Irrigation with plant extracts in ecofarming increases biomass production and mineral and organic nitrogen content of plants

摘要

Seedlings of alfalfa, rape, spinach, and wheat, potted on sandy soil, were irrigated with an aqueous extract of pea shoot (PE, 9.84 g dry weight l(-1)) or a solution of Ca, K, Mg, P, and NO3-N salts (SS) in a concentration similar to that in PE, for 31-48 days. In comparison to water-irrigated controls, both SS and PE treated plants showed nearly equal increases in shoot dry weight (29-40%), whereas PE-treated plants had higher fresh weights (38-84%) due to increased succulence. Treatment with SS did not enhance, but sometimes even reduce, the concentrations of Ca, K, Mg, and several trace elements in shoot tissues. In contrast, PE-treated plants had higher Ca, K, Mg, and organic N, but lower As and Ni contents and were thus of higher nutritive value. Reduced contents of metals in plant tissue correlated with their reduced solubility in the soil solution, which was not due to changes in pH. Fertilizer components such as K and Mg (metals of lower exchange intensity) were incorporated into the soil to release Ca, Sr, and Ba (metals of higher exchange intensity) and reduce the solubility of most trace elements and metal-complexing humic substances. In addition, application of Ca precipitated heavy metals and humic complexes directly from the soil solution. This effect was partially overcome by PE. Its carboxylic acids could act as phytochelators of metal ions and as mobilizers of the highly diffusible humic substances which carry metals to roots. It is concluded that continuous PE application replaces the quantities of Ca, K, Mg, P, and organic N, but not of NO3-N consumed during plant growth. Using PE does not add any relevant quantities of toxic metals to the plant-soil system.