Comparing organic versus conventional soil management on soil respiration

Soil management has great potential to affect soil respiration. In this study, we investigated the effects of organic versus conventional soil management on soil respiration. We measured the main soil physical-chemical properties from conventional and organic managed soil in Ecuador. Soil respiration was determined using alkaline absorption according to Witkamp. Soil properties such as organic matter, nitrogen, and humidity, were comparable between conventional and organic soils in the present study, and in a further analysis there was no statically significant correlation with soil respiration. Therefore, even though organic farmers tend to apply more organic material to their fields, but this did not result in a significantly higher CO2 production in their soils in the present study.


Introduction
Research related to the benefits of organic management 1 has become increasingly important in sustainable agriculture. Organic soil management can contribute to meaningful socio-economic and ecologically sustainable development. Kilcher states that "Organic agriculture reduces the risk of yield failure, stabilizes returns and improves the quality of life of small farmers' families" 2 . Soil management has great potential to affect soil respiration, which is an important qualitative indicator of soil microbial activity 3 . Soil respiration is released as a result of soil organic matter decomposition. The present study aims to investigate the effects of organic versus conventional management on CO 2 production of some Northern Ecuadorian agricultural soils. Our hypothesis was that major soil respiration will be observed in soils under organic management due to the increased amount of applied organic materials.

Sampling sites
Soil samples from 23 organic farms and conventionally managed neighbouring farms were analyzed. In total, 17 sampling sites were located in organic farms, while 6 sampling sites were located in chemical fertilizer-treated areas. The sampling sites were chosen according to proximity of organic and conventionally managed farms in which the same crops are produced. Further details about each of the sampling sites can be found in Table 1. Approximately 1000 g of soil samples of 0-20 cm depth were taken. The following crops were produced in the examined areas: broccoli, potato, tomato and carrot.

Soil properties
Soil moisture content was determined gravimetrically, drying the soil at 105°C for 24 hours according to Fernández et al. (2008) 4 . Soil texture was measured using sodium hexametaphosphate ((NaPO 3 ) 6 ) according to Bouyoucos (1962) 5 . To measure the soil chemical properties, the samples were sieved through a 2mm mesh and pre-incubated at 25° for 72 hours. Soil pH in distilled water (soil/water, 1/2.5, w/w) was determined according to Karkanis (1991) 6 . In addition, we measured the electrical conductivity (EC) using a glass electrode according to Karkanis (1991) 6 . Cylinder volume was determined according to Agostini et al.

Soil respiration
The experiment was applied at 25°C. 0, 1M NaOH (10ml) was placed in laboratory bottles (250ml), a sterile gauze pad were filled with 10 g of soil sample according to Witkamp (1966) 12 . After 10 days, the amount of CO 2 was subsequently measured by standardized titration against 0.1N HCl using firstly phenolphthalein and then methyl orange indicator according to Witkamp (1966) 12 .

Statistical analysis
To evaluate the behavior within results, two types of test were performed: i) Student's t-test for comparing means between conventional and organic crop systems in terms of soil respiration (kg/CO2/ha/day), organic matter (%) and nitrogen (%). Furthermore, Person's and Spearman's correlation were fixed in order to test data covariation and correlation. ii) ANOVA was used to compare conventional and organic crop system and the type of crop harvested in the sampling site.

Results
The results of soil respiration from areas of organic and conventional soil management are comparable (Dataset 1).
For soil respiration, conventional soil mean was 88.50 and organic mean was 98.64, showing and increment around 10%. However, there were no statistically significant differences between group means as determined by one-way ANOVA (p =0.15), comparing conventional and organic systems. Pearson's and Kendell's tests have showed no correlation. Soil respiration correlation coefficient with organic matter was lower than 0.05 and with nitrogen content was lower than 0.12. This analysis did not consider the differences between conventional and organic systems ( Figure 1).
There were statistically significant differences between group means as determined by one-way ANOVA (p < 0.05), comparing crop types. Furthermore, a post hoc test (Duncan) was fixed. There was only one crop (carrot) in conventional system (odds lower than 0.05) that differs drastically from the others, as pointed out in (Figure 2).
Considering soil characteristics (pH, CIC, K, and Electric conductivity), Student's t-test was applied to identify differences between conventional and organic systems. Only the characteristics Table 1. Characteristics of the conventional and organic farms chosen for the present study.    from carrot crop systems (conventional or organic) have shown differences in terms of means (p < 0.05). Furthermore, the mean of conventional crop system was lower in every characteristic evaluated. Besides, these results were in congruence with Figure 2, leading us to believe that the cropping system has no influence on soil respiration, which is in contrast to the influence that soil characteristics have over soil respiration in this study.

Conclusions
Organic farmers tend to apply more organic material to their fields, but this did not result in a significantly higher CO 2 production in their soils. The difference between organic and conventional soils (10% in mean) is not enough to conclude that the soil respiration under these two systems was different, considering the analysis of their variance.
Soil properties like organic matter, nitrogen, and humidity, were comparable between conventional and organic soils in the present study, and in a further analysis there was no statically significant correlation with soil respiration. However, biological significance should be investigated in a posteriori research including microbial community profile of the soil and specific interactions in highlands (over 2500 m.a.s.l.).

Ethics
Oral consent was obtained from the farmers for the collection of soil samples from their land. Their only request was to inform them about the results of the soil characteristics, that we have already done personally on 9 November, 2017. This article worked at the differences between organic and conventional soil management. This research examined an important and topical issue especially the soil respiration under changing plant and soil conditions.

Introduction and methods
The research investigated 23 soil samples in Ecuador. The samples were located from organic (17 samples) and conventionally managed neighboring farms (6 samples). In the research trials broccoli, potato, tomato and carrot were applied as test plant. Soil properties were measured after 1000 g soil samples of 0-20 cm depths of soil were taken in every picked area. The soil moisture, texture, pH, electrical conductivity, cylinder volume, organic matter, phosphorus content, sand/silt/clay ratio and cation exchange capacity, and the soil respiration were analyzed in laboratory. The values of the soil parameters are presented in a dataset, which inform about the important soil parameters especially the calculated soil respiration in kg (CO )/ha/day). The protocols (description of the tests) are clear and traceable, especially the formula to calculate soil respiration. The study describes the applied type of fertilizers especially the concentration of NPK fertilizers.
Comment on the Methods -The sampling time and vegetation status are important for the evaluation, this information is missing in the study. If it's possible, describe the followings: When the soil sampling happened? What was the state of the vegetation of test plants? -A bit more detail of the soil properties inform us about the actual soil status. The studied soils are classified as sandy textured soil, according to the soil classification (Franco Arenoso). The most typical parameters of the samples are the following: high sandy texture, neutral pH, good/very good organic matter-nitrogen and phosphorus content, 10-20% moisture content. I suggest describing it in the Methods.

Results
The results of the study are described with sufficient statistical analysis. It also describes the statistically significant/not significant results. There were solely statistically significant differences between crop types (for soil respiration by one-way ANOVA correlation test). -The Figure 1

Conclusion
The results have briefly evaluated and conclusions straightforward formulated. I quite agree with observations of the study that emphasizes the importance of further microbiological studies.

Is the work clearly and accurately presented and does it cite the current literature? Yes
Is the study design appropriate and is the work technically sound? Yes

If applicable, is the statistical analysis and its interpretation appropriate? Yes
Are all the source data underlying the results available to ensure full reproducibility? Yes

Are the conclusions drawn adequately supported by the results? Yes
No competing interests were disclosed.

Competing Interests:
Referee Expertise: Agricultural environmental management, soil management, agricultural soil science I have read this submission. I believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.
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