Efficiency of Reductive Soil Disinfestation Affected by Soil Water Content and Organic Amendment Rate

Reductive Soil Disinfestation (RSD) is a good method which can restore degraded greenhouse soil and effectively inactivate soil-borne pathogens. However, the approach needs to be optimized in order to facilitate its practical application in various regions. In the present work, we investigated the effect of soil water content (60% water holding capacity (WHC), 100% WHC and continuous flooding) and maize straw application rates (0, 5, 10, and 20 g kg−1 soil) on the improvement of soil properties and suppression of soil-borne pathogens (Fusarium oxysporum, Pythium and Phytophthora). The results showed that increasing the soil water content and maize straw application rate accelerated the removal of excess sulfate and nitrate in the soil and elevated the soil pH. Elevating the water content and maize straw application rate also produced much more organic acids, which could strongly inhibit soil-borne pathogens. Soil properties were improved significantly after RSD treatment with a maize straw amendment rate of more than 5 g kg−1, regardless of the water content. However, RSD treatments with 60% WHC could not effectively inactivate soil-borne pathogens and even stimulated their growth by increasing the maize application rate. RSD treatments of both 100% WHC and continuous flooding could inactivate soil-borne pathogens and increase the pathogens mortality indicated by cultural cells relatively effectively. The inhibited pathogens were significantly increased with the increasing maize application rate from 5 g kg−1 to 10 g kg−1, but were not further increased from 10 g kg−1 to 20 g kg−1. A further increased mortality of F. oxysporum, indicated by gene copies, was also observed when the soil water content and maize straw application rate were increased. Therefore, RSD treatment with 60% WHC could improve soil properties significantly, whereas irrigation with 100% WHC or continuous flooding was a necessity for effective soil-borne pathogens suppression. Holding 100% WHC and applicating maize straw at 10 g kg−1 soil were optimum conditions for RSD field operation to restore degraded greenhouse soil.

SOIL ATTRIBUTES UNDER DIFFERENT WATER MANAGEMENT SYSTEMS OF RICE PADDIES IN THE AMAZONIAN SAVANNA OF BRAZIL1

ABSTRACT The rational use of water while considering the increases in food production is a great challenge for agriculture currently. The aim of the present study was to evaluate the soil properties of rice paddy areas under different water management systems. For this, the rice cultivars BRS Tropical and IRGA 424 were grown under the following treatments: M1: Intermittent flooding; M2: Intermittent flooding, followed by continuous flooding; M3: Continuous flooding, followed by intermittent flooding; and M4: Continuous flooding for the entire plant cycle. As a control, a non-cultivated area, adjacent to the experimental plots was also evaluated. The variables analyzed were P, K+, Ca2+, Mg2+ and Al3+ contents, pH, soil organic carbon (SOC), total nitrogen (TN) Carbon Stock (C-Stock), nitrogen stock (N-Stock), Cation-exchange capacity (CEC), C/N ratio; CO2 emission, soil microbial biomass carbon (SMB), metabolic coefficient (qMic) and acid phosphatase and urease activities. There was not difference among the different water management systems for P, K+, Mg2+, CEC and C/N ratio. The SMB and the acid phosphatase and urease activities were lower under the different treatments when compared to the control. The CO2 emission under rice paddy system was influenced by the phenological phase of the crop. The variables SOC, C-Stock, SMB, C/N ratio, K+, acid phosphatase and usease activities are those most sensitive attributes observed in the soil under different water management systems during rice cultivation. Water management in the rice paddy system influenced soil by changing its quality.

Nitrous Oxide Emission from a Flooded Tropical Wetland across a Vegetation and Land Use Gradient

Whereas wetland ecosystems are among the most vital natural carbon sinks, they are also important sources of nitrous oxide (N2O), a highly potent greenhouse gas. However, due to differences in wetland characteristics, N2O emission is likely to vary across wetland types. We investigated the: 1) influence of vegetation community (Typha latifolia; Typha, Phragmites mauritianus; Phragmites and Cyperus papyrus; Papyrus) in a natural tropical freshwater wetland, and 2) impact of converting a natural tropical freshwater wetland into a rice paddy wetland on N2O emission. Results showed that N2O emission (µg m− 2 h− 1) from the natural wetland did not vary significantly (p > 0.05) among the vegetation communities during both the dry and wet seasons (Typha = 0.6 ± 1.6 [SE] and 0.5 ± 1.4, Phragmites = 0.5 ± 1.7 and 0.4 ± 1.5, Papyrus = 0.5 ± 1.3 and 0.5 ± 1.5, respectively). These emission rates insignificantly differed (p > 0.05) from those recorded in the rice paddy wetland (dry season = 0.7 ± 2.8 and wet season = 0.6 ± 2.7). There was no significant correlation (p > 0.05) between soil physico-chemical characteristics and N2O emission. We concluded that vegetation community does not affect N2O emission from a natural tropical freshwater wetland under continuous flooding. Similarly, under continuous flooding and no fertilization conditions, converting a natural tropical freshwater wetland into a rice paddy wetland does not influence N2O emission. We roughly estimated total annual N2O emissions (T yr− 1) and their carbon dioxide equivalents (CO2e; T yr− 1) from all Uganda’s natural and rice paddy wetlands as: natural wetlands = 115.1 ± 342.8 (CO2e = 30,501.5 ± 90,842) and rice paddy wetlands = 0.9 ± 2.7 (CO2e = 242.5 ± 707.6).

Minimal tillage and intermittent flooding farming systems show a potential reduction in the proliferation of Anopheles mosquito larvae in a rice field in Malanville, Northern Benin

Background Irrigation systems have been identified as one of the factors promoting malaria disease around agricultural farms in sub-Saharan Africa. However, if improved water management strategy is adopted during rice cultivation, it may help to reduce malaria cases among human population living around rice fields. This study aimed to assess the impact of the different irrigation practices on malaria transmission, as well as to evaluate the water management system that will best mitigate malaria transmission in Malanville, Benin. Methods Knowledge, Attitude and Practice (KAP) study was conducted on 104 households staying on and around the rice fields in Malanville. The study focused on the frequency of mosquito bites and preventive measures against malaria as well as soil preparation and rice planting methods. Mosquito larvae density was assessed in different water management system: continuous flooding (CF) or intermittent flooding (IF), deep tillage (DT) or minimal tillage (MT) and normal levelling (NL) or abnormal levelling (AL) in an experimental hut set-up. Larvae were collected using dipping methods and their density was determined. Results Three tillage systems, which include the use of tiller, plow and hoe, were identified on the rice field. Continuous flooding was the only irrigation system used by farmers. Retrospective data from Malanville Health Centre revealed higher malaria cases during rice production season, which was also confirmed by field participants. The density of Anopheles larvae was reduced by 80.8%, 30.8% and 40.7% (P = 0.000) during transplanting, tillering and maturation periods, respectively with intermittent flooding compared to continuous flooding. In addition, a clear reduction of larva density was observed with both intermittent flooding systems applied to minimal tillage (MT + IF + NL) and intermittent flooding applied to deep tillage (DT + IF + AL), showing that intermittent flooding could reduce the abundance of malaria vector in rice fields. Conclusion Recommending intermittent flooding technology for rice cultivation may not only be useful for water management but could also be an intentional strategy to control mosquitoes vector-borne diseases around rice farms.

Evaluation of Water Productivity and Agronomic Performance of Paddy Rice Through Water Saving Irrigation and Nitrogen Fertilization

Tanzania with 945 million hectares of land area and annual rainfall of 300 mm on 67% of its territorial land is considered as a semi-dry region in the world. Rice production in Tanzania needs to be increased to feed a growing population, whereas water for irrigation is getting scarce. One way to decrease water consumption in paddy fields is to change the irrigation regime for rice production and to replace continuous flooding with alternate wetting and drying. In order to investigate the effect of different regimes of irrigation and nitrogen fertilizer on yield and water productivity of hybrid rice, two greenhouse pot experiments comprising soils from upland and lowland production ecologies were conducted at Sokoine University of Agriculture, Tanzania during crop seasons of 2019. The experiment was arranged in split plots based on randomized completely block design with 3 replications. Water regimes were the main factor comparing continuous flooding (CF) and alternate wetting and drying (AWD) with nitrogen fertilizer levels as the sub-factor including absolute control , 0, 60, 90, 120 and 150 kg/ha. Alternate wetting and drying (AWD) improved water productivity in both upland and lowland production ecologies compared to CF. AWD increased yield under lowland production by 13.3% while in upland there was 18.5% decrease in yield. The average water use varied from 31.5 to 84 L pot-1 under upland trials, while in lowland trials it was 36 to 82.3 L. Higher yield and lower water application led to an increase in WP varying from 1.2 to 1.8 kg cm-3 under upland trials, and 0.6 to 1.5 kg cm-3 under lowland trials. The variation in water productivity among treatments was mainly due to the differences in the yield, water and nitrogen levels used in the production process. Both sets of trials recorded water saving up to 34.3% and 17.3% under lowland and upland trials, respectively. Under upland trials, the yield varied from 39.9 to 124.1 g pot-1 and in lowland trials yield ranged from 20.6 to 118.2 g pot-1 representing paddy rice. The measurements showed that less water can be used to produce more crops under alternative rice growing practices. The results are important for water-scarce areas, providing useful information to policy makers, farmers, agricultural departments, and water management boards in devising future climate-smart adaptation and mitigation strategies.

Tuning of the Amount of Se in Rice (Oryza sativa) Grain by Varying the Nature of the Irrigation Method: Development of an ICP-MS Analytical Protocol, Validation and Application to 26 Different Rice Genotypes

The amount of specific trace elements like selenium (Se) may be of health concern for humans if contained in too high (or low) quantities in staple foods like rice. Among the attempts aimed to optimize the Se concentration in rice, only few studies have been focused on the use of irrigation methods other than continuous flooding. Since intermittent irriguous methods, like sprinkler and saturation, have found to be effective in modifying the bioaccumulation of arsenic and cadmium in rice kernels, the main goal of this study is to measure the amount of the total Se contained in grains of 26 rice genotypes cultivated for two consecutive agrarian vintages in the same open field and with the same water, but differently irrigated with continuous flooding, sprinkler or saturation. To do this, an original and validated ICP-MS method has been developed. The validation parameters accounted for a high sensitivity and accuracy. Sprinkler irrigation is able to reduce in the average of 90% the amount of total Se in kernels in comparison to values measured in rice irrigated with continuous flooding. In conclusion, different irrigation techniques and rice genotypes seem to be valuable tools in order to allow in the future the customized modulation of the Se concentration in rice grain according to the needs of the various populations.