Pasture Improvement: Impact of Grazing Animals on Pasture Fertility

Table of Contents

1. Introduction
2. Urine
3. Dung
4. Other Pasture Improvement Recommendations
   • Choosing the Improvement Technique
   • Rejuvenation
   • Renovation
   • Seeding into the Sod
   • Broadcast Seeding
   • Limited Tillage
   • Frost Seeding
   • Using Livestock to Renovate Pastures
   • Fertilizing Pastures
   • Nutrient Cycling
   • Soil Tests
   • Weed Control
   • Trampling Effects
5. Related Links

Introduction

Most of the nutrients animals eat while on pasture are returned to the ground in either urine or dung. The recycling of nutrients through animals can prove to be either a valuable fertilizer source or the cause of tremendous pasture waste. If not managed correctly, the fouling of pastures can cause selective grazing and a deteriorating pasture.

Urine

Areas in the pasture contaminated with urine are not usually rejected by animals. Sheep actually prefer to graze these areas. Due to high nitrogen content in urine, plant composition in the affected areas may change. Urine patches receive the equivalent of 300–500 kg of nitrogen/ha. This level of nitrogen stimulates grass growth for up to 4 months and may depress legume growth. In hot weather, grasses and legumes may be scorched and killed by urine.

Dung

Animals avoid plants growing near dung. Grasses normally dominate these ungrazed areas, as the nutrients in the manure improves their growth. Depending on the climate, which affects how quickly the dung is broken down, and the stocking rate, the area left ungrazed can be several times larger than the area covered by dung. In fields with low stocking rates, pasture losses because of fouling can be as high as 45%. Under high stocking rates, loss is reduced to 10% or less, as competition among animals for feed force them to graze closer to the dung. More importantly, the higher density of hooves breaks up and distributes the dung across the pasture.

Dung effects the grazing behaviour of animals long after the apparent disappearance of dung from the pasture. It can take 2 pasture seasons before a contaminated area is no longer rejected (Figure 3-1). Often the areas between dung patches are overgrazed.

The pasture underneath dung deteriorates quickly as the plants are either smothered or killed by high nutrient levels. This area is then taken over by nearby plants, or from seeds in the soil or dung. Weeds then establish in a pasture’s bare patches. There are extremely high rates of nutrients from urine and dung deposited in the areas where animals camp in the pasture. In time the "camp" may become bare ground, surrounded by mature grass and weeds.

Regular harrowing with chain harrows or drag harrows pulled upside down spreads the dung, prevents damage to the pasture and wasted forage. This also uses the natural fertilizer contained in the dung.

Horses foul the same part of the pasture throughout the entire grazing season. Reduce forage wastage by providing a small grazing area at the start of the season. This reduces the area horses leave their droppings, maximizing the grazing area.

Figure 3-1. The effect of dung on grazing. Animals will avoid grazing areas contaminated with dung for long periods of time.

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Related Links

... on forages and pastures, visit Forages and Pastures (OMAFRA)
... on weed control, order Publication 75 Guide to Weed Control: Forage Crops
... on agronomy for field crops, order Pub. 811 Agronomy Guide for Field Crops: Chapter 3 Forages
... on field crop protection, order Publication 812, Field Crop Protection Guide
... on livestock, visit Livestock (OMAFRA)