| Nitrogen fertilizer plays an important role in grain production in China.However,low nitrogen input driven by green agriculture has become an important measure for agricultural sustainable development.Grain-vegetable rotation is an important and efficient planting mode in the northern two-cropping area,and Guanzhong Plain is a typical two-cropping area in the north.The garlic-maize rotation system has long-term problems of improper fertilization and lack of annual coordination.Therefore,this study conducted two consecutive years of combined trials of different nitrogen application rates in garlic and maize in Yangling,Shaanxi Province from 2019 to 2021.Two nitrogen levels were set in garlic season:conventional nitrogen application(G1,300 kg hm-2)and nitrogen reduction by 20%(G2,240 kg hm-2).Three nitrogen levels were set in maize season:conventional nitrogen application rate(M1,220 kg hm-2),nitrogen reduction by 20%(M2,176 kg hm-2)and nitrogen reduction by 40%(M3,132 kg hm-2).The effects of annual nitrogen fertilization on crop growth,photosynthetic characteristics,yield,nutrient absorption and utilization and economic benefits of garlic-maize rotation system were studied.The main research results and conclusions are as follows:（1）Regulation of annual nitrogen fertilizer on photosynthetic characteristics of garlic-maize rotation system.Co-ordination of nitrogen fertilizer in two seasons has a significant regulatory effect on the photosynthetic capacity of crops in the rotation system.With the decrease of fertilization level,SPAD and photosynthetic rate of crop leaves showed a gradual downward trend.Compared with G1,the SPAD,net photosynthetic rate,stomatal conductance and transpiration rate of garlic in G2 decreased by 7.1%,14.1%,29.8%,24.8%and 35.7%（P<0.05）.Fertilization of G2 in garlic season also reduced photosynthetic performance of maize.There was little difference in the effect of fertilization level in maize season on the photosynthetic performance of garlic.There was no significant difference in photosynthetic performance of maize at M2 and M1 levels in maize season under the condition of previous crop G1,and nitrogen reduction M3 significantly reduced the photosynthetic performance of maize.Nitrogen reduction M2 and M3 in maize season significantly decreased the photosynthetic performance of maize under G2 fertilization（P<0.05）.Among the nitrogen application combinations,G1M2 had no significant difference in the photosynthetic performance of garlic compared with the conventional G1M1 treatment.Compared with the conventional G1M1,the SPAD,net photosynthetic rate,stomatal conductance and transpiration rate of maize G1M2 at silking stage were even significantly increased by 6.1%,6.0%,10.3%and 12.6%（2020）.Fertilization combination of G1M2 reduced nitrogen fertilizer input while ensuring good chlorophyll status,stomatal opening and gas exchange of garlic and maize,promoting the accumulation of photosynthetic products and ensuring the growth and development of crops.（2）The effect of annual nitrogen fertilizer planning on crop growth in garlic-maize rotation system.Compared with G1,the growth of garlic and maize was slowed down by G2 in garlic season.The plant height,stem diameter,leaf area index and dry matter accumulation of garlic decreased by 16.8%,12.3%,16.0%and 17.7%,respectively,and that of maize decreased by4.8%,6.7%,14.3%and 12.0%,respectively.There was no significant difference in the effects of fertilization levels M1 and M2 on morphological indexes of garlic and maize in maize season,and nitrogen reduction M3 significantly slowed down the growth of crops.It shows that the fertilizer combination of garlic season G1 and maize season M2 can not only guarantee crop growth demand but also reduce fertilizer input.（3）Effect of annual nitrogen fertilizer on yield and nitrogen uptake of garlic-maize rotation system.Reasonable annual nitrogen fertilizer coordination can stabilize crop yield in rotation system.Compared with the conventional fertilization model G1M1,the garlic yield of G1M2was not significantly reduced,while the yield of other fertilization combinations decreased by3.2%-39.3%;at the same time,maize can make full use of nitrogen residue in the previous season,increase the number of grains per spike or 100-grain weight,and increase the yield by1.4%-4.8%in two years,while excessive nitrogen reduction in maize season will cause 1.2%-25.8%reduction in yield（P<0.05）.The total nitrogen accumulation of garlic and maize plants decreased with the decrease of fertilization.Compared with the fertilization level of G1 in garlic season,the total nitrogen accumulation of garlic in 2020 and 2021 decreased by 21.7%and 34.2%,and the total nitrogen accumulation of maize decreased by 3.5%and 6.6%,respectively（P<0.05）.The overall effect of fertilization level in maize season on the total nitrogen accumulation in garlic showed a trend of first increase and then decrease with the decrease of fertilization level.The total nitrogen accumulation in maize season gradually decreased with the decrease of fertilization level,and there was no significant difference between M2 and M1 under G1.G1M1 and G1M2had the highest nitrogen accumulation in garlic and maize in the two years.Reducing the amount of fertilizer can promote the transfer of nitrogen from leaves and stems to grains,and improve the nitrogen absorption and distribution ratio of grain harvest organs.（4）Effects of annual nitrogen integration on nitrogen use efficiency and economic benefits of garlic-maize rotation system.Nitrogen reduction in both seasons significantly affected crop nitrogen use efficiency.Compared with G1,G2 in garlic season decreased the nitrogen use efficiency as a whole,with the average significant reductions of 10.5%and 32.0%in garlic season and 9.4%and 18.4%in maize season（P<0.05）.Nitrogen use efficiency was higher in garlic season under M2fertilization level in maize season.The effect of nitrogen reduction in maize season on nitrogen use efficiency in maize season increased first and then decreased under G1 condition,and decreased gradually under G2 condition.Compared with conventional fertilization G1M1,the nitrogen use efficiency of garlic under G1M2 and G2M2 treatments increased by 14.8%and20.0%in 2020,and the nitrogen use efficiency of garlic under G1M1 and G1M2 treatments reached 53.34%and 51.71%in 2021.The nitrogen use efficiency of G1M2 in maize season was 47.64%and 62.99%in two years,respectively,which was 15.7%and 20.8%higher than that of G1M1 treatment（P<0.05）.Therefore,the fertilization mode of 300 kg hm-2 fertilization in garlic season and 20%nitrogen reduction in maize season(176 kg hm-2)can effectively improve the nitrogen use efficiency of rotation system and improve the utilization of farmland system resources.The net economic benefit of garlic in conventional fertilization mode was higher in two years,while the net economic benefit of maize in G1M2 treatment was not significantly different from that in conventional G1M1.The increase of income in two years was 3.1%and11.3%.The income of garlic in other nitrogen reduction modes decreased by 6.1%-55.7%,and that of maize decreased by 1.4%-22.7%.The annual net economic benefit of G1M1 was the highest,while that of G1M2 was not significantly reduced,indicating that a reasonable annual nitrogen fertilizer co-ordination can reduce input costs and ensure yield and economic benefits.In summary,the fertilization mode of conventional nitrogen application of 300 kg hm-2 in garlic season and appropriate nitrogen reduction of 20%(176 kg hm-2)in maize season can ensure the photosynthetic production capacity of crops and the growth and development of plants during the rotation cycle,promote the accumulation of nitrogen in garlic/grain,effectively improve the utilization rate of nitrogen fertilizer,reduce input while ensuring crop yield,and realize the fertilizer reduction and efficiency increase in the rotation system. |
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