Effects of long-term organic amendments and soil solarization on pepper and watermelon growth, yield, and soil fertility

Many vegetable growers rely on methyl bromide or other soil fumigants to manage soil pathogens, nematodes, and weeds. Nonchemical alternatives such as solarization and organic amendments are as yet largely unproven, but do offer promise of more sustainable solutions. The objective of this study was to evaluate the effects of long-term organic amendments and soil solarization on soil chemical and physical properties and on growth and yield of pepper (Capsicum annuum L.) and watermelon (Citrullus lanatus [Thunb.] Manst.). Main plots consisted of a yearly organic amendment or a nonamendment control. Four subplots of soil sanitation treatments consisted of solarization, methyl bromide, Telone, and nonfumigated. Each subplot was divided into two sub-subplots, one with weed control and one without weed control. Plant biomass was higher in plots with organic amendments than in nonamended plots. There were no differences in marketable pepper and watermelon yields between organic amended and nonamended plots during the 1998-99 and 1999-2000 seasons, respectively. However, higher pepper yields were produced from organic amended plots in the 1999-2000 season. Soil pH and Mehlich 1-extractable P, K, Ca, Mg, Zn, Mn, Fe, and Cu were higher in organic amended plots than in nonamended control plots. Soil organic matter concentration was 3-fold higher in amended soil than in nonamended soil. Effects of soil sanitation and weed management varied with crop and season. The methyl bromide and Telone treatments produced higher yields than soil solarization. In general, weed control did not affect plant biomass and yield for any of the crops and seasons. The results suggest that annual organic amendment applications to sandy soils can increase plant growth and produce higher or comparable yields with less inorganic nutrient input than standard fertilization programs.