Effects of N application on nitrogen and potassium nutrition and stripe rust of wheat in an intercropping system

In order to provide a theoretical basis for rational fertilization to achieve disease control and yield increase of wheat, the effects of nitrogen (N) application levels and intercropping on the absorption and distribution of N and potassium (K) and the occurrence of stripe rust of wheat were studied. A field experiment with three N application rates-0 kg(N)·hm^-2 (N0), 90 kg(N)·hm^-2 (N1), 180 kg(N)·hm^-2 (N2)-and two planting patterns (wheat monocropping, and wheat and faba bean intercropping) were set up in Anning and Eshan, Yunnan Province to study the effect of N application rate and intercropping with faba bean on the content and distribution of N and K, and the incidence and disease index of wheat stripe rust. The results showed that wheat yeld was considerably increased by N application, especially in intercropping. Compared with monocropping, intercropping significantly increased wheat yield averagely by 31.9% (Anning) and 18.0% (Eshan). The yield advantage of wheat-faba bean intercropping was obvious and the land equivalent ratio (LER) was 1.20-1.37 (Anning) and 1.16-1.27 (Eshan) at the N0-N2 levels. However, the yield-increasing effect of intercropping was decreased with increase in the N application rate. N application not only increased the yield, but also aggravated the damage of wheat stripe rust, and therefore, the incidence and disease index were increased by 2.4%-30.0% and 5.6%-38.5% in Anning, and 6.4%-22.4% and 5.3%-43.2% in Eshan, respectively. Intercropping with faba bean presented a better control effect on wheat stripe rust than monocropping. The incidence and disease index of wheat stripe rust were reduced by 9.6%-22.0% and 23.7%-33.7% (Anning) and 29.5%-36.5% and 29.3%-39.6% (Eshan), respectively. The N content was increased by N application, which mainly accumulated in the leaves, accounting for 41.3%-47.4% (Anning) and 35.9%-44.1% (Eshan) of total N absorption. However, the N content was considerably reduced by 17.8%-21.8% (Anning) and 16.2%-16.9% (Eshan), whereas the K content was significantly increased by 22.6%-23.0% (Anning) and 16.2%-18.3% (Eshan), and thus the N/K ratio in the leaves was significantly reduced under intercropping system, compared with that under monocropping system. The correlation analysis showed that the incidence and disease index of wheat stripe rust were positively correlated with the plant N content and leaf N/K ratio, and negatively correlated with the K content. The N content in wheat plants and the N/K ratio in the leaves were increased by N application and thus, the occurrence of wheat stripe rust was aggravated. On the contrary, intercropping enhanced wheat resistance to stripe rust by increasing K content and reducing plant N content and N/K ratio in the leaves, and balancing N and K nutrients in wheat plants.