Effects Of Chemical Fertilizer Replaced By Legume Green Manure On Nitrogen And Growth Of Citrus

We performed a meta-analysis to analysis the 520 observations collected from 97peer-reviewed articles,aim to assess the effects of green manure on fruit yield and quality indicators,including fruit yield,weight per fruit,soluble solid content,sugar concentration,fruit acidity,and vitamin C content.In this case,taking citrus-legume cover crop systems as an example,we conducted different green manure replacing chemical fertilizers on citrus growth under greenhouse.At the same time,¹⁵N-labeled legume green manure was used to replace different proportion of nitrogen fertilizer?0%,25%,50%,75%,100%?,to quantify the amount of nitrogen transferred to citrus after returning legume green manure to the field.Finally,as the typical citrus intercropping clover system in South of China an example,we introduct the root splitting experiment to quantify the amount of nitrogen in clover transferred to citrus.The amount of nitrogen transferred from green manure to citrus through common mycelium network was expected to provide a theoretical basis for the proportion of quantitative green manure to replace chemical fertilizer,clean production and sustainable development in citrus orchards.The main results are as follows.?1?Meta analysis showed that green manure had no significant effect on fruit yield,but significantly improved fruit quality.Soluble solid content,sugar concentration and vitamin C content increased by 16.0%,6.7%and 6.8%,respectively,but fruit acidity decreased by 11.9%.The effects of green manure on fruit yield and quality vary with different climatic conditions,green manure species,practices and cultivation duration.When the annual average temperature was higher than 20°C and the annual average precipitation was more than 800 mm,green manure can significantly improve the fruit yield,the difference was mainly due to the green manure improved the soil water content and nutrient status in orchard.Different green manure species have different effects on the fruit yield,gramineous may compete with fruit trees for water and nutrients which resulting in the reduction of fruit yield;while legumes significantly improve the fruit yield and weight per fruit.Compared with fruit trees in old age,green manure was more conducive to the improvement of fruit quality of young fruit trees;and green manure was more conducive to the improvement of fruit quality than mulching,especially legumes significantly improve fruit quality,while gramineae has no significant impact on fruit quality indicators.The correlation showed that legume and mulching could indirectly improve the fruit quality by improving the soil temperature,water and nutrient status in orchard.?2?Green manure replacing chemical fertilizer can significantly improve the stem diameter,plant height and biomass of various organs.The total biomass of citrus with green manure replacing 100%of chemical nitrogen fertilizer was the highest,which increased by 80%compared with applied chemical fertilizer only,and the biomass of citrus root,new leaves and new shoot increased with the increase of green manure replacement ratio.The length,surface area and volume of roots were increased by replacing nitrogen fertilizer with green fertilizer,which mainly promoted the growth and development of fine roots?diameter<2.5mm?and increased the activity of roots.Green manure replacing nitrogen fertilizer increased transpiration and stomatal conductance of citrus leaves,decreased intercellular CO₂ concentration,increased net photosynthesis and promoted citrus growth.The nitrogen content of root,stem,new leaf and new shoot of citrus with chemical fertilizer only were significantly higher than that of other treatments,but its nitrogen accumulation were lower than that of green manure alternatives.With the increase of green manure replaing chemical nitrogen fertilizer ratio,the nitrogen content and the accumulated in all organs increased.Among the treatments,the green manure replacing nitrogen fertilizer fully has the highest nitrogen accumulation,which was 53.5%higher than the nitrogen fertilizer applied only.Applied green manure increased the soil microbial biomass,soil organic matter,carbon and nitrogen content of soil microbial biomass,and improved soil conditions for the growth of citrus.?3?Using ¹⁵N isotope technology to label legume green manure,the amount nitrogen transfer of legume green manure to citrus was calculated.The results showed that with the increase of the proportion of green manure replacing nitrogen fertilizer,the contribution of green manure nitrogen absorbed by citrus was more and more,and the proportion of 100%replacing nitrogen fertilizer was the highest.The green manure returning and mulching could provide 43.98%and 27.01%nitrogen to citrus,respectively.75%nitrogen replaced by green manure increased the distribution of nitrogen to the root system and decreased the distribution of nitrogen to the leaves.However,there was no significant difference in the nitrogen distribution of leaves,stems and roots with the green manure mulching.The nitrogen distribution of leaves,stems and roots of citrus was 60%,20%and 20%,respectively.Replacing nitrogen fertilizer with green manure significantly increased the citrus biomass,mainly increased the biomass of stem and leaf.The biomass of citrus with green manure mulching was higher than that with green manure mulching.?4?This study demonstrated that N₂-fixation supplied 30%of total nitrogen in white clover and enhanced nitrogen accumulation in both white clover and adjacent citrus,nitrogen transfer from white clover to citrus via a common mycelium network of arbuscular mycorrhizal fungi,accounted for 1.42%?1.71%of the citrus total nitrogen after 14 days of ¹⁵N labeling.The double mycorrhization and nodulation enhanced 27.2%of nitrogen transfer from white clover.To our knowledge,this is the first report to quantify nitrogen transfer from white clover to citrus via a common mycelium network.In conclusion,the green manure returning to the field can significantly improve the growth and nutrient absorption of citrus seedlings.The growth and nutrient absorption of citrus seedlings increased with the increase of the proportion of green manure replacing chemical fertilizer.About 40%and 27%of the nitrogen in green was absorbed by citrus with green manure returning and mulching.46.92 kg N/ha can be fixed by white clover in citrus orchard every year,and about 2%of nitrogen in white clover was transferred to citrus through common mycelium network.Therefore,it is important to cultivate legume green manure and return it to the field,so as to evaluate the potential of reducing chemical fertilizer in citrus orchard.