Quantification of Seedling Emergence of Kochia (Kochia indica) Affected by Temperature, Salinity and Seeding Depth

A controlled experiment was run to quantify emergence of Kochia indica under different temperature, salinity and seeding depth levels at the Yazd National Salinity Research Center in 2013. Treatments were five day/night temperature regimes: 20/10, 25/15, 30/20, 35/25 and 40/30 °C, five salinity levels: 2, 6, 10, 14 and 18 dS m-1, and seeding depth on the surface (0 mm), 5, 10 and 15 mm. Final emergence percent, emergence rate index and elapsed time (days) to reach 50% of the maximum emergence were measured. Results showed that the highest and lowest final emergence percentage was observed in 25/15 ° C and 40/30 ° C day/night, respectively. Final emergence reduced to 9, 22, 36 and 57% in 6, 10, 14 and 18 dS m-1 compared to 2 dS m-1, respectively. Final emergence was also reduced to 30, 44 and 72% in 5, 10 and 15 mm seeding depths compared to placing seeds on the soil surface. Regression analysis showed that final emergence percentage linearly decreased with increase in salinity and seeding depth levels. In turn, elapsed time (days) to reach 50% of the maximum emergence T50, increased as salinity and seeding depth increased, so that the highest T50 was obtained for 18 dS m-1 and seeding depth of 15 mm. Increase in salinity and seeding depth was associated with a significant decrease in emergence rate index. In addition, using a logistic regression equation, emergence rate of K. indica was quantified at each day after sowing for each temperature-salinity combination to predict the distribution range of the plant in these situations.