The application of film-mulching cultivation in cotton fields can significantly increase soil temperature, improve field moisture content, promote early development of cotton plants, and increase cotton yield.

Xinjiang is an important cotton producing area in China. The area and use of plastic film is very large. With the extension of planting time, the residual quantity of plastic film is also increasing year by year. Agricultural plastic film is a kind of polymer hydrocarbon compound (polyvinyl chloride) made of polyethylene plus antioxidant and anti-ultraviolet material. It has the characteristics of large molecular weight and stable performance. It is difficult to photolysis and heat under natural conditions. Degradation is also not easily degraded by biological means such as bacteria and enzymes. It can remain in the soil for 200 to 400 years. Long-term accumulation of residual film causes soil/white pollution and destroys the farmland ecological environment. The residual film will accumulate in the tillage layer and surface layer of the soil, hindering the penetration of soil capillary water and natural water, affecting the hygroscopicity of the soil, thus impeding the movement of water and slowing the movement speed, so that the amount of moisture permeation due to film residues Increase and decrease, soil moisture content decreased, weakening the ability of the arable land to resist drought. Residual plastic film will also reduce the porosity and permeability of soil, which is not conducive to the circulation and exchange of soil air, resulting in high CO2 content in the soil, affecting soil microbial activity and the formation of normal soil structure, resulting in decreased soil fertility, resulting in reduced crop yields. . The residual plastic film has high toughness and ductility, and it is difficult for the root system to penetrate, which results in difficulty in root growth, thereby worsening the living conditions of the plant.

Although different authors have reviewed and investigated the hazards of white pollution, there are few studies on the effects of residual plastic film on the soil properties of plants and their effects on plant growth and development. Through field experiments, under the conditions that other limiting factors are met, artificially adding different amounts of plastic film to simulate different amounts of plastic film residues can effectively control the amount of plastic film in the soil, and explore the effect of residual plastic film on the growth and development of cotton under different residual plastic film. Provide theoretical understanding of the in-depth understanding of white pollution.

1 Materials and Methods

1.1 Material test

In 2003 and 2004, it was conducted at the Experimental Station of the Agricultural College of Shihezi University. The center of the test area is located at E85b59c50d, N44b18c58d. The elevation is 433~437 m, the average ground slope is 6j, and the soil texture is loamy soil. Organic matter 15.4j, basic dissolved nitrogen 63 mg/kg, available phosphorus 16 mg/kg, available potassium 208 mg/kg, total nitrogen 0.8 j, total phosphorus 1.2 j, and the groundwater depth in the test area is less than 5 m. The test variety was planted in Xinluzao 13, which was planted in northern Xinjiang. Drip irrigation with dry sowing wet sowing 0 method, a film of 4 rows, spacing 30 cm +60 cm +30 cm +60 cm. Plant spacing 10 cm, seedling preservation 19.5@104/hm2, planting on April 24, 2007.

The residual film amount of the test is set at 0, 225, 450, and 900 kg/hm24 levels (represented by A, B, C, and D, respectively), and each treatment is repeated 4 times, for a total of 16 test plots, and the plot area is 2.7 m2, which is randomly arranged. . According to the experimental design, artificially smashed mulch (2 to 3 cm wide and less than 20 cm in length, which simulates the size of the common mulching film in the field) was incorporated into the plot. The depth of the soil was 40 cm and the topsoil was 0 to 20 cm. ) and subsoil (20 ~ 40cm), each layer is blended evenly, and the original residual film in the soil is carefully selected before being mixed into the film. At the same time, the fertilizer was applied at 0-20 cm. The fertilizer amount was 245 kg/hm2 of three-component phosphate fertilizer, 2 275 kg/hm2 of potassium sulfate, and 270 kg/hm2 of nitrogen fertilizer, of which the nitrogen fertilizer was applied with urea, and 30% was used as the base fertilizer before sowing. 70% topdressing is applied 7 times during the growth of cotton. The total growth period was controlled by 4 times of salivary amination. Other agricultural operations are managed under field drip irrigation.

1.2 Methods

1.2.1 Sampling method The sampling method was used during the flowering period (90 days) of cotton. Sampling method: Choose two rows of cotton with uniform growth, no missing seedlings, no size seedlings (length 50 cm) as sampling points. Root level sampling method: Take the cotton sowing line outside the plastic film as the starting point, divide the membrane between the narrow row and the wide row, and sample in the horizontal direction with the same width of 30 cm; the root vertical direction sampling method: between the membrane, narrow row, wide row three In the horizontal direction, a root depth of 10 cm is drilled until 1 m. Remove the soil and the root sample through a 1 mm soil sieve and remove the live roots. Observe and record the metamorphosis of the root surface in contact with the film (change in growth direction, change in morphology, and it can be used to visualize the effect of the film on root growth). Part of the fine root system is collected along with the soil. The collected roots were brought back to the laboratory and rinsed repeatedly on fine gauze. The resulting root samples were manually placed on a glass plate with tweezers for scanning. The scanned roots were collected again and placed in an oven at 70e for 36 h, weighed and recorded. At the same time, all the above-ground parts of the cotton collected at the sampling site were brought back to the laboratory, dried and weighed and recorded according to different organization. Figure 11.2.2 Root Scanning and Analysis The well-drained glass plate was placed on an EPSON PERFECTION 4870 PHOTO scanner and scanned into a black-and-white TIF image file at 300 dpi pixels. The scanned TIF image files were used to calculate the morphological characteristics such as root surface area and root length density using the WinRHIZO Basic 2004 Root Analysis System software.

1.3 Data Analysis Tools

The cotton root system was used for the analysis and analysis using the root analyzer, and the variance analysis and mapping of the test data were performed using Excel 2003 and SPSS 13.0.

2 Results and Analysis

2.1 Effect of Residual Membrane on Soil Physical Properties

Soil physical properties mainly refer to soil water content, bulk density (ratio of the solid weight per unit volume to the water volume of the same volume) and porosity (volume percentage of the void volume per unit volume of soil). Treatments B, C, and D reduced water content by 1.29%, 4.39%, and 11.22%, respectively, compared to Treatment A. This was due to the residual film impeding the penetration of soil capillary water and natural water, thereby reducing the amount of moisture permeation due to the increase of plastic film residue. The soil moisture content decreased. Residual plastic film will also reduce the porosity and permeability of soil, which is not conducive to the circulation and exchange of soil air, resulting in high CO2 content in the soil, affecting the formation of normal soil structure, resulting in increased bulk density and specific gravity of the soil with increasing residual film content. And increase.

2.2 Vertical Distribution of Cotton Roots in Soil

In the soil with residual film (0-40 cm), the surface area of ​​the root system increases with the increase of the residual film volume, and the ratio of the root surface area of ​​each layer to the total root surface area of ​​the cotton also gradually increases, in the range of 0-40 cm. The root surface area of ​​layer A in the layer was 1 656.27 cm2, accounting for 55.74% of the total, while D was 2 800.08 cm2, accounting for 74.74% of the total, 69.06% higher than treatment A; but in soil without residual film ( 40 to 100 cm), the situation is reversed, and the total surface area of ​​the root system tends to decrease gradually. In the 40 to 100 cm soil layer, both A's root surface area and its proportion to the total amount are greater than other treatments. The above description shows that in 0-40 cm soil, due to the presence of residual film, a certain mechanical resistance of the soil is produced, but this resistance not only does not hinder the growth of the root system, but stimulates the growth of the root system, resulting in a large number of cotton root system proliferation. The surface area of ​​the roots also increases. As the roots of the upper layer are stimulated by the residual film, the roots are heavily proliferated. Therefore, the nutrients absorbed by the roots are also largely consumed in the proliferation of the roots, weakening the strength of the roots and lowering the roots, resulting in the failure of normal root growth. The lower surface area of ​​the lower roots of B, C and D reduced the absorption and utilization of deep water and nutrients, weakening the drought resistance of cotton. Table 2 Root Length Density (RLD) is the length of the root within a unit of soil volume. The results of the study showed that the cotton root length density between treatments differs greatly between different soil layers. In 0-40 cm soil layers, the root length density of treatment A was very similar to that of B, which was slightly smaller than that of C. However, A and D were significantly different. In all four soil layers, the root length density was lower than that of D. In each layer of 40~100 cm, the root length density of each treatment showed a decreasing trend, except that A and B decreased slowly, and C and D decreased rapidly. This shows that when the residual film amount is 900 kg/hm2, the residual film can stimulate the growth of cotton roots, resulting in a large number of root system proliferation, increasing the root length density in the soil, this phenomenon on the one hand exacerbates the root system in the soil moisture , nutrients competition, and may induce premature aging, on the other hand in the 40 ~ 100 cm soil root density is low, the use of water nutrients is not sufficient; when there is no residual mold in the soil, the spatial distribution of cotton roots is more reasonable There are more root systems under the roots, which can increase the utilization efficiency of roots for deep soil moisture and nutrients. Figure 2 In the 0-40 cm soil layer, the vertical distribution of cotton root weight in the soil is similar to Figure 2. The root weight of D is the largest, while the other three treatments have little difference, indicating that there is a large amount of residual film in the soil. Stimulate root growth. In the 40- to 100-cm soil layer, there was little difference among treatments, but the root weight of D was significantly reduced. This may be due to the fact that the upper root system consumed a large amount of nutrients, and the nutrient transported to the lower layer root system was relatively reduced, resulting in lower root weight. reduce.

2.3 Horizontal Distribution of Cotton Roots in Soil

The sampling method is to divide the sampling area by the center position of the growth of the cotton plant. The attribution of the main root is difficult to distinguish, so only the horizontal distribution of the fibrous roots is discussed. From the distribution of the root surface area in the horizontal direction of different treatments, it can be seen that the distribution of the root surface area of ​​each treatment in the horizontal direction is not the same. In 0-40 cm soil, the root surface area between each treatment membrane, narrow row and wide row increases with the increase of the residual membrane volume, and it accounts for the total root volume between the membrane, narrow row and wide row. The proportion of surface area also increases. It is worth noting that the narrow root distribution of Treatment A is larger than that between the membranes and the broad line, which indicates that the root distribution of Treatment A is mainly affected by the distribution of water and the effect of temperature increase of the plastic film due to the absence of residual film in the soil. In the narrow row of parts covered with water and concentrated water distribution, the root growth was the highest, the width of the mulching film was the next, and the film without the plastic film was the least; the treatment B was similar to the treatment A, indicating that the residual film had little effect on the treatment B; The narrow root distribution of the narrow line is larger than that between the membranes and smaller than the width line, indicating that the residual membrane has a certain influence on the treatment C; in the treatment D, a large number of residual membranes stimulate the proliferation of roots and also increase the competition of the roots, and the narrow row space is relatively Small, the competition in the root system is further exacerbated, and the root surface area is smaller than the membrane and the width. In 40~100 cm soil, the horizontal distribution of root surface area is contrary to 0~40 cm, which decreases with the increase of residual membrane volume. The proportions of the total surface area of ​​the roots in the narrow row roots of Treatment A, Treatment B, Treatment C, and Treatment D were 39.03%, 36.06%, 36.45%, and 32.03%, respectively. Because the cotton fields were fertilized with water, the water and nutrients were concentrated in narrow rows. Therefore, treatment A is easier than other treatments to obtain the moisture and nutrients needed for its own growth and development.

The average root length density of cotton is distributed at a level of 0-100 cm. Studies have shown that in 0-40 cm soil, the average root length density of treatment D is larger than other treatments, but the root length density of narrow rows is smaller than that of other treatments. Between the membranes and the width; the average root length density of the narrow rows and wide rows of treatment A is higher than that between the membranes, that is, the roots of the treatment A are distributed in a narrow row and a wide row, and there are few between the membranes. In the 40- to 100-cm soil, the root distribution of each treatment in the narrow row and wide row gradually decreased with the increase of the residual membrane, and the treatment D decreased most. Fig. 4 and Fig. 5 show the horizontal distribution of total cotton root weight in soil, and the two depths have the same trend. In 0-40 cm soil, the total root weight of the narrow row of treatment D was smaller than that between the membrane and the broad row, and the rest of the treatments were narrow row> wide row> membrane, but the root biomass of treatment D was greater than that of the other treatments; In the 100 cm soil, the roots of treatment A were the largest, and the treatment D was the smallest, while the differences in the root volume distribution within the treatment were mainly caused by the bias of the main root distribution. The main root growth bias was mainly caused by the differences in soil compaction.

3 Conclusions and discussions

3.1 Due to the obstruction of the mulching film, soil moisture and air movement are hindered, and the physical structure of the soil is broken, resulting in reduced soil moisture content and reduced porosity, while soil bulk density and specific gravity increase with the increase of residual film.

3.2 Some people think that mulching film hinder the growth of roots, and the root length and root weight of plough layer decrease with the increase of plastic film residue. Research shows that this view is not comprehensive. In 0-40 cm soil, plastic film residue had the effect of stimulating cotton root growth. The root surface area, root length density and root weight all increased with the increase of plastic film residue. In 40-100 cm soil, film residue hindered the root system. Growth, root surface area, root length density, and root weight decreased drastically with the increase of residual film in the upper layer of the soil. This was caused by excessive water and nutrient consumption in the upper root system and insufficient root transport in the lower layer. Studies have shown that under the condition of drip irrigation, water concentration is distributed in narrow rows, so the amount of roots in narrow rows is higher than that between membranes and broad rows, but when there are a lot of residual film in the soil (900 kg/hm2), this rule changes and remains Although the membrane stimulates the proliferation of roots, due to the relatively small space in the narrow row, the resistance to root growth is greater than that between the membrane and the broad row. The proliferation of the root system is less than that between the membrane and the wide row. Therefore, the amount of the narrow root row is smaller than that between the membrane and Wide line.

3.3 The root system is the most active crop nutrient and water absorption organ, and plays a very important role in the growth and development of crops and the formation of yield. Major agricultural measures such as irrigation and fertilization affect the growth, distribution, and function of the root system first, and then affect the above ground and thus affect the yield. Although a small amount of plastic film residue (<900 kg/hm2) increased root biomass, it was actually a compensatory growth of the plant, and the cotton leaf and boll weight decreased as the residual film increased (Process A and Process C and D Biological yields, etc. reached significant differences). Residue of plastic film stimulated root growth, but it also consumed a lot of nutrients, making cotton unbalanced growth on the ground and underground, and reduced crown-root ratio, which reduced the productivity of unit root weight. The residual film had a significant effect on the number of bolls per plant, boll weight and yield, and there was a negative correlation.

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