Study On The Effects Of Potassium Fertilizer Types And Dosage On The Growth And Physiological Characteristics Of Walnut

In 2020,walnut was selected as one of the most recommended tree species in the Recommending List of Excellent Tree Species in Shandong Province.It has important ornamental value,ecological value and economic value,and is an excellent ornamental tree for yard beautification and urban greening.With the rapid development of landscaping,the development and utilization of walnut has gradually attracted people’s attention.However,blind application of potassium fertilizer is common in walnut production,and too much or too little application of potassium fertilizer is not conducive to the sustainable development of walnut industry.At present,potassium chloride（KCl）and potassium sulfate（K₂SO₄）are the main types of potassium fertilizer commonly used in agricultural production.In order to explore the scientific application of potassium fertilizer in walnut,the effects of two different types of potassium fertilizers（KCl and K₂SO₄）on the growth index,photosynthesis,chlorophyll fluorescence characteristics,and the absorption and accumulation of nitrogen,phosphorus and potassium of walnut seedlings were studied using pot experiment under different potassium supply levels(0,50,100,200 and 400 mg·kg^-1).According to previous research results,field experiments were conducted to study the effects of K₂SO₄on the growth,physiological indexes,fruit yield and quality,and nutrient uptake of N,P,K of 7～8years old walnut under different K levels(0.00,0.15,0.30,0.60,1.20 kg·plant^-1).The test results are as follows:1.The effects of K₂SO₄and KCl on the growth of walnut seedlings were significantly different.The growth indexes of walnut seedlings treated with K₂SO₄increased first and then decreased with the increase of K supply level,and reached the highest when K supply level was 100 mg·kg^-1,and most of them were significantly higher than those of the control.As for potassium chloride,potassium application could not significantly improve the growth index of walnut seedlings.In general,the high potassium supply level(400 mg·kg^-1)of the two types of potassium fertilizers significantly reduced the growth index of walnut seedlings.At the same potassium supply level,the growth index of walnut seedlings applying K₂SO₄was mostly higher than that of applying KCl.The results indicated that appropriate K₂SO₄could promote the growth of walnut seedlings.2.The effects of K₂SO₄and KCl on the photosynthetic performance of walnut seedlings were obviously different.When potassium application level was 100 mg·kg^-1,K₂SO₄significantly increased the photosynthetic capacity of walnut seedling leaves compared with the control,but KCl treatment could not significantly improve all the photosynthetic capacity indexes.As for the indexes that can be significantly improved by both types of potassium fertilizer,K₂SO₄treatment is generally higher than KCl treatment.PSⅡreaction center receptor side electrons from QA to QB and PSⅡreaction center donor side put chlorine is more sensitive to oxygen complex OEC;The F_V/F_Mand PI_ABSof walnut seedling leaves with high potassium level(400 mg·kg^-1)of the two potassium fertilizers were mostly lower than those of the control,suggesting that a glut of K fertilizer,can also cause the damage of leaf PSⅡreaction center of walnut seedling,reduce the energy absorption and utilization ability,inhibiting walnut seedling leaf photosynthesis.3.Different types of potassium fertilizer and potassium application level had different effects on the nutrient absorption and accumulation of walnut seedlings.When K level was100 mg·kg^-1,K₂SO₄treatment significantly promoted the absorption and accumulation of N and K in walnut seedlings,however,KCl treatment only improved part of nutrient absorption and accumulation indexes of walnut seedlings,and at this level,the amount of K₂SO₄treatment was higher than that of KCl treatment.The dry matter accumulation of walnut seedlings treated with K₂SO₄was significantly correlated with N,P and K accumulation.Both low K and excessive K application could inhibit the absorption and accumulation of N,P and K in walnut seedlings.4.Appropriate potassium application level could improve the Growth of trunk circumference,crown width growth,SPAD value,leaf N,P and K content,as well as the fruit yield,protein and fat contents of walnut.According to the comprehensive evaluation of the membership function of each index,0.15～0.30 kg·plant^-1is the optimal potassium application level.In conclusion,different types of potassium fertilizer and potassium application levels have different effects on the growth and physiological characteristics of walnut seedlings,the yield and product quality of walnut.For walnut,K₂SO₄is the suitable type of potassium fertilizer,and 100 mg·kg^-1is the suitable potassium level at seedling stage,and 0.15～0.30kg·plant^-1is the suitable potassium level in field for the trees at the age of 7～8 years.