Benjapon Kunlanit

Cultivar-dependent responses of Jerusalem artichoke (Helianthus tuberosus L.) to combined potassium (K) and zinc (Zn) fertilization remain poorly understood, particularly under low-fertility sandy loam conditions in tropical environments. This study evaluated growth, yield, and tuber-quality responses to K and Zn fertilization in a greenhouse. A 2 × 4 × 3 factorial experiment included two cultivars [CN 52867 × JA6-23 (V1) and JA37 × HEL65 (V2)], four supplemental K application rates (0, 0.61, 1.22, and 1.83 g K pot⁻¹) and three supplemental Zn application rates (0, 0.05, and 0.10 g Zn pot⁻¹). Potassium exerted a more consistent influence on growth and tuber production than Zn, whereas Zn responses varied with cultivar, trait, and nutrient combination. Significant cultivar × K × Zn interactions were detected for tuber number (p < 0.001) and tuber dry weight (p = 0.016). At the highest K rate (1.83 g K pot⁻¹), increasing Zn reduced tuber number in V1 from 38.00 to 19.00 tubers plant⁻¹, whereas in V2 it increased from 17.33 to 26.67 tubers plant⁻¹. Across cultivars and Zn treatments, tuber dry weight increased from 38.53 g plant⁻¹ without supplemental K to 45.91 g plant⁻¹ at 1.83 g K pot⁻¹ and was positively correlated with aboveground biomass (r = 0.77) and stem diameter (r = 0.76). Multivariate analysis further illustrated associations among growth, yield, physiological, and quality traits. From a practical perspective, these results indicate that K and Zn management in Jerusalem artichoke should consider cultivar-dependent nutrient responses rather than assuming a uniform fertilizer response. However, these findings are specific to the tested fertilizer rates and controlled pot conditions and require field validation before cultivar-specific fertilizer recommendations can be established.

Nitrogen (N) management is critical for improving rice productivity, but increasing N inputs may reduce N-use productivity when grain production does not increase proportionally. This study evaluated the effects of urea rate and application method on grain weight and partial factor productivity of N (PFPN) of rice (Oryza sativa L. cv. RD49) grown in low-fertility sandy loam soil under controlled greenhouse pot conditions. Three urea rates (0.53, 1.07, and 1.60 g pot⁻¹) and two application methods—basal application (BD) and basal plus topdressing (BTD)—were evaluated across two growing seasons. Grain weight was significantly affected by urea rate, application method, and their interaction. The lowest urea rate (N1; 0.53 g pot⁻¹) maintained grain weight comparable to the highest rate (N3; 1.60 g pot⁻¹) while producing the highest harvest index and substantially greater PFPN. Grain weight exhibited a significant quadratic response to urea rate, whereas PFPN, calculated on the basis of total fertilizer N applied, showed significant linear and quadratic responses and declined markedly with increasing urea rate. BTD resulted in greater mean grain weight and PFPN than BD. These findings indicate that the lowest tested urea rate provided a favorable balance between grain production and fertilizer-N input under the conditions evaluated, while the greater grain weight and PFPN under BTD highlighted the importance of coordinating N rate and application timing. These findings provide a basis for targeted field validation of N rate and application timing for RD49 rice grown in low-fertility, coarse-textured soils.

1. Peanut (Arachis hypogaea L.) is an important legume cultivated in tropical and subtropical regions for its edible oil, protein-rich seeds, and its contribution to soil fertility through biologic...

Efficient nutrient management is vital to sustaining rice production in the sandy soils of Northeast Thailand, where zinc (Zn) deficiency and low organic matter often constrain yield. This study evaluated the effects of Zn fertilization on the growth, yield, and Zn use efficiency (ZUE) of rice (Oryza sativa L. cv. Chai Nat 1) grown under greenhouse conditions in contrasting soil textures (loamy sand and clay). Four Zn rates were applied: 0, 5, 10, and 15 kg ZnSO₄·7H₂O ha⁻¹ (0, 0.013, 0.026, and 0.039 g ZnSO₄·7H₂O pot⁻¹). Clay soil, with higher organic matter, nitrogen, and available Zn, supported greater vegetative growth, biomass, and yield than loamy sand. Zinc fertilization significantly increased plant height, tiller number, chlorophyll content, biomass, panicle number, grain number, and filled grain weight. Yield improvement in loamy sand was associated mainly with reproductive efficiency, whereas in clay it was driven by vegetative vigor, biomass accumulation, and Zn uptake. Thousand-grain weight was not affected by Zn. ZUE peaked at 5 kg ha⁻¹ in loamy sand and 10 kg ha⁻¹ in clay, with clay showing a greater overall increase in ZUE across Zn rates and loamy sand exhibiting diminishing returns at higher application rates, reflecting differences in Zn availability and retention capacity. Correlation, PCA, and SEM analyses confirmed soil-specific yield mechanisms. Overall, Zn fertilization improved rice productivity and tissue Zn concentration, with optimal rates differing by soil texture. These findings highlight the importance of site-specific Zn management in enhancing yield, nutrient efficiency, and biofortification in rice-based systems of Northeast Thailand.

The use of essential oils from certain herbal plants offers a promising alternative to synthetic insecticides for controlling the maize weevil, Sitophilus zeamais Motschulsky (Coleoptera: Dryophthoridae), a major pest that causes significant damage to stored grains. Essential oils, particularly from aromatic herbs in the Apiaceae family, are widely used in medicinal, cosmetic, and food industries and provided insecticidal properties to mitigate the environmental and health hazards associated with synthetic insecticides. This research aimed to investigate the insecticidal and repellent effects of Apium graveolens L. (celery) seed essential oil against S. zeamais. Chemical analysis of the commercially produced essential oil from A. graveolens seeds was conducted using a gas chromatograph–mass spectrometer (GC-MS), and the biological activity of the essential oil was determined by ingestion, contact, fumigation, and repellent tests. The analysis identified D-limonene (64.21%) and α-humulene (17.46%) as primary components of the oil. Toxicity assays revealed an observable contact toxicity, with higher concentrations and prolonged exposure increasing its effectiveness. The contact toxicity assays reported an LC₅₀ of 19.83 nL/adult after 72 h. Additionally, the essential oil displayed repellent effects, effectively deterring weevils at concentrations above 16 µL/L air, but its feeding deterrence was weak. The essential oil’s strong insecticidal and repellent properties, which were concentration- and time-dependent, highlighted its potential as a sustainable alternative to synthetic pesticides for integrated pest management.

The influence of the quantities and ratios of dissolved organic carbon (DOC) and dissolved nitrogen (DN) generated by different chemical quality classes of organic residues on soil microbial processes in the decomposition process is not well understood. If the DOC-to-DN ratio (hereafter, ratio) of the substrate is close to that of the microbial C-to-N ratio, then the DOC-and-DN stoichiometry of the substrate is balanced, resulting in enhanced microbial processing, i.e., carbon use efficiency (CUE). Uncertainty exists about the influence of DN and the DOC-to-DN ratio on CUE, particularly in high-quality class (high nitrogen) residue-treated soils. A long-term field experiment was used to explore the effect of the annual application of residues of different quality classes on decomposition processes, focusing on the effects of DOC, DN, and the ratio on the microbial metabolic quotient (qCO₂), which is the inverse of CUE. DOC and DN were extracted from soils during the 13th year of the experiment. Soils treated with high-quality class groundnut residue (high-nitrogen) had higher DN (5.4 ± 2.6 mg N kg⁻¹) and a lower ratio (6.8 ± 2.6) than those treated with medium-quality (medium-nitrogen) tamarind (3.0 ± 0.6 and 10.7 ± 2.2, respectively). The positive influence of DN on qCO₂ (R² = 0.49 *) in groundnut-treated soil suggested that the high bioavailability of DN reduced CUE due to imbalanced DOC-and-DN stoichiometry. This contradicted earlier published findings on high-nitrogen residues which had balanced DOC-and-DN stoichiometry. The positive influence of the ratio on qCO₂ under the tamarind-treated soil (R² = 0.60 *) indicated that its balanced DOC-and-DN stoichiometry enhanced CUE. High-quality class organic residues can result in either higher or lower CUE than their lower-quality class counterparts depending on whether the resulting DOC-and-DN stoichiometry is balanced or imbalanced.

The objectives of this study were to investigate effects of land use on accumulation of soil organic matter (SOM) in the soil profile (0–100 cm) and to determine pattern of SOM stock distribution in soil profiles. Soil samples were collected from five soil depths at 20 cm intervals from 0 to 100 cm under four adjacent land uses including forest, cassava, sugarcane, and paddy lands located in six districts of Maha Sarakham province in the Northeast of Thailand. When considering SOM stock among different land uses in all locations, forest soils had significantly higher total SOM stocks in 0–100 cm (193 Mg·C·ha⁻¹) than those in cassava, sugarcane, and paddy soils in all locations. Leaf litter and remaining rice stover on soil surfaces resulted in a higher amount of SOM stocks in topsoil (0–20 cm) than subsoil (20–100 cm) in some forest and paddy land uses. General pattern of SOM stock distribution in soil profiles was such that the SOM stock declined with soil depth. Although SOM stocks decreased with depth, the subsoil stock contributes to longer term storage of C than topsoils as they are more stabilized through adsorption onto clay fraction in finer textured subsoil than those of the topsoils. Agricultural practices, notably applications of organic materials, such as cattle manure, could increase subsoil SOM stock as found in some agricultural land uses (cassava and sugarcane) in some location in our study. Upland agricultural land uses, notably cassava, caused high rate of soil degradation. To restore soil fertility of these agricultural lands, appropriate agronomic practices including application of organic soil amendments, return of crop residues, and reduction of soil disturbance to increase and maintain SOM stock, should be practiced.

Soil capacity as a major carbon (C) sink is influenced by land use. Estimates of soil organic carbon (SOC) sequestration have mostly focused on topsoils [0–30 cm official Intergovernmental Panel on Climate Change (IPCC) soil depth]. We investigated SOC stocks and their quality as influenced by land-use changes. Soil samples were collected from five soil depths down to 100 cm of three adjacent fields each representing a different land use—forest, cassava, and rice paddy—in Northeast Thailand. Sequestration of SOC in topsoils under all land uses was higher, as indicated by SOC stocks (59.0–82.0 Mg ha⁻¹) than subsoils (30–100 cm) (27.0–33.0 Mg ha⁻¹). The soil profile (0–100 cm) of the forest had higher stocks of SOC and humic acid (115.0 and 6.8 Mg ha⁻¹, respectively) than those of cultivated land uses [paddy (100.0 and 4.8 Mg ha⁻¹, respectively) and cassava (87.0 and 2.3 Mg ha⁻¹, respectively)], which accounted for an average 30% increase in SOC sequestration over those with only topsoil. Topsoils of the forest had higher humic acid content but narrower E4:E6 ratio [the ratio of absorbances at 465 nm (E4) and at 665 nm (E6)] of humic acids (2.8), indicating a higher degree of humification and stabilization than the cultivated soils (3.2–3.6). Subsoil C was higher quality, as indicated by the lower E4:E6 ratio of humic acids than topsoils in all land uses.

Against the background of current understanding of dissolved organic carbon (DOC) adsorption onto clay surfaces, it remains unclear if bulk DOC or its fractions contribute to microaggregate formation in the top layers of coarse‐textured soils. We therefore investigated the effects of long‐term inputs of biochemically contrasting organic residues on the chemical characteristics and vertical distribution of DOC in a coarse‐textured Ultisol. During 2007–2008, DOC samples were extracted from soil profiles of a long‐term residue quality field experiment initiated in 1995. In this field experiment, groundnut stover, dipterocarp and tamarind leaf litter, as well as rice straw of contrasting biochemical quality, were applied yearly at 10 Mg ha ⁻¹ . Groundnut, dipterocarp and tamarind produced large amounts (7.1–11.8 g C m ⁻² ) of high‐molecular‐weight (HMW; > 10 kDa) DOC, which was found in high concentrations (30–50 mg C kg ⁻¹ ) in the topsoil (0–15 cm). Rice straw, however, produced large amounts (3.5 g C m ⁻² ) of low‐molecular‐weight (LMW; < 1 kDa) DOC during the initial stage of decomposition. Although the HMW DOC was retained in the topsoil (0–15 cm), the LMW DOC was rapidly translocated to lower soil depths (60–80 cm). This translocation was facilitated by the low adsorption potential of the rice straw‐derived LMW DOC on colloidal surfaces of the topsoil. There was a significant positive correlation of C in the HMW DOC with that in fine particles, indicating their contribution to microaggregate formation and thus C accumulation. It was concluded that biochemical quality of residues as a determinant of concentration and chemistry of DOC and its vertical dynamics along the soil profile must be considered for SOC accumulation in coarse‐textured soils. Furthermore, we found reasonable indications that HMW DOC contributes to microaggregate formation in topsoils. Highlights: Residue quality determined vertical dynamics of DOC in coarse– textured Ultisols. Lignin‐ and polyphenol‐rich residues produced HMW DOC in topsoil. LMW DOC derived from cellulose‐rich residues was translocated to the subsoil. There were indications that HMW DOC supported microaggregate formation in topsoils.