Meta-response functions for corn yields and nitrogen losses were estimated from EPIC-generated data for three soil types and three weather scenarios. These metamodels were used to evaluate variable rate (VRT) versus uniform rate (URT) nitrogen application technologies for alternative weather scenarios and policy options. Except under very dry conditions, returns per acre for VRT were higher than for URT and the economic advantage of VRT increased as realized rainfall decreased from expected average rainfall. Nitrogen losses to the environment from VRT were lower for all situations examined, except on fields with little spatial variability.

Potential benefits of variable rate nitrogen application are illustrated and information needs identified. Lower costs of precision farming services, higher crop prices, and greater divergence in yield response potentials across management zones reduce the spatial variability required for profitable variable rate application. Information needs include identification and measurement of management zones within a field and estimation of management zone yield response functions, crop and input prices, and the cost of precision farming services.

Farmers are interested in knowing whether applying inputs at variable rates across a field is economically viable. The answer depends on the crop, the input. their prices, the cost of variable rate technology (VRT) versus uniform rate technology (URT). and the spatial and yield response variability within each tield. Methods were investigated for determining the range of spatial variability over which the rctum t o VRT covers its additional cost compared with URT in fields with rnultiple management zones. Models developed in this article, or variants thereof, could be uscd to hclp farmers make the VRT adoption decision. : nrrrncigrincnt :one.\. riitrogctz. prc~c.isioi1 , f i r r n~i n~, site,-.s/):l,c~cijic. Key Words mcrrzagerncJiz/, .spc~/iul hrc~cik-ei~cv~ c.crriahility propol.rior~.s, spatir/l vcrrinhility, vcrrinhlp rci/c7 teclznology. vic~l(l rrsponsc ~~c~ricrhiliry.Agricultural fields consist of numerous areas that differ from one another with respect to the factors that condition crop growth (Can-' t (11.; Hannah, Harlan, and Lewis; Hibbard c,t a/.; Malzer ct ~1 1 . ; Sawyer; Spratt and Mclver). Precision farming uses a set of technologics to gather information about the heterogeneous makeup of a farm field and uses that information to make management decisions that address site-specific crop nceds within the field (Swinton and Lowenber-DeBoer). Its component technologies en-Burton C. English is a professor, S.B. Mah:~jjanashetti

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