AU2020100016A4

AU2020100016A4 - Method for three-round cultivation of double cropping rice field

Info

Publication number: AU2020100016A4
Application number: AU2020100016A
Authority: AU
Inventors: Haiming Tang; Wenguang TANG; Xiaoping Xiao; Guangli Yang
Original assignee: HUNAN SOIL AND FERTILIZER INST
Current assignee: Hunan Soil and Fertilizer Institute
Priority date: 2020-01-06
Filing date: 2020-01-06
Publication date: 2020-02-13
Anticipated expiration: 2028-01-06

Abstract

The present invention takes annual cultivation of triple-cropping crops as a cycle, including annual rotational tillage with rotary tillage for early rice and no-tillage for late rice and winter crops, and annual rice field-upland field rotation combining dry cultivation of winter crops and water cultivation of early rice and late rice, as well as a method of annular straw rotational return cultivation with winter crop straw and early rice straw returning to the field and late rice straw not returning to the field. The practical problems of long-term single soil cultivation, continuous cropping in the winter fallow period, straw burning, heavy metal pollution, and the like in the existing double cropping rice field are solved. The content of organic matter in soil is increased, the soil nutrient sustaining capability is enhanced, heavy metal Cd pollution to the soil is alleviated, the farmland ecological environment is protected, and sustainable, balanced and safe production of rice is achieved. Cd 0.5 -b 0.45 - bB b ~0.4 -cc .0-35 *025 .CK TI T2 T3

Description

METHOD FOR THREE-ROUND CULTIVATION OF DOUBLE CROPPING RICE FIELD

TECHNICAL FIELD

The present invention relates to a method for three-round cultivation of a double cropping rice field.

BACKGROUD

Any references to methods, apparatus or documents of the prior art are not to be taken as constituting any evidence or admission that they formed, or form part of the common general knowledge.

At present, mechanical rotary tillage is a main method of soil tillage in double cropping rice fields in southern China, followed by traditional tillage by livestock, and no-tillage cultivation is rarely used. However, the cropping models of the double cropping rice fields in southern China are mainly winter fallow-double cropping rice, followed by rape-double cropping rice, milk vetch-double cropping rice, and the like; a method for treating straw and winter crop straw in double cropping rice fields is mainly incineration, followed by turning over and returning to the field. Long-term tillage and rotary tillage of double cropping rice fields need to consume a large amount of human and animal labor and fuel power, which is labor-consuming and time-consuming. The soil structure is destroyed, which easily leads to soil erosion, serious soil erosion and increased evaporation of soil water. Long-term no-tillage leads to a series of problems such as soil compaction, shallow plow layer, enrichment of organic matter and nitrogen and phosphorus nutrients in topsoil and depletion of subsoil, difficulty in fusion of soil and fertilizer, low fertilizer utilization rate, increased nitrogen loss, easy generation of toxic substances by stubble mulching, reduction of soil temperature, serious diseases and pests, increase of weeds, and residual toxicity of herbicides. Since the 1980s, with the strategic transfer of surplus rural labor force and the adjustment of rural industrial structure, the agricultural production in winter has shown a gradient downward trend. The area of winter fallow fields in double cropping rice areas in southern China has increased dramatically, resulting in serious waste of natural resources such as land, temperature, light, water and fertilizer. At the same time, long-term continuous cropping of rice resulting from the winter fallow period easily results in serious diseases and pests, lack of nutrient elements in soil, poor physical and chemical properties and the poisoning phenomenon caused by accumulation of harmful substances. Straw and winter crop straw contain a large amount of organic matter and nutrients needed by crops. Direct incineration not only wastes precious resources, but also damages soil structure, pollutes air environment, and easily causes fire and traffic accidents. At the same time, with the rapid development of industry and agriculture, under the influence of industrial three wastes and agricultural activities themselves, the problem of heavy metal pollution in rice fields in southern China is becoming more and more serious. Long-term total straw returning to the field causes heavy metal elements absorbed in the straw to be also returned to the rice field, which is not conducive to the reduction of heavy metals in rice field soil.

SUMMARY

In view of the defects of the prior art, the present invention provides a method for three-round cultivation of a double cropping rice field, which can fully utilize light and heat resources, reduce soil erosion, sustain soil nutrients, reduce diseases and pests, save labor and time, save energy, coordinate water, fertilizer, gas and heat resources in soil, improve water and fertilizer utilization rate, reduce heavy metal pollution in rice field soil, and realize sustainable, balanced and safe production of rice.

The present invention provides a method for three-round cultivation of a double cropping rice field, where with annual cultivation of triple-cropping crops as a cycle, each cycle includes the following steps:

step a: raising early rice seedlings in the last ten days of March, performing rotary tillage of a rice field in the middle ten days and last ten days of April, and then manually throwing or mechanical transplanting the raised early rice seedlings;

step b: raising late rice seedlings in the middle ten days and last ten days of June, mechanically harvesting the early rice in the first ten days and middle ten days of July, reserving low stubble of the early rice, using all the harvested rice for mulching and returning to the field, performing stubble cleaning, weeding and soil conditioning, manually throwing or mechanical transplanting the raised late rice seedlings with no tillage, and keeping a wet state of the rice field soil;

step c: mechanically harvesting the late rice in middle ten day of October, reserving low stubble of the late rice, collecting straw from the field, and removing the straw from the rice field for centralized treatment; and step d: directly seeding winter crops 7-10 days before harvesting the late rice in step c with no tillage, harvesting the winter crops in April of the next year, and after the harvesting, returning stalks of the winter crops to the field through rotary tillage and turning over.

In step a, the early rice seedlings are raised by using a soft disc in the last ten days of March, the sowing quantity of hybrid early rice is 2.5-3.0 kg per 667 m², the sowing quantity of conventional early rice is 4-5 kg per 667 m², the rice seedling raising in the soft disc is centralized rice seedling raising, the seedling age is controlled at 25-30 days, the early rice is thrown in the middle ten days of April, the throwing density of the hybrid rice is 18000-20000 plants per 667 m², and the throwing density of the conventional rice is 20000-22000 plants per 667 m²; before harrowing for the last time, 30 kg of 40% compound fertilizer (20-8-12) is applied per 667 m² as base fertilizer, and after the field is flattened, the early rice is thrown; after the early rice seedlings turn green, the field is irrigated to make the water surface higher than the field surface by no more than 5 cm, 5-7.5 kg of urea and 5 kg of potassium oxide are used per 667 m² and applied by mixing with a pre-emergence herbicide; after the application, a water layer is maintained for 5-7 days, and the field naturally dries.

In step b, the late rice is sown on June 15-23, the seedlings are raised using a plastic soft disc, the sowing quantity of the hybrid late rice is 1.5-2.0 kg per 667 m², the sowing quantity of the conventional late rice is 3-4 kg per 667 m², and uniconazole is sprayed on the hybrid late rice in a two-leaf stage to control the excessive growth of the late rice seedlings; the late rice seedlings are thrown on July 15-23; the throwing density of the hybrid late rice seedlings is 18000 plants per 667 m², and the throwing density of the conventional rice is 20000 plants per 667 m²; 35 kg of 40% compound fertilizer (20-8-12) is applied per 667 m² as base fertilizer; after returning to the field, 250 ml of gramoxone is used per 667 m², 1 kg of potassium chloride or 200 g of deep tillage-free soil conditioner is added, and 50 kg of water is added, and the mixture is sprayed to carry out stubble cleaning, weeding and soil conditioning; and after the late rice seedlings turn green, 7.5-10 kg of urea and 7.5-10 kg potassium oxide are used as topdressing per 667 m², and are mixed with the pre-emergence herbicide for application.

In step c, the straw collected from the field is no longer returned to the field.

In step d, the winter crops mainly refer to milk vetch, ryegrass or rape and are sown in a no-tillage direct seeding mode in the first ten days and middle ten days of October, the seeding quantity of the milk vetch is 2.5 kg per 667 m², the seeding quantity of the ryegrass is 1.5 kg per 667 m², and the seeding quantity of the rape is 0.3 kg per 667 m²; after the seeding, the rice field is kept dry, and weeds are removed.

By adopting the method, the present invention has, at least in embodiments, the following advantages:

1. The rotational tillage combining rotary tillage for early rice and no-tillage for late rice and winter crops can not only prevent soil compaction, shallow plow layer, enrichment of nutrients in topsoil and depletion of subsoil through rotary tillage, but also save energy, labor and time and time, protect soil structure, reduce soil erosion and sustain soil nutrients through no-tillage.

2. The rice field-upland field rotation combining dry cultivation of winter crops and water cultivation of early rice and late rice can improve the utilization rate of natural resources such as land, temperature, light, water and fertilizer by increasing cultivated winter crops, the harm of diseases, pests and weeds can be alleviated through the rice field-upland field rotation, soil gleization and secondary gleization are prevented, and the poisoning phenomenon caused by accumulation of harmful substances in the soil is prevented.

3. The straw return combining winter crop straw and early rice straw rotational returning to the field and late rice straw not returning to the field can increase organic matter in soil, improve soil fertility and reduce environmental pollution by returning an appropriate amount of straw to the field, and by not returning an appropriate amount of straw to the field, comprehensive utilization can be performed, so that the resource utilization efficiency is improved, the heavy metal pollution to the rice field rice is reduced, and sustainable, balanced and safe production of rice is achieved.

4. Straw collected from the field is not returned to the field, and is used as raw materials for biogas fermentation to produce clean energy, or ammoniated to produce high-quality cattle and sheep feed, thus reducing environmental pollution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows contents of Cd in soils under different cropping models in winter;

in FIG. 1, CK: winter fallow-double cropping rice; Tl: ryegrass-double cropping rice; T2: milk vetch-double cropping rice; T3: rape-double cropping rice;

FIG. 2 shows effects of different tillage methods and straw returning to the field on the content of organic matter in soil; and

FIG. 3 shows effects of different tillage methods and straw returning to the field on heavy metal Cd content of soil.

DESCRIPTION OF THE EMBODIMENTS

Specific embodiments of this patent will be described in further detail below.

A method for three-round cultivation of a double cropping rice field takes cultivation of triple-cropping crops a year as a cycle, and includes annual rotational tillage with rotary tillage for early rice and no-tillage for late rice and winter crops, and annual rice field-upland field rotation combining dry cultivation of winter crops and water cultivation of early rice and late rice, as well as a method of annular straw rotational return cultivation with winter crop straw and early rice straw returning to the field and late rice straw not returning to the field.

Embodiment 1

From September 2004 to October 2013, a 9-year long-term positioning experiment was conducted in the rice field in the net room of Hunan Soil and Fertilizer Research Institute. The experiment included four cropping models: milk vetch-double cropping rice, ryegrass-double cropping rice, rape-double cropping rice, winter fallow-double cropping rice.

In 2013, the hybrid rice Lingliangyou 211 was selected as the early rice variety. The hybrid rice was sowed on March 30 with a sowing quantity of 2.5 kg per 667 m². The seedlings were raised in soft discs. The seedlings were thrown on April 28 with a density of 20000 plants per 667 m². Before throwing, the experimental field was subjected to rotary tillage. At the same time, the winter crop straw was turned over and returned to the field. 30 kg of 40% compound fertilizer (20-8-12) was applied per 667 m² as base fertilizer. On April 30, a pre-emergence herbicide was mixed and 7.5 kg of urea and 5 kg of potassium fertilizer were applied per 667 m². Water management was performed in a moistening irrigation mode, and Daoteng, triazophos, imidacloprid, abamectin, isoprothiolane and other chemicals were used to control diseases and pests twice, and the early rice was harvested on July 12.

In 2013, the late rice variety Fengyuanyou 299 was selected as the hybrid rice. The hybrid rice was sowed on June 20 with a sowing quantity of 2.0 kg per 667 m². The seedlings were raised in soft discs. No-tillage throwing was carried out on July 20 with a density of 18000 plants per 667 m². Before throwing, the early rice straw was used for mulching and returned to the field, 250 ml of gramoxone was used per 667 m², 1 kg of potassium chloride was added, 50 kg of water was added and coarse spray was performed at 5 o'clock in the afternoon, and irrigation was performed after 24 h to submerge rice stubble for stubble cleaning, weeding and soil conditioning. At the same time, 35 kg of 40% compound fertilizer (20-8-12) was applied per 667 m² as base fertilizer, a pre-emergence herbicide was mixed on July 25, 10 kg of urea and 7.5 kg of potash fertilizer were applied per 667 m². Water management was performed in a moistening irrigation mode, and Daoteng, imidacloprid, abamectin, isoprothiolane and other chemicals were used to control diseases and pests three times, and the late rice was harvested on October 16. The late rice straw did not return to the field, aired and collected as a biogas fermentation raw material and cow and sheep feed.

Winter crops such as milk vetch, ryegrass and rape were sowed by no-tillage direct seeding on October 10, 2012. The variety of the milk vetch was Ningbo bridge, the variety of the ryegrass was “ultra-high Italian ryegrass”, and the variety of the rape was “Fengyou 728”. The sowing quantity of the milk vetch was 2.5 kg per 667 m², the sowing quantity of the ryegrass was 1.5 kg per 667 m², and the sowing quantity of the rape was 0.3 kg per 667 m². After sowing, ditches, glyphs and surrounding ditches are dug, 20-30 ml of “haloxyfop” herbicide was used per 667 m² in the 3-5-leaf stage of weeds, 15-30 L of water was added, and the herbicide was used to remove weeds; after the late rice was harvested, 10 kg of urea and 25 kg of calcium

2020100016 06 Jan 2020 superphosphate were applied per 667 m² as base fertilizer, 8 kg of urea was applied per 667 m²on the first ten days of November and the last ten days of February, 2013 respectively, the milk vetch and the ryegrass were harvested on April 10, 2013 and the straw was all turned over and returned to the field, and after the rapeseeds were harvested on April 28, the straw was turned 5 over and returned to the field.

After 9 years of long-term study on different cropping models, soil nutrients, heavy metal Cd and crop yield in rice fields have shown certain differences. As can be seen from Table 1, Table 2 and FIG. 1, compared with the winter fallow-double cropping rice model, the soil organic carbon in three models of milk vetch-double cropping rice, ryegrass-double cropping 10 rice and rape-double cropping rice increased by 1.1, 0.9 and 0.8 g/kg, respectively, with a growing rate of 8.5%, 7.0% and 6.2%, respectively; available phosphorus increased by 6.5, 4.3 and 3.7 mg/kg respectively, with a growing rate of 21.8%, 14.4% and 12.4% respectively; and rapidly available potassium increased by 9.5, 2.4 and 5.2 mg/kg respectively, with a growth rate of 17.9%, 4.5% and 9.8% respectively. Available nitrogen in the two models of milk 15 vetch-double cropping rice and ryegrass-double cropping rice increased by 13.1 and 14.9 mg/kg respectively, with a growing rate of 8.5% and 9.7%, respectively, while the available nitrogen in the rape-double cropping rice model decreased by 6.4mg/kg, with a drop rate of 4.2%.

The two models of milk vetch-double cropping rice and rape-double cropping rice significantly reduced the content of heavy metal Cd in soil, with a drop rate of 17.3% and 11.7% 20 respectively. Although the content of heavy metal Cd in ryegrass-double cropping rice model increased by 4.9%, there was no significant difference.

The milk vetch-double cropping rice model had a milk vetch yield of 2818.3 kg per 667 m², an early rice yield of 538.9 kg per 667 m² and a late rice yield of 450.7 kg per 667 m², and the early rice yield and the late rice yield increased by 16.5% and 3.4% respectively compared with 25 those of the winter fallow model. The ryegrass-double cropping rice model had a ryegrass yield of 1747.6 kg per 667 m², an early rice yield of 542.4 kg per 667 m² and a late rice yield of 463.7 kg per 667 m², and the early rice yield and the late rice yield increased by 17.2% and 6.4% respectively compared with those of the winter fallow model. The rape-double cropping rice model had a rape yield of 160.9 kg per 667 m², an early rice yield of 503.9 kg per 667 m² and a 30 late rice yield of 483.1 kg per 667 m², and the early rice yield and the late rice yield increased by 8.9% and 10.9% respectively compared with those of the winter fallow model.

The above research shows when milk vetch, ryegrass, rape and other crops are cultivated in double cropping rice fields in winter, through rice field-upland field rotation and by combining the early rice straw and winter crop straw returning to the field, compared with when the winter 35 fallow model is adopted, the soil organic carbon content and soil nutrients are increased, the content of heavy metal Cd in the soil is also reduced, and the grain yield is increased.

Table 1 Effects of different cropping models on soil nutrient content

Cropping model	Organic carbon <g/kg)	Available nitrogen (fllg/kg)	Available phosphorus (mg/kg)	Rapidly available potassium (ing/kg )
Winter fallow· double cropping rice	12.9	153. 6	29.8	53. 2
Milk vetch-double cropping rice	14.0	166. 7	36. 3	62.7
Ryegrass-double cropping rice	13.8	168. o	34. 1	55. 6
Rape-double cropping rice	13.7	147.2	33. 5	58.4

Table 2 Crop yields under different cropping models

	Winter crop	Early rice	Late rice
‘hji uppiiic; mouci
	Yield	Yield	Growth rate	Yield	Growth rate
(kg per 667 m2)	(kg per 667 m2)	(%)	(kg per 667 m2)	(%)
Winter fallow-double cropping rice /	462. 7		435. 7	/
(ck)
Milk vetch-double cropping rice	2818.3	538. 9	16.5	450. 7	3. 4
Ryegrass-double cropping rice	1717. 6	542. 4	17.2	463. 7	6. 4
Rape-double cropping rice	160.9	503. 9	8.9	483. 1	10. 9

Embodiment 2

From 2005 to 2013, a long-term positioning study on different tillage methods and straw returning to the field was conducted in Tian’e Village, Huilongpu Town, Ningxiang County, Hunan Province. The experiment consisted of four treatments, namely, early rice and late rice double cropping no-tillage with straw mulching and returning to the field (NTS), early rice and late rice double cropping turning over with straw turning over and returning to the field (CTS), 15 early rice and late rice double cropping turning over without returning straw to the field (CT) and early rice and late rice double cropping rotary tillage with straw turning over and returning to the field (RTS), and the treatments were repeated 3 times, with a plot area of 66.7 m². The experiment was conducted under moistening irrigation and quantitative fertilization. In 2013, the early rice variety was Xiangzaoxian 45 and the late rice variety was Xiangwanxian 13.

Its field management was basically the same as that of the winter fallow-double cropping rice model in Embodiment 1.

Soil organic matter has a strong function of water and fertilizer conservation and is an important index to measure soil fertility. As can be seen from FIG. 2, under the conditions of long-term rotary tillage (RTS) and long-term turning over (CTS), returning straw to the field increased the content of organic matter in soil, which increased by 10.58 g/kg and 4.18 g/kg respectively compared with the long-term tillage without returning straw to the field (CT). In long-term no-tillage (NTS), since straw mulches the surface of the rice field, aerobic decomposition is performed, the nutrient decomposition speed is fast, the accumulation of organic matter is less, and the content of the organic matter was reduced by 6.03 g/kg compared with that of the long-term tillage without returning straw to the field (CT).

The soil nutrient content and soil cation exchange capacity are important indicators to measure the nutrient preserving capability of soil. The higher the soil nutrient content is, the greater the soil cation exchange capacity is, and the greater the nutrient preserving capability of soil is. From Table 3, it can be seen that RTS is the highest in soil nutrient content and soil cation exchange capacity, followed by CTS, CT No.3 and NTS the lowest. This shows that long-term rotary tillage with straw returning to the field has the highest soil nutrient content and soil cation exchange capacity, the strongest soil nutrient preserving capacity, and the long-term no-tillage has a poorer situation.

Table 3 Effects of different tillage methods and straw returning to the field on soil nutrient contents mg/kg, cmol/kg

Treatment	Available nitrogen	Available phosphorus	Slowly available potassium	Rapidly available potassium	Cation exchange capacity
CT	192.4	6. 12	116.5	40.0	14. 1
NTS	157.6	3. 55	106.3	30.0	12.6
CTS	209. 5	7.40	125. 1	44. 0	14. 7
RTS	209. 3	7. 85	127.5	48.0	15.9

From FIG. 3, it can be seen that long-term rotary tillage with straw returning to the field (RTS) and long-term turning over with straw returning to the field (CTS) aggravated heavy metal Cd pollution to the soil. Compared with long-term rotary tillage with straw returning to the field (CT), the content of Cd in soil increased by 0.083 and 0.006 mg/kg respectively, with a growth rate of 23.1% and 1.7% respectively, while the soil heavy metal Cd in long-term no-tillage with straw returning to the field (NTS) decreased by 0.023 mg/kg, with a drop rate of

6.4%.

From Table 4, it can be seen that the content of heavy metal Cd in rice under long-term tillage without returning straw to the field (CT) was the lowest, the content of heavy metal Cd in rice under long-term rotary tillage with straw returning to the field (RTS) was significantly higher than that under other treatments, and the content of heavy metal Cd in roots under long-term no-tillage with straw returning to the field (NTS) was significantly higher than that under other treatments. From the comparison of contents of heavy metal Cd in different parts of rice plants, it was shown as root > straw > rice. However, due to the different biomass in different parts, it was shown as straw > rice > root. Therefore, the content of heavy metal Cd absorbed in different parts of unit area was shown to be significantly higher in straw than in root, and was significantly higher in root than in rice.

Table 4 Effects of different tillage methods and straw returning to the field on heavy metal Cd in different parts of late rice

Treatment	Relative content of Cd (mg/kg)	Biomass (kg per 667 m2)	Total content of Cd in unit area (mg per 667 m2)
Rice	Straw	Root	Rice	Straw	Root	Rice	Straw	Root
CT	0. 53	7.28	7.44	350. 91	713. 79	109. 83	187. 04	5196.39	817. 63
NTS	0. 63	7. 99	9. 96	409. 46	701.26	100. 67	256. 32	5603. 76	1002.71
CTS	0. 64	6. 60	7. 69	402. 72	850. 67	107. 69	257.54	5617.82	827. 60
RTS	0.85	6. 35	7. 65	391.78	903. 39	114.24	333.01	5736. 99	873. 76

It can be seen from Table 5 that according to the total content of Cd absorbed by straw per unit area was 5603.76-5736.99 mg per 667 m², and the content of Cd in soil was 0.336-0.442 mg/kg. Calculated on a basis of 150000 kg of soil per 667 m², all Cd in the soil can be absorbed theoretically by performing straw absorption 9-11.6 times. That is, if the straw is subjected to centralized treatment without returning to the field, all Cd in soil can be eliminated by performing straw recovery 9-11.6 times.

Table 5 Comparison of contents of theoretically reduced heavy metal Cd in straw under different tillage methods

2020100016 06 Jan 2020

Treatment	Content of Cd in soil	Total content of Cd in soil	Total amount of Cd in straw	Number of times required for theoretically eliminating Cd
(rag/kg)	(mg per 667 m2)	(mg per 667 m2)	(Times)
CT	0.359	53850	5196. 39	10. I
NTS	0.336	501()0	5603. 76	9. 0
CTS	0.365	54750	5617. 82	9. 7
RTS	0. 142	66300	5736. 99	11.6

It can be seen from Table 6 that the early rice yield under CTS was the highest and was 393.6 kg per 667 m², with an increase of 38.9, 24 and 20 kg per 667 m² compared with those under NTS, CT and RTS respectively, and there was no significant difference between treatments. The late rice yield under NTS was the highest and was 409.1 kg per 667 m²; there was no significant difference between yields under NTS, CTS and RTS, the late rice yield under CT was the lowest and was 351.3kg per 667 m², which was significantly lower than those under NTS, CTS and RTS. The annual yield was highest under CTS, reaching 796.1 kg per 667 m²; there was no significant difference between the yields under CTS, NTS and RTS, and the annual 10 yield under CT was the lowest, reaching 720.9 kg per 667 m², significantly lower than those under NTS, CTS and RTS. It showed that returning straw to the field significantly increased the annual rice yield, especially the late rice yield. Under the condition of returning straw to the field, different tillage methods had certain influence on the rice yield, but the difference was not significant, which was showed as CTS > RTS > NTS.

Table 6 Effect of different tillage methods and returning straw to the field on rice yield Unit: kg

Treatment	Early rice	Late rice	Annual
CT	369. 6 + 14. 5a	351. 3 ±8. Ob	720. 9± 11. Sb
NTS	354. 7 ±16. 7a	409. 1 ± 11. la	763. 8±20.9ab
CTS	393. 6 ±28. la	402. 4 ±16. 0a	796. l±23.9a
RTS	373. 6 ±39. 6a	391. 3 ±12. 4a	764. 9 ±27. 4ab

The above research shows that long-term rotary tillage and long-term turning over with straw returning to the field in double cropping rice fields can increase the content of organic matter in soil and enhance the soil nutrient sustaining capacity, but at the same time it also increases the pollution of heavy metal Cd in soil. Although long-term no-tillage with straw mulching and returning to the field and long-term turning over without returning straw to the field reduce the pollution of heavy metal Cd in soil, the content of organic matter in soil is also reduced, the soil nutrient sustaining capacity is reduced, and the annual grain yield is also reduced. This shows that there are some disadvantages in long-term use of a single tillage method with long-term straw returning to the field or long-term straw not returning to the field. It is necessary to adopt the rotational tillage combining turning over, rotary tillage and no-tillage, and a method of returning of an appropriate amount of straw to the field or rotational returning of early rice straw and late rice straw, so that the content of organic matter in soil can be increased, the soil nutrient sustaining capacity is enhanced, the content of Cd in soil can be reduced, the pollution of heavy metal Cd in soil is reduced, and finally sustainable, balanced and safe production of rice is achieved.

In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. The term “comprises” and its variations, such as “comprising” and “comprised of’ is used throughout in an inclusive sense and not to the exclusion of any additional features.

It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect.

The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted by those skilled in the art.

Claims

Claims

2020100016 06 Jan 2020

1. A method for three-round cultivation of a double cropping rice field, wherein with annual cultivation of triple-cropping crops as a cycle, each cycle comprises the following steps:

step a: raising early rice seedlings in the last ten days of March, performing rotary tillage of a rice field in the middle ten days and last ten days of April, and then manually throwing or mechanical transplanting the raised early rice seedlings;

step b: raising late rice seedlings in the middle ten days and last ten days of June, mechanically harvesting the early rice in the first ten days and middle ten days of July, reserving low stubble of the early rice, using all the harvested rice for mulching and returning to the field, performing stubble cleaning, weeding and soil conditioning, manually throwing or mechanical transplanting the raised late rice seedlings with no tillage, and keeping a wet state of the rice field soil;

step c: mechanically harvesting the late rice in middle ten day of October, reserving low stubble of the late rice, collecting straw from the field, and removing the straw from the rice field for centralized treatment; and step d: directly seeding winter crops 7-10 days before harvesting the late rice in step c with no tillage, harvesting the winter crops in April of the next year, and after the harvesting, returning stalks of the winter crops to the field through rotary tillage and turning over.
2. The method for three-round cultivation of a double cropping rice field according to claim 1, wherein in step a, the early rice seedlings are raised by using a soft disc in the last ten days of March, the sowing quantity of hybrid early rice is 2.5-3.0 kg per 667 m², the sowing quantity of conventional early rice is 4-5 kg per 667 m², the rice seedling raising in the soft disc is centralized rice seedling raising, the seedling age is controlled at 25-30 days, the early rice is thrown in the middle ten days of April, the throwing density of the hybrid rice is 18000-20000 plants per 667 m², and the throwing density of the conventional rice is 20000-22000 plants per 667 m²; before harrowing for the last time, 30 kg of 40% compound fertilizer (20-8-12) is applied per 667 m² as base fertilizer, and after the field is flattened, the early rice is thrown; after the early rice seedlings turn green, the field is irrigated to make the water surface higher than the field surface by no more than 5 cm, 5-7.5 kg of urea and 5 kg of potassium oxide are used per 667 m² and applied by mixing with a pre-emergence herbicide; after the application, a water layer is maintained for 5-7 days, and the field naturally dries.
3. The method for three-round cultivation of a double cropping rice field according to claim 1, wherein in step b, the late rice is sown on June 15-23, the seedlings are raised using a plastic

2020100016 06 Jan 2020 soft disc, the sowing quantity of the hybrid late rice is 1.5-2.0 kg per 667 m², the sowing quantity of the conventional late rice is 3-4 kg per 667 m², and uniconazole is sprayed on the hybrid late rice in a two-leaf stage to control the excessive growth of the late rice seedlings; the late rice seedlings are thrown on July 15-23; the throwing density of the hybrid late rice seedlings is 18000 plants per 667 m², and the throwing density of the conventional rice is 20000 plants per 667 m²; 35 kg of 40% compound fertilizer (20-8-12) is applied per 667 m² as base fertilizer; after returning to the field, 250 ml of gramoxone is used per 667 m², 1 kg of potassium chloride or 200 g of deep tillage-free soil conditioner is added, and 50 kg of water is added, and the mixture is sprayed to carry out stubble cleaning, weeding and soil conditioning; and after the late rice seedlings turn green, 7.5-10 kg of urea and 7.5-10 kg potassium oxide are used as topdressing per 667 m², and are mixed with the pre-emergence herbicide for application.
4. The method for three-round cultivation of a double cropping rice field according to claim 1, wherein in step c, the straw collected from the field is no longer returned to the field.
5. The method for three-round cultivation of a double cropping rice field according to claim 1, wherein in step d, the winter crops mainly refer to milk vetch, ryegrass or rape and are sown in a no-tillage direct seeding mode in the first ten days and middle ten days of October, the seeding quantity of the milk vetch is 2.5 kg per 667 m², the seeding quantity of the ryegrass is 1.5 kg per 667 m², and the seeding quantity of the rape is 0.3 kg per 667 m²; after the seeding, the rice field is kept dry, and weeds are removed.