Yard Trimmings as a Source of Nitrogen for Crop Production

Compost Science & Utilization, (2004), Vol. 12, No. 1, 11-17

A.I. Bary, C.G. Cogger and E.A. Myhre

Washington State University Puyallup Research and Extension Center, Puyallup, Washington

Yard trimmings from sources rich in grass clippings have the potential to supply nutrients for crop production. Our objectives were to estimate N availability from yard trimmings and determine their effects on crop production, soil nutrients, and organic matter levels. We conducted a field experiment, comparing three consecutive years of yard trimmings applications (22, 44, or 66 Mg ha-1 yr-1 dry weight) with inorganic N (112 kg N ha-1 yr-1) and zero-N controls in a silage corn (Zea mays L.) - winter triticale (Triticosecale spp.) rotation. The yard trimmings were screened and ground, and allowed to heat for a short period. They were incorporated each spring before planting corn. We measured crop yield and N uptake, and estimated apparent N recovery (ANR). We measured soil inorganic N two weeks after yard trimmings application and after corn harvest. In a one-year on-farm demonstration, we compared three sources of yard trimmings applied at a single rate. Yard trimmings applied at 44 Mg ha-1 dry weight provided sufficient available N to replace inorganic N. For silage corn grown with summer irrigation, estimated ANR in the crop was 7% in Year 1, 19% in Year 2, and 18% in Year 3 at the 44 Mg ha-1 yard trimmings rate, compared with a mean ANR of 65% for the inorganic N treatment. Postharvest soil nitrate residual (0- to 120-cm depth) was similar for the 44 Mg ha-1 treatment and inorganic N treatment. We observed variation in N availability with year and source of material. Yard trimmings also increased soil test K and organic matter.

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