Remote sensing of winter wheat tiller density for early nitrogen application decisions

There is increasing evidence that scouting of winter wheat (Triticum aestiv um L.) fields to determine tiller density at Growth Stage (GS) 25 is useful in deciding if N should be applied. However, to obtain an accurate average of field tiller density, frequent and intensive measurements must be made, A solution to this problem may be remote sensing, The objectives of this s tudy were to determine (i) if a spectral index or digital counts in the nea r infrared (NIR), red (R), green (Gf, or blue (B) wavelengths could be used to estimate GS-25 tiller density across environments and (ii) if the inclu sion of within-field references would improve the estimation of GS-25 tille r density for determining N recommendations. Research was conducted at four site-gears in 1998 and 1999 using two wheat varieties, At three locations, a randomized replicated strip-plot design with three seeding rates was use d. The fourth location was an on-farm test with one seeding rate. Spectral indices and individual NIR, R, G, and B digital counts were tested for corr elation with tiller density at each site. Tiller density at GS 25 and NIR d igital counts were round to be consistently correlated (0.67 less than or e qual to r less than or equal to 0.87). The inclusion of within-field tiller density references resulted in a high correlation (r = 0.88) between relat ive tiller density and relative NIR digital counts across environments, Usi ng relative NIR digital counts to predict tiller density would have resulte d in the correct N recommendation 82% of the time.