Non Technical Summary
Rice systems are unique from other agricultural systems in a number of ways. Most rice is grown in flooded soils. Flooding soils, however, alters soil chemistry which impacts the production of greenhouse gases (GHG) and nutrient use-efficiency. Given the significance of rice it is important to develop management practices that are able to maintain high yields while at the same time minimizing adverse effects to the environment and optimizing its positive benefits. The broad issues of water use, nutrient use efficiency and GHG are all important drivers of the long-term sustainability of rice systems. Furthermore, these factors are all interrelated. For example, how one manages water affects nutrient use efficiency, water quality and GHG production. Over the past 10 years, my research group in rice agro-ecosystems has focused on how to maximize rice yields in an efficient way. Straw burning has been largely replaced with incorporating straw which then led to a reduction in the rate of fertilizer-N input and improved water fowl habitat. Alternative seeding practices are being explored that reduce herbicide use. Questions are addressed how straw and fertilizer management practices affect the quality of run-off water, in particular water soluble organic compounds, a key concern when the water is subsequently used for drinking water. The ultimate goal is to produce rice with the least environmental impact without jeopardizing the economic livelihood of rice farmers. One key component of a comprehensive framework on sustainability is the emissions of GHG. Currently, there is only limited information available on the annual amount of GHG emitted from rice fields as most GHG measurements are taking during short periods in the spring and early summer. This may give inaccurate estimates of GHG emission when extrapolated across the year. The two main GHG of interest are methane and N2O. As N2O is about 10 times more potent than methane, reducing N2O emissions could have a large effect on reducing the greenhouse gas warming potential from rice fields. However, management practices that reduce methane emissions will likely lead to an increase in N2O emissions and vice versa as they are controlled by opposing conditions related to the availability of O2. Here we propose to develop an annual GHG budget for methane and N2O in wet and dry seeded fields. Wet and dry seeding are the two primary means of establishing rice in the US and they differ substantially in terms of early season water management and thus the potential to emit GHG. I am a strong believer that the value of the research findings is controlled on how well the findings are applicable and implemented. Therefore, the research is conducted in farmer's fields to reflect farmer's management practices.
Animal Health Component
Research Effort Categories
Goals / Objectives
The overall objective of this project is to develop production guidelines for California rice growers which are economic viable and environmentally sound and develop mitigation strategies to reduce greenhouse gas emissions and nutrient losses. The specific objective is to quantify N2O and CH4 emissions in California rice systems and develop mitigation strategies. Rice systems emit both nitrous oxide and methane (CH4). N2O gas has 296 times the global warming potential of CO2 and is responsible for nearly 60% of total greenhouse gas (GHG) emissions associated with U.S. agriculture. Accordingly, a better understanding of how soil and fertilizer management practices influence N2O emissions is needed. Recent climate change policies have accentuated this situation, especially within California which has set a national precedent by adopting an aggressive piece of legislation that aims to reduce statewide GHG emissions to 1990 levels by 2020 (known as AB 32). It is known that agricultural practices such as tillage, flooding, draining, and N fertilization contribute to N2O emissions and may, therefore, be regulated in the future. Previous research indicates that substantial GHG emissions, mostly CH4, can occur when rice is grown under flooded, anaerobic conditions. Although the factors driving CH4 are fairly well known, those determining N2O emissions from rice systems are less understood. Nevertheless, it is known that N fertilization and water management practices play important roles. N inputs tend to increase N2O emissions compared to unfertilized rice soils, yet high N application rates do not necessarily result in increased fluxes, as background soil N emissions are variable and denitrification processes are strongly influenced by soil type and pH15. Research is necessary to determine the potential for N2O emissions in California rice production systems and link peak fluxes rates with specific management practices. The long-term objectives are to (1) determine N2O and CH4 baseline emissions in conventional dry seeded establishment systems and (2) develop appropriate mitigation strategies where necessary. Previously conducted research highlighted the importance between agronomic management and environmental quality in rice systems, where management practices appear to regulate GHG emissions more than N fertilizer rate. In general, emissions were higher from the continuously flooded system than for the dry seeded system. Methane emissions were not directly affected by addition of fertilizer N but N2O emissions were. Frequent flood-drain cycles resulted to high N2O emission events. To mitigate emissions applying N deep into the soil as aqua ammonia may reduce N2O losses compared to surface N applications. In dry seeded systems N fertilizer should not be applied before permanent flood. The lowest Global Warming Potential (GWP) on a yield scaled basis was in systems where optimal N rates were applied that resulted in optimal yields. Over applying N fertilizer resulted in an increased GWP on a yield scaled basis.
Experimental Procedure to Accomplish Objectives 1.Greenhouse gas emissions, N rate and seeding On-farm experiments will be implemented with contrasting rice establishment practices:conventional water seeded and dry seeded. The N rates ranging from 0, 80, 140, 80/60 split, 200 and 260 kg N ha-1 will be applied and adjusted to the system and variety. As growers often apply the majority of their N as aqua ammonia and a smaller portion of their N to the soil surface, an additional split N treatment of 80 + 60 kg N ha-1 will be included to assess the effect of N placement on GHG emissions. In the drill seeded system, N rates ranging from 0, 80, 140, 80/60 split and 200 kg N ha-1 will be applied as urea to the soil surface immediately prior to the permanently flood. As growers often apply a small amount of N at planting in drill seeded systems and the majority before the permanent flood, an additional split N treatment is also included to assess the effects of N application timing on GHG emissions. All treatments will be replicated at least three times. On-farm experiments will be conducted on soils representative of the Sacramento Valley rice growing region to ensure that results are relevant to rice growers and the California rice industry. N2O and CH4 emissions will be measured for each N treatment using the closed chamber technique and concentrations will be determined using gas chromatography. Multiple chambers will be installed per replication to reduce the variability of measurements. To capture peak gas fluxes, intensive sampling will occur at each site throughout the period immediately following critical management phases. N2O and CH4 emissions will be determined specifically for water management and tillage practices within each N treatment, and total N2O budgets will be calculated for each system. Plants may be sampled at critical growth stages to analyze N uptake values during the season. Fertilizer N recovery rates and grain yields will be calculated for each N treatment, using zero N plots as a measure of soil N availability. N2O emissions per unit of crop N uptake, i.e., yield, will be determined for different N rates in each of the establishment systems. 2.Variety testing and methane emissions There is some evidence that different varieties of rice show different rates of CH4 emissions. Currently, it remains unknown whether rice varieties grown in CA show different rates of CH4 emissions or if it is economically feasible and effective of reducing CH4 emissions by changing rice varieties. To be able to determine of changing rice varieties can be a mitigation strategy of reducing CH4 emissions, baseline data on the amount of CH4 that is emitted by the major rice varieties grown in CA need to be established. CA rice varieties will be grown in small field plots and the seasonal amount of CH4 emitted determined using the sampling protocol outlined above. If significant differences in total CH4 emitted are observed, a more long-term strategy needs to be developed on how rice varieties can be selected that show reduced emissions of CH4 but are also of economic interest to the farmers.