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/m2) was positively significant correlated with the
average soil temperature through the period of cuts. The minimum dry weight
values (1.67 kg/m2) was at the 2nd cut at the temperature average (13.20°C),
while the maximum values of dry weight (6.70 kg/m2) was at the 23rd 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.