High Temperature-preventing Cultivation Technology of Single-season Middle Rice for High Yield and High Quality in Jianghuai Area

Dewen ZHANG Wei ZHANG Youzun XU Wanlin WANG Dewei TAI Xiaozhong ZHANG Xueyuan SUN

Abstract   In recent years， with the global climate change， the frequency and duration of high temperature in summer and autumn have increased， causing high temperature heat damage to summer crops such as rice and maize. From the end of July to early August is the main period of high temperature occurrence， during which the daily average temperature above 30 ℃ is a high probability event， and even the highest temperature is above 38 ℃， while this period coincides with the booting-blooming-filling stage of the single-season middle rice in Jianghuai， especially the middle-season  indica  rice， so it often leads to the degradation of rice spikelets， pollen abortion， difficulty in pollen dispersion， and even difficulty in heading， resulting in a serious decline in the seed setting rate and poor filling of grains， which finally affect the yield and quality. Based on the goal of high-yielding high-quality rice cultivation， this paper proposed targeted technical measures for single-season middle rice from the aspects of planting time sequence optimization， selection of high-temperature-resistant varieties， population construction， fertilizer and water management technology， and how to compensate for the occurrence of unexpected disasters to promote plant growth. This study provides technical support for high-yielding high-quality stress-resistant and disaster-reducing rice cultivation technology.

Key words   Single-season middle rice; Jianghuai area; High temperature damage; High yield; Good quality; Cultivation technology

Rice is one of the main food crops in China. The rice planting area in China is about 30 million hm 2  [1] ， which accounts for 28.1% of the total area of food crops， but its output accounts for 40.6% of the total food production. With the acceleration of the industrialization process and the continuous increase of carbon  emissions  in the atmosphere， the "greenhouse effect" has been continuously strengthened， and the extreme high temperature and heat damage have occurred frequently， which has attracted widespread attention from all over the world. In all rice-producing regions of the world， high temperature and heat damage has become the main disaster factor affecting the normal growth of rice. Most of the rice-producing areas in Anhui Province belong to the middle and lower reaches of the Yangtze River， with a rice area of  1.76 million  hm 2. The Jianghuai area of Anhui Province is dominated by single-season  indica  rice， which is vulnerable to high temperature and heat damage. Especially in 2013 and 2017， the continuous high temperature and heat damage resulted in an area of about 200 000 hm 2-266 700 hm 2 of rice damage in Anhui Province  [2-4] . High temperature mainly affects the growth and development process of rice from two aspects： on the one hand， high temperature damages the flowering and fertilization process of rice. If the continuous high temperature above 35 ℃ occurs in the  booting  stage， flower organs of rice are not fully developed， and pollen is stunted， and has reduced vitality. During the heading and flowering stage， if the temperature is above 35 ℃， heat damage will occur， which will affect the elongation of loose pollen and pollen tubes， leading to the formation of empty shell grains that cannot be fertilized， resulting in a decrease in the seed setting rate， low 1 000-grain weight， or even no harvest. On the other hand， high temperature damages the grain filling process of rice， and also causes a significant decrease in 1 000-grain weight and rice quality  [5-8] . In order to deal with the serious negative impact of high temperature heat damage on rice production， this paper proposed technical solutions to ensure the high quality and high yield of Jianghuai rice under high temperature conditions through the selection of rice varieties and the improvement of cultivation measures.

Selection of Varieties and Fields 

Selection of varieties

Varieties with strong heat resistance are chosen. Varieties with different heat tolerance have obvious differences in the degree of disaster.  Indica  rice with  japonica  blood and varieties with Teyou and Xieyou series as the female parent and the 559 series as the male parent have relatively poor heat resistance and low seed setting rate. In years with high temperature heat damage， varieties with heat resistance coefficient greater than 0.7 and rice heat resistance above "average" are generally selected， such as Wandao 153 and Huiliangyou 985.

Selection of fields

The selection requires good water sources， matching canal systems， reasonable ditch layout， fertile soil， deep soil layer， timely water supply， good drainage and irrigation conditions， and certain water storage capacity， and the height difference of a field should not exceed 3 cm.

Seedling Raising and Sowing Methods 

Seedling raising method 

Target

Seedling quality： The seedlings are 25-28 d old， with a leaf age of 5-6 leaves. A single plant has 1-3 large tillers. The seedlings are sturdy， and have green and beautiful leaves. They are free of diseases and insects.

Selection of seedling fields

It is advisable to choose leeward sunny fields with convenient irrigation and drainage， soft soil， few weeds and high fertility. The soil is prepared in a dry mode and the bed is prepared in a dry mode as well. Leveling is performed with water to make the seedling bed flat at the surface and loose at the bottom. Good air permeability is conductive to root growth.

Preparation of seedbeds and fertilization

Enough base fertilizer is applied， including compound fertilizer （N∶ P∶ K=15∶ 15∶ 15） about 450 kg/hm 2 and decomposed farmyard manure or nutrient soil 7 500 kg/hm 2. After fertilization， ploughing is performed， and the fields are harrowed with water to make combined seedling fields.  Borders with a width of 1.5 m are made， and the furrows have a width of 25 cm and a depth of 20 cm. The collapsed borders are placed for 6 to 12 h for sowing. The seedling beds should be flat， soft at the surface and loose at the bottom， and have good air permeability. The furrows are deep and straight， with smooth drainage and irrigation. The ratio of seedling field to field is 1∶ 10 for large seedlings.

Soaking and pregermination

The seeds are soaked for 2 d before soaking. They are soaked with 500 times dilution of trichloroisocyanuric acid for 24-36 h， or 15 g of chlorothalonil is added to 9 kg of water to obtain a solution， which is used to soak 6 kg of rice seeds for 60 h， or the seeds are soaked with 1% lime water for prevention and control of bakanae disease. The seeds are soaked until the grains are transparent and rinsed until there is no odor， and they are pre-germinated. When the seeds break and show white roots， they are ready to be planted， or they could only be soaked and disinfected without pre-germination.

Seeding method 

Sowing

Seeds are sown in late April to early May. The heading date is arranged in mid-August， so that the rice heading period avoids high temperature heat damage. Specifically， 50-75 g of hybrid rice seeds is sown per square meter of net seedbed， and 15 kg of hybrid rice and 30 kg of conventional rice are sown per hectare in the field， respectively. When planting， the bed surface should be dry and not waterlogged， and the seeds should be sown quantitatively by border. Sowing is carried out first， followed by supplementation. The seeds are evenly dropped and lightly pressed to make them closely contact the slurry.

Seedling field management field

Water management： After  sowing，  the water in the walkway should be drained. On sunny days， there should be a certain amount of water in the furrows， and the surface of the seedling bed should be moist without excessive water. From the second leaf to the third leaf stage， wetting and shallow irrigation are combined. From the 3-leaf stage to transplanting， as the seedlings gradually grow， the transpiration of the leaf surface increases， and more water is required. Therefore， a shallow water layer should be kept in the seedling bed， without submerging the heart leaves.

Top dressing management： It is mainly performed in two times. The first is the "weaning fertilizer"， and the 3-leaf stage of rice is the "weaning stage". However， the protein nitrogen in rice seeds has been decomposed in the one leaf and one heart stage， and the temperature is low in spring and the fertilizer effect is slow， so it is recommended to apply the "weaning fertilizer" in the one leaf and one heart stage， and the dosage is generally 275-120 kg/hm 2. The second time is for the "transplanting fertilizer"， which is topdressed about a week before transplanting， and the general dosage is 45-75 kg/hm 2.

Control of diseases， insects and weeds： In the seedling stage， sheath blight and rice thrips are mainly controlled. Weeds are removed manually or with herbicides when there are weeds.

Field Planting 

Base fertilizer

The base fertilizer is applied before ploughing， and the surface fertilizer is applied after harrowing. For the base fertilizer，  15 000  kg of decomposed farmyard manure or 750 kg of cake fertilizer， 150 kg of urea， 600 kg of phosphorus fertilizer， and 112.5 kg of potassium chloride are applied per hectare.

Field preparation

After the previous crops such as rapeseed and wheat are harvested， dry ploughing should be done in time with a ploughing depth of 15 cm， and the fields are sun-dried for 3-4 d. Then， irrigation and harrowing are performed to evenly mix the soil and the fertilizer. The difference in the height of the field surface should not exceed 3 cm， and there are no exposed stubbles and weeds.

Transplanting

Depending on the growth period of varieties， transplanting is carried out from late May to early and mid-June. The transplanting is carried out with wide row and short space between plants. Specifically， the row spacing is 27.0-33.3 cm， and the plant spacing is 10.0-13.3 cm  [9] . 240 000 to 270 000 holes are planted per hectare， and the number of seedlings per hole depends on the fertility level， variety （combination） characteristics and quality of seedlings. For hybrid rice， 1-2 seedlings are planted per hole， and for conventional rice， 2-4 seedlings are planted. The seedlings should be transplanted shallowly， uniformly， steadily， and straightly. 1.2-1.5 million basic seedlings are planted per  hectare.  If seedlings cannot be transplanted in time， the basic seedlings will be adjusted as appropriate according to an increase of 150 000 seedlings for every 5 d of delay.

Dewen ZHANG  et al.  High Temperature-preventing Cultivation Technology of Single-season Middle Rice for High Yield and High Quality in Jianghuai Area

Field Management 

Target

The seedlings start to tiller within 5-7 d after planting， and reach full tillering within 13-15 d， and enough seedlings can be reached within 20-25 d. The ratio of the highest number of tillers to the number of panicles is 1∶ （1.2-1.3）. The rows are closed while the top is not closed at the full heading stage. A single stem has 4-5 green leaves， and the stalks are green and seeds are yellow when harvested.

Fertilizing amount

Fertilization principle for high temperature resistance： The excessive application of nitrogen fertilizer should be controlled while increasing the application of phosphorus and potassium fertilizers to improve the photosynthetic efficiency and transpiration rate of rice plants， reduce the temperature in paddy fields and slow down the heat damage of high temperature. For medium-fertility fields， the total amounts of pure nitrogen， phosphorus pentoxide and potassium oxide applied were 180-210，  75-90  and 165-195 kg/hm 2， respectively. In the nitrogen fertilizer， the base fertilizer accounts for 50%-60%， tiller fertilizer accounts for 20%， and panicle-grain fertilizer accounts for 20%-30%. The phosphate fertilizer is all used as the base fertilizer， and the ratio of base fertilizer to panicle-grain fertilizer in the potassium fertilizer is 6∶ 4  [10] .

Fertilizing method

4-5 d after transplanting， 75.0-112.5 kg of urea is applied as the tiller fertilizer per hectare. At the jointing stage， 60-75 kg of urea is applied per hectare （for medium-ear type varieties）. At the booting stage （when the young ears are 1-2 cm）， 75-90 kg of urea and 75 kg of potassium chloride are applied per hectare. Fertilizer-deficient fields can be sprayed with foliar fertilizers or growth regulators at the heading stage.

Water management

Plants are transplanted with shallow water， which is dried naturally 4-5 d after planting. Top dressing is carried out with the re-greening fertilizer， and weeding is performed in the fields， which are then dried for 2-3 d. After irrigation， a 2-3 cm of shallow water layer is kept in the fields to promote tillering. When the number of stems and tillers per hectare reaches 90% of the expected number of ears， the water is drained to roast the field in time， lightly， and the fields are roasted for several times. For the fields in which the plants grow vigorously after re-watering， the fields can be again subjected to drying， which is repeated until jointing. Irrigation is performed with deep water in the fields during the heading and flowering stages to help to reduce the temperature of the ear layer， so as to effectively reduce the degree of heat damage. Fields with suitable conditions can be irrigated by day  irrigation  and night drainage or with long-running water， in a mode of which the effect of disaster avoidance is better. Before and after， wetting and intermittent irrigation should be kept， and alternated dry and wet conditions are adopted until yellow and ripe. Water is cut off  7 d  before maturity  [11-12] .

Prevention and control of diseases and pests 

Prevention and control principle

The principle is prevention first and comprehensive prevention and treatment. Seeds are  sterilized  before sowing， and the control of diseases and pests should be strengthened in the seedling stage. It is necessary to  avoid  too much fertilizers， too many seedlings， lodging or remaining green when it is the time to become yellow and ripe. Series irrigation and long-term deep irrigation are strictly prohibited. Attention should be paid to the protection of natural enemies and elimination of field weeds. It is necessary to strengthen the monitoring and reporting of diseases and insects， implement appropriate agent use， and overall control. The two times of general prevention and control in mid-to-late July and mid-to-late with agents should be done well.

Disease control

The main diseases of middle-season rice are rice blast， bacterial blight， sheath blight and rice false smut. Rice blast is treated with 75% tricyclazole 900 g/hm 2 in the early stage of disease prevention and control. Sheath blight is controlled by spraying to the base of the stems with 20% Jinggangmycin 750  g/hm 2  mixed with 600 kg of water during the jointing-booting stage， and once again after 5-7 d. Bacterial blight is controlled by spraying with 20% bismerthiazol powder 2 250 g/hm 2 mixed with 600 kg of water. Rice smut disease is prevented by spraying with 20% triazolone EC 750 ml+20% jinggangmycin 600 g/hm 2 mixed with 900 kg of water 7 d before and at the beginning of the heading stage. In case of rainy and humid weather， the agent is sprayed once again during the full heading stage.

Pest control

According to the forecast， the best control periods of rice thrips， rice leaf rollers，  Chilo suppressalis  and  Tryporyza incertulas  are determined， and Bt， regent， bisultap and avermectin can be selected to control pests in the middle and later stages  [13] . According to the occurrence of rice planthoppers， 48% Lorsban EC 1 500 ml/hm 2 or 10% imidacloprid powder 230-450 g/ml is sprayed at the booting and heading stages of rice.

Weeding

A 5 cm of water layer is kept in the fields 4-5 d after transplanting， and 750 ml of mefenacet bensulfuron is sprayed per hectare or 1 500 ml of "Yelao" is mixed with soil and spread  evenly，  to control weeds in paddy fields.

Harvesting

After harvesting at the stage of yellow ripeness， the seeds should be air-dried in time. The grains should not be dried on the pavement such as gravel and asphalt roads， and exposure to the sun on cement sites should be avoided.

Dewen ZHANG  et al.  High Temperature-preventing Cultivation Technology of Single-season Middle Rice for High Yield and High Quality in Jianghuai Area

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 Editor： Yingzhi GUANG   Proofreader： Xinxiu ZHU