Nitrate leaching under different levels of irrigation for three turfgrasses in southern Puerto Rico

Abstract

Inadequate nutrient and irrigation management of turfgrass may result in nitrate (N0₃) losses by leaching, and may contribute to elevated N0₃-N concentrations in groundwater. A field study was conducted to evaluate the effect of three irrigation levels on the N03-N concentration in soil solution and the mass of total N0₃-N lost by leaching for three grasses: Bermuda [Cynodon dactylon (L.) Pers.], Centipede [Eremochloa ophiuroides (Munro.) Hack], and Zoysia manila [Zoysia matrella (L.) Merr.]. The study was conducted at Juana Díaz, Puerto Rico, on a San Antón soil (fine-clayey, montmorillonitic, isohyperthermic Cumulic Haplustolls) from June 2001 until September 2002. Soil water N03-N concentrations below the root zone were obtained from water samples collected from suction lysimeters. The levels of irrigation applied were 75,100 and 125% of the daily evapotranspiration (ET), calculated by using the pan evaporation method. Grass was fertilized with 165 kg N/ha/yr, split into four applications. The Bermuda grass exhibited the highest rate of horizontal growth (cover), reaching maximum cover in 45 days, whereas the others reached maximum cover in 120 days. Bermuda grass was the most efficient in reducing the loss of N03-N, with a mean annual soil water concentration below the root zone of 3.24 mg/L, whereas Zoysia and Centipede grasses were less efficient with mean annual soil water concentrations below the root zone of 17.4 and 17.8 mg/L, respectively. The soil solution concentration of N0₃-N did not change significantly for the Bermuda grass with increases in the level of irrigation. However, lower mean annual N0₃-N concentrations were observed for the Centipede and Zoysia grasses at the irrigation levels of 100% and 75% ET, with mean values of 14.0 and 11.1 mg/L, respectively. The Bermuda grass had an acceptable color index at the 100% ET, and resulted in decreased N0₃-N concentrations and mass losses. On the other hand, Zoysia and Centipede grasses presented a commercially acceptable color index and minimal N0₃-N leaching at the 75% ET irrigation level. The results from this study provide valuable information related to water and nutrient management for the turfgrass industry in southern Puerto Rico.