Study On Characteristics Of Nitrogen Requirement And Nutritional Diagnosis Of Walnut

Walnut is an important ornamental fruit tree and landscaping tree species in China.The poor planting site conditions,extensive conservation process,low soil fertility and improper application of fertilizers of walnut are common,which seriously influence the growth and development,yield level and economic benefits of walnut,and reduce the ornamental value and ecological benefits of walnut.Reasonable fertilization as the main means of conservation management is the key to healthy growth of walnut.In this study,typical walnut production gardens in three ecological regions of Shandong province,mountain,piedmont and plain,were selected to investigate the status of fertilizer and water management and evaluate soil fertility,meanwhile,walnut was used as the test plant to study the nitrogen requirements characteristics seedling stage and fruiting stage of walnut through pot experiments and a field experiment,and the optimal nitrogen application range and critical SPAD value were determined,which provide the basis for scientific fertilization of walnut.The main conclusions are listed as follows:1.The proportion of farmers who irrigated and fertilized walnuts in the mount ainous area was 16.7%and 29.2%,respectively,which were lower than that of in piedmont plain and plain,and management practices were not detailed.The proporti on of farmers who applied chemical fertilizers and organic fertilizers were 67.0%a nd 56.0%in the piedmont plain,and 80.0%and 20.0%in the plain.There was no organic fertilizer input in the mountainous area.The total nutrients input in the plai n region was 1603 g/plant,which was 1.2 and 10.1 times that of the piedmont plai n and mountainous regions,respectively.The nutrients input in the plain region was mainly nitrogen,and N:P₂O₅:K₂O nutrient input ratio was 1.0:0.5:0.5.Piedmont plain and mountainous area had the most phosphorus nutrient inputs,followed by n itrogen,and the least potassium.The physical and chemical properties of soil organ ic matter,alkalyzable nitrogen,available phosphorus,available potassium,EC,and p H in soil layers of 0～20 cm and 20～40 cm in the three ecological regions were si gnificantly different.The fertility of 0～20 cm soil layer in the piedmont plain was fertile,and the soil layer of 20～40 cm in the mountainous regions was poor,and t he soil fertility were comprehensively represented by the piedmont plain regions>pla in regions>mountainous regions.2.The differences between’Xiangling’and’Jizhuamian’walnut seedlings were mainly reflected in the average root diameter,root activity and aboveground nitrogen uptake,while the other growth and nutrient uptake indexes were not significantly different between the two cultivars.Compared with’Xiangling’,the average root diameter of’Jizhuamian’seedlings increased by 62.2%,and the aboveground nitrogen uptake was 1.39 times as much as that of’Xiangling’seedlings.Nutrient uptake of the seedlings of’Jizhuamian’was mainly achieved by improving root activity and increase root diameter rather than increasing root length and absorption area.The two walnut cultivars showed significant differences in nitrogen uptake of different forms.’Jizhuamian’seedlings had more preference for nitrogen uptake of NH₄⁺-N,but’Xiangling’had no obvious bias.In the NH₄NO₃ treatment with half of NH₄⁺-N and half of NO₃^--N,there was no significant difference in the nitrogen concentration and nitrogen uptake in shoots of’Jizhuamian’seedlings compared with（NH₄）₂SO₄ treatment,indicating that NO₃^--N absorbed by seedlings could replace part of NH₄⁺-N.The interaction between walnut varieties and nitrogen forms was extremely significant（p<0.001）.The amount of nitrogen application significantly affected the dry matter accumulation of walnut seedlings 90 days after transplanting,and the dry matter of both the aboveground and underground parts of walnut seedlings showed a trend of firstly increasing and then decreasing with the increase of nitrogen application rate.Significantly differences were found in the root length of each nitrogen treatment at different growth stages.In the early stage after transplanting,the amount of nitrogen supply（150 mg/kg）could promote the growth of root length,and by 135 days after transplanting,the root reached the longest length even without nitrogen applied,which shows that walnuts can increase the length of the root growth in response to a lack of nitrogen conditions.While the excessive nitrogen application（>225 mg/kg）inhibited the root growth and then root got shorter.The relationship between root growth and root diameter of walnut seedlings was characterized by thickening first and then increasing length.Nitrogen application significantly affected the photosynthetic characteristics of functional leaves of walnut seedlings.The leaf transpiration rate,net photosynthetic rate,stomatal conductance and intercellular CO₂ concentration all increased first and then decreased with the increase of nitrogen application rate,and all reached the maximum value at the nitrogen application rate of 150 mg/kg.135 days after transplanting,there was a close correlation between aboveground dry matter and nitrogen application rate of walnut seedlings（p<0.001）.The optimal N application rate for walnut seedlings was6.5～157.5 mg/kg based on the relative aboveground growth rate of 75%and 95%.3.The results of fruit-bearing stage walnut nitrogen fertilizer experiment in plain regions show that the maximum increments of walnut height,trunk circumference and crown width were 1.28 m,7.10 cm and 0.88 m,respectively,when the nitrogen application rate was0.25 kg/plant.The single fruit weight of walnut increased first and then decreased with the increase of nitrogen application rate,and reached the highest value（15.5 g/plant）when the nitrogen application rate was 0.25 kg/plant.There was no significant difference in the protein content of walnut kernels between different nitrogen fertilizer treatments,but the crude fat content of walnut kernels reached a significant level.The crude fat content of walnut significantly increased with the increase of nitrogen application rate.According to the simulation results of linear plus platform equation,when the nitrogen application rate was0.68 kg/plant,the crude fat content of walnut reached the highest level,which was 61.1%.195 days after fertilization,leaf nitrogen concentration was apparently correlated with SPAD value and single fruit weight,respectively.When nitrogen concentration was 1.90%,walnut single fruit weight reached the maximum value of 15.4 g,and the corresponding SPAD value was 41.6.This critical value can be used as a simplified nutritional diagnostic index for fertilization guidance.