Impact Of Replacing Wheat Varieties And Varying Water And Nitrogen Inputs On Wheat Yield Formation And The Efficient Utilization Of Water And Nitrogen

The study focuses on northern China,where wheat is the most important food crop.Ensuring food security under limited water and nutrient supply is of great sig-nificance,and the increase in crop yield is largely attributed to genetic improvement and effective management practices,such as proper water and fertilizer inputs.None-theless,breeding water and fertilizer-efficient varieties and optimizing supporting cul-tivation measures remain key factors in stabilizing and improving wheat production.To achieve this goal,this study utilized eight representative wheat varieties from the Guanzhong area,dating back to the 1950s.Three irrigation levels were tested,includ-ing no irrigation（W0）,60 mm irrigation during the wintering period（W1）,and 60mm irrigation during both the wintering period and jointing period（W2）.Three nitrogen application levels were also assessed,ranging from N0(0 kg·hm^-2)to N1(120kg·hm^-2)and N2(240kg·hm^-2).The main findings are as follows:（1）Results showed that there was a decreasing trend in LAI（leaf area index）with the change of wheat varieties.The high-stem varieties from the 1950s and 1960s had the highest theoretical maximum value.With an increase in nitrogen application rates,LAI and its expansion rate also increased.However,the effect of irrigation amount on LAI was relatively small.The SPAD value of leaves increased with the increase of variety replacement and nitrogen application rate,with irrigation having little effect.Dry matter accumulation and accumulation rate also increased with an increase in variety replacement or water and nitrogen input.Overall,variety replace-ment and water and nitrogen input had a positive effect on wheat photosynthetic pro-duction.The study found that the effect of photosynthetic efficiency,represented by SPAD,was greater than that of photosynthetic area（LAI）on photosynthetic produc-tion.Under different water and nitrogen supply conditions,the photosynthetic pro-duction capacity of new wheat varieties was better.（2）Results showed that with an increase in variety replacement and nitrogen application rate,the distribution ratio of dry matter to reproductive organs and the harvest index both increased.Additionally,the amount of pre-anthesis dry matter translocation and post-anthesis dry matter accumulation increased with an increase in variety replacement or water and nitrogen input.The efficiency of pre-anthesis dry matter translocation also increased significantly with variety replacement,from16%-19%in the 1950s to 28%-32%in the 2020s.Furthermore,the proportion of post-anthesis dry matter accumulation to biomass increased with the increase of ni-trogen application.Interestingly,under the conditions of this study,the irrigation amount had little effect on the translocation and distribution of dry matter in wheat.（3）Previous studies on the interplay between water and nitrogen availability in wheat have often neglected variety differences.As per the yield analysis,different water and nitrogen treatments demonstrated a significant increasing trend in wheat yield with the rise of planting years（p<0.01）,and the yield increase rate under the W2N1 condition was the highest,reaching 635.04 kg·hm-2;conversely,the yield in-crease rate under the W1N0 condition was the lowest,at only 497.46 kg·hm^-2.The relative growth rate of the harvest index was 7.22%per decade,consistent with the wheat yield trend.In a two-year experiment,more than 90%of the GY was directly and indirectly explained by irrigation,nitrogen,variety,and yield components.The study examined how variety replacement and water and nitrogen input affected wheat yield components.Results showed that with an increase in variety replacement or wa-ter and nitrogen input,the yield components of wheat grains demonstrated a positive trend.The increase in spike number per unit area was the most significant contrib-uting factor to the increase in yield,followed by 1000-grain weight,while the contri-bution of grain number per spike was the smallest.On average,the increase in grain yield,spike number per unit area,grain number per spike,and 1000-grain weight with variety replacement under different water and nitrogen treatments were613kg·hm^-2·10a^-1(14.0%·10a^-1),229,000spike·hm^-2·10a^-1(6.2%·10a^-1),0.65grain·spike^-1·10a^-1(2.2%·10a^-1,and 1.84g·1000 grain^-1·10a^-1(4.8%·10a^-1),respectively.Among the three experimental factors,variety replacement contributed the most to the increase in grain yield,with path coefficients of 0.60 and 0.48 in the two experimental years,re-spectively.The contribution of nitrogen fertilizer application was the second-most substantial factor affecting yield,with path coefficients of 0.34 and 0.21 in the ex-perimental years,respectively,while the contribution of irrigation was the lowest,with path coefficients of 0.12 and 0.06 in the experimental years,respectively.（4）Five nitrogen utilization evaluation indexes,namely,nitrogen absorption efficiency（NUPE）,nitrogen utilization efficiency（NUTE）,nitrogen physiological utilization efficiency（PE）,nitrogen agronomic utilization efficiency（AE）,nitrogen partial productivity（PFP）,and two water utilization evaluation indexes,namely,grain yield water utilization efficiency（WUEgy）and biomass water utilization efficiency（WUEbm）,were used to develop a comprehensive evaluation index for the water and nitrogen utilization efficiency of eight varieties.These varieties were classified into water and nitrogen efficient,medium-efficient,and inefficient categories based on the years of cultivation.Specifically,the 2020s varieties were considered water and ni-trogen efficient,the 2000s and 2010s were considered water and nitrogen medi-um-efficient,while the 1950s,1960s,1970s,1980s,and 1990s were considered water and nitrogen inefficient.In addition,the study identified several agronomic indexes that were highly correlated with water and nitrogen use efficiency,including biomass,harvest index,plant height,and SPAD.（5）Both UAV multispectral data and ground measured data were collected and analyzed,and spectral parameters highly correlated with wheat growth were iden-tified.Using a regression analysis method,the study established an inversion model for biomass,SPAD,and other indexes related to water and nitrogen efficient utiliza-tion during jointing,booting,flowering,and filling stages of wheat.The model can be utilized for monitoring wheat growth and improving the acquisition efficiency of rel-evant agronomic indexes.Please act as a reviewer to adjust and polish the content while keeping the meaning of the sentence unchanged:The results showed that:The main research con-clusions show that both variety replacement and water and nitrogen input promote wheat photosynthetic production,and the increase of photosynthetic efficiency（SPAD）dominates the improvement of photosynthetic production capacity.The ma-terial transport and distribution efficiency increased with the variety replacement and water and nitrogen input.The variety replacement mainly increased the dry matter accumulation and transport efficiency before flowering,and the nitrogen input mainly increased the dry matter production after flowering.Variety replacement and water and nitrogen input promoted grain yield,and quality replacement contributed more to yield increase than nitrogen and water input.The water and nitrogen use efficiency showed an increasing trend in the process of variety replacement.Based on UAV mul-tispectral,the relevant key agronomic indicators can be efficiently monitored.