Towards environmentally sustainable growing media for strawberry cultivation: Effect of biochar and fertigation on circular use of nutrients

Abstract

In controlled environment horticulture, nutrients are retained in horticultural substrates, resulting in additional export of the nutrients provided through fertigation. To increase feasibility of the circular use of renewable growing media, nutrient retention in the substrate should remain low during cultivation. The aim of the present study was to examine the effect on nutrient retention (1) if nutrient input via fertigation is reduced and (2) if alternative growing media are used. Nutrient dynamics were studied for soilless strawberry cultivation in two full-scale greenhouse trials with the short day cultivar Elsanta and with a new substrate blend with 25% v/v wood fiber and 15% v/v green compost versus a conventional peat-based blend (75/15/10% v/v peat/coir/perlite). The conventional fertigation regime was compared with a reduced fertigation regime, which contained 65% of the standard concentration for N, P K, Mg, Ca and S. The first trial was a nine month autumn-spring cycle; the second trial was a two month autumn cultivation. Peat-reduced blends with or without wood-based biochar resulted in the same fruit yield as the peat-based blends. Trial length and fertigation regime interacted to affect yield, with significantly lower yield in the long trial under reduced fertigation versus conventional fertigation, and higher yield under reduced fertigation in the shorter trial. These findings indicate that nutrient concentrations in the applied fertigation should not be reduced during the long autumn-spring cycle. Ca (76–88%), Mg (70–85%) and N (61–81%) are mainly retained in the spent medium, while K is mainly retained in the aboveground biomass (> 60%). K contents in the peat-reduced substrate clearly decreased during cultivation, the peat-reduced blend may thus be a source of K. Wood-based biochar in the blend (3–10% v/v) showed no effect on either nutrient retention or nutrient balance.