Medium-Term Effects of Sprinkler Irrigation Combined with a Single Compost Application on Water and Rice Productivity and Food Safety.

Traditional rice (Oryza sativa L.) management (tillage and flooding) is unsustainable due to soil degradation and the large amount of irrigation water used, an issue which is exacerbated in the Mediterranean region. Therefore, there is a need to explore rice management strategies in order to improve water-use efficiency and ensure its sustainability. Thus, field experiments were conducted to determine the medium-term effects of different irrigation and tillage methods combined with a single compost application on water and rice productivity, as well as food safety in a semiarid Mediterranean region. The management systems evaluated were: sprinkler irrigation in combination with no-tillage (SNT), sprinkler irrigation in combination with conventional tillage (ST), which were implemented in 2015, and flooding irrigation in combination with conventional tillage (FT), and their homologues (SNT-C, ST-C, and FT-C) with single compost application in 2015. In reference to rice grain yield, the highest values were observed under ST treatment with 10 307 and 11 625 kg ha-1 in 2018 and 2019 respectively; whereas between FT and SNT there were no significant differences, with 8 140 kg ha-1 as mean value through the study. Nevertheless, sprinkler irrigation allowed saving 55% of the total amount of water applied in reference to flooding irrigation. Furthermore, the highest arsenic concentration in grains was found under FT but it decreased with compost application (FT-C) and especially with sprinkler irrigation, regardless of tillage management systems. However, sprinkler irrigation favors the cadmium uptake by plants, although this process was reduced under SNT in reference to ST, and especially under amended compost treatments. Therefore, our results suggested that a combination of sprinkler irrigation and compost application, regardless of the tillage system, could be an excellent strategy for rice management for the Mediterranean environment in terms of water and crop productivity as well as food safety.

Combined use of biochar and alternative management systems for imazamox induced pollution control in rice growing environments.

Imazamox (IMZX) is a persistent herbicide having probable risks for non-target organisms in the environment and water contamination. Alternatives to conventional flooding rice production, including biochar amendment, may induce changes in soil properties which can greatly modify the environmental fate of IMZX. This two-year study is the first to evaluate how tillage and irrigation practices, with or without fresh or aged biochar (Bc), that are alternatives to conventional rice production impact IMZX's environmental fate. The treatments were: conventional tillage and flooding irrigation (CTFI), conventional tillage and sprinkler irrigation (CTSI), no-tillage and sprinkler irrigation (NTSI), and the corresponding Bc-amendment treatments (CTFI-Bc, CTSI-Bc, and NTSI-Bc). Fresh and aged Bc amendment decreased IMZX's sorption onto the soil in tillage treatments, with Kf values decreasing 3.7 and 4.2-fold (fresh case) and 1.5 and 2.6-fold (aged case) for CTSI-Bc and CTFI-Bc, respectively. The transition to sprinkler irrigation reduced IMZX persistence. Overall, Bc amendment also reduced chemical persistence with half-life values decreasing 1.6 and 1.5-fold for CTFI and CTSI (fresh year) and 1.1, 1.1, and 1.3-fold for CTFI, CTSI, and NTSI (aged year), respectively. Sprinkler irrigation reduced IMZX leaching by up to a factor of 2.2. The use of Bc as amendment led to a significant decrease in IMZX leaching only under tillage conditions, but notable in particular for the CTFI case where leaching losses were reduced in the fresh year from 80% to 34% and, in the aged year, from 74% to 50%. Hence the change in irrigation from flooding to sprinkler either alone or in combination with the use of Bc (fresh or aged) amendment could be considered an effective way to sharply mitigate IMZX contamination of water in environments where rice is grown, particularly in those managed with tillage.

Effects of Combined Use of Olive Mill Waste Compost and Sprinkler Irrigation on GHG Emissions and Net Ecosystem Carbon Budget under Different Tillage Systems.

Traditional rice (Oryza sativa L.) production by flooding is a source of greenhouse gases (GHG), especially methane. The high consumption of water, as well as the chemical and physical degradation caused by these traditional practices in rice soils, is promoting a decrease in rice production in the Mediterranean area. The aim of this study was to monitor GHG emissions and the net ecosystem carbon balance (NECB) from rice produced with sprinkler irrigation techniques and also assess the impact of olive mill waste compost (C-OW) application and tillage on GHG emissions and the NECB. A field experiment for irrigated rice production was implemented by considering four different treatments: (1) tillage (T); (2) no tillage-direct seeding techniques (DS); (3) application of C-OW followed by tillage (TC); and (4) application of C-OW followed by direct seeding (DSC). The C-OW was only applied in the first year at a dose of 80 Mg ha-1. GHG emissions were monitored over three years in these four treatments in order to estimate the direct (first year) and residual (third year) effects of such practices. The application of C-OW caused an increase of 1.85 times the emission of CO2-C in the TC-DSC compared to the T-DS in the first year. It is noteworthy that the TC treatment was the only one that maintained an emission of CO2-C that was 42% higher than T in the third year. Regardless of the treatments and year of the study, negative values for the cumulative CH4 were found, suggesting that under sprinkler irrigation, CH4 oxidation was the dominant process. A decrease in N2O emissions was observed under direct seeding relative to the tillage treatments, although without significant differences. Tillage resulted in an increase in the global warming potential (GWP) of up to 31% with respect to direct seeding management in the third year, as a consequence of the greater carbon oxidation caused by intensive tillage. DS presented a positive NECB in the accumulation of C in the soil; therefore, it provided a greater ecological benefit to the environment. Thus, under Mediterranean conditions, rice production through a sprinkler irrigation system in combination with direct seeding techniques may be a sustainable alternative for rice crops, reducing their GWP and resulting in a lower carbon footprint. However, the use of C-OW as an organic amendment could increase the GHG emissions from rice fields irrigated by sprinklers, especially under tillage conditions.

Environmental fate and efficiency of bispyribac­sodium in rice soils under conventional and alternative production systems affected by fresh and aged biochar amendment.

Irrigation and tillage practice alternatives to conventional flooding production, with or without organic amendments, are attracting great interest to adapt rice cultivation to climate change. However, they can alter the behaviour of pesticides and their efficiency against weeds. A two-year field experiment was conducted to investigate how the environmental fate and the weed control efficiency (WCE) of bispyribac­sodium (BS) were influenced by biochar produced from holm oak prunings (BHO) testing both the fresh and the aged effects. The treatments were: flooding irrigation and tillage (FT), sprinkler irrigation and tillage (ST), sprinkler irrigation and no-tillage (SNT), and the corresponding homologues with BHO addition (FT-BHO, ST-BHO, and SNT-BHO, respectively). Fresh BHO amendment decreased the sorption of BS onto the soil in all treatments, while, after aging, it also decreased sorption in FT-BHO (1.3-fold) but increased it in SNT-BHO and ST-BHO (1.1-fold). BHO addition reduced BS persistence under non-flooding and flooding incubation conditions, except for FT under the former condition for which t1/2 increased ≈1.5-fold in both years. The addition of BHO led to a decrease in BS leaching from 58.3 % and 44.6 % and from 70.4 % and 58.1 % in ST and FT to 50.1 % and 38.3 % and 63.6 % and 50.3 % in the homologue amended soils for the fresh and aged years, respectively. While fresh BHO addition decreased the WCE of BS in SNT-BHO, ST-BHO, and FT-BHO on average by a factor of 1.5, with aged BHO there was only such a decrease (by a factor of 1.4) in FT-BHO. The use of BHO could be effective for reducing water contamination by BS in flooding or sprinkler irrigation rice farming as long as conventional tillage is used. But it may also contribute to greatly reducing the herbicide's efficiency, although with time to allow aging, this reduction would only persist under conventional flooding production.