Using corn as an experimental material, root-dividing experiments were conducted to study the effect of bulk density on corn growth under different soil moisture conditions. Seed roots were evenly distributed in separate tin barrels filled with soil-based soil. The results of measurements using a weight-meter showed: Soil bulk density Divided into 4 kinds of treatment: low volume weight (both sides of the bulk density are 1.20 g#cm- 3), the middle weight (both side weights are 1. 33 g#cm- 3), high bulk density (both side weights are 1. 45 g #cm- 3) and mixed bulk density (1.20 g#cm-3 on one side and 1.45 g#cm-3 on the other). Soil moisture control at high matric potential (-0. 17 MPa) and low matrix Potential (- 0·86 M Pa) in two levels. The results showed that when the plant growth in compacted soil or soil matric potential decreased from -0. 17MPa to - 0. 86MPa, the root length, root dry weight, and dry land Weight is significantly reduced, and the dry weight of the aboveground part is reduced more. Compacted soil reduces the root length and also increases the diameter of the root. Both the increase in soil bulk density and the high soil resistance caused by reduced soil moisture content make The speed of leaf expansion decreases and the plants become smaller. Plants grown in compacted soil become smaller not only because of the reduced rate of leaf expansion. At the same time, the leaf area of ​​the mature leaves was reduced. However, when the plants were grown in the mixed bulk density soil, the growth of the roots in the low-concentrated-heavy soils was strengthened, compensating even the over-compensated deficiency of the root growth in the high-concentration soils. The growth status is close to that of plants grown in low bulk density soils. Related Products: Artificial Climate Room Milling Machine Battery Vibration Lamp Leisuwash S90 Vehicle Wash System Leisuwash specializing in manufacture Automatic Car Wash Machine, Touchless Car Wash , Automatic Touchless Car Wash, touchless car wash equipment, robot car wash, smart car wash system, leisuwash 360, leisuwash leibao 360, laserwash 360, leisuwash touchless car wash machine, leisu wash touchless car wash automatic, leisu wash 360 high pressure touchless car wash equipment, robo car wash, touch free car wash, leisuwash 360 touch free car wash, leisuwash 360 price, automatic car wash price, leisuwash in malaysia, no touch automatic car wash machine, leisuwash 360 mini, leisuwash SG fully automatic car wash equipment.
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1 Introduction Soil bulk density increases, soil hardness also increases, Soil hardness is expressed by soil mechanical resistance. Soil bulk density influences plant growth in the form of mechanical resistance. The effect of soil mechanical resistance on plant growth is first manifested in the root system. The effect of growth on the effect of soil mechanical resistance on root growth was similar, ie, the root elongation slowed down and the root became shorter and thicker in compacted soils. The results of soil bulk density on the growth of the aboveground part of the plant showed different results. Most studies have shown that plants grown in high soil-concentration soils have lower dry matter masses, both plant height and shoot, than those grown in low bulk density soils. However, Goodman and Ennos believe that high-concentration soils have little effect on plant shoots, even The researchers believe that there is no impact on the aboveground parts. In the past, the study of soil mechanical resistance generally used uniform soil bulk density treatment and adequate water supply conditions. However, in studying the effects of drought on plant growth, the role of soil mechanical resistance was often neglected. However, Under natural conditions, the soil bulk density in the soil is often inconsistent. They all directly affect the spatial variation of soil mechanical resistance, and compact, dry soils usually also have high mechanical resistance. Therefore, it is not sufficient to study the effects of uniform soil bulk density on plant growth under sufficient water supply conditions. This study was conducted under conditions of drought and wetting conditions. Next, the effect of soil bulk density on the growth of maize was studied, in particular, the spatial variation of soil bulk density (mixed bulk density) and the effect of uniform bulk density soil on corn growth. 
2 Materials and Methods
2.11 soil and soil collection Chinese Academy of Sciences Institute of Soil and Water Conservation experimental field topsoil (cultivated layer), air dried over 2 mm sieve, 1 kg of soil mixed with urea 5. 8 g, potassium dihydrogen phosphate 5. 8 g. Then make the soil absorb moisture To about 8% moisture content (dry soil weight), it is easy to compact the soil. The white iron bucket with a diameter of 18 cm and a height of 26 cm is divided into two vertically from the middle with a steel plate 18 cm wide and 25 cm long. The center has a 4cm diameter semi-circular groove for sowing the corn. The soil is compacted to a bulk density of 1.2, 1.33 and 1.45 g#cm- 3. The soil bulk density is divided into 4 treatments: the low bulk density is 1.2 ( On both sides of the drum are 1. 2 g#cm- 3) , with a medium capacity of 1.33 (both sides of the drum are 1.33 g#cm- 3), with a high bulk density of 1.45 (both sides of the drum are 1.45 g#cm- 3 ) and mixed bulk density mix (1. 2 g # cm - 3 on one side and 1. 45 g # cm - 3 on the other side) (Table 1). The first 3 soils are uniformly compacted soils. In all treatments the soil was placed 3 cm away from the side of the barrel. Each soil was 14 barrels in weight. 
2.12 Determination of soil matrix potential The ring knife method was used to measure the water holding capacity in the field. The 1.33 g #cm-3 soil water characteristic curve was determined by the pressure membrane method of the electronic load cell and the water holding capacity of 1.33 g #cm-3 was calculated in the field. Soil matric potential at 51% and 70%. The thermogravimetric hygrometer (SC-10, Decagon Devices, Inc., Pullman, WA, USA) was used to determine the same soil matrix potential of 1.2 g#cm-3 and 1. Soil moisture content of 45 g # cm - 3 (standardized at 25 e NaCl solution). The soil water content under these two soil matrices is used as the soil moisture control point in this experiment (Table 1).
2.13 Soil mechanical resistance was measured using a PVC pipe with a diameter of 10 cm and a height of 20 cm, and was loaded into the soil as an artificial soil column, and the specific weights were 1. 2, 1. 33, and 1. 45 g # cm - 3, respectively. Column water content was 10%, 14%, 18%, 22%, and 26%, respectively, and repeated twice. After water was added, the plastic film was tightly closed and placed for 30 days to measure the mechanical resistance of the soil. Mechanical resistance was measured using a soil hardness tester. (TE-3, Nanjing Soil Instrument Factory) Determination. The hardness tester is 20 cm long and the plunger can be rotated when moving. The front end has a probe with a diameter of 11.2 mm and a cone angle of 450. When the soil has a certain resistance, the probe is blocked. Into the soil, forcing the spring to compress, the compression of the spring reflects the mechanical resistance of the soil encountered by the probe and is recorded on the ordinate of the recording paper by the stylus pen. The resistance encountered by the probe on the soil 20 cm can be measured continuously. After the 5 cm soil column was taken out of the soil and dried for 24 h, the soil moisture content was measured. The soil mechanical resistance and the soil moisture content were plotted on the corresponding sections on the recording paper to determine the moisture content at a specific soil moisture content. Resistance curve (see specification for details). The mechanical resistance of heavy soil is shown in Table 1. 
2.14 Planting and water control Before sowing, 7 barrels of water for each type of bulk density soil added soil matrix potentials to -0.86 MPa and -0.17 MPa, respectively (Table 1). Corn seed (Shandan No. 9 orthogonal) 0. 5% copper sulphate solution was sterilized for 3 min and put on water-absorbing paper to germinate. After the seed root was extended to 2 cm, it was evenly sowed in the middle of the iron drum. The seeding depth was 2 cm, and the seed dorsoventral surface was vertically separated. The plate is so that the seed root is evenly distributed on both sides of the intermediate baffle, 1 per barrel. For compacted soil, 2 cm of soil around the loose seeds is sown. After sowing, the soil-proof surface is covered with a plastic film to evaporate and dehydrate. After sowing, the corn is transferred to the step. In a growth chamber (Conviron PGV36 Controlled Environments, Asheville, Nort hCaro lina, USA), the relative humidity in the growth chamber is 75%, the illumination length is 12 h, and the photosynthetically active radiation is 500 Lmol#m-2 #s-1 The light period/dark period temperature is 28/23 e. The soil moisture is kept constant by the weighing method (?5g), and the mixed bulk density is controlled by the combination of TDR measurement. The first 10 days every 5 days. For drought-treated, For the first 5 days, add a small amount of water around the seeds with a straw every day to keep the soil around the seeds. Wetting, the afternoon time, promote growth, early growth and avoid wet processing inconsistencies. 10 to 20 days once every two days, once a day later.
2.15 Determination of plant growth Leaf area determination: Every 5 days after sowing, the length and width of each leaf was measured with a ruler every two days until the leaves no longer grow. The leaf length is the length from the tip of the leaf sheath to the tip, and the leaf width The width of the middle part of the leaf until the 30th day. Leaf area = length @ width = 0. 7. After the plants have been grown in the growth box for 60 days, the aboveground parts are kept in the blast drying oven 105 e for 20 minutes and then 70 e. Bake for 24 h and record separately. Carefully remove the roots, rinse the roots on both sides, stain with 0.5% methyl blue for 12 h, scan the roots with a scanner, and use Image Analysis Software (Image Analysis). Software, CID, Inc., Vancouver, WA) Determined the length of the roots, then baked in an oven at 70 e for 24 h, and weighed the records, respectively. Data were counted in a Microsoft Excel 2000 worksheet using SPSS10.0 (Inc. 1999). ) Make a significant test.
3 Results and Analysis
3.11 Effect on Root Growth The success of the rooting experiment is based on whether or not the root system can be evenly distributed to the left and right sides of the partition in uniformly compacted soils. It can be seen from Fig. 1 that whether the soil moisture content is low or Under the condition of high soil moisture content, there was no significant difference in the dry weight of roots evenly compacted on both sides of the soil (P < 0. 05), indicating that the root system was evenly distributed on both sides of the partition, no one was biased, and the partial root was successful. The difference in the dry weight of the roots treated on both sides of the mixed-concentration (mix) was significant, which was the result of differences in bulk density between the two sides. Under drought stress, the dry weight of the roots decreased significantly with increasing bulk density (Fig. 1), D1. 45 The dry weight ratio D1. 2 was reduced by 37%; the mixed bulk density Dmix root growth was significantly tilted to the low bulk density soil, the dry matter quality on both sides was different by 45%, and the root dry weight in 1. 2 g#cm-3 was more than D1. 2 The amount of soil in the half (approximately 120% of the average amount of D1. 2); and under wet treatment, the difference in total weight of root weights of different volume weight is much smaller, W1. 45 of the dry weight of the root system than W1. 2 only 14% reduction, 31% difference between dry weight of roots in both sides of mixed bulk density processing Wmix , 1. 2 g #cm - 3 The dry weight in the soil also exceeds the amount of half of the soil in the W1. 2 (113% of the average amount of W1. 2), indicating that the root growth is also low at high soil moisture content. The weight of the soil leans.
3.12 Effects on above-ground growth If some of the treated plants are initially stressed by soil moisture and high mechanical resistance, they will inevitably be too weak for seedlings and will differ significantly from wet and low mechanical resistance treatments. In later experiments, The basis is not the same and the comparability is lost; if the drought-treated and wet-processed soil matrices start at the same (- 0. 17 MPa), the water consumption of the seedlings will be very small, and the soil will be difficult to reach the drought treatment for a long time. The required moisture content. To this end, we used the method described in 214 to make the drought-treated seedlings grow at the same time as the wet treatment. Figure 2 shows the leaf area of ​​the seedlings after 5 days of emergence under different weight densities under drought stress and wet treatment. There was no difference in seedlings treated on the 5th day, indicating that there was no difference between the treatments in the early growth stages of the corn plants. Figure 3 shows the dynamics of the leaf area of ​​maize in different bulk density soils over time under soil drought and wet conditions. Leaf area and soil in single bulk density treatment There is a negative correlation between the bulk density and the difference between the later treatments. The difference between the drought treatments is greater than the wet treatment, and the 30th day The leaf area treated by D1.2 was 44% larger than that of D1.45 treatment, while that of wet treatment only differed by 22%. As with the root growth, the leaf area of ​​mixed mixed weight treatment was not significantly different from that of 1.2 treatment. Processing Wmix even exceeded the leaf area of ​​W1.2.
3.13 The results of continuous measurement of leaf area change on the 4th leaf showed that the 4th leaf area was continuously measured (Fig. 4). Drought reduced the expansion rate of the 4th leaf and extended the time required for full expansion, such as the 4th leaf of drought treatment. The 20th day was fully developed, while the wet treatment was fully developed on the 16th day. At the same time, the final leaf area was reduced by the drought treatment. Whether the soil was dry or moist, the 4th leaf leaf area growth rate was also increased with the increase of soil bulk density. Slower, and eventually the leaf area was also reduced, but the differences between the treatments under drought were more significant, such as D1. 45 The maximum leaf area of ​​the 4th leaf was reduced by 23.8% from D1. 2 and W1. 45 The decrease of W1. 2 was only 10.6%. Whether dry or wet, the maximum leaf area of ​​the mix treated with the bulk density of 1.2 g#cm-3 was similar (Figure 4). 
3.14 Effect on dry matter accumulation Table 2 shows that the above-ground dry weight decreases with increasing bulk density, and the difference between drought treatments is greater than that of wet treatment. Under dry conditions, the D1. 45 treated aboveground dry weight ratio D1. 2 The treatment was reduced by 55%, whereas the dry weight of W1.45 under wet treatment was only 14% lower than that of W1.2. Like the change of root system and leaf area, whether it was under dry conditions or under wet conditions There was no difference between the dry matter quality and the 1.2 treatment. The drought-treated root and shoot ratio was larger than that of the wet treatment. Drought increased the root to shoot ratio as the bulk density increased, but the Dmix root to shoot ratio was not different from that of D1.2. There was no difference in root-to-crown ratios between wet treatments. 
4 Discussion The effect of soil bulk density on the growth of maize roots was consistent with the results reported by previous authors. Monitoring results of soil moisture meters showed that the growth rate of roots in compacted soils was slowed down. Drought made mixed roots grow with a focus on low bulk density. On this side, there is a compensatory effect. The reason may be: The roots in low-consistency soils are less resistant to growth, and the roots in high-constrained soils are more resistant to growth, slower growth, and certain conditions for photosynthetic products used for root morphogenesis. Next, the amount of roots assigned to a small part of the resistance is increased. This result is inconsistent with the report by Bingham et al. [4] because, apart from the plant species they are testing (wheat and barley), soil moisture may also be important. The reason, because their experiment is a sufficient supply of water, just as this experiment under the effect of high soil moisture, this effect is lower under the lower water content. This compensated effect of root system in mixed bulk density soil indicates the adaptability of root system to non-uniform bulk density soil.
The study of the influence of soil bulk density on the growth of plant parts has different results. Although the causes of these different results are related to plant species, the main reason for our results may be the difference in soil moisture. The impact not only manifests in the slower leaf expansion rate, but also in the reduction of single leaf area [3] and thinning of leaf thickness. Our results also show that high bulk density soils reduce the leaf expansion speed and reduce the final leaf area. It is the main reason for the reduction of dry matter in the shoots and even the whole plant, because the reduction of leaf area directly affects the accumulation of photosynthetic products. Many researchers believe that the influence of bulk density on plants is indirect, which may be through the change of soil water and gas heat conditions. The effects, such as the changes in leaf growth, are often caused by compaction causing soil water deficits. However, some reports have shown that mechanical resistance does not cause changes in leaf water potential. Therefore, it cannot be explained by compacted soils affecting plant water status. Effects of soil mechanical resistance on aboveground growth. Young et al. In experiments with full supply of gas, it was observed that the elongation rate of wheat and barley after the mechanical resistance of the root system was reduced to a minimum after 10 min, which fully shows that the mechanical resistance has a direct impact on the growth of the leaves. Young et al. The bulk density of the sand body, that is, the same mechanical resistance experienced by all parts of the root system, is the same as the result of the single bulk density treatment of this experiment. The expansion speed of the leaf is slowed with the increase of the soil bulk density. However, the bulk density of each part of the field soil is often different, and the root volume is uniform to the bulk density. Perception may be different from perception of inhomogeneous soils (Young, personal communication). Hussain et al. reported that the growth rate of tomatoes (ACO1AS) in mixed soils with a bulk density of 1. 1 ~ 1. 5 g # cm - 3 was consistent with a single bulk density. 1. The speed in 1g#cm-3 is the same; Kirkegaard et al., Hartung et al., and Montagu et al. also observed this phenomenon. This experiment also obtained similar results, that is, the mixed weight of corn in mixed soil under both dry and wet conditions. The growth rate in the mix soil is the same as that in 1.2. It is not yet clear why the plant's perception of spatial variation in soil bulk density is different. It has been reported that the root system Source hormones may be involved in this response, which may be the result of plants' long-term adaptation to heterogeneous mechanical resistance soils in nature. The effect of soil bulk density on root/shoot ratios has inconsistent results. It has been reported that the effect of bulk density on root/shoot ratio is not significant, or Increase. The difference in measurement results from these load receptors may be the result of inconsistent soil moisture status in each study. The results of this experiment show that only the bulk density at low soil water potential has an effect on the root/shoot ratio of maize, while the high soil moisture content The effect is not obvious (Table 2). Stirzaker et al. (2007) determined through experimental and theoretical calculations that in wet soils, whether loose or compact soils have little effect on root water and fertilizer absorption, our results also show that roots under high soil moisture conditions There was no difference in the crown ratio, but under drought conditions, the ratio of root to crown increased with the increase of soil bulk density. Is this the effect of mechanical resistance on the absorption capacity of water and fertilizer in the root for further study.