Utilization of Soil and Fertilizer N by Oats in Relation to the Available N Status of Soils

Effects of rates of NaN 15 O 3 on the amounts of N derived by plants from soil and fertilizer in relation to the N and organic matter status of soils were determined. The 12 soils ranged more than fourfold in relative capacity to supply N to the crops. A values, with few exceptions, were independent of N level applied and were highly correlated with dry matter yields (r = 0.939) and total N uptake (r = 0.981) from zero‐N pots. The uptake of soil N increased with level of N applied. This was attributed primarily to reactions involving rhizosphere microorganisms.