Matric and Osmotic Potential Effects on Seedling Emergence at Different Temperatures

Abstract

AbstractCrop seeds and seedlings are exposed to drought, salinity and/or low soil temperatures in some areas. Therefore, the combined effects of these stresses on germination and emergence is of considerable interest. A growth room study was conducted to determine the effects of matric and osmotic potential at different temperatures on the rate and total number of seedling emergence for wheat (Triticum aestivum L. cv. Neepawa) and two rapeseed species, Polish type (Brassica campestris var. Tobin) and Argentinean type (B. napus var. Westar). Twenty‐four treatments [3 species ✕ 2 matric potentials (−0.02 and −0.2 MPa) ✕ 4 osmotic potentials (−0.03, −0.3, −0.6 and −1.2 MPa)], each replicated four times, were arranged in a completely randomized design in two insulated tanks through which water from a temperature regulated water bath was calculated. Temperature at seed depth (15 mm) was maintained at 3, 6, 12, and 15 °C in four separate experiments. In each treatment ten seeds were planted in a 300‐mL container packed with a sandy loam soil (Entic Haploborall) to give a density of 1.25 g cm−3. For all species time to 50% emergence (T50) increased with decreasing temperature. Polish rape (the smallest seed) emerged fastest at all temperatures and soil water potentials followed by Argentinean rape and then wheat (the largest seed). Differences between species generally became less pronounced with increasing temperature at all soil water potentials. for soils with the lowest matric potentials the relationship between t50, and total potential (ΨT) was linear and almost all the variability in t50, could be explained by changes in osmotic potential. Effects of ΨT on emergence were most pronounced at intermediate temperatures. Except for wheat at 3 °C, the rate of emergence at the lowest osmotic potential was significantly slower in wet soils than in dry soils so that there was significant deviation from the linear relationship between t50, and #x03A8;T, established for the dry soils. These results suggest that to avoid salt accumulation around seeds in saline soils it may be advantageous to delay seeding until the soil matric potential is low enough that water uptake by seeds is through vapor flow.