1950年美国在华盛顿州对于生长迟缓的30年生花旗松林带进行了施肥。这个林分在1910年采伐以后,曾经过度的清烧林场,土壤是砾质壤土,由地表向下,18吋深的地层为砾质砂壤土,其下10—15呎深的地层为砾质壤砂土。由地表向下深6吋的土壤的含氨量为0.10— In 1950, the United States applied fertilizers to the slow-growing 30-year-old Douglas fir forest belt in Washington State. The forest had been cleared of forest farms after harvesting in 1910. The soil was gravelly loamy, down from the surface. The 18-in-deep formation was gravel sandy loam and the 10-15 foot-deep formation was gravel Soil and sand. The 6-inch-deep soil from the surface has an ammonia content of 0.10-