Knowledge of temperature effects on whole canopy photosynthesis, growth, and development of potato (Solanum tuberosum L.) is important for crop model development and evaluation. The objective of this study was to quantify the effects of temperature on canopy photosynthesis, development, growth, and partitioning of potato cv. Atlantic under elevated atmospheric CO 2 concentration (700 mL L 21 CO 2 ). Potato plants were grown in day-lit plant growth chambers at six constant day/night temperatures, (12, 16, 20, 24, 28, and 32°C) during a 52-d experimental period in 1999 in Beltsville, MD. Main stem length and main stem expanded leaf number were measured nondestructively at 4 d intervals while leaf, stem, root, and tuber weights were obtained by destructive harvesting at biweekly time intervals. Canopy level net photosynthesis (P N ) was obtained from gas exchange measurements. The optimum temperature for canopy photosynthesis was 24°C early in the growth period and shifted to lower temperatures as the plants aged. Total end-of-season biomass was highest in the 20°C treatment. End-of-season tuber mass and the ratio of tuber to total biomass decreased with increasing temperature above 24°C. Accumulated biomass was a linear function of total C gain with a common slope for all treatments. However, the proportion of C allocated to tubers decreased with increasing temperatures. High respiration losses decreased total C gain at higher temperatures. When simulating photosynthesis and C assimilation in crop models, source-sink relationships with temperature and photosynthesis need to be accounted for.

An understanding of the genetic and environmental factors affecting the leaf area of a cereal crop is needed for accurate yield predictions by crop models. Field trials were conducted with three cultivars of winter wheat (Triticum aestivum L. em. Theil) at Manhattan, KS, under dryland and irrigated conditions and with six cultivars of spring wheat at Phoenix, AZ, in 1982 and 1983, respectively. Because leaf growth is strongly influenced by temperature, the rate of leaf appearance was expressed as leaves/thermal unit (Tu=[(TMu+TMIN)/2)-Tb); where Tu is thermal units, TMAX and T MIN are maximum and minimum daily temperatures, respectively, and Tb is the base temperature below which growth essentially ceases. The T, determined for three winter wheat cultivars, was not significantly different from ooc (P~O.OS). Phyllochron interval (PI), the inverse of leaf appearance rate, was determined from the inverse of the slope of the regression of Haun scale growth units against accumulated Tu. The R 2 values for these regressions were not less than 0.97 and 0.99 for spring and winter wheat cultivars, respectively. The PI was shorter for nonirrigated than irrigated winter wheat leaves (P~0.01) a~d for spring wheat leaves formed prior to double ridges than those formed later (P~0.01). Differences in PI were found among both spring and winter wheat cultivars (P~O.OS). These results illustrate the importance of determining PI for quantifying growth characteristics that determine the leaf area of a cereal crop.

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There are a few field methods available to directly measure water evapotranspiration (ET) along with its two components, evaporation from the soil (E) and from the crop (T). One such technique that measures T, uses sensors to calculate the sap flow (F) of water through the plant stem and is based on the conservation of mass and energy, i.e., the stem heat balance method. This instrument consists of a flexible heater that is wrapped around the plant stem with temperature sensors to measure the difference in temperature of F below and above the heater. This is a null method, where all inputs and outputs are known and the calculated F is a direct measure of T. This method has been used to measure T in a variety of crops, including cotton, grapes, olive trees, soybean, ornamental and horticultural crops. A new version of the EXO-Skin TM is the Stem Gauge Dual Channel Design (SGDC TM), which was commercially introduced and had a radically new design resulting in a different energy balance, compared to the original design, which needed experimental verification. An initial evaluation was done with potted cotton (Gossypium hirsutum, L.) plants in a greenhouse experiment showing that values of cotton-T measured with the new sensor were accurate; however, this comparison was limited to daily T < 2 mm/d. Thus, our objective was to expand the initial evaluation of the new sensor under field conditions and for daily values of cotton-T in the 2-7 mm/d range, representative of the semiarid Texas High Plains. For this purpose, cotton was planted on 12 June 2017 on a 1000 m 2 plot in a soil classified in the Amarillo series at the facilities of the USDA-ARS, Lubbock, TX. For a period of 15 days, 2 to 16 Sep 2017, we measured hourly cotton-T with the new sensors and with portable growth chambers (0.75 m × 1 m cross-section, and 1 m height) where water vapor flux was measured at a 10 Hz frequency using an infrared gas analyzer. We used three chambers and, in each chamber, the new sensors were installed on four cotton plants. We used linear regression analysis to compare hourly and daily values of cotton-T measured with the sap flow gauges against T measured by the chambers. Using a t-test (p < 0.001) we tested if the slope of the