Variations of Soil Temperature in Sandy Soil and Their Relations to Alfalfa Plants

Abstract

To study the variations of soil temperature in sandy soil and their relations to Alfalfa plant growth, eight thermal sensors were placed in two sites at different depths in a sandy soil at Ismailia Agricultural Research Station, and cultivated with alfalfa crop (Medicago sative) under sprinkler irrigation. After the plantation of alfalfa seeds, four plots were chosen for soil temperature (A, B, C, and D); each one represented one meter square plot. Two sites; one between A and B and the other between C and D plots were chosen to put the temperature sensors at four depths of; 0.05, 0.10, 0.15 and 0.30 m. At the end of the experiment, the average of the two sites was calculated for each depth. The alfalfa plants were cut every 28 days for each plot (seven days apart in dual way between the four plots) from January till October, where they equal 40 cuts/10 months. The results revealed that soil temperature decreased at the day night until the seventh to eightieth O'clock a.m., after sunrise it increased at the day light until the third to fifth O'clock p.m. at the surface layers depth for the previous months, while the values of the studied deepest layer (0.3m) decreased at day night until the ninth to tenth O'clock a.m., and after sunrise, it increased until the sixth to eighth O'clock p.m. after sunset. The minimum soil temperatures were 6, 6.64, 6.07 and 9.33ºC in February and the maximum were 35.58, 34.83, 38.15 and 31.79°C in July for the aforementioned depths, respectively. Alfalfa dry weight (kg/m 2 ) was positively significant correlated with the average soil temperature through the period of cuts. The minimum dry weight values (1.67 kg/m 2 ) was at the 2 nd cut at the temperature average (13.20°C), while the maximum values of dry weight (6.70 kg/m 2 ) was at the 23 rd cut at soil temperature average (26.20°C). The available K, Mn and Zn showed no significant correlation with soil temperature, while the available Fe was highly significant correlated with soil temperature. There were negative significant correlations between plant NPK concentrations and soil temperature, and this related to dilution with increase plant growth, whereas the uptake of P and K showed positive and significant correlation with soil temperature. Key words: alfalfa crop, sandy soil, soil temperature. INTRODUCTION:Soil temperature is a factor of primary importance in determining the rates and directions of soil physical properties and strongly influences its biological processes, such as seed germination, seedling emergence and growth, root development and microbial activity (Hillel, 2004). A change in soil temperature, caused by a gain or a loss of heat from the soil, depends on the specific heat and the