Management of organic amendments in Florida citrus production systems

Prior to World War II, most of the N applied to Florida citrus groves was i n natural organic fertilizer forms like animal manures or seed meals. The a dvent of synthetic chemical fertilizers decreased organic fertilizer use su ch that it makes up only about 0.1% of all fertilizers applied to citrus to day. However, interest in applying organic amendments to citrus is rising b ecause of increased supplies and decreased costs of non-hazardous organic w astes. Citrus growers apply these materials for perceived or real improveme nts in soil physical, chemical, and biological properties, but the main ben efit appears to be increased nutrient availability. The use of organic mate rials as an N source is being considered as a best management practice (BMP ) for N management because organic N is released to the plant more graduall y than water-soluble, inorganic fertilizer N. Current organic amendments ap plied to citrus groves (biosolids, poultry waste, and composts) differ subs tantially from those applied in the past. Poultry waste is the most expensi ve, followed by compost and biosolids. Application rates are determined by a process design that takes into account the crop N requirement and the N m ineralization rate. The Fla. Dep. of Agric. and Consumer Serv. (FDACS) inte rim BMP rule for citrus states that the contribution of plant-available N f rom natural organic N sources for the Ist year after application shall be 5 0% of the total N concentration. Mineralization rate studies are being cond ucted to refine this figure for Florida conditions. Knowledge of mineraliza tion rates will be critical for accurate nutrient management planning.