Variation And Limiting Factors Of Yield Gaps And Nitrogen Efficiency Gaps Of Winter Wheat And Summer Maize

Closing the yield gaps and nitrogen efficiency gaps is an important approach to achieve high yield and high resource use efficiency?DH?in a large scale.And the premise of it it's to identify the variation of yield gaps and nitrogen efficiency gaps in smallholder farmers of winter wheat and summer maize.Based on the data from a series of farm surveys in Xushui County,Hebei Province from 2012 to 2016,this research first analyzed the variation of yields gap and nitrogen efficiency gaps of winter wheat.Secondly,we explored which management practices and soil nutrient contents in relation to the variation.Thirdly,we used boundary line analysis to identify the relevant yield loss factors,to explore possible interactions and to quantify their contribution to the yield gap.A DH system was designed based on the analysis and tested in farmers'fields.The main results were as follows:1.There existed temporal-spatial variation of yield gaps of winter wheat and summer maize.The wheat yield varied stronger in the same year than in different years for the coefficient variation of wheat yield in the same year changed in the range of 5.9%-13.8%,less than 15.0%in different years.The yield gap in same year varied from 889-1998 kg·hm^-2,the total yield gap was 1707 kg·hm^-2.The average PFP_N variation range of farmers was 25.5 to 36.5 kg·kg^-1.The PFP_N coefficient variation range was 17.6%-33.9%,less than the annual PFP_N stability index 13.1%.PFP_N was more unstable than yield.The proportion of farmers who got high yield and high nitrogen efficiency in 2012-2016 years was below 22.2%.The ratio of the same farmers to high yield or high efficiency for three consecutive years was 18.2%and 4.5%,respectively.2.The summer maize yield varied stronger in the same year than in different years for the coefficient variation of yield in the same year changes in the range of 8.2%-15.5%,less than 16.8%in different years.The yield gap varied from 1473.4-3481.8 kg·hm^-2 and the total yield gap was 3690.9 kg·hm^-2.The PFP_N variation range of maize was 21.4-69.3 kg·kg^-1.The PFP_N coefficient variation range was 20.3%-41.5%,and the annual PFP_N stability index was 33.2%.The inter-annual efficiency gap was 112.5 kg·kg^-1.Compared to crop yield,the PFP_N varied stronger.The proportion of farmers who got low yield and low nitrogen efficiency in 2012-2016 years was 66.9%.For the PFPN,72%of total fields were unstable,for the summer maize yield,66%of total fields were unstable.The ratio of the same farmers to high yield or high efficiency for three consecutive years was 0%and 6.3%,respectively.3.The variation of yield gaps and nitrogen efficiency gaps was closely related to variation of management factors and soil factors.And the sowing,sowing date,nitrogen applications were top three limiting factors to wheat yield gap.Density is the most important factor affecting the production of summer maize.4.From the point of yield component,the spikes per hectare were the most important component to crop yield.Boundary line analysis showed that seeding date was the most limiting factor to spikes per hectare of winter wheat with highest contribution rate?26.7%?,followed by basal N input?22.1%?,seeding rate?14.5%?.The harvest density of summer maize was decided by sowing rate.5.The results of farm test of DH system were showed as follows.The average wheat yield had no significant difference among improved practices and nitrogen precision management?IP+N?treatment,improved practices?IP?treatment and farmer practices?FP?treatment.The average PFPN of wheat had significant difference among three treatments;IP treatment increased PFP_N by 20.9%,and IP+N treatment increased PFP_N by 60.6%,compared to FP treatment.The results of farm test of summer maize were showed below,IP+N treatment increased summer maize yield by 32%.The average PFP_N of summer maize of IP+N treatment increased PFP_N by 32.3%compared to FP treatment.In conclusion,there existed a wide variation of yield gaps and nitrogen efficiency gaps in smallholder farmers of winter wheat and summer maize,and the variation strongly linked to farmers'managements and soil condition.The DH system based on agronomy diagnoses could increase grain yield and nitrogen use efficiency,and it's an important approach to achieve high yield and high resource use efficiency in a large scale.