Biochar's fitness as an amendment in bell pepper transplant and field production

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Carpenter, Brandon
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Ajay Nair
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Biochar, a carbon-rich co-product derived from the pyrolysis of biomass for fuel for energy production, often exhibits beneficial chemical and physical properties when added to soils and soilless substrates. Research into the use of biochar to improve plant productivity and growth has increased over the past decade. Much of this research has been done in controlled environments, and often these experiments focus on using biochar as an alternative to sphagnum peat, or on how biochar affects plants grown in soil. Few studies have investigated biochar's effects on a specific plant in both greenhouse and field production, and from seed to harvest. The objective of this research was to explore the possibility of using biochar in both the transplant and field production of bell pepper Capsicum annuum L.

In the transplant experiment using a randomized split-plot design biochar was mixed in a retail substrate (Jiffy Mix® Growers Choice #901, Lorain, OH. Biochar was added to Jiffy Mix® at rates of 0%, 20%, 40%, 60%, and 80% (w/w). Bell pepper var. `Paladin' was direct-seeded and grown 53 days in cell-flat sizes of 50, 72, and 98 at each of the five levels of biochar addition. In the field experiment biochar was incorporated into a Clarion loam and an Anthrosol consisting of sand and pea gravel at the rates of 0 kg.m-2 (control), 1.1, 2.2, and 4.5 kg.m-2 in 2012. Bell peppers were then grown on black plastic mulch and bare soil beds for two seasons.

Pepper seed germination increased as compared to the control in the 50- and 72- cell-trays with additions of 20%, 40%, and 60% biochar; however, biochar had no effect on germination in the 98-cell-tray. Plant height and dry weight were reduced as the biochar percentage increased, and as cell size decreased. Height and dry weight, measured at 53 days, decreased at differing rates within both factors, showing less variation between biochar treatments in the 98-cell-flat and less variation between cell volumes at the 80% biochar treatment level. Indirect estimate of chlorophyll using SPAD readings showed similar trends to the height and dry weight. Nitrate-N in the substrate was reduced by the end of the experiment except in the 60% and 80% biochar mixes, which had more nitrates at 53 days after planting.

Field trial results indicated biochar did not increase marketable fruit production in either soil type. Biochar did, however, affect leaf chlorophyll content in both fields, although not in the same year. Biochar decreased extractable NO3–N in both fields (2012). Potassium concentrations were increased in the Clarion loam field both years. Biochar also decreased the amount of nitrate that was leached from the root zone into lysimeters in Clarion loam (2012) and sand Anthrosol (2013). Reductions in leaf chlorophyll content were seen in the same field in the same years as reductions in the nitrates leached from the root zone were seen. Our results indicated that biochar can be added to commercial soilless substrate at rates up to 40% without detrimental effects on pepper transplant production. We also concluded that additions of biochar up to 4.5 kg.m-2 are possible without causing losses in production; however productivity was not increased, so growers may have difficulty justifying the extra expense associated with biochar application. Our results also suggest that nitrates may be a concern when higher rates of biochar are added. This indicates that adding biochar to soils with the express purpose of sequestering carbon is possible, but more work should be done to insure no losses in productivity are seen.

Wed Jan 01 00:00:00 UTC 2014