Processing methods of organic liquid fertilizers affect nutrient availability and yield of greenhouse grown parsley

The demand for organic foods is increasing globally, but a key limiting factor to the production of organic greenhouse produce is the lack of certified liquid fertilizers. In this experiment, four organic fertilizers were produced using either acidic extraction, anaerobic digestion or both of ensiled biomass of organic red clover and white mustard. The resulting fertilizers were applied to greenhouse-grown parsley either alone, or in combination with nitrogen (N)-enriched water produced by flushing acidic water with ammonia, to determine their effect on plant growth and the nutrient concentrations of parsley. Six combinations of fertilizer treatments were included in the greenhouse experiment. Three treatments received either fertilizers derived from acidic extraction, anaerobic digestion or both and three treatments received fertilizers derived from acidic extraction combined with N-enriched water. Conventional inorganic liquid fertilizer, chicken manure extract and no liquid fertilizer (only water) were added as control treatments. A higher N-min (ammonium and nitrate) to potassium (K) ratio was found in fertilizers after anaerobic digestion compared to acidic extraction. All organic fertigation treatments resulted in high pH, high K and chloride concentrations and high NH4/NO3 ratios in the root zone. In addition, high electrical conductivity (EC), P, K and Mg concentrations were found when only acidic extracted fertilizers were applied. Application of plant-based organic fertilizers without amending with N-enriched water resulted in biomass yields that were 21-26% lower than the inorganic fertigation control. However, fertigation with chicken manure extract, or a combination of fertilizer derived from acidic extraction and N-enriched water, resulted in similar plant growth as inorganic fertilizer. The lower yield from fertilizer derived from acidic extraction was due to elevated EC levels in the growing medium. Our results suggest that yield of greenhouse-grown parsley using either organic fertilizers combined with N-enriched water or chicken manure extract is similar to conventional fertilizer.