Copper (Cu) Availability and Dry Matter Yield of Maize (Zea mays L.) As Affected by the Application of Liquid and Solid Organic Amendments in a Cu Contaminated Soil.

Usually, organic amendments, i.e compost and manures, have been applied on the soil row in solid state, but in the last years liquid organic products (humic extracts) are being used. These amendments are basically a mixture of concentrated humic (HA) and fulvic acids (FA). In some fertile soils of central Chile the available concentrations of Cu in the arable layer are highly elevated, which reduce the plant development. There is not information on the effect of humic extracts on Cu availability and plant response in these soils. The objective of this work was to evaluate the effect of different liquid and organic amendments on the availability of Cu and  dry matter yield of maize plants. Plants were grown in 5-L pots during 2 months. Treatments consisted of the application of liquid humic acids (HA), liquid humic extract (HA+FA), compost, manure and earthworm humus obtained from sewage water in mixture with conventional NPK fertilization at three organic C (OC) rates equivalent to the C-AH+AF of the materials. Control treatments with only chemical fertilization and without OC either fertilization (CUF) where included. Results indicated that that dry matter yield (root and shoots) was increased with the rate compost and manure (p≤0.05), without having impact of the other treatments in comparison to the CF treatment. A significant effects (p≤0.05) of the treatments on the available Cu (CaCl₂-Cu and DTPA-Cu), pH, electrical conductivity (EC), and soluble carbon (Cws). Available Cu was related to the soil pH and Cws. However, a differential effect of the treatments was noted when comparing the CaCl₂-Cu and DTPA-Cu as indicators of Cu availability. Treatments with liquid amendments showed a reduction of the available Cu but cause lower plant growth because increments of the EC specially at higher C rates. These results suggest that by regulating the type and rate of organic amendments could be possible to modify Cu availability for reducing its toxicity to plants.