Agron. Sustain. Dev. 25 (2005) 213-223
DOI: 10.1051/agro:2005016

Yield variation in organic winter wheat: a diagnostic study in the Southeast of France

Christophe David^a, Marie-Hélène Jeuffroy^b, John Henning^c and Jean-Marc Meynard<sup>d

a</sup>  ISARA Lyon, 69288 Lyon Cedex 02, France
^b  UMR d'Agronomie INRA-INA PG, BP 01, 78850 Thiverval Grignon, France
^c  McGill University, Department of Agricultural Economics, 211 Lakeshore, Sainte-Anne de Bellevue, QC, Canada H9X 3V9
^d  INRA SAD, BP 01, 78 850 Thiverval Grignon, France

(Accepted 18 January 2005)

Abstract - A diagnostic method for assessing regional variations in yield was implemented for a network of 24 organic wheat fields located in two neighboring regions, Diois and Val de Drôme (France). We studied: yield and its components; field environmental conditions of the fields; relations between indicators of potential limiting factors and yield components; and linkages between crop management and yield-limiting factors. The yield performances were low and variable (3.5 ± 1.4 t·ha^-1). The relative kernel number (RKN) was significantly related to nitrogen nutrition and weed density at flowering. The nitrogen nutrition index (NNIf) had a strong and positive effect on relative kernel number, while weed density (1/WF) had a negative effect. The percentage of kernel number variation explained by the regression model (RKN = 0.112 + 0.609 × NNIf + 0.2 × 1/WF) was adequate (Adj. R² = 0.53) with a RMSE of 0.09. The duration of the period of grain filling, reflected in the temperature sum, had a strong and positive effect on relative kernel weight (RTKW), while soil compaction and high temperature had a negative influence. Adjusted R² for the model was 0.42 with a RMSE of 0.16. The results confirm that legumes preceding crops improve nitrogen nutrition on subsequent winter wheat, e.g. the Nitrogen Nutrition Index at flowering (NNIf) = 0.51 ± 0.12 for a crop rotation with a rate of legumes over 37% vs. 0.41 ± 0.11 for a crop rotation with a rate of legumes under 25%. Alfalfa preceding crops significantly limited the weed density at harvest while stony soils and early sowing (before November 1st) enhanced weed density.

Key words: organic farming / winter wheat / yield / limiting factors / diagnostic method

Corresponding author: Christophe David davidc@isara.fr

© INRA, EDP Sciences 2005