Effect of Cattle Manure Application on the Gaseous Regime of a Sandy Soil

ABSTRACT

Organic amendments are essential to the sustainability of soils, as they help maintain the soil's physical and chemical properties. But, when applied in large dosage amounts, these amendments can drastically change the soil gas composition and have detrimental effects on plant roots and the microbial population. For 208 h, the present study monitored the O₂ deficit and loads of CO₂ and NH₃ in 750 mm deep sand columns, after applying cattle manure at rates equivalent to 0, 20, 40 and 80 tons/ha, within a layer at a depth of 150 mm to 250 mm. Also, a first order model using a manure biological oxygen demand (BOD) reaction rate coefficient k₁ and a soil re-aeration rate k₂ were used to model the O₂ deficit occurring over time in the soil columns. The results indicated that all three gases demonstrated a peak O₂ deficit, and loads of CO₂ and NH₃ after 16 h of manure application and in proportion with the rate of manure application. These peaks dropped quickly during the next 24 h, followed by a steady state up to 168 h and then a gradual loss of gas deficit and loads thereafter. This indicated that the manure/soil layer, at a depth of 150 mm to 250 mm, started to loose its permeability, 24 h after applying the manure. The first order model adequately simulated the soil column O₂ deficit and loads of CO₂ and NH₃, as long as the value of the re-aeration rate k₂ drops exponentially with time, as of 24 h. More research work is required to be able to predict the manure/soil gas permeability and its effect on the soil's gaseous regime.

KEYWORDS:

• Organic amendment
• oxygen
• carbon dioxide
• ammonia
• soil gas regime
• soil biological oxygen demand