Effects of tillage management and timing and mode of nitrogen application on bread wheat yield and yield components in an irrigated bed planting system in northwestern Mexico

Project leader: Prof. Dr. A. Bürkert
Doctoral Student: Kathrin Grahmann
Duration: 2013 - 2015
Funding: DAAD

The Yaqui Valley located in Northern Mexico near Ciudad Obregón is agro-climatically representative of areas where 40% of the wheat is produced in the developing world (Indian, Pakistani Punjab, Nile Valley). This area is characterized by grain yields >6 t ha^-1 and high fertilizer inputs which average for wheat 275 kg N ha^-1. This intensity explains the necessity to find more efficient N fertilizer strategies. Firstly, eutrophication of water bodies due to its over-application should be prevented and NOx/N₂O emissions and NO₃ leaching should be reduced. Secondly, and maybe more important for the farmer, production costs need to be reduced by more efficient fertilizer application, since N fertilizer is one of the most important and expensive inputs for farmers. Worldwide nitrogen use efficiency (NUE) averages 33% in cereals (Raun and Johnson, 1999), indicating the potential to improve NUE by improved management and varietal selection. Cropping systems have changed in the Yaqui Valley over the last decades. During the last 25 years more than 95% of the farmers changed from flood irrigation on the flat to planting on raised beds with furrow irrigation. Another drastic change was that farmers changed their residue management from burning them to incorporating the residues. Finally, in the last 20 years researchers tried to increase the sustainability of the beds by making them permanent through avoiding tillage (only reshaping of beds) and retaining residues on the surface.

This project aims to:

1. Quantify the effect of tillage practice, residue management and crop rotation on nitrate leaching, immobilization, mineralization, ammonia volatilization, residual soil N and plant uptake of N fertilizer in an irrigated, arid wheat production system.
2. Evaluate the effect of timing of N application (basal, split, application at 1^st node for wheat and 4 to 5 leaf stage for maize) on NUE and grain quality in conventional and CA systems.
3. Determine the effect of mode of N application (broadcast, banded with disc in the furrow or top of the bed) on NUE in conventional and CA systems.
4. Translate results from (1) to (3) into recommendations for farmers of alternative management practices that will reduce both N leaching losses and trace gas emissions, while remaining grain quality and yields.