Assessing soil phosphorus efficiency and water quality threats from manures and fertilisers

Abstract

This thesis focuses on the use of phosphorus (P) on agricultural land, especially how to improve P use efficiency and reduce potential P losses. The aim was to identify these “win-win” scenarios in four laboratory and plot experiments.

First, at laboratory scale under controlled environmental conditions, soil test P was monitored on contrasting Irish soil types. Soil composition was found to be a driver for both P availability and potential P losses post P application of manure/fertiliser. The first 70 days post application was also shown to have higher potential for P losses.

Second, a further microcosm study was conducted to focus on contrasting P manure/fertiliser types over the 70 days period on both agronomic and environmental soil tests. While fertiliser type can be ranked from most to least efficient, timing of application should also be considered regarding P fertilisation.

Third, a long-term agronomic plot trial was conducted to compare grass yield and quality from plots receiving cattle slurry or chemical P under growing conditions. No significant difference was found between treatments over the three years of experiment, confirming the results obtained in the previous experiments.

Finally, and in conjunction with the agronomic plot trial, a leaching trial was conducted at three sampling regimes exposed to natural rainfall conditions. While no difference in P concentration in leachate was found between treatments, no concluding evidence prevailed at these sampling regimes.

This thesis provides understanding of manure P use efficiency and potential environmental P losses, at a time when fertiliser use is at a premium. It concludes with a P use decision support tool to adapt to personal farm/land situations, and lead to more production with less potential for P losses to the environment. The research also provides insights for a more circular/autonomous P usage to reduce reliance on P imports and improve P recycling from manures.

Date of Award	Dec 2022
Original language	English
Supervisor	Phil Jordan (Supervisor), David P. Wall (Supervisor), Per-Erik Mellander (Supervisor) & Sara Vero (Supervisor)