Response of Hybrid Peach × Almond Trees to Increasing Rate of Soil-Applied Urea and Compost Nitrogen

ABSTRACT

The aims of the present study were to verify that high mineral N, specifically nitrate, may reduce plant growth by inducing a toxic effect on plants. GF667 plants were fertilized with urea or compost at rising rates of N (mg kg⁻¹): 0, 200, 500, and 1000. At 8, 37, and 94 days after fertilization, plant growth, tissue N, root starch concentrations, electrolyte leakage (E. L.), superoxide dismutase (SOD), and catalase (CAT) enzymes were measured. Unlike compost, urea application promoted a linear increase of soil nitrate and ammonium during the experiment. Plant growth responded to urea-N application rates according to a second degree function with the highest plant biomass found at a urea-N rate between 200 and 500 mg N kg⁻¹; and higher rates decreased plant growth. SOD and CAT showed no response to source and rate of N, while E. L. was higher in roots fertilized with urea-N.