Root-Zone Amendments of Biochar-Based Fertilizers: Yield Increases of White Cabbage in Temperate Climate

Abstract

The use of biochar is an important tool to improve soil fertility, reduce the negative environmental impacts of agriculture, and build up terrestrial carbon sinks. However, crop yield increases by biochar amendment were not shown consistently for fertile soils under temperate climate. Recent studies show that biochar is more likely to increase crop yields when applied in combination with nutrients to prepare biochar-based fertilizers. Here, we focused on the root-zone amendment of biochar combined with mineral fertilizers in a greenhouse trial with white cabbage (Brassica oleracea convar. Capitata var. Alba) cultivated in a nutrient-rich silt loam soil originating from the temperate climate zone (Bavaria, Germany). Biochar was applied at a low dosage (1.3 t ha−1). The biochar was placed either as a concentrated hotspot below the seedling or it was mixed into the soil in the root zone representing a mixture of biochar and soil in the planting basin. The nitrogen fertilizer (ammonium nitrate or urea) was either applied on the soil surface or loaded onto the biochar representing a nitrogen-enhanced biochar. On average, a 12% yield increase in dry cabbage heads was achieved with biochar plus fertilizer compared to the fertilized control without biochar. Most consistent positive yield responses were observed with a hotspot root-zone application of nitrogen-enhanced biochar, showing a maximum 21% dry cabbage-head yield increase. Belowground biomass and root-architecture suggested a decrease in the fine root content in these treatments compared to treatments without biochar and with soil-mixed biochar. We conclude that the hotspot amendment of a nitrogen-enhanced biochar in the root zone can optimize the growth of white cabbage by providing a nutrient depot in close proximity to the plant, enabling efficient nutrient supply. The amendment of low doses in the root zone of annual crops could become an economically interesting application option for biochar in the temperate climate zone.

Suitability of Co-Composted Biochar with Spent Coffee Grounds Substrate for Tomato (Solanum lycopersicum) Fruiting Stage

“…Plants grown in a highly nutrient-rich environment usually develop lower root mass but higher leaf and stem mass fractions, promoting light interception and photosynthesis [41]. Moreover, Grafmüller et al [42] suggested that adding nutrient-enhanced biochar in the root area may act as a hotspot for the plant, which requires fewer fine roots for nutrient supply. Below-ground biomass was inversely proportional to compost dilution.…”

Granulation compared to co-application of biochar plus mineral fertilizer and its impacts on crop growth and nutrient leaching

“…Five replicate pots per treatment were either prepared for cultivation with or without leaching events, the latter including a non-fertilized control (CTRL-0) to test for leaching of native soil nutrients and mineralized N (Table 1 ). A control group without fertilizer/biochar application and without leaching events was not conducted as a pre-trial showed that no cabbage head development could be expected 13 . Five additional pots for NPK, gBBF, and B + NPK without leaching were set up for repeated sampling to measure soil N speciation and urease activity over time (cf.…”

An Overview of Climate Change Impacts on Agriculture and Their Mitigation Strategies

“…The biochar-based efficient use of fertilizer can avoid the manufacturing fraction of fertilizers and associated GHG emissions [79]. Biochar-based fertilizers can increase crop productivity significantly and further increase crop productivity in soils which are not responsive to common fertilizers (Figure 3A) [80].…”