Comparing nitrate leaching in lettuce crops cultivated under agroecological, transition, and conventional agricultural management in central chile

Nitrogen overfertilization is a common horticultural practice in central Chile, leading to the risk of nitrate leaching and contamination of aquifers and groundwater. The aim of the present study was to evaluate the effect of organic amendments on NO₃-leaching. Three sites with different management systems were selected: Agroecological (AE, 3-yr agroecological management), Transition (TR, starting agroecological management), and Conventional (CN, traditional conventional management). Two lettuce (Lactuca sativa L.) growing cycles (autumn-winter and spring-summer) were implemented at each site. Nutrition at AE and TR was based on organic fertilizers and microorganisms, and inorganic N fertilizers were used at CN. The pore water was sampled at the beginning and at the end of each cycle at the 70 cm depth. Lettuce yields and unit weight were measured. There was a significant effect of the site and time of sampling (both p = 0.000) on the NO₃-concentration in leached water. At the beginning of the first cycle, nitrate leaching was 2.2 times higher at TR and CN (370 ± 81 mg L^-1) compared with AE (163 ± 54 mg L^-1), reflecting the loss of previously accumulated soil N. Afterward, leaching at CN remained higher than at AE and CN, significantly varying between sampling times; however, it decreased by 37% to 80% compared with the initial measurement. Leaching at both AE and TR remained stable within a low range of 38 to 96 mg L^-1. Results showed that organic soil management is able to maintain a low rate of nitrate leaching in the soil compared with conventional management.