THE EFFECT OF RICE CULTIVARS ON METHANE EMISSION FROM IRRIGATED RICE FIELD

Rice plants have been reported to affect methane (CH4) emission from rice fields. The objectives of this study were to determine the effect of rice cultivars on CH4 emission from flooded rice and to develop crop management strategies with low emitting rice cultivars while sustaining high yield. The four rice cultivars studied were Memberamo, Cisadane, IR64, and Way Apoburu. The CH4 emissions were determined in the wet season of 2001/2002 (November-February) using an automated closed chamber technique in an irrigated field condition. Farmyard manure at the rate of 5 t ha-1 was given to the plots to ensure carbon was not limited. Root weight, root length, biomass, and number of tillers were determined at 17, 36, and 57 days after transplanting (DAT). The results showed that the mean CH4 emission was highest in the plot planted with Cisadane (94.8 kg CH4 ha-1), and the lowest with IR64 (37.7 kg CH4 ha-1). The plots treated with emberamo and Way Apoburu resulted an intermediate CH4 emission at the average of 61.1 and 58.9 kg CH4 ha-1, respectively. There was no significant difference in yield between the cultivars tested. The yield of Memberamo, Cisadane, IR64, and Way Apoburu were 5.882, 5.764, 5.873 and 6.065 t ha-1, respectively. Statistical analysis showed that there were no significant differences in the root weight and root length among cultivars. However, Cisadane gave the highest dry matter weight (222 g hill-1) at 57 DAT compared to the other cultivars (175-190 g hill-1). Plant tillers did not show significant differences between the cultivars. Regression analysis showed that CH4 flux was significantly related with root weight, root length, aboveground biomass, and number of plant tillers. This finding shows that the use of selected cultivars, such as IR64, can potentially lower CH4 emission without scarifying yield

Nitrogen Management in a Maize-Groundnut Crop Rotation of Humid Tropics: Effect on N2O Emission

Development of appropriate land management techniques to attain sustainability and increase the N use efficiency of crops in the tropics has been gaining momentum. The nitrous oxides (N2Os) affect global climate change and its contribution from N and C management systems is of great significance. Thus, N transformations and N2O emission during maize-groundnut crop rotation managed with various N sources were studied. Accumulation of nitrate (NO3 –) and its disappearance happened immediately after addition of various N sources, showing liming effect. The mineral N retained for 2–4 weeks depending on the type and amount of N application. The chicken manure showed rapid nitrification in the first week after application during the fallow period, leading to a maximum N2O flux of 9889 μg N2O-N m–2 day– 1. The same plots showed a residual effect by emitting the highest N2O (4053 μg N2O-N m–2 day– 1) during maize cultivation supplied with a halfrate of N fertilizer. Application of N fertilizer only or in combination with crop residues exhibited either lowered fluxes or caused a sink during the groundnut and fallow periods due to small availability of substrates and/or low water-filled pore space (<40%). The annual N2O emission ranged from 1.41 to 3.94 kg N2O-N ha–1; the highest was estimated from the chicken manure plus crop residues and half-rate of inorganic N-amended plots. Results indicates a greater influence of chicken manure on the N transformations and thereby N2O emission