Keywords
soil respiration, conventional soil management, organic soil management
This article is included in the Agriculture, Food and Nutrition gateway.
soil respiration, conventional soil management, organic soil management
Research related to the benefits of organic management1 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 activity3. 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 CO2 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.
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 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 ((NaPO3)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. (2014)7. Soil organic matter was determined according to Walkley and Black (1934)8. We measured the phosphorous content according to Olsen (1954)9. The Sand/Silt/Clay ratio was determined by Bouyoucos’s method (1936)10, while the cation exchange capacity was determined according to ISO 11260 (1994)11 protocol.
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 CO2 was subsequently measured by standardized titration against 0.1N HCl using firstly phenolphthalein and then methyl orange indicator according to Witkamp (1966)12.
The below formula was applied to calculate soil respiration:
m(CO2) = VxNx22 CO2
And CO2 production (for 10 days):
mg(CO2) * 100g – 1 * 10 day – 1 = methyl orange factor * HCI – phenolphthaleinloss) * NAOH factor * 2, 2 * Moisture multiplication factor
where
We determined the volume of the examined soils (counting with 0 – 20 cm depth) using topsoil calculator tool (https://www.tillersturf.co.uk/topsoil-calculator). The results of soil respiration was then estimated in kg(CO2)/ha/day.
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.
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 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.
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. 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.).
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.
Dataset 1: Raw data for various parameters calculated in conventional and organic managed soils. Parameters as follows: pH, Organic material (percentage), Total Nitrogen (percentage), Match (mg/kg), Potassium (cmol/kg), Electrical conductivity (dS/m), CIC (cmol/kg), Soil moisture content (percentage), Sand (percentage), Silt-limo (percentage), Clay (percentage), Texture (class), Soil respiration (kg/CO2/ha/day). DOI, 10.5256/f1000research.13852.d19552913
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Competing Interests: No competing interests were disclosed.
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Agricultural environmental management, soil management, agricultural soil science
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Version 1 02 Mar 18 |
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