Nitrate leaching through climatologic water balance in a fertigated coffee plantation

Rafael Pivotto Bortolotto,Isabeli Pereira Bruno,Klaus Reichardt,Luís Carlos Timm,Adilson Nunes Da Silva,Durval Dourado-Neto

doi:10.1590/s0034-737x2013000600006

Abstract

Nitrate losses from soil profiles by leaching should preferentially be monitored during high rainfall events and during irrigation when fertilizer nitrogen applications are elevated. Using a climatologic water balance, based on the models of Thornthwaite and Penman Monteith for potential evapotranspiration, drainage soil water fluxes below the root zone were estimated in a fertigated coffee crop. Soil solution extraction at the depth of 1 m allowed the calculation of nitrate leaching. The average nitrate concentration in soil solution for plots that received nitrogen by fertigation at a rate of 400 kg ha-1, was 5.42 mg L-1, surpassing the limit of the Brazilian legislation of 10.0 mg L-1, only during one month. For plots receiving 800 kg ha-1 of nitrogen, the average was 25.01 mg L-1, 2.5 times higher than the above-mentioned limit. This information indicates that nitrogen rates higher than 400 kg ha-1 are potentially polluting the ground water. Yearly nitrate amounts of leaching were 24.2 and 153.0 kg ha-1 for the nitrogen rates of 400 and 800 kg ha-1, respectively. The six times higher loss indicates a cost/benefit problem for coffee fertigations above 400 kg ha-1.

Highlights

Irrigated coffee plantations have increased significantly in the last years in Brazil, mainly in coffee growing areas, which traditionally were not used to grow this sort of crop
The coffee crop assessed in this study received periodical fertigations, and their contribution coupled with rainfall are shown in Table 5, which contains estimated values of drainage soil water fluxes
The two models of potential evapotranspiration used in the climatologic water balance calculations lead not to very different values of drainage soil water fluxes

Summary

Introduction

Irrigated coffee plantations have increased significantly in the last years in Brazil, mainly in coffee growing areas, which traditionally were not used to grow this sort of crop. During the last two decades, coffee cultivation in Brazil was extended from traditional coffee growing areas to the Brazilian savanna or “cerrado” plains, as those of Bahia state. Coffee growers in this region have been using nitrogen (N) rates (of the order of 600 - 800 kg ha-1 year-1 of N) far above those applied in other coffee producing areas (150 - 450 kg ha-1 year-1 of N) (FAO, 2010; Bortolotto et al, 2011; Bruno et al, 2011; Neto et al, 2011). Without any scientific basis for these excessively high N application rates, losses to the environment are likely to be occurring (Milroy et al, 2008; Sitthaphanit et al, 2009)

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Results

Conclusion