Effect of Soil Amendment on Soil Microbial Activity and Asparagus Yield under a Replant Situation

Replant suppression is a major threat to asparagus production worldwide. Soil amendment may help improve soil quality and could enhance plant growth and yield. Therefore, studies were conducted from 2007 to 2009 to test effects of soil amendment on asparagus production. Treatments included dairy compost (25 t/ha in 2007 and 12.5 t/ha in 2008), mustard bran (5 t/ha), SoilBuilder (R) (microbial soil amendment at 19 L/ha), TerraClean (R) (19 L/ha of the mixture of 22% hydrogen dioxide and 5% peroxyacetic acid), control with fungicide treated crowns, and control with untreated crowns. The studies were conducted at two commercial farms under a replant situation. Site 'A' was unfumigated and site 'B' was fumigated with metam sodium. A randomized complete block design with four replications was used. Plots were managed by growers following commercial production practices. Evaluations consisted of soil microbial biomass and community structure assessments, and asparagus yield. In all sites soil samples from the compost treatment showed the highest microbial biomass. However, this did not translate into higher microbial functional diversity suggesting that compost application increased the size of the microbial population without causing a major shift in the composition of the population. On the other hand, mustard bran treatment showed high microbial diversity suggesting that there are more functional groups under that treatment. In site B where the soil was fumigated and crowns treated at planting, there was no benefit of applying compost or mustard bran. SoilBuilder r and TerraClean r reduced yield. In unfumigated soil, both crown treatment and soil amendments enhanced crop yield and spear number. Our results thus show that soil amendment affects soil microbial activity in asparagus production. However, final yield is influenced by other practices like crown treatments and soil fumigation.