Long-term effect of tillage systems on soil microbiological, chemical and physical parameters and the incidence of charcoal rot (Macrophomina phaseolina) in soybean

PEREZ-BRANDÁN C.; ARZENO J.L.; HUIDOBRO J.; GRUMBERG B.; CONFORTO C.; HILTON S.; BENDING G.D.; MERILES J.M.; VARGAS GIL S.

CROP PROTECTION

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2012 vol. 40 p. 73 - 82

0261-2194

Direct seeding (DS) systems have been widely preferred over conventional tillage (CT) because they improve microbial biomass, increase soil organic matter (OM) and nutrient accumulation and stratification with depth, and improve aggregate stability and soil structure, favouring the development of healthy plants. A 20-year field experiment was employed with the aim of evaluating the effect of tillage systems on biological, chemical and physical aspects of the soil, and to establish whether there was a correlation of these parameters with the incidence of charcoal rot  (Macrophomina phaseolina) of soybean and crop yield. Direct seeding presented higher values than CT in the following parameters: culturable fungi (26.33 x105 vs. 2.33 x105 CFU g-1 dry soil), bacteria (182 x107 vs. 64 x107 CFU g-1 dry soil), microbial respiration (0.77 mg CO2 g-1 week-1 vs. 0.45 mg CO2 g-1 week-1),and fluorescein diacetate (FDA) hydrolysis (4.17 ug fluorescein g-1 h-1 vs. 1.70 ug fluorescein g-1 h-1 in CT. Fungal and bacterial community fingerprints, generated using terminal restriction fragment length polymorphism (T-RFLP) analysis, of Intra transgenic spacer regions of rRNA and 16S rRNA genes, respectively, were influenced by the tillage system. Also FAME profiles showed that microbialcommunity structure in DS and CT was clearly different. DS samples contained significantly higher total microbial biomass than the other tillage treatments, but there were no significant differences in fungal biomass or any consistent trend with respect to stress index. Our results show that microbial communities were more abundant and active in DS than in CT in response to high nutrient content in soil. Indeed, DS systems presented higher soil OM, total N, K, and Ca than CT. Electrical conductivity and aggregate stability (AS) were also improved by DS; however, bulk density (BD), sand, silt and clay content were not affected by tillage systems. Soybean grown in high-quality soil was not affected by charcoal rot; however, under CT, disease incidence in soybean was 54%; these differences are correlated to the higher microbial abundance and activity under DS, the biological component being akey factor determining soil capacity to suppress the soilborne pathogen. Accordingly, we recorded a negative significant correlation between disease incidence and culturable fungi and bacteria, actinomycetes, microbial respiration, OM, total N, K, Ca, water holding capacity, silt content, AS, and crop yield.