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<br />I <br />I <br />'I' <br />i' <br />t <br />I <br />1: <br />t <br />a, <br />I <br />I, <br />I <br />t <br />I' <br />1\ <br />a <br />I <br />t <br />l' <br /> <br />1869 <br /> <br />The diurnal temperature variation, thermal periodicity, has an <br /> <br />impact on crop growth response and yield. Plants vary in their <br /> <br />response to thermal periodicity. For example, high nighttime <br />temperatures accelerate tomato growth. Night temperature is also <br />the dominate factor for potato production with the optimum <br />temperature about 54 degrees F. Decrease in night temperature has <br />been shown cO increase the sucrOSe content of sugar beets. <br /> <br />Late spring and early autumn frosts can significantly reduce crop <br /> <br />yield and in severe cases cause the loss of the entire crop. The <br /> <br />critical periods whenfrost can be most damaging during plant growth <br />are germination, flowering, and fruiting. There are marked <br />differences between plant species and physiological development <br /> <br />stages and the ability of plants to tolerace freezing temperature <br /> <br />conditions. Winter annuals such as wheat, barley, and oats are <br />considerably more tolerant of frost during part of their life cycle <br />than summer annuals such as corn and potatoes. Deciduous trees <br />often tolerate extreme cold when dormant but are very sensitive to <br /> <br />frost when in the vegetative stage, especially during flowering. <br /> <br />General temperature condi t ions depicted by records from several NOAA <br /> <br />weather stations located in the vicinity of the reservations are <br />shown on Tables 3.2, 3.3, and 3.4. Figures 3.1, 3.2, 3.3, and 3.4 <br /> <br />show isotherms for July and January mean minimum and maximum <br /> <br />temperatures. Temperature generally decreases from south to north <br />and from west to east. Temperature is inversely correlated with <br /> <br />3- 7 <br />