EFFECTS OF SOIL FUMIGATION AND N SOURCE ON SOIL INORGANIC N AND TOMATO GROWTH

Soil fumigation, commonly used in vegetable production, may alter the rate of nitrification, affecting availability of N for crop use. The o bjective of this research was to examine effects of soil fumigation an d N fertilizer source on tomato growth and soil NO3-N and NH4-N in fie ld production. Experiments 1 and 2 included application of methyl brom ide at 420 kg ha(-1) to a Norfolk sandy loam (fine loamy siliceous the rmic Typic Kandiudult) in combination with preplant applications of ca lcium nitrate, ammonium nitrate, and ammonium sulfate at 144 kg N ha(- 1). An additional fumigant, metam-sodium, was included in the second e xperiment at 703 L ha(-1) (268 kg sodium methyldithiocarbamate ha(-1)) . Experiment 3 included methyl bromide and metam-sodium, with ammonium sulfate as the sole source of N applied at 144 kg N ha(-1). In the fi rst two studies, fumigants had little or no effect on soil NH4-N or NO 3-N concentration. Tomato plants were larger and fruit yield was great er in fumigated plots, but there were few growth or yield responses to N source. In the third experiment, fumigants increased concentration of soil NO3-N and NH4-N at 16 days after fumigation (DAF), however, th ere was no effect on nitrification owing to fumigants. It appears that N source selection to overcome inhibition of nitrification is not nec essary in plant production systems that involve fumigation.