Increasing Wood δ15N in Response to Pig Manure Application

Intensive livestock management impacts forest and trees in different ways. Pig manure is a major source of nitrogen (N) pollution of surface and ground waters in some European regions such as north-eastern Spain, but it is understudied how manure application impacts agroforestry systems. How pig manure affects tree radial growth and the N cycle was assessed by measuring N concentrations in soil, leaves and wood and δ15N in tree-ring wood in two tree species widely planted for agricultural (Prunus dulcis) and reforestation (Pinus halepensis) purposes in the study area. Soil physicochemical characteristics and the biomass and structure of major soil microbial groups were also measured. Trees irrigated with pig effluent (manure application) and control trees not subjected to manure application were compared. Soil N, phosphorus (P) and potassium (K) concentrations of fertilized trees increased, but soil microbiota biomass decreased. Similar growth between fertilized and non-fertilized pine trees was found, but lower growth in fertilized almond trees was observed. Leaf N concentrations decreased but δ15N wood increased in trees subjected to pig manure application. Pig manure application alters the N cycling in the soil and within trees.