Crop phenology is fundamental for understanding crop growth and development, and increasingly influences many agricultural management practices. Water deficits are one environmental factor that can influence crop phenology through shortening or lengthening the developmental phase, yet the phenological responses to water deficits have rarely been quantified. The objective of this paper is to provide an overview of a decision support technology software tool, PhenologyMMS Vl.2, developed to simulate the phenology of various crops for varying levels of soil water. The program is intended to be simple to use, requires minimal information for calibration, and can be incorporated into other crop simulation models. It consists of a Java interface connected to FORTRAN science modules to simulate phenological responses. The complete developmental sequence of the shoot apex correlated with phenological events, and the response to soil water availability for winter and spring wheat (Triticum aestivum L.), winter and spring barley (Hordeum vulgare L.), corn (Zea mays L.), sorghum (Sorghum bicolor L.), proso millet (Panicum milaceum L.), hay/foxtail millet [Setaria italica (L.) P. Beauv.]. and sunflower (Helianthus annus L.) were created based on experimental data and the literature. Model evaluation consisted of testing algorithms using "generic" default phenology parameters for wheat (i.e., no calibration for specific cultivars was used) for a variety of field experiments to predict developmental events. Results demonstrated that the program has general applicability for predicting crop phenology and can aid in crop management.

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Spatial variation of winter wheat (Triticum aestivum L.) phenology across complex terrain has received little attention despite its importance for assessing overall crop status and making key precision management decisions. Temperature is the environmental factor explaining the greatest variation in phenology, and temperature varies across a landscape. Our primary hypothesis was that variability in thermal time (TT) by landscape position could explain the phenological variation, with a secondary hypothesis that spatial patterns of TT and phenology were related to terrain attributes. Four years of phenology and soil and air temperature data were collected from a 100-ha fi eld in northeast Colorado. Five developmental stages were monitored at 10 landscape sites each year. Terrain attributes were computed using 5-m-grid land surface elevation data. Spatial diff erences in reaching developmental stages across sites varied from 2 to 12 d within a year. Up to 96% of the phenological variation among years was explained when using a general TT model pooling all data. Refi ning the TT model, however, by using either air or soil TT at specifi c sites partially supported the primary hypothesis only for the relatively wetter 2004-2005 and 2006-2007 years (regression relationships explained up to 72% of the variation). Similarly, terrain attributes occasionally explained spatial patterns of phenology in the two wetter years, and attributes with the highest explanatory power varied among years and developmental stages. Further research is needed to better understand the controlling environmental factors and predict spatial patterns of wheat phenology for precision management using terrain attributes.

Considerable variability and patchiness have been observed within sites of native range dominated by blue grama [Botielow gra&z(H.B.K.) GrIffItha] range at the Central Plains Experhuental Range, Weld County, Colorado. Patches contalnhtg tall plants of blue grama with many seedstalks were interspersed with patches of short plants with few seedstalks. Differences in plant height were not entirely related to soil properties. Relative differences ln plant height among plants collected in the field were maintained when these plants were grown in a greenhouse environment. "Dry spots" (usually 2 to 4 m in dlameter) that contain dark-colored, wllted plants have s&o been observed during dry, hot weather. We found several differences in soil properties that could be responsible for the dry spots. Ail differences in soil properties were within the range for the soil series of the experimental site, an Ascalon flne sandy loam (Arldic Arglustoll). Sixty-two plants of blue grama were collected based on their variability from a single pasture, increased vegetatively in the greenhouse, and transplanted into a spaced-plant nursery. In the third growing season following transplanting, mean v8lues for measurements on replicated clones ranged from 202 to 719 reproductive culms per ramet, 25 to 46 cm height of reproductive cuhus, 17 to 24 cm basal diameter, 39 to 93 grams dry matter per remet, and from 11 June to 20 July for first anthesls. Somatic chromosome numbers were determined for 60 plants and 55 were tetraploids (4x = 40), 3 were pentaploids (5x = SO), and 2 were hexrploids (6x q 60). We concluded that the observed variablllty and patchlness apparently result from a comblnatlon of both gene& and edaphic f&on.

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