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Fluid Journal : Winter 2011
detailed analysis of a global database that defines a robust, generic relationship between maize N uptake (U) and grain yield. The Maize-N model structure is predicated on the relationship between yield response and uptake efficiency defined by Agronomic Efficiency (AE), which is the product of N recovery efficiency (RE) and Physiological Efficiency (PE) whereby: AE = RE x PE = (Y-Y0)/N; RE = (U-U0)/N; PE = (Y-Y0)/ (U-U0). N requirement may be attained as a function of both yield potential and efficiencies of N use by the crop. The definitions of parameters are: • N=(Y--Y0)/AE • N = (U-U0/RE = (U-IN)/RE • Y = expected yield (kg ha-1) • Y0 = yield without N application (kg ha-1) • U = total crop N uptake (kg ha-1) • U0 = IN = total crop N uptake without Summary: The Maize-Nitrogen (N) model deploys a series of systematic and mechanistic analyses of climatic information, soil properties, and crop system characteristics for a given field. It is composed of three modules: 1) a maize yield module for estimating yield potential and its variation, 2) a carbon (C) and N mineralization module for estimating the indigenous soil N supply, and 3) a yield response module for estimating economically optimal N rate. Compared with conventional N rate recommendation schemes, the Maize-N model provides an analysis of biophysical and climatic parameters that govern N supply, N-use efficiency (NUE), and uptake in maize production systems. Maize-N also estimates the climate- adjusted, site-specific yield potential (Yp) for today's modern hybrids. The Maize-N model provides a knowledge-based decision-aid that is global in scope. The link to Maize-N is: http://www.hybridmaize.unl.edu/maizeN.shtml Maize-N model computer simulation program recommends nitrogen rates for maize crops. Fertilizer N rate algorithms currently used in the U.S. Corn Belt are highly empirical in nature and use varying degrees of stochastic analysis based on statistical analysis of regional N response curves. As a result, their utility is limited to the region in which they are developed and they offer little scientific insight as to the biophysical components governing the variation in actual N need. The Maize-N model has been designed to incorporate site-specific weather information and management data to drive estimations of both maize yield potential and indigenous N supply. Indigenous soil N supply is estimated from daily time-step simulation of C and N mineralization of crop residues, soil organic matter, and manures. Site specific long-term average yield potential is provided by the Hybrid-Maize simulation model (www.hybridmaize. unl.edu) as a subroutine from which the upper limit of attainable yield is calculated. The user may also input site yield history in lieu of simulated yield. These components of the maize growth environment are coupled to estimates of both maize N resource use efficiency and physiological efficiency derived from The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Winter 2011 • Vol. 19, No. 1, Issue #71 Drs. Daniel Walters, Tri Setiyono, Haishun Yang, Kenneth Cassman, and Achim Dobermann Winter 2011 The Fluid Journal 04 fertilizer addition (kg ha-1) • AE = agronomic efficiency of applied N (kg yield increase/kg N applied • RE = recovery efficiency of applied N (kg N recovered in the crop/kg N applied). For any N recommendation scheme to work, it must be able to estimate 1) likely maize yield for the season: Ya = attainable yield as a function of Yp, 2) indigenous soil N supply (IN) to the crop, 3) RE of fertilizers, and 4) economically optimal N rate (EONR) based on maize yield response to N rate, and fertilizer cost and price of maize spherical response surface within the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model. Maize-N uses estimates of these four components of the N demand-supply relationship in a maize system. Figure 1 displays the inputs required, process functions, and outputs of the Maize-N model. Yield potential. Using long-term weather records and crop management specifications input, Maize-N simulates yield potential for each year in the weather data file. It then computes the mean yield potential and its coefficient of variation (CV). The yield simulation module is based on the Hybrid-Maize Moving Toward A Global Approach To Nitrogen Management In Maize "Maize-N provides a knowledge-based decision aid"
Early Spring 2011