| Fertilization has always been an important means to increase grain yield and improve grain quality,but unreasonable fertilization will not only cause fertilizer waste,but also bring huge pressure on the environment,and increase the possibility of crops suffering from diseases and pests.Different fertilizer levels will have different effects on crop planting patterns and production processes.Herbivores will also choose suitable plants and feeding sites according to plant morphology and chemical information,and may also have direct or indirect impact on the parasitic or predatory natural enemies of phytophagous insects.Wheat（Triticum aestivum L.）is one of the most important food crops in China.The damage of wheat aphid to wheat is the main reason of wheat yield reduction.This paper mainly explores the relationship between the occurrence of wheat aphid and the 3 levels of fertilizer,and investigates the impact of different levels of fertilizer application on the natural enemies of wheat aphids so as to seek the optimal conditions for the increase of wheat yields.The main results are as follows:1.Change of fertilizing levels in wheat fieldAt the tillering and heading stage of wheat,the content of available nitrogen,available phosphorus and available potassium in the soil of wheat planting area were measured under 3fertilizer levels（without fertilization,N-P-K:17-20-5,N-P-K:15-15-15）.The results showed that the content of soil nutrients in the heading stage of wheat was lower than that in the tillering stage:under the fertilizer levels of 1000 kg·hm-22 N-P-K ratio of 17-20-5,the content of available nitrogen,available phosphorus and available potassium decreased by 12.6%,32.4%and 55.2%respectively,under the fertilizer levels of 1000 kg·hm-22 N-P-K ratio of15-15-15,the content of available nitrogen,available phosphorus and available potassium decreased by 13.2%,41%and 62.5%respectively,under the condition of no fertilization,the content of available nitrogen,available phosphorus and available potassium decreased by17.8%,19.7%and 45.1%respectively.The decrease of available phosphorus and available potassium was the biggest when the ratio of N-P-K to 1000 kg·hm-22 was 15-15-15,while in non fertilization treatment,hydrolyzable nitrogen decreased the most.2.Effect of different fertilizing levels on wheat aphidIn the field experiment in 2019,One-way ANOVA showed that the two fertilization measures would significantly increase the occurrence of wheat aphid.At the peak time of wheat aphid occurrence,1000 kg·hm-22 N-P-K ratio of 15-15-15 will extremely significant increase the number of S.avenae alatae in wheat field,and significant increase the number of S.avenae apterae.It will also significantly increase the occurrence of R.padi alatae,but it has no significant impact on R.padi apterae.The ratio of N-P-K to 1000 kg·hm-22 was 17-20-5,which significantly increased the occurrence of S.avenae alatae and S.avenae apterae,but had no significant effect on the occurrence of R.padi alatae and R.padi apterae.From the perspective of annual occurrence,under the fertilizer levels of 1000 kg·hm-2N-P-K ratio of 15-15-15,the annual occurrence of S.avenae alatae and S.avenae apterae increased significantly,while the annual occurrence of R.padi alatae and R.padi apterae had no significant effect.1000 kg·hm-22 N-P-K ratio of 17-20-5 can significantly increase the annual occurrence of S.avenae alatae and S.avenae apterae,but had no significant effect on the annual occurrence of R.padi alatae and R.padi apterae.3.Effect of different fertilizing levels on natural enemies of wheat aphidThree fertilizer levels have no significant differences.When the ratio of 1000 kg·hm-2nitrogen,phosphorus and potassium is 15-15-15,the population of parasitoids could be significantly increased.The effect of N-P-K ratio of 1000 kg·hm-22 on the population number of parasitoids was not significant,and the higher potassium level could increase the population number of parasitoids.4.Effect of different fertilizing levels on wheat yieldThe yield of wheat can be increased by two fertilization approaches.The yield of wheat can be increased significantly by the fertilizer level of 17-20-5 with 1000 kg·hm-22 N-P-K ratio,and the yield of wheat can be increased by 19.5%;the fertilizer level of 15-15-15 with 1000kg·hm-22 N-P-K ratio has no significant effect on the yield of wheat,and the yield of wheat can be increased by 9.4%.The effect of fertilizer level of 17-20-5 in 1000 kg·hm-22 N-P-K ratio on wheat yield is higher than that of 15-15-15 in 1000 kg·hm-22 N-P-K ratio. |
