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Oregon State Univ., Columbia Basin Agricultural Research Center, P.O. Box 370, Pendleton, OR 97801
* Corresponding author (Stephen.Machado{at}orst.edu)
Effects of factors influencing spatial and temporal variability of crop yields are usually expressed in crop growth patterns. Consequently, monitoring crop growth can form the basis for managing site-specific farming (SSF). This experiment was conducted to determine whether crop growth patterns forecast grain yields. Effects of irrigation rates (50 and 80% evapotranspiration, ET), elevation, soil texture, soil NO3-N, arthropods, and diseases on corn (Zea mays L.) growth and grain yield were evaluated at Halfway, TX, in 1998 and 1999. Data on plant height, leaf area index, leaf dry matter, stem dry matter, and ear dry matter were collected from geo-referenced locations (DGPS). These data were used to derive total dry matter, crop growth rate, and net assimilation rate (NAR). Grain yields at DGPS locations were classified into four distinct clusters. In 1998, a dry season, clusters were strongly influenced by elevation and soil texture. Grain yields were higher at high elevations where water use was high and soil texture was heavy compared with low elevations. Grain yields at low elevations also were reduced by common smut [Ustilago zeae (Beckm.) Unger] that preferred dry conditions. In 1999, a relatively wet season, clusters included areas with different elevation and soil texture combinations. Measured parameters forecast grain yields better in 1998 than in 1999. Differences in NAR were evident before the 12-leaf stage, making NAR a potentially useful measurement for early in-season management decisions. Biomass measurements, for which differences were observed after the 12-leaf stage, also may be used to formulate decisions for both in-season and the following season's management.
Abbreviations: CGR, crop growth rate • DGPS, differential global positioning system • EDM, ear dry matter • ET, evapotranspiration • LAI, leaf area index • LDM, leaf dry matter • LEPA, low energy precision application system • NAR, net assimilation rate • SDM, stem dry matter • SI, soil index • SSF, site-specific farming • TDM, total plant dry matter • VRT, variable rate technology
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