Abstract
A greenhouse trial assessed the effects of biochar and vermicompost as partial substitutes of conventional growing media on leafy vegetables’ yields and changes of NH4+-N and NO3−-N in growing medium and leachates. Six growing media mixtures [(a) coir, (b) coir + biochar, (c) coir + vermicompost, (d) peat, (e) peat +vermicompost, (f) peat + biochar] combined with three nitrogen (N) rates [0% (0 g N·pot−1), 50% (0.5 g N·pot−1), and 100% (1.0 g N·pot−1) commercial recommendation] were arranged in a split-plot design with three replicates. On average, the yield gap between 100% N and 50% N was improved when biochar and vermicompost were used as substitutes of coir (32% and 28% vs. 49%) and peat (14% and 18% vs. 27%). The concentrations of NH4+-N in the leachates for peat + biochar varied between 17.20 and 1.00 mg·L−1. The concentrations of NO3−-N in the leachates varied between 130.0 and 1.0 mg·L−1for coir + vermicompost, and 60 and 1.0 mg·L−1for peat + vermicompost. The residual NO3−-N in peat + biochar growing media and the leachates did not match the changes observed for NH4+-N, and the much lower residual NH4+-N indicates possible NH4+-N retention by biochar and loss through volatilization in the early growth stages. Our results show that partial substitution of peat with biochar and coir with vermicompost maintained acceptable crop yield at 50% N due probably to N supply by vermicompost and decreased residual mineral N and loss by biochar in the leachates which could be beneficial for the environment.
Highlights
Organic materials mainly agricultural and municipal food wastes are becoming integral parts of highly performing growing media to support soilless production systems (Zulfiqar et al, 2019)
Fresh yield varied between 8.4 g pot–1 for coir and 240 g pot–1 for peat amended with biochar in 0% N pots; 228 g pot–1 for peat and 470 g pot–1 for peat amended with biochar in 50% N pots; and 314 g pot–1 for peat and 544 g pot–1 for peat amended with biochar in 100% N pots (Fig. 1a)
Cabbage and lettuce fresh yields were reduced at 50% N application rates compared with the commercial recommendations, but the extent was limited under amended growing media compared with conventional growing media alone
Summary
Organic materials mainly agricultural and municipal food wastes are becoming integral parts of highly performing growing media to support soilless production systems (Zulfiqar et al, 2019). This shift is driven by concerns over environmental impacts of non renewable materials such as peat used in conventional growing media (Barrett et al, 2016). Organic materials have been extensively studied and their benefits in soil-based conventional and organic production systems are well documented (Huang and Gu, 2019; Bhat et al, 2018; Pereira et al, 2017) They can be used as soil conditioners to improve soil structure, water holding capacity and fertility. A better understanding of organic materials used in soilless production is crucial to match N supply and plant demand and reduce N losses without compromising yields
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