Banana leaf and glucose mineralization and soil organic matter in microhabitats of banana plantations under long‐term pesticide use

Abstract

Soil organic matter (SOM) and microbial activity are key components of soil quality and sustainability. In the humid tropics of Costa Rica 3 pesticide regimes were studied-fungicide (low input); fungicide and herbicide (medium input); and fungicide, herbicide, and nematicide (high input)-under continuous banana cultivation for 5 yr (young) or 20 yr (old) in 3 microhabitats-nematicide ring around plants, litter pile of harvested banana, and bare area between litter pile and nematicide ring. Soil samples were incubated sequentially in the laboratory: unamended, amended with glucose, and amended with ground banana leaves. Soil organic matter varied with microhabitat, being greatest in the litter pile, where microbes had the greatest basal respiration with ground banana leaf, whereas microbes in the nematicide ring had the greatest respiration with glucose. These results suggest that soil microbes adapt to specific microhabitats. Young banana plantations had similar SOM compared with old plantations, but the former had greater basal microbial respiration in unamended and in glucose-amended soil and greater first-order mineralization rates in glucose-amended soil, thus indicating soil biological quality decline over time. High pesticide input did not decrease microbial activity or mineralization rate in surface soil. In conclusion, microbial activity in tropical volcanic soil is highly adaptable to organic and inorganic inputs.

Glucose mineralization in soils of contrasting textures under application of S-metolachlor, terbuthylazine, and mesotrione, alone and in a mixture

“…These results are comparable with previous studies, which reported that soil samples from high pesticide input (application of herbicides, nematicides, and fungicides) did not have decreased basal microbial respiration or mineralization rates, because some pesticide residues could serve as carbon or energy source to microorganisms and are degraded and assimilated by these microorganisms (Hussain et al 2009b;Blume and Reichert 2015). Joly et al (2015) also reported that although the pollution pressure was maintained throughout the experiment (by herbicides: S-metolachlor, mesotrione, and nicosulfuron; adjuvants, and/or degradation products), the Limagne soil microbial communities appeared to be quite resistant to the different treatments; and the bacterial and fungal diversity estimated by fingerprinting analyses remained unchanged, such as microbial biomass evaluated by the microbial carbon measurement in the presence of metolachlor (White et al 2010).…”

“…First order reaction models were fitted to observe cumulative evolved CO 2 for each herbicide (control, S-metolachlor + terbuthylazine + mesotrione, S-metolachlor, terbuthylazine, and mesotrione), using linear and nonlinear regression analyses (Blume and Reichert 2015). The selection of model Table 1.…”

“…Thus, future studies are required to integrate the soil microbial community structure with the different levels of glucose additions. Blume and Reichert (2015) reported that adding substrates (glucose and ground banana leaves) to soil increased microbial respiration for all sites [5 banana plantations with diverse pesticide management (herbicide, nematicide, and fungicide), plantation age (5 yr and 20 yr)], and microhabitats (bare area, litter pile, and nematicide ring). With the addition of glucose, a readily degradable substrate, no differences were observed for plantation age or pesticide use rate.…”

“…We calculated decay constants (k) for site only (Table 2) without correction for microbial biosynthesis; thus, the constants reflect the net mineralization rates as described by Blume and Reichert (2015).…”

“…However, microbial adaptation may occur in surface soil under agricultural uses exposed to herbicides, interfering positively, providing an increase in the metabolism of these products by the microorganisms (Reis et al 2008;Hussain et al 2009a), but also interfering negatively by intoxicating soil biota (non-adapted organisms) or having no effect (Pereira et al 2008;Mahía et al 2008;Blume and Reichert 2015). Soils rich in SOM and with residual concentration of herbicides may increase the herbicide degradation rate, as shown for atrazine by Mirgain et al (1993) in laboratory microcosm conditions, possibly because of microbial adaptation to repeated herbicide exposure.…”