The Effects Of Different Substrate And Fertilizer Ratios On The Growth And Physiology Of Sour Pummelo Seedlings

Seedless honey pummelo is a high-quality agricultural product in Hainan,but the breeding of high quality seedlings restricts the development and promotion of its industry.In this study,sour pummelo seedlings(seedless honey pummelo rootstock seedlings)were used as experimental materials,and the agricultural wastes(coconut coir,sugarcane ash and rapeseed cake)were mixed with the local topsoil in Chengmai in 9 different ratios,using topsoil as comparison to study the effects of different substrate ratios on the growth indexes such as seedling height,diameter,leaf number and on the physiological indexes such as chlorophyll content,soluble sugar content,and mineral element content.Nitrogen,phosphorus and potassium were mixed in 6 different ratios,using no fertilizer as comparison to study the effects of different fertilizer ratios on the growth indexes such as seedling height,diameter,leaf number and on the physiological indexes such as chlorophyll content,soluble sugar content,and mineral element content,in order to to provide a scientific basis for seedling cultivation and fertilization techniques in seedless honey pummelo industry.The results were shown below:(1)The physicochemical properties of substrate had significant or extremely significant correlation with the growth and physiological indexes of sour pummelo seedlings.It is considered that the substrate which has small aeration porosity,bulk density and A/W ratio,large total porosity and water-holding porosity,high pH,EC and nutrient content is more suitable for the growth of sour pummelo seedlings.Among all treatments T5(1/3 coconut coir,1/3 topsoil and 1/3 rapeseed cake)has good performance.Bulk density was 0.65 g/cm3,total porosity was 44.48%,aeration porosity was 6.16%,water-holding porosity was 38.32%,A/W ratio was 0.16;pH was 6.89,EC was 2.44 mS/cm,hydrolyzable nitrogen content was 177.53 mg/kg,available P was 841.21 mg/kg,available K was 2316.98 mg/kg,organic matter content was 6.00%.(2)Different substrate ratios had significant effects on the growth and physiological indexes of sour pummelo seedlings.Among all treatments,T5(1/3 coconut coir,1/3 topsoil and 1/3 rapeseed cake)had the best comprehensive performance.Average height was 35.76 cm,average diameter was 4.32 mm,average leaf number was 24.40 and healthy index was 1.48,which was 48.38%,35.00%,54.43%and 45.10%higher than CK treatment;average total root surface area was 1121.04 cm2,average total root volume was 78.48 cm3,which was 37.71%and 71.09%higher than CK treatment;average soluble sugar content was 3.69 mg/g,average soluble protein content was 14.10 mg/g,which was 39.77%and 41.57%higher than CK treatment;the content of total nitrogen of shoot was 2.04%,the content of total phosphor of shoot was 0.24%,the content of phosphor root was 0.31%and the content of total potassium of shoot was 1.36%,which was 37.84%,71.43%,106.67%and 81.33%higher than CK treatment,all the indexes were significantly or very significantly different from CK.Followed by T2(2/3 coconut coir,1/6 topsoil and 1/6 rapeseed cake)and T9(2/3 topsoil,1/6 sugarcane ash and 1/6 rapeseed cake).The worse treatment were T1(2/3 coconut coir,1/6 topsoil and 1/6 sugarcane ash),T4(1/3 coconut coir,1/3 topsoil and 1/3 sugarcane ash)and T7(1/6 coconut coir,2/3 topsoil and 1/6 sugarcane ash).Considering the factors of seedling growth status,substrate weight and cost,the cultivation substrate with 1/3 coconut coir,1/3 topsoil and 1/3 rapeseed cake was chosen as the optimum substrate ratio for the sour pummelo seedlings.(3)Different fertilizer ratios had significant effects on the growth and physiological indexes of sour pummelo seedlings.Among all treatments,W3(N:P2O5=1:0.25)was the best treatment.Average height was 31.97 cm,average diameter was 4.58 mm;,and average leaf number was 26.20,which was 29.43%,10.36%,40.86%and 44.91%higher than CK treatment;average chlorophyll content was 62.39 SPAD,average soluble sugar content was 4.49 mg/g,average soluble protein content was 10.95 mg/g,which was 20.72%,62.09%and 55.32%higher than CK treatment;the content of total nitrogen of shoot was 2.98%,the content of total nitrogen of root was 5.01%and the content of total potassium of root was 0.60%,which was 31.28%,153.03%and 62.16%higher than CK treatament,all the indexes were significantly or very significantly different from CK treatment,then followed by W2(N:P2O5:K2O=1:0.25:0.25).The effect of single application of nitrogen fertilizer is relatively poor,which showed that the effect of combination fertilization was better than that of single application.So N:P2O5=1:0.25 was chosen as the optimum fertilizer ratio for the sour pummelo seedlings.