Nitrogen leaching and soil nitrate, nitrite and ammonium levels under differing fertilizer management in an irrigated wheat system in northern Mexico

Journal Articles
20091 small nutrient cycling in agroecosystems

Nitrate leaching from agricultural soils can represent a substantial loss of fertilizer nitrogen (N), but a large variation in losses has been reported. We report N leaching losses under four N fertilizer treatments and two farmer's fields in the Yaqui Valley, Mexico. In these irrigated wheat systems, farmers typically apply 250 kg N as anhydrous ammonia (knifed in) or urea (broadcast), with 75% applied directly before planting and 25% at the time of the first post-planting irrigation. Over two wheat seasons, we compared typical farmer's practices to alternatives that applied less N and more closely timed fertilizer application to plant demand. Field lysimeter measurements and predictions from a water transport simulation model (called NLOSS) were used to determine the amount of N leached over the season. Approximately 5 and 2% of the applied N leached below the root zone with the typical farmer's practice in 1995-96 and 1997-98, respectively. The alternative treatments reduced N leaching losses by 60 to 95% while producing comparable economic returns to the farmers. Leaching losses from the two farmer's fields were substantially higher (about 14 and 26% of the applied N). Our results indicate that the typical farmer's practice leads to relatively high N leaching losses, and that alternative practices synchronizing fertilizer application with crop demand can substantially reduce these losses.

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