Contour-levee irrigation systems are commonly used in rice cultivation in Latin American and the Caribbean countries, but research-based criteria for irrigation timing have not yet been determined under field conditions. In this study, we determined the relationship between soil volumetric water content (SWC) and field water table (FWT) for potential use in developing practical irrigation criteria based on FWT. Field experiments were conducted at four farms in Ibagué, Colombia from 2017 to 2018. The SWC at different soil depths and the FWT were constantly measured over the crop cycle using soil moisture sensors and piezometers with water level sensors, respectively. The resulting relationships were fitted with linearplateau models and validated with satisfactory prediction performances. The FWT at actual irrigation timings was observed and compared with the FWT at field capacity at 10 cm soil depth (reference FWT) using the validated relationship. The observed range of threshold FTWs (-46.2 to -9.2 cm) was comparable to the reference FWTs except one field (-21.4 to -12.9 cm). Although developing practical irrigation criteria as FWT still requires thresholds of SWC under a target contourlevee irrigation system, this study demonstrated the relationships between FWT and SWC in fields in Colombia.
To investigate whether the application of excessive amounts of cations (Na+ or K+) can promote plant growth and quality, hydroponically cultivated rapeseed plants were treated with high (100 mM), moderate (20 mM), or standard (6 mM) concentrations of NaCl or KCl. The treated plants were analyzed regarding their fresh weight, photosynthetic parameters, and abundance of selected phytochemicals with potential benefits for human health. Growth and photosynthesis were inhibited by the high cation concentration, while the effects of the moderate cation concentration were similar to those induced by the standard concentration. Additionally, the glucosinolate content increased following the application of 20 mM NaCl or KCl. Meanwhile, the chlorophyll and β-carotene contents increased significantly in response to 20 mM KCl, but not 20 mM NaCl.In summary, rapeseed quality improved, while growth was maintained, following the application of 20 mM NaCl or KCl,but KCl had a greater effect than NaCl.
The effect of hybrid vigor on the fruit yield in Japanese sweet pepper (Capsicum annuum L.) was investigated by comparing dry matter production, canopy light-intercepting characteristics and canopy photosynthesis of F1 cultivars to those of their parent lines. The greater yields in the F1 cultivars were caused by both higher dry matter partitioning rate into fruits and total dry matter production. There was no difference in the leaf photosynthetic capacity between the F1 cultivars and their parent lines. The canopy photosynthetic rate, total dry matter production, and yield showed significantly positive correlations with the photosynthetic photon flux absorbed within the plant canopy. The hybrid vigor caused higher plant statures with richer foliage, which led to more effective vertical profiles of leaf area, light absorption, and photosynthesis within the respective canopies. These factors caused a sufficiently higher canopy photosynthesis to produce greater dry matter production and maintain a higher dry matter partitioning rate into fruits, which resulted in higher yields. These results suggest that the vertical profiles of light-intercepting characteristics and photosynthesis within the canopies, which are evaluated by agro-meteorological methodology, are effective selection indices for breeding plants with higher yields.
We evaluated effects of different air temperature and light quality/intensity on growth and folate biosynthesis in leaf lettuce using a plant growth cabinet with light-emitting diodes (LEDs) combining red, green and blue (RGB) lights. Leaf lettuce was cultivated under combination conditions with 3 different air temperatures (20℃, 25℃ and 28℃) and 4 different light irradiations (photosynthetic photon flux density [PPFD] of 150 µmol m-2s-1 [P150]/RB, P150/RGB, P200/RB and P200/RGB) for 21 days. At the end of the cultivation, growth endpoints including edible portion weight, and folate contents were examined. The results demonstrated significant effects of air temperature and light quality and intensity on lettuce growth and folate biosynthesis. Under the optimal combination condition that we identified, 25℃ and P200/RGB, the edible portion weight and folate contents in leaf lettuce were 15-62％ and 83-137％ greater, respectively, compared to any light conditions at 20℃, an optimal temperature for conventionally growing leaf lettuce. Addition of green LED to red and blue LEDs maximized leaf lettuce growth and folate biosynthesis. Plant factory with optimal air temperature and light conditions utilizing RGB LED lights is a promising novel agriculture concept maximizing plant growth and critical nutrients such as folate.