| dc.description.abstracteng | Summary
Rice is the most important food crop in Asia. However, rice production in Asia is facing tremendous challenges in the 21st century. Fast-growing populations are demanding larger rice supplies under the increasingly difficult production conditions of declining water availability and quality. Furthermore, rice cultivation produces large amount of rice residues. With currently increasing trends in cropping intensity, the amounts of residues that are burned on the field are expected to increase dramatically, unless crop residues are managed more sustainably. Comparative research on the effects of different water and rice residue management practices on nutrient balances and greenhouse gas emissions are needed. They will provide information on the environmental and agronomic consequences of choices in rice residue management practices, including direct incorporation of rice residues into the soil, application of rice-residue compost, burning of rice residues on the field, and use of rice residues as fodder for livestock. The outcome of such studies can then be used to find the best option for rice residue management.
In a survey of rice residue management in northern Vietnam, we examined the present cropping systems and the patterns of crop residue management prevalent in three different ecological zones of northern Vietnam. We compared the farmers’ practices of either burning or incorporating the residues of their rice crops, and furthermore, calculated involved costs and benefits. Our data demonstrate that the burning of crop residues might be an erroneous trend from an ecological perspective, but is rational from an economic point of view. Based on this finding, we argue that a change of the prevalent burning practice cannot be achieved without the farmers getting their extra expenses refunded.
A field study was therefore conducted to quantified soil nutrient balances of paddy rice fields under different crop-residue management practices in northern Vietnam. All plots received mineral N, P, and K fertilizer in addition. We found that soils with (1) direct incorporation of rice residues into the soil, (2) application of rice-residue compost, and (3) burning of rice residues on the field showed a positive nutrient balance, which indicates that soil fertility can be maintained under these practices and that amounts of chemical fertilizers can be considerably reduced. Without fertilizers reduction, there is a risk of eutrophication in surrounding surface waterbodies. In contrast, use of rice residues as fodder for livestock, resulted in a negative nutrient balance in paddy soils, which indicates the need for returning nutrients to the soils. From these findings, we conclude that knowledge about the effects of rice-residue management practices on nutrient cycles may help to optimize the use of fertilizers, resulting in a more sustainable form of agriculture in northern Vietnam.
Silicon (Si) is known to have beneficial effects for plants, in particular for rice, which is a strong Si accumulator. It helps mitigate environmental stresses and soil nutrient depletion. In some regions plant available Si in soil might be limited and have detrimental effect on rice agriculture. Here we study the impact of three rice residue management practices (burying, burning and manure production for use on the field) in Si-depleted rice fields from northern Vietnam. The different Si reservoirs in soils and the plants Si content were measured under these different practices. Our results show a strong correlation between the different soil Si reservoirs and plants Si content. Our results show no significant difference between the different management practices in terms of Si bio-availability and Si uptake by plants. These new data also suggest also raise the question whether Si-depleted environment may proportionally lose Si faster through grain harvest than other less Si-depleted environment.
In order to compare the fluxes of methane (CH4) and Nitrous oxide (N2O) from rice paddy fields managed by differently treated crop residue inputs (direct incorporation of rice residues into the soil (I), application of rice-residue compost (CR), burning of rice residues on-site burning of rice residues (B)) under two water management systems, a field experiment was performed in Bac Giang Province in northern Vietnam. The field experiment was carried out on spring rice and summer rice seasons. The results indicate that water management is a major factor in reducing CH4 emissions. The alternate wetting and drying (AWD) management led to a reduction of CH4 emissions by 15-42% for the CR treatment, by 27-47% for the B treatment, and by 36-45% for the I treatment. Similarly, AWD management resulted in a reduction of global warming potential (GWP) by 16-36% (CT), 15-39% (CR), 27-40% (B), and 35-40% (I), respectively. The treatment I led to the highest CH4 emissions, while the control (CT) showed the lowest CH4 emissions under both water management systems. Rice yields were slightly higher for treatments including with mineral and organic fertilizers compared to only mineral fertilizer (CT). In conclusion, we recommend a combination of treatment I with AWD water management, as this combination resulted in reduced greenhouse gas emissions while ensuring high rice yields. | de |