Testing the Feedback Inhibition Hypothesis of Soil Enzymes: N Fertilization Impacts on N-hydrolytic Enzyme Activities in Tropical Agroecosystems

Abstract

Soil enzymes drive nutrient cycles and serve as an indicator of soil health. This study investigated the activity of seven soil enzymes involved in nitrogen cycling (N-acetyl-D-glucosaminidase (NAG), leucine aminopeptidase (LAP), alanine aminopeptidase (ALA), methionine aminopeptidase (MET), glycine aminopeptidase (GAP), glutamic acid aminopeptidase (GLU), and deaminase) after synthetic N fertilizations under field conditions. Twenty-one coffee fields, divided into 4 plots each subjected to one of four treatments: nitrogen (N) in the form of UREA at a rate of 285 kg N ha-1, potassium (K) in the form of muriate of potash (MOP) 350 kg K ha-1, nitrogen and potassium (NK) as a combination of the two individual rates, and no fertilization (UCL). This study aimed to evaluate the feedback inhibition of soil enzymes after fertilization treatments. It was hypothesized as a suppression of enzymatic activity due to the increased availability of N. Fertilization interaction findings did not provide field-based evidence that fertilization can suppress or stimulate soil N-hydrolytic enzymatic pathways refuting the feedback inhibition hypothesis. Additionally, an interaction between sampling timepoint and soil N-hydrolytic enzymes was found evidencing additional factors affecting enzyme activity in soils. Understanding these biochemical responses enhances our ability to optimize fertilization strategies, balancing productivity with long-term soil health.