The value of sustainable rice straw management
Rice straw is produced as a byproduct of rice production at harvest. Rice straw is removed with the rice grains during harvest and it ends up being piled or spread out in the field depending if it was harvested manually or using machines. Ratio of straw to paddy ranges from 0.7-1.4 depending on the variety and growth. Globally, roughly 800 to 1,000 million tons per year of rice straw is produced, with about 600 to 800 million tons per year produced in Asia. This continues to rapidly increase due to shorter turnaround time required for intensified rice cropping. The introduction of game-changing combine harvesters which solves the high labor cost associated with manual straw collection addresses only half the battle. Straw incorporation in soil for fertilization in intensive systems is also not possible with two to three crops per year because the turnaround time is too short for decomposition, resulting to poor soil fertilization properties which ultimately hinders crop establishment.
With little options, open-field straw burning has increased dramatically over the last decade. Improved rice straw management and technologies that can help reduce the environmental footprint of and increase revenues from rice production and processing are therefore important for sustainable rice production systems.
Rice Straw Management Options
IRRI and its partners are conducting research on improved rice residue management and technologies that can help reduce the environmental footprint of and increase revenues from rice production.
Rice straw in principle can be processed and used in agriculture for purposes such as soil improvement through carbonization and composting, in bio-energy production, and to produce materials for industrial uses such as silica and bio-fiber. However, not all the options are economically feasible because the costs of materials produced from rice straw, including transportation cost, are still higher than for materials produced from the other traditional or existing feedstocks. Sustainable rice straw management is currently practiced with the following scalable options:
Incorporation of rice straw into paddy soil can maintain and enhance soil fertility with a proper management. However, ineffective management of straw incorporation can result in a decrease in production efficiency and increased greenhouse gas emissions. It should be noted that slow decomposition is often the reason why farmers do not want to incorporate crop residues. Some research has been undertaken on speeding this up, for example, by using fungal inoculums.
Collection of rice straw spread in the field by combine harvesters is only economically feasible with mechanized collection. It plays an important role in the rice straw supply chain to prepare feedstock for further uses. The rice straw balers currently used Asian countries are presented in here.
Rice straw mushrooms, Volvariella volvacea, are considered to be one of the easiest mushrooms to cultivate because of their short incubation period of 14 days. This tropical species thrives best at 30‒35 °C for mycelia development and at 28‒30 °C for fruiting body production. Outdoor mushroom production is a common practice as it has low investment cost, however its yield is just 0.8 kg of mushroom per 10 kg of dried straw. Indoor mushroom growing with higher investment cost produces about 2 kg higher yield per 10 kg of dried straw.
Rice straw has too few nutrients to be used as the only source of food for cattle but is a good feed additive and can also be treated to increase the supply of energy and protein. In general, the daily recommended maximum intake of rice straw by ruminants is 1.0 to 1.5 kg per 100 kg live-weight per day. Urea-treated straw (rice straw is ensilaged with 2-3 % urea) can increase intake and digestability of this rice straw based feed.
Compost is produced based on mixing of rice straw, animal manure, and enzymes using the turner and ensilage to optimize the composting process. Mechanized composting can significantly improves the bio-physical processes of composting. The compost product can be used as medium for growing vegetables and other crops or spread on the rice field as soil amendment. It enhances nutrient (i.e., nitrogen and carbon contents) and organic matter content of the soil.