Influence of soil frost and air temperature on spring growth of timothy in northern Sweden
1990
Landstroem, S. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Vaextodlingslaera)
An investigation of the onset of growth and the rate of growth of timothy during 7 years in northern Sweden (Umeaa) is reported. Observations and samplings were made twice a week from snow-melt until just before midsummer (late June). The growth rate was determined by harvesting small plots at intervals of 3 or 4 days. Measurements of minimum temperature and of the soil frost melting from the ground surface and downwards were made. The very first signs of growth were irregular and therefore the onset of growth was defined as the time when the leaves were so large that the whole field changed into a new green colour. It was concluded the the rule for onset of growth in northern Sweden is the following: onset of growth of timothy mostly occurs 3-4 days after the daily mean temperature has reached +5 deg C with the condition that the soil frost must have melted to at least 20 cm depth, otherwise the onset of growth is delayed until 3-4 days after the soil frost has melted to 20 cm depth. A marked increase in temperature resulted within one or two days in an increase in growth rate. A considerable decrease in temperature gave almost immediately a lower growth rate, at least in earlier stages of development. Relations between growth rate and temperature degree sums with different base temperatures (0 deg, +3 deg, +5 deg C) were analysed with non-linear regression. A temperature degree sum (base 0 deg C) from the onset of growth gave the highest coefficient of determination (0.97). The maximum value of crude protein content in timothy occurred about 20 days after the onset of growth, and the maximum value of digestibility was reached about 5 days later. In normal years the appearance of the first node was related to the time for the start of the decline in digestibility.
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