Abstract

In citrus orchards, nitrogen uptake efficiency (NUE) is between 40 to 60% where any excess of nitrate is subjected to leaching below the rooting zone. The compound, 3,4-dimethylpyrazole phosphate (DMPP) inhibits the nitrification process in soil thus reducing/delaying nitrate leaching. The objective of this study was to evaluate the performance of DMPP added to ammonium sulphate (AS+DMPP), compared to ammonium sulphate (AS) and calcium-potassium nitrate (CPN), in fertigation of bearing orange trees grown outdoors in drainage lysimeters. Fertilizers were ¹⁵N-labeled to trace N through soil-plant-drainage system. Soil was sampled monthly from April to December and trees were destructively harvested in December. In trees fertilized with AS+DMPP, increased biomass was observed with a more profuse development of root system and higher fruit yield. Fertilizer ¹⁵N uptake significantly increased with DMPP addition. In AS+DMPP amended soils, increased values of -¹⁵N and lower -N concentrations were recorded from April to June as evidence of the inhibitory effect of DMPP on the nitrification process during this period. In CPN and AS fertilized soils, ¹⁵N losses in drainage solutions represented 9-10% of the fertilizer supplied whereas less than 3% was leached when DMPP was added. At the end of the cycle, highest NUE was recorded in the AS+DMPP treatment (69%), while CPN and AS had lower values (61% and 54%, respectively). Therefore, the use of DMPP enables a more efficient utilization of the fertilizer-N in citrus trees, minimizing the risk of nitrate-N pollution in groundwater. However, DMPP supply should be considered during spring fertilization, since high temperatures of summer months significantly reduced its activity.

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