| At present, peat is usually taken as the medium of nutrient soil for cultivation of citrus container seedlings. However, continuing exploitation of peat had led to not only the damage of ecological environment but also the increase of peat price with the reduction of resources. Although the substitutes of peat had been widely studied in previous, there was no information in regard to application of citrus peel residues, the byproduct in citrus production, in cultivation of citrus seedlings. To clarify the feasibility using fermented citrus peel residues to replace peat for cultivation of citrus container seedlings, and to discover new medium of nutrient soil, the physiology and growth characteristics of citrus container seedlings that cultured in citrus peel residues containing nutrient soil (abbreviated as CPNS below) were analyzed in this study. It will also help to alleviate the environment pollution problem caused by citrus peel residues.One year old OR mandarin [Temple (Citrus temple hort. ex Y. Tanaka)×Dancy (Citrus tangerina hort. ex Tanaka)] grafted on trifoliate orange (Poncirus trifoliata (L.) Raf.) and Ziyangxiangcheng (Citrus junos Sieb. ex Tanaka) rootstocks were used as experimental materials in this study. These OR mandarin plants were cultured in CPNS which consisted of fermented citrus peel residues and three types of soils, Red soil (CPNS1), Suining purple soil (CPNS2) and ShaxiMiao purple soil (CPNS3), in volume ratio of1:1,1:2,1:3,1:4. Furthermore, the commonly used peat nutrient soil (peat:chaff:sand=1:1:1) was used as control (CK). The contents of nutrient elements of CPNS were determined, and the effects of this soil on OR leaf characteristics, nutrient elements contents, relative chlorophyll, photosynthetic characteristics, increment and biomass were also analyzed. The results are as follows:1. The contents of avail N, P and K of CPNS1, CPNS2and CPNS3were higher than those of CK, and the pH varied from6.57-8.17. Among the three groups of CPNS, CPNS1had the highest available nutrient. After a growth season, the contents of nutrient elements in all CPNS were decreased, especially for available N.2. Among all CPNS cultured OR plants, CPNS1and CPNS3cultured OR plants had better leaf area, circumference, length, width and thickness. Moreover, these.leaf characteristics in CPNS1cultured OR plants showed big differences as the ratio of citrus peel residues and red soil. When the citrus peel residues and Red soil were mixed in ratio of1:2and1:4, and the citrus peel residues and ShaxiMiao purple soil were mixed in ratio of1:3the OR plants had the biggest leaves.3. Compared with CK, the contents of N, P, Mg, S, Fe and Zn in OR leaves grafted on Ziyangxiangcheng rootstocks increased when cultured in CPNS1, CPNS2and CPNS3, while the contents of K, Mn and Cu reduced, and the content of Ca was unchanged. For the OR plants on trifoliata orange rootstocks, the contents of N, P, Mg, S and Zn increased while K, Fe and Cu reduced, and Ca and Mn were unchanged. It should be pointed out that the contents of Mg and Zn in CK cultured OR leaves were deficient widely, and increasing of Mg and Zn in CPNS cultured OR leaves have helped to alleviate this problem.4. The contents of chlorophyll were lowest and highest in CPNS1and CPNS3cultured plants, respectively. Between CPNS1and CPNS3, when the citrus peel residues and ShaxiMiao purple soil was mixed in ratio of1:3the chlorophyll was highest. For the net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2concentration (Ci) and transpiration rate (Tr), they performed the similar trends with chlorophyll in all treatments.5. The CPNS3cultured OR plants had the highest plant height, stem diameter, whole plant weight and dry weight and fresh weight of shoots and roots, followed by CPNS2and CPNS1. The height and stem diameter of all plants were equivalent to CK, and the biomass of most plants was also equivalent to CK. When the citrus peel residues and ShaxiMiao purple soil was mixed in ratio of1:3and1:2, all the growth indexes of OR plants were highest, and which were significantly higher than CK.In conclusion, these results indicated that the fermented citrus peel residues could replace peat to be used as the medium of nutrient soil for cultivation of citrus container seedlings. Among CPNS1, CPNS2and CPNS3, CPNS3had the best effect, especially when the fermented citrus peel residues and ShaxiMiao purple soil was mixed in volume ratio of1:3. All the growth indexes of OR plants cultured in this soil were significantly better than in CK. Moreover, the cost of CPNS was only half of peat nutrition soil. Therefore, using fermented citrus peel residues to replace peat for cultivation of citrus container seedlings can not only reduce the cost but also alleviate the pollution caused by citrus peel residues, and which has double benefits to both economic improving and environment protection. |
