A rapid procedure for estimating nitrogen mineralization in manured soil

A routine soil testing procedure for soil N mineralization is needed that i s rapid and precise. Not accounting for N mineralization can result in the over-application of N, especially in soils with a history of manure applica tion. Our objectives were to compare results from a recently proposed rapid laboratory procedure with: (1) long-term N mineralization under standard l aboratory conditions, and (2) actual forage N uptake from soil receiving da iry cattle (Bos taurus) manure in a 2-year field study. The rapid procedure is based on the quantity of CO2-C evolved during 24 h under optimum labora tory conditions following the rewetting of dried soil. Dairy cattle manure was surface applied beginning in 1992 at annual rates of 0, 112, 224, or 44 8 kg N ha(-1) to field plots on a Windthorst fine sandy loam soil (fine, mi xed, thermic Udic Paleustalf) near Stephenville, Texas (32 degreesN, 98 deg reesW). Results of the one-day CO2 procedure were highly correlated with so il N mineralized from samples collected in March of 1995 (P=0.004) and 1996 (P<0.001) and with forage N uptake (P<0.001) both years of the study. Resi dual inorganic N in the same soil samples was poorly correlated with soil N mineralization and forage N uptake.