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CROP ECOLOGY, PRODUCTION & MANAGEMENT

Incorporating Radiation and Nitrogen Nutrition into a Model of Kernel Number in Wheat

^a UMR d'Agronomie INRA-INA PG, BP 01, 78850 Thiverval-Grignon, France
^b INRA, UMR SAGAH INRA/INH/Université d'Angers, 42 rue Georges Morel, BP 57, 49071 Beaucouzé cedex, France

Corresponding author (jeuffroy{at}bcgn.grignon.inra.fr)

Wheat (Triticum aestivum L.) kernel number per square meter (KN) depends on radiation, temperature, and crop N nutrition. Some models of KN using climatic data or N nutrition characteristics as input variables account for variations either in radiation and temperature or in N nutrition, but not for both. Our objective was to produce a model of KN that accounts simultaneously for variations due to radiation, temperature, and crop N nutrition, and that has input variables that are simple to measure or to simulate. Field experiments were conducted over 3 yr with ‘Trémie’ winter wheat. Treatments involved the application of N fertilizer at different dates and rates to achieve various N deficiencies and the use of shading nets for various periods during spike growth to reduce incident radiation. Crop N status was assessed by determining N nutrition index (NNI) at anthesis. The KN was counted, it ranged from 9420 to 31 036 kernels m^-2. Two characteristics of N nutrition (NNI at anthesis and IDD, the duration of deficiency before anthesis multiplied by its intensity) and three characteristics of radiation and temperature (photothermal quotient calculated from 45 d before anthesis to anthesis, from 30 d before anthesis to anthesis and from 20 d before anthesis to 10 d after anthesis) were used as input variables. Six relationships combining one characteristic of N nutrition and the photothermal quotient over one period were estimated. The best fit was obtained for a relationship between KN and the logarithm of NNI at anthesis and photothermal quotient over the 45 d preceding anthesis (R² = 0.883, n = 19). This relationship could be useful for estimating KN in crop models, as its input variables are simple to simulate.

Abbreviations: DM, dry matter • IDD, intensity of deficiency before anthesis multiplied by duration of deficiency before anthesis • KN, kernel number per square meter • Nc, critical N concentration • NNI, nitrogen nutrition index • PAR, photosynthetically active radiation • Q, photothermal quotient • Q20+10, photothermal quotient from 20 d before anthesis to 10 d after anthesis • Q30, photothermal quotient from 30 d before anthesis to anthesis • Q45, photothermal quotient from 45 d before anthesis to anthesis