Growth Analysis Based on Degree Days

Comparisons of growth analysis functions within and among experiments are often confounded by sources of variation other than those imposed by treatment. we suggest use of a temperature index, such as modified growing degree days, as the divisor in growth functions to facilitate treatment comparisons within certain experiments and to reduce the effects of differing temperature regimes among experiments on these comparisons. Three experiments were identified to provide data to analyze this new approach. Mean absolute growth rate (GR) and mean relative growth rate (RGR) were compared in two experiments with maize (Zea mays L.) conducted in eastern Nebraska. Previously published values of RGR and mean net assimilation rate (NAR) of barley (Hordeum vulgare L.) grown under controlled environments in a soil temperature and P fertility study were also evaluated. Use of modified growing degree days, rather than days, as the divisor in these growth functions led to the recognition of physiological differences due to or associated with treatment, which were previously masked by normal crop response to temperature, and clarified other treatment differences by reducing the effect of temperature

Spatial Ramifications of Crop Selection: Water Quality and Biomass Energy

The use of GIS in concert with simple or complex simulation modeling provides an unparalleled way to generate new data and to help a variety of audiences understand spatial patterns of data. From improved understanding, policy incentives can be crafted to reduce adverse environmental impacts of agricultural production at lower costs than would be necessary otherwise. In this chapter, two case studies demonstrate how GIS and modeling can be used to understand how crop selection and soils interact to effect environmental outcomes across an agricultural landscape. We addressed the needs of two distinctly different audiences: (1) a public drinking water supplier faced with increasing nitrate in a ground water source and (2) variety of stakeholders involved with planning a new biomass conversion facility to produce renewable fuels from grain or cellulosic feedstock. In both cases, the GIS output documents the benefits of the perennial legume alfalfa (Medicago sativa L.) in particular landscape areas, and provides a mechanism to compare alfalfa with corn (Zea mays L.) and soybean (Glycine max [L.] Merr.). GIS modeling files are attached (below) in a zipped folder (size \u3e 2.8 Gbytes)