How does Ecotain plantain reduce nitrate leaching?
Based on the research, it appears plantain reduces nitrate leaching via four mechanisms
Urine dilution effect Nitrate leaching occurs due to a high concentration of nitrogen (N) in the urine patch.
When Ecotain plantain is included in the cow’s diet, the number of urination events and total urine volume increases. Consequently, the urinary N concentration decreases.
A meta-analysis of animal experiments showed urinary N concentration dropped, on average, by 30%, depending on the conditions and the proportion of Ecotain plantain in the diet, due to 17% greater urine volume and 22% reduced total N excretion2. Why is there an increase in urine volume? At least in part, it is because animals fed plantain ingest more water from the pasture. Ecotain has, on average, around 30% lower dry matter content than perennial ryegrass3. Where Ecotain makes up more than 30% of the diet, water intake through the feed alone exceeds animal requirements4.
It is possible there are other factors contributing to a diuretic effect of plantain. We are investigating these in the Plantain Potency and Practice Programme.
Animal partitioning effect Nitrogen consumed by ruminants is partitioned into different pools, including milk, faeces and urine.
Exactly how much N goes into each output depends on the animal’s diet. When Ecotain plantain is included in a cow’s diet, the portion of N intake partitioned to urine falls, and the amount partitioned to faeces and milk rises, compared to perennial ryegrass. That is due to a lower proportion of soluble proteins and a higher carbohydrate to protein ratio3,4.
Mechanisms 3 and 4:
Direct and indirect soil N retention effects Research using lysimeters has shown Ecotain plantain may retain N in the soil, giving plants more time to use the excess N in a urine patch, and reducing loss via leaching and N2O emission.
Lysimeter studies in the Forages for Reduced Nitrate Leaching programme showed nitrate leaching from urine patches was significantly reduced (70-80%) under Ecotain, even when the urine was from cows grazing ryegrass/ clover pastures5. We believe this is due to release of plant secondary compounds from the roots and litter that slow down the rate of nitrification, i.e., the conversion of ammonium to the more soluble nitrate. This effectively gives the pasture more time to use N before it’s lost from the root zone.
This effect may be further enhanced with the addition of urine from cattle or sheep grazing Ecotain (the indirect N retention effect). Soil microcosm incubation studies showed a significant drop in the nitrification rate from urine derived from dairy heifers and sheep that grazed plantain monocultures, compared with ryegrass/clover mixtures6,7,8.
Currently, Overseer’s estimates of nitrate leaching do not reflect any effects on nitrification rate, but research suggests these effects are potentially large. The Plantain Potency and Practice Programme will improve our understanding of the soil mechanisms, and the extent of the effects under different proportions of Ecotain in pasture, for different soil types and climates.
Various studies have shown there is less water drainage below the root zone under Ecotain pastures. This is another potential contributing mechanism to reduced leaching5.
Plantain in Overseer
When plantain is modelled in Overseer, farmers can expect to see, on average, a 6% reduction in nitrate leaching for every 10% of plantain in the pasture. However, the estimated reduction will vary between farms. This is because of different soils and climate, and differences in use of supplements, which determine the proportion of plantain in the diet ingested.
Currently, Overseer estimates the reduction in nitrate leaching resulting from changes to urinary N only. We expect the magnitude of these modelled reductions to increase when the soil effects of plantain are also accounted for, after the current research programme is completed.
How plantain affects GHG emissions
Plantain has been shown to reduce N2O emissions from the urine patch by up to 50% in pastures with 30-50% plantain (Agritonic cultivar)1 . As with nitrate leaching, the reductions were attributed to direct plant/soil effects and an indirect effect from urine from animals grazing plantain. We need to better understand the mechanisms of these effects before N2O emissions reduction from plantain can be included in models like Overseer.