Value of Manure and Sewage Sludge as N Fertilizer
1978
Pomares-Garcia, F. | Pratt, P. F.
A greenhouse pot experiment in a Hanford soil (Typic Xerorthent) with rates of feedlot manure at 0, 20, 40, and 60 metric tons/ha and sewage sludge at rates of 0, 10, 20, and 30 metric tons/ha combined factorially with 0, 50, 100, 150, and 200 mg N/kg of soil as (NH₄)₂SO₄ was conducted using barley (Hordeum vulgare L.) and sudangrass (Sorghum sudanense (Piper) Stapf.) as test crops. The objectives were to measure the net mineralization of N in the organic materials, to compare the availability of N in the organic materials with the N in (NH₄)₂SO₄ and to determine the critical levels for N and NO₃ in barley. The available N from the organic materials was estimated from the amounts required to equal the N in (NH₄)₂SO₄ in terms of barley forage production. Net mineralization was determined by soil analyses. Yields of barley forage were increased by additions of organic materials and (NH₄)₂SO₄. The addition of either manure or sludge decreased the response to (NH₄)₂SO₄. In a 2.5-month period after application, the manure gave an average of 0.65 kg of available N/ton, whereas the sludge gave 7.05 kg of available N/ton. This represents 4.2% of the total N from the manure and 17.0% of the total N in the sludge. In a 10-month period only 17.2 and 40.9% of the N in manure and sludge, respectively, had mineralized. The estimated critical levels of total N and NO₃⁻-N in barley forage were 2.0 and 0.12%, respectively. These values were independent of the N source. The minimum content of total N in barley forage at which NO₃⁻-N began to increase was about 2.0%. The level of NO₃⁻-N in plant tissue was more sensitive than total N to changes in N supply.
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