|Mc Sorley, Robert - University Of Florida|
|Wang, Koon-hui - University Of Hawaii|
|Saha, Shubin - University Of Kentucky|
|Mc Govern, Robert - University Of Florida|
Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2017
Publication Date: 6/5/2017
Citation: Burelle, N.K., Mc Sorley, R., Wang, K., Saha, S.K., Mc Govern, R.J. 2017. Rhizosphere microorganisms affected by soil solarization and cover cropping in Capsicum annuum and Phaseolus lunatus agroecosystems. Applied Soil Ecology. 119:64-71. doi:10.1016/j.apsoil.2017.06.001.
Interpretive Summary: Field experiments were conducted to evaluate the effects of soil solarization or cover cropping on bell pepper and lima bean on rhizosphere microorganisms. In Experiment I, flat surface solarization, raised bed solarization, cowpea cover crop alone, and their combination were compared with methyl bromide fumigation and an untreated control for effects on rhizosphere bacteria and fungi on bell pepper. In Experiment II, effects of cover cropping on rhizosphere microorganisms were examined on lima bean with three summer cover crop treatments: sunn hemp, cowpea, and fallow as main plots, and three organic mulch treatments: sunn hemp hay, cowpea hay, and no hay as subplots. Overall results of these studies indicate that rhizosphere soil fungal populations are more consistently reduced throughout the growing season of bell pepper by MB than cover cropping and solarization. Rhizobacterial populations appear to be relatively resistant to fumigation and could rebound to high levels by the end of the crop in fumigated soil. No-till cover cropping where the cover crop residues were left as organic mulch could result in more abundance of rhizosphere fungi such as R. solani and F. oxysporum on lima bean. Cowpea hay as organic mulch increased siderophore producing bacteria, gram positive bacteria, and fluorescent pseudomonads in one year but not in both years. Although the current studies did not suggest a consistent enhancement of rhizobacteria by cover cropping, future research should examine the effects in a continuous no-till system for more than two years.
Technical Abstract: Field experiments were conducted to evaluate the effects of soil solarization or cover cropping on bell pepper (Capsicum annuum) and lima bean (Phaseolus lunatus, L.) rhizosphere microorganisms. In Experiment I, flat surface solarization (FSS), raised bed solarization (RBS), cowpea (Vigna unguiculata) cover crop alone (CP), and their combination i.e. cowpea cover cropping followed by raised bed soil solarization (CP+RBS) were compared with methyl bromide fumigation (MB) and an untreated control (UTC) for their effects on rhizosphere bacteria and fungi on bell pepper. In Experiment II, effects of cover cropping on rhizosphere microorganisms were examined on lima bean in a 3×3 split-plot designed experiment with three summer cover crop treatments: sunn hemp (SH) (Crotalaria juncea, L.), cowpea (CP), and fallow (F) as main plots, and three organic mulch treatments: sunn hemp hay (SHH), cowpea hay (CPH), and no hay (NH) as subplots. Rhizosphere bacteria including siderophore producers, gram-positive spore-formers, and fluorescent pseudomonads were assessed, as well as two species of fungi, Fusarium oxysporum and Rhizoctonia solani. In year 1 of Experiment I, CP+RBS reduced F. oxysporum and R. solani in the rhizosphere, resulting in levels similar to those in MB fumigation. This was not observed in year 2. Heavy rainfall in year 2 resulted in a severe outbreak of Pythium on bell pepper, which was most destructive in MB fumigated plots. Effects of solarization and cover cropping on rhizosphere bacteria also differed between the two years. Fluorescent pseudomonads were more abundant across the treatments in year 1, but were greatly reduced in year 2, when the Pythium outbreak occurred. In Experiment II, populations of rhizobacteria of lima bean were not affected by cover crop in both years of the study. At the end of year 1, isolation of R. solani from lima bean roots increased in SHH plots. SH cover crop reduced gram-positive spore forming bacteria and fluorescent pseudomonads. In year 2, CP followed by CPH had higher levels of fungi and bacteria than CP followed by either NH or SHH.