Soybean yields have remained below 2.0 t ha−1 for over 30 years in Asian countries; however, few studies have analyzed national statistical data in detail to explore the underlying factors. This is the first study to analyze precisely and comprehensively factors involved in the historical soybean yield suppression in Japan by using national production-cost and other statistics, coupled with a crop model. Panel data of 5–6 land-size sections for 1987–2018 were prepared to analyze the regression of actual yield against 13 production input-related variables, model-predicted potential yield, and agricultural social capital score by each data class for the whole country (i.e., Japan), two climatic regions (temperate and subarctic), and two field types (converted paddy and upland). Although potential yield rose by 8
The red pericarp trait is controlled by Rc and Rd, is prevalent in weedy rice, and is associated with seed dormancy and longevity. However, the individual and combined effects of these genes on seed adaptation remain unclear. We developed near-isogenic lines (NILs) carrying ‘Kasalath’ Rc and/or Rd alleles in the ‘Koshihikari’ background and evaluated seed dormancy, freezing tolerance, and overwintering ability under controlled and field conditions, using ‘Koshihikari’, ‘Kasalath’, and the Japanese weedy rice accession ‘JP_1177’ as controls. NILs carrying Rc, Rd, or both did not have the deep primary dormancy typical of weedy rice. Under field conditions, these lines germinated prematurely and failed to survive winter, unlike ‘JP_1177’. However, the NIL carrying both Rc and Rd had higher freezing tolerance than the other lines, suggesting an interaction between these genes. These findings indicate that the red pericarp trait does not confer deep dormancy but may increase seed longevity primarily by improving low-temperature tolerance and overwintering ability in soil. These results provide insights into the adaptive significance of the red pericarp trait in temperate environments, although our data are limited to a cultivated temperate japonica (Koshihikari) background.
This study aimed to improve estrus management in Japanese Black cows by investigating the effects of controlled internal drug release (CIDR) treatment on luteal function including luteolysis and estrous characteristics. Cows with normal estrous cycles were divided into three groups, and CIDR treatment was initiated on day 5 (Group 1), 10 (Group 2), or 16 (Group 3) of the estrous cycle and continued for 12 days. Plasma progesterone (P4) levels, luteal diameter, and luteal blood flow (LBF) were monitored during treatment, and correlations among these parameters were analyzed. Additionally, the interval from CIDR removal to estrus, and the incidence of standing (ST) behavior during estrus were evaluated. All luteal parameters changed in a cycle-dependent manner, irrespective of CIDR treatment. Significant correlations were observed between P4 levels and both luteal diameter and LBF. The interval from treatment withdrawal to estrus was significantly longer in Group 1 (4.6 ± 2.2 days) than in Groups 2 (2.1 ± 0.4 days) and 3 (2.2 ± 0.7 days). Silent heat, defined as estrus without ST behavior, occurred in 27.3% of cows in group 1 and 10.0% in Group 2, but not in Group 3. These findings suggest that initiating CIDR treatment in the early luteal stage and removing it just before or during luteolysis, causes variability in estrus timing after treatment and increases the risk of silent heat. When implementing estrus synchronization using CIDR in the field, both the timing of treatment initiation and removal should be carefully considered.
Accurate diagnosis of nitrogen status is essential to prevent excessive nitrogen fertilization and maintain productivity. Critical nitrogen dilution curves (CNDCs) serve as nitrogen diagnostic tools for numerous crop species. The critical nitrogen concentration (Nc) represents the minimum nitrogen concentration (%N) required to achieve maximum yield. Despite the substantial nitrogen requirements of spinach, the diagnostic criteria for assessing its nitrogen status have rarely been investigated. Here, the applicability of two frameworks, sequential (a method that has been used over the years) and hierarchical (a method that has recently garnered interest), was examined to estimate the CNDC for spinach for processing. The CNDC for spinach for processing was estimated at Nc = 5.03W-0.099 using a sequential framework and Nc = 4.67W-0.030 using a hierarchical framework. The power exponent estimated in this study was smaller than that of other crops, revealing that spinach maintained a high %N until the late growth stage. The nitrogen nutritional status of a crop can be determined using the nitrogen nutrition index (NNI), which is calculated by dividing the observed %N by the Nc. The response of crop productivity to nitrogen can be represented by variations in daily intercepted radiation (DIR) and radiation use efficiency (RUE). Spinach for processing remains under cultivation even after the saturation of radiation interception, with productivity in the later stages of the growing season reliant on RUE. At harvest time for spinach for processing, the RUE was regressed using a quadratic model with NNI as the explanatory variable, indicating that the response of RUE to NNI reached saturation or even slightly declined at high NNI levels. NNI = 1.11 (sequential framework) or NNI = 1.29 (hierarchical framework) may serve as criteria for maintaining RUE at elevated levels and preventing overfertilization. The findings of this study provide essential insights into nitrogen management strategies for optimizing spinach productivity, providing a foundation for sustainable fertilization practices that balance yield efficiency with environmental responsibility.
