2018 ASHS Annual Conference

This study compares the relative rate of nitrate and phosphate losses, and crop yield from 100% Coconut Coir (organic) or Perlite (inorganic) soilless root support substrates (SRSS) during the culture of Swiss chard (Beta vulgaris L.) cv. Acelga in a nonrecirculating hydroponic system (NRHS). Excess nutrient solution (15N–2.2P–12.5K plus micronutrients, supplied at 200 mg nitrogen/liter, pH 6.5 – 7.2) delivered by drip emitters to the SRSS during each cropping cycle, flowed to drainage via 2-inch PVC pipes. Mean ambient day/night temperature and relative humidity during the cropping cycle were 22.9/8.5 C and 86.5/54.0%, respectively. We grew Swiss chard seedlings from the third true-leaf stage until the second harvesting at 103 days after transfer into hydroponic culture (DAT). Weekly leachate sampling from the NRHS for determination of nitrate and phosphate concentration started when the seedlings were fully established and capable of active mineral nutrient absorption. We analyzed the samples for nitrate and phosphate using the Dionex™ ICS-5000+ Capillary High Performance Ion Chromatograph System equipped with conductivity detector. Compared with the inorganic, the organic SRSS significantly reduced leachate nitrate and phosphate concentration by ~78% (p = 0.0130) and ~66.5% (p = 0.0001), respectively, compared with Perlite over a 103-day sampling period. The organic and inorganic SRSS reduced nitrate leaching losses by 77.8% (p = 0.0004) and 51.4%, (p = 0.0113), respectively, compared with the source nutrient solution (SNS) collected from the emitter. Although the phosphate concentration of the leachate were 56.2% and 38.0% less than that of the SNS in the organic and inorganic SRSS, respectively, overall differences averaged over the cropping cycle were not significant (p = 0.05), due to variability between batches of samples. Crop grown in the organic SRSS had significantly greater marketable leaf yield and leaf dry weight (LDW) (p < 0.05), but there were no differences in leaf count. Crop grown in the organic SRSS had higher leaf water content (LWC) (p < 0.0047) compared with the inorganic in one of the two replicates of the experiment. Reductions in nitrate and phosphate losses by both organic and inorganic SRSS over the cropping period can amount to significant savings in fertilizer cost at the percentages observed in this study. However, the organic SRSS shows a greater capacity to minimize potential environmental pollution by nitrate or phosphate discharge from small-scale nonrecirculating hydroponic operations, without limiting the growth and leaf yield of Swiss chard.