Soil provides physical space and various resources to support root growth, while water, nutrients, and air have a great influence on root growth. Soil pore size and distribution, texture, structure, temperature, aeration, and water content affect the ability to store and transport these factors to roots and root growth. Root elongation is greatly affected by soil profile characteristics. When the soil root pressure exceeds the mechanical resistance of the soil, the roots can elongate. If there is a hard layer in the soil profile, the root growth will be limited. With the help of cultivating, although loosening the soil particles and destroying the granules can change the physical properties of the soil, the roots have room for expansion. However, excessive use of heavy machinery for ploughing, harvesting, and other planting work will cause the pores in the soil to be compacted. Unfavorable root elongation, organic matter can not only supply nutrients to the plant, but also contribute to improving the soil environment conducive to root growth. Therefore, in order to have a good growing environment for crop roots, we must first understand some soil physical properties that will affect the development of crop roots, and then improve them.
Soil Physical Properties Affecting Crop Root Growth and Its Improvement Methods
First, the overall density The so-called overall density, its significance is the ratio of a certain volume of water weight. In addition to the naturally-formed hard palate, other overall effects such as trampling of livestock, wheels, and mechanical effects of plowing soil will increase the overall density. When the overall density increases, the total porosity will decrease. The overall density and porosity will change due to the addition of ploughs, traffic or organic matter. In general, the topsoil of soil ploughs does not have a higher overall density than plough topsoil. Frequent traffic is higher than the density of soils where traffic is frequent. The overall density will change at the same time due to seasonal changes. This is partly due to changes in freezing, precipitation pressure, and biological activity. Changes in the overall density will result in changes in soil texture, structure, and organic matter content.
Soil organic matter also affects the overall density of the roots. The forest topsoil has a lower overall density than the subsoil due to the presence of plant debris on the surface. If the overall density of the soil is too high, root growth will be limited. American scholars Rosolem and Takahashi (1996) found that when the total density of red brick soil increased from 1.06 Mgm-3 to 1.45 Mgm-3 and 1.69 Mgm-3, the root growth of soybean decreased by 10% and 50%. Foil and Ralston (1967) found that the root growth was severely restricted when the overall density was greater than 1.02 Mgm-3. Shieraw and Alston (1984) observed that the total soil density was equal to or greater than 1.2 Mgm-3. The growth of seedling roots will be reduced. When the total soil density increases, the root length of corn seedlings will decrease and the root diameter will increase. Sainju and Good (1993) found a negative correlation between root length density and overall soil density, and between root length density and porosity. Positive correlation. To prevent the increase of the overall density of the soil, the number of ploughs should be reduced firstly, and plowing should be performed when the soil is wet and dry to avoid the soil being ploughed when the soil is too wet, and the residues of the plant after harvesting should be kept as much as possible. In the field to increase organic matter content.
2. Soil Aeration and Moisture Content Soil pores are filled with moisture and air. Soil aeration is closely related to water content. The ratio of air and moisture in pores affects the activity of plant root systems. Due to poor drainage, water soaking and mechanical compaction will impede the ventilation of the soil and thus limit the growth of roots. In order to achieve fertilization and prevention of pests and diseases, it is often due to repeated trampling of land or the results of extensive application of fertilizers and irrigation, although nutrients and moisture are solved. However, aeration has also become the biggest limiting factor for yield. Roots are often limited by deeper soil profiles. This is because deeper air permeability is gradually reduced. Poor ventilation often reduces water absorption and causes early plant withering and will reduce roots. Permeability of water, in addition to insufficient ventilation of the soil, can easily cause the state of pressure, resulting in the production of toxic substances that cause poor root growth. The soil contains more than 10% of the pores occupied by air to maintain ventilation. Insufficient air will limit root growth intensity. Cardner and Danielson (1964) found a high correlation between soil penetration rate and percentage of aeration porosity (r=0.998) and oxygen diffusion rate (ODR). The oxygen concentration is sensitive to root growth. When the soil ODR falls below 58 Mgm-2s-1, root growth is limited.
Too high a soil moisture content can easily lead to a gas pressure state, while for some poorly mobile nutrients such as phosphorus, the diffusion rate often depends on the amount of moisture. Drought conditions cause roots to penetrate deeper soils and have a higher root distribution in the subsoil than on the surface. American scholars Kalisz (1987), Darker, and Van Lear (1996) believe that plant growth has higher root densities in arid and semi-arid locations than in humid regions. However, soils that are too dry can increase mechanical resistance. And limit the growth of roots. The way to improve soil aeration and water content is to properly drain water. When fertilizing and working in the field, excessive soil compaction should be avoided. Moderate ploughs are used to provide opportunities for convection between soil air and the atmosphere.
Third, the temperature of the soil temperature due to soil color, soil particle surface roughness, debris and soil moisture content will change, it will affect the root of reproductive, root growth rate and lateral root generation rate, the American scholar Box (1996 ) It is believed that when the temperature is low, the root tip grows horizontally. However, when the temperature rises, the root will grow in a vertical downward direction. The roots of various plants have a moderate temperature for their growth, such as winter wheat and The optimum temperature for root growth of spring wheat was between 12 and 18°C. The roots of cotton and corn were best grown at 24°C. The roots of sweet potato grew best when the soil temperature was 18.5°C, and the roots of apple grew when the soil temperature was about 21°C. Preferably, soil temperature has a significant effect on the type of roots and the absorption of nutrients. The way to maintain soil temperature can cover crops to ease changes in the microclimate and ground temperature. In addition, the coverage of crop residues can also regulate ground temperature. Organic matter is easy to absorb heat due to its darker color, which can increase the temperature of the soil and help cultivate crops in early spring.
Fourth, organic matter organic matter can supply nutrients to plants, but it can also improve soil physical conditions. It reduces overall density, improves soil pellet and water infiltration rates, and increases water volume. Soils containing large amounts of organic matter are less likely to be compacted. Urger and Kaspar (1994) found that soil organic matter can cause earthworms to move; when organic matters are suitable, earthworms can even dig to a depth of two meters. Therefore, large holes are formed in the compressed soil, and water can be added to the earth to increase water. The movement and penetration of the roots, if contained in a soil profile with higher organic matter accumulation, will have a higher root density than other profiles. In order to maintain soil organic matter content, we should first increase the content of soil organic matter. First we should increase the content of soil organic matter, which can increase the soil organic matter and reduce the loss of soil nutrients; at the same time, we should avoid continuous cropping in the same field. It is best to use leguminous and non-legume Green manure cropping system; and too frequent plough times will accelerate the consumption of organic matter, so the number of ploughs should be reduced. In order to reduce the erosion loss of organic matter in Table 7, it is a good idea to cover the fields.
The above are some of the physical properties that affect root growth. If we can improve these characteristics and create a good soil environment, it will contribute to the growth and development of roots. Factors that affect root growth include, of course, not only physical factors, but also need to cooperate. Some nutrition management, after properly improving the soil environment improvement and fertilizer management methods, can make the crop roots grow well and the plants have a healthy tree vigor.