2 The causes of cold injury and late lodging in wheat in spring and its relationship with variety
2.1 Winter wheat freezing injury
2.1.1 genetic factors
The cold resistance of wheat cultivars is a comprehensive problem affected by genetic and panicle differentiation processes and environmental conditions. From a genetic point of view, the cold resistance of wheat is a quantitative trait controlled by multiple genes, with an additive effect, and the interaction between genotype and environment is relatively large. Generally, the winter cultivars have strong cold resistance, and they are semi-winter. Spring varieties have poor cold resistance. The heritability of cold resistance is low, ranging from 30.7% to 81.4%. There is a phenomenon of super-parent separation in hybrid offspring. For example, the cold resistance of wheat hybrid F1 tends to be pro-parent or is intermediate inheritance, and the cold resistance of F2 is continuously separated, and super-parent separation may occur. Since the cold resistance of wheat is higher in heredity in early generations and the heritability of offspring is lower, the cold resistance of varieties with strong cold resistance will be reduced after several generations of planting.
2.1.2 Spike differentiation process and weather factors
The process of young panicle differentiation in wheat directly affects its ability to resist cold. When growth cones begin to elongate and enter young panicle differentiation, tolerance to low temperature begins to decline, but the decline is not significant; when entering the dihedral phase, it will be significantly decreased, and the freezing rate will be extremely high after the rift stage, especially young. Spike length 5 ~ lOmm is most vulnerable to frost damage by infertility. In the spring of 2007, it was warmer and warmer, and the temperature was rising fast. On the basis of the pre-winter prosperous growth of some wheat fields, spring seasons also took place. The period of returning green, getting up and jointing was advanced 7-10 days, and the spike differentiation process was abnormally advanced. The ability to “pour the cold†significantly decreased, resulting in severe early spring frost damage and late frost frost damage on March 6 and April 3, which resulted in frozen leaves, young ears, spikelets, and stamens.
2.1.3 Cultivation Management
Reasons for the pre-winter and spring prosperous growth of wheat Before and during the winter, the temperatures are high. Before the temperature rises too fast in early spring, some wheat fields are planted too early (some crops are planted on September 23) and the sowing rate is too large (150-225 kg/hm2). ), resulting in prosperous wheat fields, early differentiation of young spikes, and reduced cold resistance. On March 6th and April 3rd, 2007, serious frost and frost weather occurred, which mainly caused damage to semi-winter semi-winter wheat that was sown prematurely, had too much sowing, and had too much fertilization. The normal wheat fields with suitable sowing date, proper seeding rate and reasonable fertilization are basically unharmed or very harmless. Prosperous and non-prosperous wheat fields have significant differences. In summary, the cold resistance of wheat varieties is constrained and affected by many factors. In addition to the strong cold resistance of the varieties themselves, the main factors are human factors and meteorological factors. The catastrophic late spring weather is inevitable, but artificial cultivation measures can be adopted to prevent severe weather and enhance the cold-resistance ability of varieties. There is a certain relationship between chilling injury and wheat cultivar in spring, but the main problem is not the variety, but the combination of prosperous growth caused by human factors, advance of growing period and severe weather. Practice has proved that the semi-wintering cultivars can effectively reduce the degree of frost damage in spring and even avoid freezing injury through proper sowing and proper control of fertilization. On the contrary, premature blind sowing of winter varieties will also lead to prosperous and ear differentiation and reduce their cold resistance. Therefore, the cold resistance of varieties cannot be evaluated by using early sowing and long-term seeding and frost damage caused by large fertilizers, large waters, and large sowing amounts.
2.2 Late wheat lodging
2.2.1 Fertility tolerance
The lodging resistance of wheat is an essential characteristic of the high-fertilizer varieties. Fertilization resistance is the response characteristic of wheat to fertilizers, especially nitrogen fertilizers, and lodging resistance is closely related to fertilizer resistance. The fertility of wheat is mainly related to nitrate reductase in the plant. Nitrate reductase is a rate-limiting enzyme and inducing enzyme. It plays a key role in nitrogen metabolism. Its activity is negatively correlated with the fertility of wheat. The stronger the vigor, the weaker the fertilizer, and the weaker the vigor, the stronger the fertility. Therefore, excessive application of nitrogen fertilizer, nitrate reductase activity and nitrogen metabolism in wheat plants increased, and the lodging resistance was reduced.
2.2.2 Stem traits
Wheat lodging resistance also has a complex relationship with other traits such as plant height, physical and physiological strength of the stem, its effect on stem base weight and stem base strength, crush resistance, toughness and elasticity, and root system The relationship between size and depth is large. The physical and physiological strength of stems is related to the thickness of stems and stems, the length of stems, the length of internodes, the coverage of sheaths, the number, shape, size, and arrangement of vascular bundles. In addition, the distribution and accumulation of photosynthetic products of the high-resistance-tolerant product species between stems and panicles are relatively balanced and reasonable.
2.2.3 Cultivation conditions and weather factors
From the perspective of cultivation, the relationship between lodging resistance, sowing rate, sowing date, fertilizing amount, and population size of the wheat is significant. For example, in 2006-2007, many wheat fields in Jining City were seriously prosperous due to cultivation reasons before winter and early spring. The number of panicles per unit and panicles per unit area was too large, the internodes of the base were too long, the culm walls became thinner, and the ability to withstand wind disasters decreased significantly in the later period. . From May 20 to 22, heavy winds and heavy rain continued to occur, and a large area of ​​lodging occurred. In short, the lodging resistance of wheat is a complex issue, which is directly related to internal factors such as fertility and culm characteristics of varieties, but also closely related to cultivation factors and meteorological factors. Variety lodging resistance has a certain limit, can exhibit lodging resistance under reasonable cultivation and normal weather conditions, but in poor cultivation and management (large fertilizer, large water, large sowing volume, blind early sowing, etc.) and bad weather ( Under strong winds and heavy rain conditions, it showed a reduction in lodging resistance and even loss of lodging resistance. Therefore, the lodging of large areas on some plots is not only a matter of breed but more importantly due to cultivation and meteorological factors.
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