Relationships between nitrogen application rate soil nitrate-nitrogen, plant nitrogen concentration and wheat scab

【Objectives】 Scab has become one of the major diseases affecting yield and quality of wheat. An experiment was set up to study effect of nitrogen fertilization on wheat scab and to explore relations between nitrogen fertilizer and soil nitrogen, plant nitrogen concentration and wheat scab under different nitrogen levels. 【Methods】 A field experiment was conducted using 5 nitrogen rates (N 0, 120, 180, 240 and 360 kg/ha) and a multi-spike wheat cultivar YuMai49-198(YM49-198) and a large spike wheat cultivar ZhouMai16 (ZM16) in randomized blocked, and wheat scab was investigated by “wheat scab forecastingtechnical specifications”. 【Results】 The soil nitrate nitrogen contents and accumulation amounts in 0-90 cm soil layer are increased with the increase of N application rate. There are no significant differences in soil nitrate nitrogen contents at 0-30 cmand the accumulation amounts in 0-90 cm soil layerunder N0, N120 and N180, and the contents and amounts are significantly lower than those under N240 and N360 at the maturity. The morbidities and disease index(DI) of wheat scab are increased with the increase of N application rate, and there are significantly differences among different treatments. The morbidities and DIs of YM49-198 under the N treatments are higher than those under the N0 treatment by 29.5%-132.0% and 35.9%-225.2%, respectively, and those of ZM16 are 42.4%-161.8% and 41.7%-206.9%. The morbidities and DIs of the two wheat cultivars under N0, N120 and N180 are not significant different, and are significantly lower than those under N240 and N360. However, the disease of ZM16 is more serious since the morbidities and DIs are higher than those of YM49-198 by 7%-25% and 28.0%-63.6%, respectively. The scab morbidity and DI are positively correlated with soil nitrate content, and linearly correlated with nitrate-nitrogen accumulation in 0-90 cm. The stem sap nitrate concentrations at the booting, anthesis and filling stages, the total nitrogen contents at the jointing and anthesis stages have significant differences among the treatments, and are significantly and positively linear correlated with the scab morbidity and DI. 【Conclusions】 The soil nitrate nitrogen contents and accumulation amounts are increased with the increase of the N application rate. The soil residual nitrate is lower under conditions of nitrogen rate less than 180 kg/ha, and thus, the scab disease is lighter. The morbidity and DI of wheat scab are increased with the N application rate, which illustrates that higher nitrogen fertilizer will aggravate wheat scab disease at the jointing and anthesis stages. Therefore, to reducing the scab disease, appropriate nitrogen rate, soil nitrate and plant nitrogen concentration are needed during this period. Considering the residual nitrate in soil, the yield and scab, the appropriate nitrogen amount is N 180 kg/ha.