Composting and time of application affect corn (Zea mays L.) grain yield and dry matter response to deep-bedded swine (Sus scrofa L.) manure

Swine production in hoop structures is a relatively new deep-bedded husbandry system in which a solid manure/bedding pack accumulates. Currently, no guidelines are available to producers as to the optimal time (fall or spring) and form (composted or fresh) for applying hoop manure for the greatest crop performance and environmental protection. The main objective of this research was to test the effects of composting and time of application on corn (Zea mays L.) dry matter production and grain yield. Two field plot experiments were conducted near Boone, Iowa, each during two growing seasons. Results indicated no difference in grain yields among the fall applied hoop amendments, but inconsistent yield results from the spring applied fresh manure. Parameters used to indirectly monitor plant and soil N status suggested that spring-applied fresh manure did not supply plants with N as effectively as the other hoop amendment treatments. However, an experiment designed to closely examine the temporal relationship between soil N derived from spring applied fresh and composted manure and plant N uptake indicated no treatment differences. Analyses of corn growth responses to the spring applied hoop amendments suggested that fresh hoop manure may sometimes exhibit phytotoxic effects on corn seedlings and that composted manure may aid in drought tolerance relative to the effects of spring-applied fresh hoop manure. Mean N supply efficiency, defined as N fertilizer equivalency as a percentage of the total N applied, was greatest for fall-applied composted manure (34.7%), intermediate for fall-applied fresh manure (24.3%) and spring-applied composted manure (25.0%), and least for spring-applied fresh manure (10.9%). Based on these results, the optimum management strategies would be to apply fresh manure in the fall rather than composting it for spring application, and to compost fresh manure removed from hoops in the spring for fall application. These results are based on agronomic production only; economic and environmental impacts of N losses associated with the time and form of application could affect these recommendations