Using Time-to-Event Model in Seed Germination Test to Evaluate Maturity during Cow Dung Composting

Abstract

Maturity is a matter of concern for the utilization of livestock manures after composting because of the phytotoxicity of immature compost. The seed germination test is widely used for evaluating the maturity of compost. However, the process of seed germination was not studied by establishing a model for evaluating the maturity. Here, we established a time-to-event model for the data of germination proportion over time in a seed germination test with cow dung compost at different composting times. Results show that the profile of the seed germination proportion over time for Chinese cabbage (Brassica rapa L.) and garden cress (Lepidium sativum L.) were both well described by the model. Seed germination was delayed in composts at the early stage of composting from parameter t50 (half germination time) of the model. Parameter t50 was significantly negatively related to radicle length (RL), which indicated that there is an organic relationship between seed germination (i.e., radicle emergence) and radicle elongation. In conclusion, the immature compost can hinder seed radicle elongation by delaying seed germination.