Nitrogen Excretion by Dairy Cows Grazing Plantain (Plantago lanceolata) Based Pastures during the Lactating Season.

The use of plantain pasture in dairy systems can potentially reduce nitrogen (N) leaching losses via the lower N concentration in the urine (UNc) of cows. Reducing the urinary N load while cows graze pastures can reduce the risk of N leaching losses from urine patches. Research needs to demonstrate that these environmental benefits are not at the expense of milk production and farm profit. Three groups of 20 cows grazed in the following three pasture treatments: (i) plantain, (ii) plantain-clover mix (plantain, red [Trifolium pratense] and white clover), or (iii) ryegrass-white clover (wc) pastures, from spring to autumn for two years. Each year, pasture intake, diet quality, milk production and animal N (milk and urine) excretion were evaluated in spring, summer, and autumn. The cows grazing the plantain and plantain-clover mix pastures produced similar milk solids as cows grazing ryegrass-wc pasture but reduced their UNc during summer and autumn, when compared to those grazing the plantain-clover mix and ryegrass-wc pastures. Plantain reduced urinary N loads onto pastures by a greater number of urine patches with lower urinary N loading rates. The results demonstrate that plantain pastures do not diminish milk solids production from cows, and the lower UNc from summer to autumn could reduce N being lost to the environment.

The proportion of deposited urine patch intercepted by a delayed inhibitor application.

Nitrification inhibitors can reduce nitrous oxide (N2O) emissions and nitrate leaching losses from agricultural soils. Technologies have been developed to detect and target urine patches for inhibitor application, thereby reducing the total amount of inhibitor used. However, in practice there will be a time delay between the urine deposition and inhibitor application, potentially leading to physical separation of the inhibitor and urine that could reduce the effectiveness of the inhibitor compared to when the inhibitor and urine are well mixed. In this study, 2L of cattle urine was applied on two soil types in New Zealand. Twenty-four hours later the inhibitor dicyandiamide (DCD) was applied. The soil was sampled within 18 h and again after a rainfall event. DCD concentrations were measured in the 0-20 mm, 20-50 mm, and 50-100 mm depth ranges. The movement of the urine in the soil was simulated using the HYDRUS model. Before the rain most of the DCD was within the top 20 mm and intercepted 21-29% of the urine. After the rainfall event the DCD concentration decreased in the 0-20 mm layer and increased in the 20-50 mm layer. 18-55% or 63-79% of the urine was intercepted by DCD at a concentration of >4 ppm using the measured and modelled DCD concentrations, respectively. However, only 0-27% or 0-53% of the urine was intercepted at a DCD concentration >10 ppm.