Effects of microwave irradiation by means of a horn antenna in the process of seed extraction on Scots pine (Pinus sylvestris L.) cone moisture content and seed germination energy and capacity

The paper presents the results of experiments involving the exposure of Scots pine (Pinus sylvestris L.) cones to microwave radiation. The pine cones were obtained from the Maskulinskie and Brzesko Forest Districts (both in Poland). Pine cone length, thickness, and weight were determined and found to be significantly different between the two locations. Pine cones were exposed to 2.45-GHz microwaves emitted by a horn antenna, which was either fixed or moving at a speed of 0.002 m s−1 over the cones. Total microwave emission time ranged from 30 to 441 s, depending on the test variant. The measured parameters included changes in pine cone moisture content as well as the germination capacity and viability class of the extracted seeds. It was found that pine cone moisture content decreased on average by 0.3 to 6 %, depending on the amount of microwave radiation applied. It was found that pine cone size, the amount of microwave radiation, and the distance between the cones and the horn antenna affected seed germination and viability class. In most experimental variants, the seeds were damaged by microwaves. Viable seeds (classes I and II) were obtained after 30 s of exposure to microwave radiation from a fixed horn antenna positioned at a distance of 0.04 m over the cones. The application of a moving antenna positioned 0.14 m over the cones resulted in seeds of viability classes II and III following a single microwave sweep over the seeds.