When geese frequent lawns, a common question arises: is their waste a natural fertilizer or a lawn killer? Animal manure contains nutrients necessary for plant growth but can be damaging in high concentrations. The impact of goose droppings shifts drastically depending on volume and location, moving from a mild nutrient source to a localized biological and chemical hazard. Examining the scientific reality of its composition reveals why this misconception persists.
The Chemical Composition of Goose Droppings
Goose droppings contain the basic chemical building blocks turfgrass needs to grow, similar to other animal manures. Analysis shows the dried waste contains macronutrients, averaging around 2.2% Nitrogen (N), 1.0% Phosphate (\(\text{P}_2\text{O}_5\)), and 2.0% Potash (\(\text{K}_2\text{O}\)) by dry weight. This naturally occurring mixture of nitrogen, phosphorus, and potassium (NPK) is chemically similar to commercial fertilizers, which fuels the belief that the waste is beneficial.
A significant portion of the nitrogen is uric acid, the white component seen in fresh droppings. Uric acid is highly concentrated, differentiating the droppings from a slow-release, controlled fertilizer. Fresh droppings contain high amounts of Total Kjeldahl Nitrogen (TKN) and Total Phosphorus (TP). While these elements are technically plant food, their uncontrolled application leads to nutrient shock.
The Consequence of Nutrient Overload on Turf
The issue with goose droppings is their concentration and frequency of deposition, not the presence of nutrients. A single goose deposits substantial waste daily, and flocks create intense, localized fertilizer applications far exceeding the grass’s needs. This high concentration of nitrogen, primarily from uric acid, acts as a “hot” fertilizer. It rapidly desiccates the grass tissue, causing fertilizer burn, which results in the distinct brown, dead patches where droppings accumulate.
When uric acid breaks down, it undergoes nitrification, releasing hydrogen ions that lower the soil’s pH. This soil acidification stresses turfgrass roots, impeding the absorption of essential nutrients like calcium and magnesium. Furthermore, the nutrient ratio is often unbalanced, with a nitrogen-to-phosphorus ratio much higher than the 3:1 or 4:1 ratio found in balanced turf fertilizers.
An excessive nitrogen load promotes rapid, weak growth and creates a nutrient imbalance, favoring the growth of weeds over healthy turf. When large quantities of droppings wash into nearby water bodies, the excess nitrogen and phosphorus cause water pollution. This nutrient runoff triggers rapid algal growth and eutrophication in ponds and lakes, disrupting the aquatic ecosystem.
Biological Hazards and Physical Damage to Grass
Goose droppings introduce biological and physical stressors that harm turfgrass and create health risks, beyond the chemical imbalance. The waste is a known carrier of numerous zoonotic pathogens.
Biological Hazards
The waste carries bacteria such as E. coli and Salmonella, and parasites like Giardia. These biological hazards contaminate the grass and soil surface, posing a health risk to people and pets using the area.
Physical Damage
The physical presence of the droppings causes direct damage to the turf. The bulk of the moist, dense waste physically smothers the grass blades underneath, blocking sunlight and air. This localized deprivation causes the grass to die, leading to dead patches beyond those created by fertilizer burn.
The constant activity of foraging geese also contributes to soil damage. Flocks clip the grass blades too short, reducing the leaf area needed for photosynthesis and stressing the plant. Repetitive trampling by heavy birds leads to soil compaction, which restricts water penetration and impedes healthy root development.