Potential Pasture Nitrogen Concentrations and Uptake from Autumn or Spring Applied Cow Urine and DCD under Field Conditions.

Jim Moir,Hong Di,Keith Cameron

doi:10.3390/plants5020026

Abstract

Nitrogen (N) cycling and losses in grazed grassland are strongly driven by urine N deposition by grazing ruminants. The objective of this study was to quantify pasture N concentrations, yield and N uptake following autumn and spring deposition of cow urine and the effects of fine particle suspension (FPS) dicyandiamide (DCD). A field plot study was conducted on the Lincoln University dairy farm, Canterbury, New Zealand from May 2003 to May 2005. FPS DCD was applied to grazed pasture plots at 10 kg·ha−1 in autumn and spring in addition to applied cow urine at a N loading rate of 1000 kg·N·ha−1, with non-urine control plots. Pasture N ranged between 1.9 and 4.8% with higher concentrations from urine. Results indicated that urine consistently increased N concentrations for around 220 days post deposition (mid December/early summer) at which point concentrations dropped to background levels. In urine patches, pasture yield and annual N uptake were dramatically increased on average by 51% for autumn and 28% for spring applied urine, in both years, when DCD was applied. This field experiment provides strong evidence that annual pasture N uptake is more strongly influenced by high urine N deposition than pasture N concentrations. FPS DCD has the potential to result in very high N uptake in urine patches, even when they are autumn deposited.

Highlights

Nitrogen (N) is essential for pasture growth, and is often the key limiting nutrient in grazed grasslands [1]
Mean annual pasture N concentrations in urine patches increased in autumn in both years as a result of DCD application (p < 0.001)
The largest difference between autumn urine patches was in year 2, where DCD treated patches had mean annual N concentrations

Summary

Introduction

Nitrogen (N) is essential for pasture growth, and is often the key limiting nutrient in grazed grasslands [1]. As pasture growth in the animal urine patch typically responds to the high N loading, grazed pastures typically form a visual mosaic of “lumpy” urine patches and flat “inter-urine” areas. The urine patch of the grazing animal has been identified as the main source of N leaching losses in grazed grasslands [4,5]. The potential of N leaching losses from cow urine patches is high, during the winter period when soils are draining [7]. Considerable recent research has focused on reducing N leaching losses and gaseous N emissions from the urine patch of the grazing dairy cow [8]. A key development in this field has involved the application of the nitrification inhibitor

Objectives

Results

Conclusion