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 delta N-15 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 delta N-15 wood increased in trees subjected to pig manure application. Pig manure application alters the N cycling in the soil and within trees.

Automated summary

Intensive livestock management can cause nitrogen pollution in water bodies, but the impact of manure application on agroforestry systems is not well understood. This study assessed how pig manure affects tree growth and the nitrogen cycle in two commonly planted tree species. The results showed that fertilized trees had higher soil nutrient concentrations but lower soil microbial biomass. Pine trees showed similar growth between fertilized and non-fertilized trees, while almond trees showed lower growth when fertilized. Leaf nitrogen concentrations decreased, but wood nitrogen isotopes increased in trees subjected to pig manure application. This suggests that pig manure alters nitrogen cycling in both soil and trees.