Edited by: Henrique Manuel da Fonseca Trindade, University of Trás-os-Montes and Alto Douro, Portugal
Reviewed by: Jose Antonio Pascual, Consejo Superior de Investigaciones Científicas (CSIC), Spain; Berta De Los Santos, Centro IFAPA Las Torres (CAPDER - JA), Spain
This article was submitted to Waste Management in Agroecosystems, a section of the journal Frontiers in Sustainable Food Systems
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
Biodisinfection using fresh sheep manure in August is effective in controlling
Greenhouses of pepper (
Between 1982 and 2005, soil disinfestation with methyl bromide was the way to palliate the effects of
The combination of solarization with biofumigation shows that the two methods have synergic effects (Katan,
If water saturation levels are not reached, but organic amendments containing a high carbon content are used anaerobiosis occurs under the plastic during biodecomposition (anaerobic soil disinfestation, ASD) which affects the pathogens (Shennan et al.,
European Union restrictions on the use of chemical products, as well as the increase in the surface area dedicated to ecological agriculture, require the use of soil organic amendments for soilborne disease management. Biodisinfection using fresh sheep manure in August gives good results in controlling
In order to fit the start of the biodisinfection to the end of the cropping season it is necessary to commence in October. Using the amendments that are typically used in August (fresh sheep manure), the biodisinfection does not reduce the levels of pathogens, and are thus unviable (Guerrero et al.,
Moreover, the southeast of Spain is in a vulnerable zone due to nitrates (Directive 91/676/CEE, of 12 December, relating to the protection of waters against contamination produced by agricultural origin nitrates) which means that there are restrictions on the contribution of nitrogen. This premise severely limits the use of organic matter in the zone.
The objective of this study was to obtain biodisinfection amendments that are effective in controlling
The field experiment was carried out over two crop seasons in an experimental sweet pepper greenhouse of 1,000 m2, at the experimental station of the IMIDA, located in the Campo de Cartagena, Region of Murcia (southeast Spain), where pepper has been grown periodically for over 20 years.
The clay loam soil was free from pathogens and was not previously disinfested.
The biodisinfection was performed in October for both seasons, starting on 2 October 2019 and 9 October 2020, respectively. Treatments were arranged in a randomized complete block design with four replicates and were repeated in the same plots in each of the two seasons. Each experimental unit consisted of a 60 m2 plot. The treatments evaluated were: T1: wheat husk (Alimer SCoop)+fresh sheep manure (WH+FSM) 3.5 (2+1.5) kg m−2; T2: sunflower pellets (Alimer SCoop) (S) 3.5 kg m−2; T3: (FSM): 3.5 kg m−2; T4: Control (non-amended and non-covered with plastic). Amendments and the non-amended control soil treatment were analyzed in the 2 years (
Composition of organic amendments and non-amended control soil treatment.
Total OM % | 91.3 ± 22.1 | 93.8 ± 23.0 | 52.23 ± 3.92 | 2.82 ± 0.65 |
Total N g kg−1 | 22.8 ± 1.5 | 48.5 ± 2.3 | 16.5 ± 0.10 | 0.7 ± 0.39 |
C/N | 20.4 ± 14.9 | 11.5 ± 14.1 | 17.9 ± 1.38 | 9.54 ± 0.81 |
P2O5 g kg−1 | 25.2 ± 01.1 | 14.4 ± 3.2 | 0.95 ± 0.03 | 0,11 ± 0.04 |
K2O g kg−1 | 20.1 ± 01.5 | 17.4 ± 1.2 | 3.98 ± 0.11 | 2.18 ± 0.13 |
pH | 6.54 ± 0.5 | 6.47 ± 2.2 | 8.50 ± 0.05 | 7.71 ± 0.23 |
Electrical conductivity (25°C) dS m−1 | 2.59 ± 0.86 | 2.89 ± 0.41 | 8.62 ± 0.07 | 3.99 ± 0.54 |
Moisture% | 8.12 ± 0.15 | 5.60 ± 0.12 | 51.53 ± 1.25 | 42,45 ± 1.07 |
The amendments were applied and plots were rototilled to a depth of 25–30 cm. The soil was irrigated using a drip irrigation system using 3 L h−1 emitters spaced 0.40 × 0.60 m for 4 h on 2 consecutive days. Amended soil was covered with a 0.05 mm-thick transparent polyethylene film. The plastic was maintained for 6 weeks. The “Beniel” (Syngenta Seeds) pepper cultivar was planted in December at the habitual density of the zone: 1 m separation between rows and 0.4 m between plants in the same row (2.5 plants m−2).
The inoculum was obtained from a
Oospores of
- Ambient greenhouse temperature and soil temperatures in one replicate plot of each treatment at 15 and 30 cm depth were registered with 12-bit S-TMB-M017 temperature Hobo probes (accuracy < 0.2°C) connected to an H21-002 Hobo datalogger. Readings were taken every 30 min throughout the biodisinfection treatment.
- Soil oxygen percentage content in one replicate plot of each treatment at 15 cm depth was registered with SO-200 galvanic cell type oxygen Apogee-Instruments probes (accuracy < 0.02% O2) buried at a depth of 15 cm connected to an H22-001 Hobo datalogger. Readings were taken every 30 min throughout the biodisinfection treatment.
- Viability of
- Infectivity of
- Marketable yield. Each 15 days, from April through to August in each season, the production of the plants was harvested and weighed separately for each treatment replicate plot. This variable was expressed in kg m−2. Each replicate plot consisted of two rows and 45 plants were harvested from each row.
The effects of treatments were studied using two way analysis of variance (ANOVA) with the Software Statgraphics Centurion 16. In order to fulfill the assumptions of analysis of variance (homocedasticity and normality), the infectivity bioassay data were transformed using arcsine (√x/n), where x = total number of dead plants and
Temperatures exceeding 38°C were reached in the amendments consisting of wheat husk+fresh sheep manure, in the sunflower pellets, and fresh sheep manure, at 15 cm in the first season. In the second season, although the largest number of hours was accumulated in the order of 33°C, the soil was subjected to temperatures of up to 37°C for certain periods of time at both soil depths, 15 and 30 cm. In the second season, the lowest number of accumulated hours above 33°C was found in the non-treated control. There were no temperatures exceeding 42°C in any of the treatments (
Number of cumulative hours in each crop cycle at 15 and 30 cm soil depth within different temperature ranges.
Wheat husk + Fresh sheep manures | 15 | 48 | 51 | 120 | 0 |
30 | 0 | 0 | 39 | 0 | |
Sunflower pellets | 15 | 66 | 57 | 40 | 0 |
30 | 0 | 0 | 18 | 0 | |
Fresh sheep manures | 15 | 60 | 52 | 223 | 0 |
30 | 0 | 0 | 147 | 0 | |
Control | 15 | 0 | 0 | 30 | 0 |
30 | 0 | 0 | 0 | 0 |
There was a period of anoxia during the biodisinfection process in both seasons in all the biodisinfection treatments (
Evolution of the percentage of oxygen in each treatment during the biodisinfestation process started in October at 15 cm depth. Abscisa axis: days from the start of the biodisinfestation. First and second seasons.
Effect of biodisinfection treatments on
Wheat husk + Fresh sheep manure | 2.89 ± 3.40bA | 3.34 ± 2.23bA |
Sunflower pellets | 4.46 ± 4.93bA | 4.66 ± 4.5bA |
Fresh sheep manure | 3.29 ± 2.91bB | 8.88 ± 3.98aA |
Control | 22.8 ± 6.71aA | 5.11 ± 2.85abB |
The results obtained in the bioassay were different at 15 cm and 30 cm soil depth (
Infectivity of introduced soil inoculum of
Wheat husk + Fresh sheep manures | 77.7± 12 a | 77.7± 12 ab |
Sunflower pellets | 77.7± 19 a | 88.9 ± 19 ab |
Fresh sheep manures | 77.7 ± 18 a | 100.0 ± 0 a |
Control | 44.4 ± 19 b | 66.6 ± 3 b |
Yields were significantly higher in the biodisinfested plots than in the control. The effect of biodisinfection treatments on marketable yield was significant in the first season [
Marketable yield (kg m−2) in each crop cycle.
Wheat husk + Fresh sheep manures | 9.43 ± 1.06 a | 6.86 ± 1.30 a |
Sunflower pellets | 9.72 ± 1.79 a | 6.96 ± 0.80 a |
Fresh sheep manures | 9.21 ± 1.17 a | 6.30 ± 1.20 a |
Control | 8.23 ± 0.44 b | 5.00 ± 0.39 b |
In our trial, the temperatures obtained during the biodisinfection carried out in October with the amendments of wheat husk+fresh sheep manure, sunflower pellets, and fresh sheep manure exceeded 38°C in the first season, varying between 51 and 57 h, but no in the second. At both seasons soil temperatures accumulated in October during the biodisinfection in the greenhouse were considerably lower than those obtained for the month of August in the same zone (Guerrero et al.,
The biodisinfection with the assayed amendments induce anoxia in the soil for several weeks, which is one of the factors indicated for Gamliel et al. (
The efficacy of the biodisinfection when temperatures are low improves with the contribution of amendments that are rich in organic matter or by increasing the amount of carbon that is applied to the soil. The contribution of 4 mg C g−1 of soil has been recommended to improve the efficacy of ASD at low temperatures (Butler et al.,
The efficacy or failure of soil biodisinfection may be due to the soil characteristics, the degree of moistening, the electrical conductivity, the characteristics of the plastic, and the period of solarization (Chellemi,
In the north of Spain, the survival of oospores of
Despite the low disinfectant efficacy assessed by the reduction in the survival of
One strategy employed when biodisinfection fails due to the climate or crop cycles is to turn to anaerobic disinfection. This strategy has been applied in limiting solarization conditions in Japan (Shinmura,
The effect of the application of organic matter produced a yield increase in both seasons. Although there was no naturally occurring presence of pathogens, the increased yield in the biodisinfested plots might be explained by the reduction of soil fatigue in the crop. The fatigue accumulated in greenhouses used for pepper monocropping is highly specific toward pepper (Guerrero et al.,
The principal cause of this fatigue is considered to be biotic and related with the extent to which the soils are contaminated with
In those plots where FSM was not used in this study, the yields were similar to those in which it had been used. This fact is of great interest since the cropping zone of Southeast Spain is subject to organic matter restrictions. Moreover, it is known that the incorporation of organic correctives improves soil properties and fertility, as reported by Bonanomi et al. (
The results obtained with the carbon-rich and balanced amendments and in time periods that are compatible with the pepper crop cycle in greenhouses in southeast Spain, showed a yield improvement. This increased yield may also be due to the effect highlighted by Núñez-Zofío et al. (
In conclusion, using the specific organic amendments, significant reductions were obtained in the viability of the inoculum resting structures of
The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author/s.
MG designed the experiment and wrote the original draft. CL, VM, MM, and AM supervised the experiment and contributed to the data. SL revised the manuscript. All authors approved the submitted version.
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.