Drought is a non-biological factor that prevails and severely restricts corn production. In order to reduce the impact of drought, one of the commonly used foreign countries is to regulate the cultivation of corn; the second is to improve the growth environment of corn. Looking back at the progress made in corn breeding, it can be found that the purpose of drought resistance was to prevent drought by initially planting early-mature corn. In addition, some cultivation measures are adopted to mitigate the effects of drought, such as selecting suitable sowing time to reduce the possibility of encountering drought during growth; decreasing density and reducing the amount of tillage to increase the available water of the crop. Other cultivation measures such as maintaining soil fertility, controlling weeds and diseases also play an important role in improving drought resistance of corn. First, choose to escape the drought and high drought resistance varieties in those areas due to rainfall, cold or crop rotation and other factors that make the corn's growth cycle has become very limited, the selection of suitable varieties is very important. A precocious species is much more likely to survive a late-stage drought than a late-maturing variety. However, precociousness is only an important condition for adapting to arid environment. In general, the yield potential of early maturing varieties is small, and the yield is still low in rainy years. In addition, the early maturing of a variety does not mean it can resist the drought encountered during the growth. Moreover, the difference in the amount of available water in the soil in tropical arid regions is also significant. Therefore, a variety that has excellent performance in different water conditions, different fields and different years is a stable and high-yield variety. Crop breeders have accumulated a lot of knowledge about improving crop drought resistance. Most drought-resistant corn breeding projects have to be improved and adjusted for quite some time. For example, CIMMYT began its drought-resistant breeding in 1975 with a tropical lowland corn group Tuxpeno Crema I (now renamed Tuxpeno Sequia). By the mid-1980s, it had expanded to five tropical lowland corn groups; the breeding of tropical highland corn groups began in the early 90s; in 1997, the drought-resistant breeding of tropical mid-latitude corn germplasm began in South and East Africa. Second, the appropriate sowing date, reasonable density, and the method of cultivation according to local conditions, sowing date, is an important necessary consideration for the yield of corn in arid regions. Sowing at suitable soil moisture and temperature, the germination and emergence rate increased significantly. In those areas that are restricted by the rainy season, suitable early sowing may reduce the impact of late flooding by drought. Late sowing due to factors such as labor and land preparation often results in excessive plant height, easy lodging, and relatively few grains per plant. Both these factors and the increase in the probability of occurrence of drought during the late growth period can lead to serious losses in production. Other cultural measures to reduce the effects of drought are to reduce the planting density of corn to ensure that a minimum amount of water is needed to produce an effective ear. In areas where the average annual rainfall in South Africa is 500-600 mm, more mature maize varieties are usually planted at a row spacing of 2 m and a density of 10,000 plants per hectare. Farmers often choose crops that can produce high yields in rain-saturated years. It is not very important whether they are resistant to drought. Similar methods can also be used in relation to the required nutrients for each strain. For example, in areas with low soil fertility, plant density can also be reduced to ensure the minimum nutrient requirement per plant. Adjust farming methods. Most of the reduction-tilling trials conducted on farms in South Africa demonstrated that the same yield can be obtained after two or three years of de-farming compared with traditional bulldozer plows, and that the livestock used and the time spent are relatively small. Can sow early. Another way of farming is to plow the ground on a harvest or in winter, which saves the time and energy of the site before the next growing season to achieve early planting. 3. Sufficient water interception and preservation of dry areas Due to the lack of irrigation facilities, other measures are taken to retain the rainfall, which are directly used for the growing period of maize. These include: farming, water collection and cover. 1. Tillage cultivation can increase soil water content and facilitate the early growth of crop roots, allowing them to obtain the moisture stored in the soil. Tillage can also control weed growth that competes with crops for moisture. However, different farming methods are adopted depending on the type of soil. For example, sandy soil in South Africa has almost no aggregate structure, it is very strong in drought, and it is easy to crust. Solid sub-layer soil makes it difficult for the plant's root system to penetrate downwards. For such soils, tillage is necessary, but farming should be minimized. Deep ploughing is conducive to the downward growth of the plant roots, increasing the depth of the root down the crop will increase the amount of available water. More than 90% of the moisture absorbed by a typical corn comes from moisture within 70 cm of the tillage layer. However, in semi-arid areas where farmland is used for livestock, their traditional grazing land can only reach a depth of 10-15 cm. Solid soils, rocks, and acid sub-layers all impede the deep rooting of the roots. This will lead to earlier and more severe droughts. 2. Water pooling can be pooled by reducing runoff or using different methods for runoff water, leaving it for the dry season. In the semi-arid area of ​​Bango, Kenya, corn and sorghum are irrigated along the mountain. In semi-arid regions of West Africa, the use of similar methods is very effective. 3. Coverage In semi-arid areas, 50% of the total evapotranspiration is lost from the surface. This value is higher in the early stages of crop growth. Covers can act to reduce evaporation of water and lower surface temperatures. In tropical areas with occasional concentrated rainfall, the main role of the cover is to reduce runoff, increase infiltration, and, secondly, reduce soil loss. In semi-arid regions of western Mexico, crop residue cover can significantly increase corn yield, significantly increasing soil moisture capacity compared to traditionally cultivated fields. A series of tests conducted on a farm field with an average yield of 2 tons per hectare in a semi-arid area of ​​Jalisco, Mexico, showed no-tillage, chemical control of weeds and fields using cover and two rounds of cultivation and chemical control. Compared with the grass field, the soil moisture content increased by 65% ​​and the grain yield increased by 100%. Fourth, increase water use efficiency Drought and other pressures such as diseases, weeds and intercropping crops with the crop's water competition, soil acidification and low fertilizer and other joint effects to affect crop growth. The incidence of leaf and panicle diseases in the general drought season is relatively low. Weeds that compete with crops for available moisture often lead to more severe drought and prolonged periods of time. In areas of semi-arid sandy soil where cattle are used for farmland, weeds can be effectively and economically controlled through bulldozer plows, and soil moisture can also be significantly maintained. Although intercropping crops will also compete with corn for available water and reduce corn production, they will reduce the economic losses caused by drought during the sensitive period of maize. In many dry corn producing areas, the most important cultivation measure is the management of soil fertility. In non-temperate corn producing areas, it is generally accepted that drought and low fertilizer are the most important factors limiting corn production.
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