A lysimeter investigation of nitrogen gains and losses under various systems of covercropping and fertilization, and a discussion of error sources

The net gain or loss of soil nitrogen was studied in lysimeters at Riverside for ten years under four series of treatments: (1) fall applications of cereal straw (5,000 pounds per acre); (2) a mustard winter covercrop; (3) purple-vetch winter covercrop; (4) sweet-clover winter covercrop. In each series, one lysimeter was given no fertilizer, one 100 pounds, and one 200 pounds of nitrogen per acre per year as nitrate. A summer-harvested crop (first barley, later Sudan grass) was grown in all lysimeters. Total nitrogen and organic matter in the soil at the outset and at five-year intervals, amounts of nitrogen removed by cropping and leaching, and amounts added in seed, rain, irrigation water, and fertilizer were recorded.