water loss, but decrease the concentrations of certain cytokinins that stimulate expansive growth and prevent premature leaf senescence. Further understanding of the ionic and biophysical alterations in the rhizosphere environment that cause increased xylem concentrations of the ethylene precursor (ACC) is needed. Interactions of these plant hormones with plant nutrient status and xylem nutrient delivery may be important in tuning plant responses to their environment. Xylem proteomics is an emerging area that will help understand mechanisms of plant stress adaptation. Using omics techniques to underpin rootstock-mediate plant improvement is likely to improve crop yields in dry or saline soil.     

Influence of soil edaphic factors and their critical limits on seedling emergence of corn (Zea mays L.)

Summary In the present investigation the influence of various soil physical parameters on seeding emergence of corn (Zea mays L.) and their critical limits was studied in order to obtain a proper crop stand. The effect of soil compaction, resulting into various bulk densities on some soil physical properties was also studied. Seedling emergence decreased with increasing bulk density, soil suction, seed placement depth, soil strength and with decreasing oxygen diffusion rates. The critical values for these soil physical parameters were found to be 1.4 g/cm³, 3 atm., 4 cm, 1.0 kg/cm² and 40×10^-8 g O₂/cm²/min bulk density, soil suction, seed placement depth, soil strength and oxygen diffusion rates respectively. Increasing bulk density decreased the soil water content, oxygen diffusion rates and increased the soil strength. re]19751117 Soil Science Department     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Soil compaction and the growth of vining peas

The effects of differing soil conditions at two sites on the growth of vining peas are described. The work was carried out over several seasons having contrasting rainfall at the time of crop emergence. Topsoil compaction induced by tractor wheelings reduced plant population and yield of vining peas by up to 70%. On the compacted plots peas were unable to compensate for the low population which was demonstrated by the inclusion of a non-compacted treatment thinned to the same population as the compacted plots. The severity of compaction was greatest when soil conditions were dry at emergence and least severe when wet. It is suggested that compaction resulted in increased ethylene production in the root and shoot tissues and this may be a causal agent of the observed growth modifications. Recultivation of a compacted seed bed prior to sowing resulted in better establishment and higher yields than with the topsoil compacted but final yields were variable when compared to a ploughed control. Double digging did not increase yield above a ploughed control. In one year a 25% yield reduction was attributed to this treatment. The reasons for the reduction in yield are complex but it is suggested that the causal agent was modfied soil and plant water relations resulting in altered crop physiology. Tramlining the crop reduced yield in one year but when the frequency of wheeling damage is considered they would be unlikely to affect productivity.     

Iron toxicity to rice in an acid sulfate soil as influenced by water regimes

Summary The effects of two water regimes: Continuous flooding and flooding with soil drying on iron toxicity to rice in an acid sulfate soil was studied by continuously growing 7 crops of IR-32 rice in pots under the two water treatments. There was no plant growth upto the second crop under both water treatments due to iron toxicity. But there was good growth of rice under the continuous water regime from third cropping onwards, however, there was no growth of rice in the flooding with soil drying treatment even upto the seventh crop due to iron toxicity.The results of the study bring out that keeping an acid sulfate soil flooded for a few weeks and then planting rice when iron in soil solution has dropped below toxicity level may be a possible management practice for lowland rice culture on such soils. Drying and reflooding an acid sulfate soil on the other hand aggravates soil acidity and keeps iron in solution in high amounts to be toxic to rice plant.     

Effect of soil compaction and nitrogen placement on weed population,yield and moisture use pattern of rainfed wheat

Summary Field experiments showed that soil compaction did not affect wheat yield significantly under rainfed conditions. Weed population was significantly reduced due to soil compaction. Compaction decreased total moisture use and increased water use efficiency. There was better and profitable utilization of stored soil moisture from the compaction treatments as compared to no compaction treatment.Placement of nitrogen about 10 to 15 cm deep in the soil directly below the seed resulted in significant increase in the yield of wheat crop grown under rainfed conditions. Weed population was not affected due to nitrogen placement. Total moisture use reduced due to nitrogen placement. Under rainfed conditions, deep placement of nitrogen was important for increasing the efficiency of fertilizer as well as water utilization by wheat crop.     

Yield and yield components of maize and soil physical properties as affected by tillage practices and organic mulching

Maize (Zea mays L.) is an important grains cereal crop. Lots of farmers using tillage and mulching practices influence the final yield, to maintain up with the growing demand for food, fuel and feed. Field experiments were conducted to investigate the effects of tillage practices (i.e. conventional tillage CT, reduced tillage RT, deep tillage DT) and wheat straw mulching (i.e. no mulch and wheat straw mulch of 4, 8 and 12 Mg ha⁻¹, SM0, SM1, SM2 and SM3 respectively) on the growth, yield and yield components of maize and some of soil physical properties. The results showed that compared with RT, DT and CT decreased soil bulk density, as well as led to increase soil water content. Application of mulch treatments increased soil water content. DT and CT have been associated with greater plant height, yield components, grain and biomass yield than RT treatment. Plant height, yield components, grain and biomass yield as well as soil water content increased following mulching treatments. Mulching treatment of SM2 had the largest positive effects on maize yield. DT and CT that have potential to break the compacted zone in soil leading to a better soil environment and crop yield. The application of wheat straw mulch could be an efficient soil management practice for corn production in arid subtropical climate region.     

Effects of water regime on growth,yield, and nitrogen uptake of rice

Summary The effects of water regime on the performance of rice were investigated in a greenhouse experiment and two field experiments. The greenhouse experiment involved four water regimes (continuous flooding, and soil drying for 16 days — begun 2, 5, and 8 weeks after transplanting — followed by reflooding), four soils, and 0 and 100 mg N/kg. Soil drying raised the redox potentials of all soils beyond the aerobic threshold. Averaged for soils and N levels, yields from treatments in which soil drying was begun at 2 and 5 weeks after transplanting were lower than that from the continuously flooded treatment, but the simple effects of soil drying on yield and N uptake depended on the soil and the growth stage of the plant. None of the soil-drying treatments had adverse effects in the soil high in N but soil drying at 2 and 5 weeks after transplanting had adverse effects in the soil low in N. The field experiments tested the effects of three water regimes (continuous flooding, alternate drying and flooding every 2 weeks, and soil drying for 2 weeks at 6 weeks after transplanting following by reflooding), and 0, 50, 100, and 150 kg N/ha on a nearly neutral clay soil, during two seasons. None of the soil-drying treatments depressed growth, yield, or N uptake by rice at any level of N in either season. Nitrate was absent after drying, so denitrification was not possible on subsequent flooding. The adverse effects on yield of alternate flooding and drying, attributed to nitrification-denitrification, may be insignificant in wetland fields carrying an actively growing rice crop.     

Penetration of cover crop roots through compacted soils

Tap-rooted species may penetrate compacted soils better than fibrous-rooted species and therefore be better adapted for use in “biological tillage”. We evaluated penetration of compacted soils by roots of three cover crops: FR (forage radish: Raphanus sativus var. longipinnatus, cv. ‘Daikon’), rapeseed (Brassica napus, cv. ‘Essex’), two tap-rooted species in the Brassica family, and rye (cereal rye: Secale cereale L., cv. ‘Wheeler’), a fibrous-rooted species. Three compaction levels (high, medium and no compaction) were created by wheel trafficking. Cover crop roots were counted by the core-break method. At 15–50 cm depth under high compaction, FR had more than twice and rapeseed had about twice as many roots as rye in experiment 1; FR had 1.5 times as many roots as rye in experiment 2. Under no compaction, little difference in root vertical penetration among three cover crops existed. Rapeseed and rye root counts were negatively related to soil strength by linear and power functions respectively, while FR roots showed either no (Exp.1) or positive (Exp. 2) relationship with soil strength. We conclude that soil penetration capabilities of three cover crops were in the order of FR > rapeseed > rye.     

Root foraging and yield components underlying limited effects of Partial Root-zone Drying on oilseed rape, a crop with an indeterminate growth habit

We report on two experiments with oilseed rape (Brassica napus L.) to test if partial root-zone drying techniques improve yield in a crop in which vegetative and reproductive growth overlap (indeterminate growth habit), and to investigate what plant morphological responses contribute to the yield that is realized. Deficit irrigation resulted in smaller plants with smaller yields but larger seeds compared to treatments with shallow groundwater (first experiment) and with fully watered conditions (second experiment). Different partial root-zone drying treatments (water supply patterns) under deficit irrigation, however, had little effect on plant growth and yield components (number of branches, branch lengths, number of pods, etc.). Our results suggest that partial root-zone drying doesn’t work well with oilseed rape. Detailed measurements of soil water contents and root distribution indicate that roots were extremely plastic, effectively foraging for water, and these root responses may have overwhelmed physiological effects of partial root drying on the shoot. Furthermore, in crops with indeterminate growth with a short vegetative growth phase, partial root-zone drying may be ineffective in enhancing the major yield components. Further reasons for the lack of success are discussed.     

Effect of sodium fertiliser on water status and yield of sugar beet

Effects of sodium fertiliser on growth, water status and yield of sugar beet crops were measured in 1974 and 1975. Sodium increased leaf area index early in the growing period, the water content of the leaves and the final yields of root dry matter and sugar in both years. In 1974, it increased leaf relative water content and diffusive conductance under conditions of moderate soil moisture deficit in August but had no effect in June or September when soil moisture deficits were low. There was also no effect in June 1975 but later, when there was a severe drought, sodium decreased leaf water potential. Further evidence of an interaction between sodium and soil moisture on leaf water status was obtained from a reappraisal of results of field experiments made between 1965 and 1976. Sodium increased sugar yield through at least two different physiological mechanisms; it improved interception of radiation by the crop by increasing leaf area early in the season and it improved the efficiency of leaves under conditions of moderate water stress.     

半干旱黄土高原地区春小麦地膜覆盖研究概述

在黄土高原半干旱地区春小麦上进行的地膜覆盖试验表明,地膜覆盖通过改善耕层土壤生态环境条件,即通过改善水,热状况,活化土壤养分,对提高水分和养分利用效率,实现粮食增产具有重要作用,但近年来在生产实践和科学实验中发现,不合理的长期全生育期地膜覆盖,因在作物生长前期和中期覆膜作物较不覆膜作物生长好,覆膜作物在生长期水分蒸腾损失严重,土壤水分的蒸散（蒸发＋蒸腾）损失远比不覆膜土壤严重,在作物生长后期降水少或没有补充灌溉时,会产生严重的水分肋迫现象,显著抑制小穗分化和灌浆,最终导致收获得指数和产量下降,同时,地膜覆盖的增产作用在一定程度上是以耗竭土壤肥力,特别是在有机物质为代 的,因此,不正确的地膜覆盖（如全生育期的地膜覆盖）,不仅有时起不到显著的增产作用,而且易造成土壤养分,特别是土壤中硝态氮的累积和损失,肥料利用效率降低,土壤生态条件恶化,下降,难以持续高产,因此在确定地膜覆盖范式时,必须要考虑底墒,作物生育期降水,地膜覆盖的阶段性和氮肥的施用等。     

Early growth of Brazilian pine (Araucaria angustifolia[Bertol.] Kuntze) in response to soil compaction and drought

Soil compaction leads to changes in soil physical properties such as density, penetration resistance and porosity, and, by consequence, affects root and plant growth. The initial growth of Brazilian pine is considered as being more affected by soil physical than chemical conditions, and the presence of a well-developed tap root system has been associated with this fact. A greenhouse experiment was conducted in order to evaluate the impact of soil compaction on the growth of Brazilian pine seedlings and on their susceptibility to a simulated drought period. In the first phase of the experiment, the effects of three levels of soil compaction on root morphology and plant growth were examined. Soil cylinders were artificially compacted in PVC tubes. Pre-germinated seeds were planted, and 147 days later 10 plants from each treatment were harvested for analysis. Higher values of soil density were associated with a shorter and thicker tap root. Growth of lateral roots and shoots remained unaffected at this stage. In the second phase, half of the plants (12) in each compaction treatment were drought-stressed by withholding water for a period of 77 days. Increased soil compaction again resulted in reduced length and increased diameter of the main tap root. This time, the effects were also extended to the lateral roots. Shoot extension growth and overall plant mass, however, increased with soil compaction. This greater mass accumulation in plants growing under increased soil compaction may be attributed to a more intimate contact between roots and soil particles. Drought stress reduced both root and shoot growth, but root mass was more negatively affected by drought stress in plants growing under high levels of soil compaction. Future investigations on the effects of soil compaction on the initial growth of Brazilian pine should include a wider range of compaction levels to better establish the relationship between soil physical parameters and plant growth.     

土壤水分胁迫对玉米形态发育及产量的影响

未来气候变化可能加剧的干旱化将对我国主要粮食和最重要的饲料作物玉米产生严重影响。为增进玉米对干旱化响应与适应的理解及制定应对策略 ,利用大型活动遮雨棚及池栽对玉米进行了全程水分控制试验研究。对不同土壤水分胁迫下的玉米形态表征、生长发育及产量的分析表明 ,玉米受干旱胁迫的影响程度因受旱轻重、持续时间以及生育进程的不同而不同 ,受旱越重 ,持续时间越长 ,影响越甚。大喇叭口期前 ,玉米株高和生物产量受有限供水或轻度干旱影响不算很大 ,但从大喇叭口期后直至抽雄和灌浆期 ,轻度干旱胁迫持续久了也会对株高和生物产量产生较大不良影响。严重干旱胁迫则从拔节始至灌浆期均对株高和生物产量影响更为不利。进而引起果穗性状恶化 ,穗粒数和百粒重减小 ,最终导致经济产量大幅下降。说明玉米生育前期(大喇叭口期前 )进行有限的控水可行。而玉米生育前期干旱胁迫将使生育进程明显延缓 ,严重干旱胁迫可使抽雄、吐丝期较水分充足滞后 4 d左右 ,并引起成熟期推迟