Most corn planted on tropical acidic soils suffers substantial yield loss caused by low crop phosphorus (P) uptake. Humic acid is recommended to increase crop P uptake since it is capable of competing with P to be bound to soil adsorption complexes. Humic acid extracted from composted manure (MHA) is a good alternative to humic acid because it is more reactive and has a higher complexation ability compared with leonardite. Therefore, the effectiveness of soil-applied MHA combined with P was evaluated to improve corn yields in acidic soils from the aspect of crop nutrient uptake efficiency and crop physiological performance. Two high-yielding corn cultivars that are highly accepted by Indonesian farmers and resistant to downy mildew disease were subjected to five different types of MHA and P combinations. The amount of P fertilizer was equivalent to 120 mg P₂O₅ kg⁻¹ soil. The H₁₀P₁ produced the most significant result in terms of total crop dry weight, grain dry weight, and corn yield. The highest efficiency for P uptake in the leaves and grains was found with H₁₀P₁ and H₅P₁, respectively. Although chlorophyll content was not substantially improved, the stomatal apertures 7 weeks after planting (WAP) were significantly increased with H₁₀P₁ and H₁₅P_1. The photosynthetic rate and nitrate reductase (NR) activity at 10 WAP were significantly increased with H₅P₁ and H₁₀P₁, respectively. The results clearly indicated significant increases in the efficiency of crop P uptake and physiological performance for stomatal aperture, photosynthetic rate, and NR activity can highly contribute to higher corn yields.

Different weeding frequencies (WFs)―0WF, 2WF, 4WF, 6WF, and 8WF―were adopted in an organic rice field to investigate their influence on weed types, rice and weed biomass, rice tiller and weed number, N concentration, and N uptake. The study field was located in Tsuruoka, Yamagata, Japan. Rice (cv. Sasanishiki) was planted from May to September 2019, and all weeding events were carried out until 49 days after transplantation (DAT) using a rotary weeder. Rice and weed samples were collected at 60, 88, and 110 DAT. Echinochloa crus-galli (E. crus-galli), Schoenoplectus juncoides, and Monochoria vaginalis (Burm. f.) were the most commonly found weeds. High weed diversity was observed at both 6WF and 8WF, E. crus-galli was the dominant weed at 0WF. Compared to 0WF, 2WF displayed a significantly decreased weed biomass. However, at 8WF, the weed biomass was reduced by 79.0%, the rice biomass was increased by 277%, and the rice tiller number was almost three times higher than that at 0WF and 110 DAT. Compared to 0WF, a significantly increased rice N uptake was observed at 4WF, and rice N uptakes achieved at 6WF and 8WF were two and four times higher than those at 0WF, respectively. Higher weeding frequencies provide notable benefits in suppressing weeds and supporting rice growth, especially in N uptake competition with weeds.

Huanglongbing is known as a destructive disease in citrus production. Investigation on plant response and development of huanglongbing disease against heat treatment on ‘Siam Purworejo’ (Citrus nobilis (Lour)) and ‘Nambangan’ (C. maxima (Burm.) Merr.) was done. High-temperature treatment was applied by covering plants with an enclosed screen. The treatment plant has three types of CLas pathogen infection status. The result showed that heat treatments could significantly increase new flushes. It was found that intensity of HLB infected plant decreased. The treatments effect on the proline level was dependent on cultivar, leaves age and HLB-infection status. Chlorophyll content of HLB infected plants increased due to high temperature. High-temperature increased Fe content in the artificially infected plant, whereas Zn contents increased in the leaves of infected plants by vector. ‘Nambangan’ had higher Fe content than ‘Siam Purworejo’ on uncovered plants. CLas bacteria still persisted in infected plant based on real-time PCR analysis.

The type of vegetation and soil organic matter affect the carbon fraction, nitrogen fraction and soil carbon stocks that contribute to the global carbon cycle. Therefore, the calculation of the composition of the fractions in different land covers is very important as a potential indicator of the effect of land management practices on soil organic carbon dynamics and supports the reduction of carbon dioxide (CO2) and soil carbon storage. This research aimed to determine the composition of the carbon fraction, nitrogen fraction and soil carbon stock in different land cover. There were six types of land cover with vegetations of 10-year-old bamboo, 30-year-old bamboo, 50-year-old bamboo, bulrush, a mixture of brushwood and bulrush, and a mixture of Albizia falcataria and brushwood, each of which was sampled three times. Soil samples were used to determine microbial biomass, particulate organic, humic acid, fulvic acid and soil carbon stock. The six land cover types showed significant differences in all fractions and soil carbon stocks. Fifty-year-old bamboo vegetation has the highest carbon storage of 0.029 g g-1 soil. The stable carbon fraction, in the form of humic acid and fulvic acid, in 50-year-old bamboo vegetation is more excellent than that in other vegetation. This study shows that 50-year-old bamboo vegetation has the potential to sequester carbon and store carbon in forms that decompose slowly, namely humic acid and fulvic acid, in the soil for a longer period.

Methane (CH4) emission from paddy rice fields is a global concern; however, engineering plant spacing can decrease CH4 emission. Due to this, field research was conducted to measure CH4 emissions from rice fields planted using jarwo 2:1 spacing, which has a 25 × 12.5 cm and 50 cm for the plant-free area (PFA), compared to tegel, which has a spacing of 25 × 25 cm. Each field was treated with organic fertilizer (mixture of cow manure and neem compost in a ratio of 1:1) with one of four doses: 0, 3, 6 and 9 tons/ha. The results showed that chemical properties such as soluble-Fe, soil organic matter (SOM), soil acidity (pH), and redox potential (Eh) were significantly correlated with CH4 emissions (0.52***, 0.47**, 0.36*, and -0.27* respectively). Jarwo 2:1 had lower CH4 emissions than tegel on all doses of fertilizer. The most efficient dose of fertilizer was 3 tons/ha applied jarwo 2:1 because it was able to produce rice up to 12 tons/ha with CH4 emissions of only 34 kg/ha/season, while CH4 emissions in tegel was 39 kg/ha/season. It is concluded that jarwo 2:1 with 3 tons/ha organic fertilizers can be recommended to farmers because it produces lower CH4 emissions and higher rice yield.

Peat and its substratum have different geology and parent materials. Studies on peat formation and spatial patterns of peat deposits have been widely reported, but little is known about patterns of peat thickness across tropical peat landscapes. We studied the relationship between surface relief and peat thickness on Tebing Tinggi Island (Indonesia) by considering peat surface altitude, peat thickness and substratum altitude. The research location is unique, being a small (~ 70 × 30 km) predominantly peat-covered island separated by a strait from the mainland of Sumatra and its more extensive peat deposits. Geomorphological features on the island were identified using a digital terrain model (DTM) developed from LiDAR data, together with observations on peat cores. The results indicate that the topography of the peat landscape does not reflect peat thickness. Thick peat can be found at the edge of a peat dome if it overlies a basin or valley in the substratum, while thinner peat can be found at the centre if it overlies a mound in the substratum. It is also important to note that the shapes of the peat surface and the substratum surface are not the same; a flat peatland surface may have an undulating substratum and vice versa.