Soil impedance as a factor reducing crop seedling emergence, and its relation to soil conditions at sowing, and to applied water.
Seeds of calabrese, carrot, onion and sugar beet were sown in the field on successive occasions. Soil integral impedance (work done in penetrating the soil to 15 mm depth) was measured at the time of seedling emergence. There were negative linear relationships between seedling emergence and soil integral impedance, which accounted for over 80% of the variation in emergence of carrot, onion and sugar beet, and 67% of the variation in calabrese. In a laboratory experiment there was a marked interaction between temperature and soil integral impedance in the case of calabrese, but not the other crops. Pre-emergence losses of onion and calabrese were due largely to the failure of seedlings to emerge through the soil after germination, rather than failure of seeds to germinate, and it seems likely that this was also true of carrot and sugar beet. A multiple regression equation was derived relating soil integral impedance to soil compaction and soil surface moisture content at sowing, and to water applied after sowing.