Effects of Composting Rice Stubble in Rice Field Condition on Water Quality and Azolla Yields

Abstract

The objective of this research is to study appropriate methods for azolla cultivation in rice field conditions. The experiment was conducted in a completely randomized design (CRD). Azolla was grown in 18 pits, comprised of three pits for each of 6 different growth methods. The cultivation was conducted three times, each spanning 10 days. The treatments were as follows. In treatment 1 (control), clean water without added nutrients was used as a growth medium. In treatment 2, 46% urea fertilizer was added to clean water and then used as a growth medium. In treatment 3 and 4, rice field soil and rice stubble compost were used respectively. In treatment 5, rice field soil was mixed with 46% urea fertilizer and used as a growth medium, while, in treatment 6, it was combined with rice stubble composted. Water quality factors, consisting of water temperature, pH, dissolved oxygen, electrical conductivity, total nitrogen content, and microorganism count, were measured before and after azolla cultivation. Azolla yield i.e., fresh and dry weight, were also quantified. The results prior to azolla cultivation showed that water temperature was not different (p>0.05) in all treatments. Treatment 6 had the lowest pH (p<0.05). Treatment 5 resulted in the highest electrical conductivity and total nitrogen content, followed by treatment 2 (p<0.01). Water in treatment 1 and 2 had the highest dissolved oxygen content (p<0.05). Treatment 6 led to the highest microorganism count, followed by treatment 3 (p<0.01). After the azolla cultivation, water temperature was similar in all treatments (p>0.05), while treatment 6 had the lowest pH (p<0.05). Treatment 6 also led to the highest electrical conductivity of water, followed by treatment 5 (p<0.01). Dissolved oxygen content was highest in treatment 1 and 2 (p<0.05). Treatment 5 had the highest nitrogen content, followed by treatment 6 (p<0.01). Treatment 6 produced the greatest microorganism count, followed by treatment 4 (p<0.01). The fresh weight of azolla under treatment 5 was highest, followed by treatment 6 (p<0.01). Treatment 5 and 6 also led to the greatest azolla dry weight (p<0.01). Correlation analysis revealed that water temperature, total nitrogen content, electrical conductivity, and microorganism count were positively associated with azolla yields. In conclusion, the treatment with rice field soil and urea fertilizer provided the best fresh weight of azolla. Nevertheless, the treatment with rice stubble compost and rice field soil led to the highest dry weight of azolla similar to the rice field soil and urea fertilizer treatment. Therefore, the use of rice stubble compost is suitable for promoting azolla growth in rice fields. Such use could be an environmentally friendly alternative to burning rice stubbles that farmers often conduct if this use is adapted to each farmer’s situation.