| Intensification of agriculture and low recycling of the agricultural wastes had led to serious environmental pollution in China.There is an urgent need to explore new and better options to reuse the large amount of agricultural wastes.Substrate cultivation is considered as an efficient way to utilize the agricultural wastes thereby reducing environmental pollution.However,suboptimal management of nutrient solution may lead to nutrient accumulation in root-zone,which limited plant nutrient uptake and decreased yield and quality of vegetable crops.The management of nutrient solution is generally affected by several factors,such as the methods of nutrient solution supply,substrate types and nutrient formula.Hence,in this study,four greenhouse experiments were conducted,from 2014 to 2017,to comprehensively evaluate the effectiveness of different substrate cultivations,which include(i)the effects of open and closed systems on the intensity and characteristics of root-zone nutrient accumulation,(ii)the effects of rockwool,coir and peat+vermiculite substrates on electrical conductivity(EC),ion composition of root-zone solution,nutrient uptake,yield,fruit quality of tomato and nutrient use efficiency,(iii)the effects of different Cl-and NO3-levels on anion composition of drainage,nutrient uptake,tomato and nutrient use efficiency,and(iv)the effects of different K/Mg and Ca levels on ion composition of root-zone solution,nutrient uptake,yield,fruit quality of tomato and nutrient use efficiency.The results were summarized as follows:(1)Both open and closed systems showed nutrient accumulation and ion imbalance.The EC in root-zone solution increased gradually during the growing period and the highest values in open and closed systems were 11.9 and 17.2 mS cm-1,respectively.The contribution rate of nutrient ions to EC was NO3->K->Ca2+>Mg2+>SO42->H2PO4-.In both open and closed systems,the ratios of K+,Ca2+ and H2PO4-to total ion concentration decreased,but the ratios of Mg2+,NO3+ and SO42-increased during the growing period.The increased EC and ion imbalance generally led to decreased yield but increased fruit blossom-end rot(BER).In summary,the closed system was more efficient than open system in saving both water and fertilizers.(2)Different substrate cultivations significantly influenced EC and pH in root-zone solution.Both EC and pH in root-zone solution were higher in coir and peat+vermiculite cultivations than in rockwool cultivation.After harvest,the EC in root-zone solution were 12.3,17.2 and 16.6 mS cm-1 in rockwool,coir and peat+vermiculite,respectively.The pH in root-zone solution after harvest(compared with the initial pH in root-zone solution)decreased by 1.4,1.3 and 0.7 in rockwool,coir and peat+vermiculite,respectively.Different substrates led to different salt stress levels in plants.Coir and peat+vermiculite substrates could alleviate the negative effects of salt stress on BER and yield.(3)Different substrate cultivations influenced the ion composition of root-zone solution.In general,coir cultivation increased the K+ concentration in root-zone solution,while peat+vermiculite cultivation decreased K+ and H2PO4-concentrations but increased Ca2+ concentration.(4)Stage variation characteristics of EC in root-zone solution was found both in different nutrient solution supplying methods and different substrate cultivations.The greatest change of EC occurred at fruit expanding stage and early stage of harvest in open system,and occurred at middle stage of harvest in closed system and different substrate cultivations.(5)Substituting part of the NO3-by Cl-in the nutrient solution could increase NO3-use efficiency and reduce the leaching of NO3-.Compared with standard nutrient solution treatment(SN),leaching of NO3-decreased by 0.6 t hm-2 yr-1 in high chloride treatment(HC).Increasing Cl-concentration could promote the Ca uptake of plant.(6)Compared with low K+/Mg2+ ratio(6.5),increasing the K+/Mg2+ ratio(13.0)could alleviate K+ depletion and Mg2+ accumulation.Improving the Ca2+ concentration of nutrient solution could increase the Ca content in plant.Compared with control,the high Ca2+ level treatment increased the Ca content of old leaves,new leaves and furits by 4.1%,36.3%and 8.1%,respectively. |
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