Measuring Soil Nitrogen Mineralization Under Field Conditions

The amount and rate of soil N mineralization are important components that can be used to predict preplant N fertilizer application and to evaluate the need for N fertilization during crop growth. This study's purpose was to evaluate the buried polyethylene bag technique as a method for characterizing the N mineralized under field conditions during the cropping season. Soil (Xerollic Calciorthids) was placed in polyethylene bags and buried in the 0 to 45 cm root zone of fallowed soils and where corn (Zea mays L.) and potato (Solanum tuberosum L.) were being grown. The NO?-N content of the soil in the bags was compared with that in the root zone at selected time intervals (10 to 14 days) from April to October. The soil NO?-N concentrations in the buried polyethylene bags were similar to those in irrigated fallow soils from April to October after correction for different soil water contents. The N-mineralization rate between sampling intervals had an average temperature coefficient (Q??) of 2.3 between 10 C and 30 C. The relative N mineralization rate was proportional to the soil water content expressed as a percentage of the available water-holding capacity. The N uptake by corn and potato crops predicted from NO?-N changes in the rooting zone and in the buried polyethylene bags resembled those measured by plant sampling. The buried polyethylene bag technique has potential for monitoring the soil N mineralization process during the cropping season and for estimating N uptake by crops. It also provides an alternative method for estimating soil N availability for future crops and its use should maximize N-fertilizer efficiencies