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Leaf Area Index (LAI) is a fundamental indicator of plant growth status in agronomy and environmental research. With the rapid development of drone technology, the estimation of crop LAI based on drone imagery and vegetation indices is becoming increasingly popular. However, there is still a lack of detailed research on the feasibility of using image texture to estimate LAI and the impact of combining texture indices with vegetation indices on LAI estimation accuracy. In this study, two key growth stages of winter wheat (i.e., the stages of green-up and jointing) were selected, and LAI was calculated using digital hemispherical photography. The feasibility of predicting winter wheat LAI was explored under three conditions: vegetation index, texture index, and a combination of vegetation index and texture index, at flight heights of 20 m and 40 m. Two feature selection methods (Lasso and recursive feature elimination) were combined with four machine learning regression models (multiple linear regression, random forest, support vector machine, and backpropagation neural network). The results showed that during the vegetative growth stage of winter wheat, the model combining texture information with vegetation indices performed better than the models using vegetation indices alone or texture information alone. Among them, the best prediction result based on vegetation index was RFECV-MLR at a flight height of 40 m (R2 = 0.8943, RMSE = 0.4139, RRMSE = 0.1304, RPD = 3.0763); the best prediction result based on texture index was RFECV-RF at a flight height of 40 m (R2 = 0.8894, RMSE = 0.4236, RRMSE = 0.1335, RPD = 3.0063); and the best prediction result combining texture and index was RFECV-RF at a flight height of 40 m (R2 = 0.9210, RMSE = 0.3579, RRMSE = 0.1128, RPD = 3.5575). The results of this study demonstrate that combining vegetation indices and texture from multispectral drone imagery can improve the accuracy of LAI estimation during the vegetative growth stage of winter wheat. In addition, selecting a flight height of 40 m can improve efficiency in large-scale agricultural field monitoring, as this study showed that drone data at flight heights of 20 m and 40 m did not significantly affect model accuracy. [ABSTRACT FROM AUTHOR]

Silage maize is cultivated due to its high nutritional value as a forage. China's recent agricultural policy promotes the popularization and cultivation of silage maize. The production of silage maize is affected by planting density and nitrogen application. Based on investigating the planting habits of local farmers, we adjusted the planting density and nitrogen application rate to optimize the growth of silage maize. This study was conducted to investigate the effects of planting density (65,000 plant ha−1 (D1), 80,000 plant ha−1 (D2), and 95,000 plant ha−1 (D3)) and nitrogen rate (150 kg ha−1 (N1), 230 kg ha−1 (N2), and 310 kg ha−1 (N3)) on growth, yield, and quality of silage maize using a two-factor random block design. Planting density and nitrogen fertilizer significantly affected plant height, stem diameter, leaf area index, crude protein, neutral detergent fiber, acid detergent fiber, and starch of silage maize. In summary, the combination of a planting density of 80,000 plants ha−1 and a nitrogen application rate of 310 kg ha−1 produced a higher crude protein and starch yield and better palatability and quality; this result can aid silage maize growth. [ABSTRACT FROM AUTHOR]

Soil salinization is more aggravating than ever before and techniques are needed to mitigate this problem; understanding salinity-fertilizer relationship is of considerable economic importance for promoting crop growth and productivity in saline soil. A pot experiment was done in a greenhouse to determine whether the N could alleviate the negative effect of different salts compositions on the growth, and physiological attributes of the two most used Sudan sorghum (Sorghum bicolor (L.) Moench) cultivars (Wadahmed and Tabat). The plant was subjected to the salt stress at 0, 0.3419 M NaCl, and 0.1408 M Na2SO4, and four levels of N application 0, 4, 8, and 12 g N kg-1 soil, designated as N0, N1, N2, and N3, respectively. Results showed that Na2SO4 was reduced plant height, leaf area index, number of leaves, dry weight (DW), chlorophyll a, total chlorophyll content, and increased soluble protein content, activities of peroxidase (POD) and catalase (CAT) activities by 16.4%, 29.7%, 61.5%, 28.7%, 39.6%, 12.7%, 99.7%, 34.3%, 51.8%, respectively, when compared with the non-saline treatment. The Na2SO4 salt had a more harmful effect than NaCl. This study revealed that N fertilizer was successful for alleviating the adverse impacts of both types of salt. In this study, 12 g N kg-1 soil was most effective on most of the measured parameters of two sorghum cultivars. These findings demonstrated that the N soil amendment application could alleviate the harmful impact of salinity. 'Wadahmed' was more tolerant to salinity stress than 'Tabat' during the boot stage of sorghum plant. [ABSTRACT FROM AUTHOR]

Knowledge of changes associated with the progression of growth‐related characteristics in rice plant is essential to make strategies for future breeding and crop management. However, thus far, little attention has been given to the identification of temporal changes of the traits concomitant with the year of release in rice genetic breeding. The objective of this study was to explore genetic gain for yield accrued in association with evolution of the growth phenotypes in a 2‐year field experiment conducted on the Yangtze River Basin of China. Fifteen rice (Oryza sativa L.) cultivars, including 5 super high‐yielding rice, bred or widely cultivated from 1936 to 2005, were grown in irrigated field conditions with appropriate doses of commercial fertilizers during the rice‐growing season from May to October in 2013 and 2014. In both years, SPAD reading was high during vegetative and early grain filling stages, but it declined sharply at maturity. In general, SPAD reading increased with the progression in year of release of the cultivars and it correlated with yield benefit accrued. Similar to SPAD, the evolutionary trend also accounted for significant increases in LAI (leaf area index) and SLW (specific leaf weight), CGR (crop growth rate), LAD (leaf area duration), S/LA (spikelets/leaf area), and NAR (net assimilation rate). All growth parameters, except NAR, correlated positively with grain yield. Conversely, K (extinction coefficient) exhibited significant decline along with year of release, meaning more erect canopies. Gain of SLW in the newer cultivars enabled better light energy interception probably with higher RUE, which associated with increased SPAD amounting to low K values. It was opined that the reduced K improved light distribution across the leaves, which contributed to a grain yield advantage through increase of sink size (S/LA) over the 70‐year period. [ABSTRACT FROM AUTHOR]

Since genetic improvement greatly promoted an increased yield japonica inbred rice in east China after the 1990s, better root characteristics were certainly expected. In 2018 and 2019, nine japonica inbred rice released in the 1990s, 2000s, and 2010s were investigated to evaluate the changes in root morpho-physiology and identify root traits that contributed to the positive yield trends during the genetic process. The 2010's rice had 8.0 and 4.3% higher grain yield than the 1990's and the 2000's rice, respectively (p < 0.05). Genetic yield gain was mainly attributed to the increased spikelets per panicle. Compared with the 1990's and the 2000's rice, the 2010's rice had higher shoot biomass at heading and maturity (p < 0.05), as well as root biomass (p < 0.05), especially for root biomass of 15–30 cm soil depth. Leaf area index (LAI), soil-plant analysis development (SPAD) values, and leaf photosynthetic rate at middle grain-filling period (MGP) and late grain-filling period (LGP) were all increased. The 2010's rice had consistently higher root length and volume, root oxidation activity, and root bleeding rate at MGP and LGP than the 1990's and the 2000's rice (p < 0.05). Positive correlations were detected between root length and volume, root oxidation activity, and root bleeding rate at MGP, LGP, and SPAD values, leaf photosynthetic rate at MGP and LGP, and higher shoot biomass accumulation after heading and grain yield (p < 0.05 or p < 0.01). The present study implied that genetic improvement optimized post-heading root morphology and physiology, which maintained shoot stay-green and facilitated biomass accumulation and yield increase in japonica inbred rice during the genetic process since the 1990s. [ABSTRACT FROM AUTHOR]

Early-maturing japonica/indica hybrids (EJIH) have recently been released, performing a yield potential of 13.5 t ha−1 and greater yield increase over conventional japonica rice (CJ) and hybrid indica rice (HI) in production. More spikelets per panicle and improved grain-filling efficiency underlined the basis for the superior yield performance of EJIH. However, few studies are available on the panicle traits and grain-filling characteristics of EJIH, as well as their differences to CJ and HI. In our study, two EJIH, two CJ, and two HI cultivars with similar growth patterns were grown in the same fields. EJIH had a 12.2–18.8% increased (p < 0.05) grain yield relative to CJ and HI, mainly attributed to their higher daily grain yield. Although it had a lower panicle per m2, EJIH exhibited 28.0–38.3% more (p < 0.05) spikelets per m2 from an increase of 58.0–87.8% (p < 0.05) in spikelets per panicle than CJ and HI. Compared with CJ and HI, EJIH had a higher single panicle weight and more grains in the six parts of the panicle, especially in the upper secondary branches (US) and middle secondary branches (MS). EJIH exhibited a higher leaf area index (LAI), leaf area duration (LAD), leaf photosynthetic rate, and SPAD values after heading, which helped increase shoot biomass weight at heading and maturity and post-heading biomass accumulation. For CJ and HI, the grain-filling dynamics of grains in the six parts were all well simulated by the Richards equation. For EJIH, the grain-filling dynamics of grains in the lower secondary branches (LS) were well fitted by the logistics equation, with the Richards equation simulating grain positioning on the other five parts. EJIH had a lower mean grain-filling rate (GRmean) and longer days and grain filling amounts (GFA) during early, middle, and late stages than CJ and HI. Our results suggest EJIH gave a yield advantage over CJ and HI through a higher daily grain yield. The panicle traits and grain-filling characteristics differed greatly among the three cultivar types. Compared with CJ and HI, EJIH had lower GRmean and higher days and more grains in the panicle during early, middle, and late stages, which contributed to an increased GFA after heading, improved filled-grain efficiency, and higher grain yield. [ABSTRACT FROM AUTHOR]

Grain yield was greatly increased during the genetic improvement of japonica inbred rice since the 1980s in Jiangsu, east China; thus, an improved plant morphology should be expected, considering that plant morphology is a decisive factor determining grain yield. Twelve representative japonica inbred rice released from 1983 to 2013 were grown in the same fields in 2019 and 2020. Grain yield increased (p < 0.01) at 63.3 kg ha−1 year−1 across 2 years among rice cultivars released in different periods. The genetic improvement in grain yield was associated with increased spikelets per panicle. Single panicle weight, number of primary and secondary branches, and number of grains on primary and secondary branches were all increased with a year of release. Generally, the width of top three leaves positively correlated (while angle of top three leaves and light extinction coefficient negatively) correlated (p < 0.01) with year of release. Leaf area per tiller and leaf area index at heading and maturity, specific leaf weight, leaf photosynthetic rate, and SPAD values after heading were all increased linearly with year of release. Plant height exhibited a positive (p < 0.01) trend with year of release, as well as stem weight per tiller and K and Si concentrations of stem. Spikelets per panicle, width of top three leaves, plant height, and leaf area index, and specific leaf weight after heading positively correlated (while angle of top three leaves and light extinction coefficient negatively) correlated (p < 0.01) with grain yield and single panicle weight. Our results suggested that modern japonica inbred rice exhibited expanded sink size by spikelets per panicle, higher leaf area through leaf width, optimized leaf photosynthetic capacity, lower leaf angle and light extinction coefficient, and enhanced stem strength. These improved plant morphologies facilitated yield increases of japonica inbred rice since the 1980s in east China. [ABSTRACT FROM AUTHOR]

Because of inadequate water resources and poor irrigation facilities, salinity and drought stresses often co-occur in rice production in saline lands. Nevertheless, little information is available on the agro-physiological traits and grain yield of rice when subjected to combined salinity × drought stress. We evaluated the individual and interactive influences of salinity and drought on rice yield and agro-physiological characteristics using two rice cultivars, Nanjing 9108 (salinity-tolerant rice) and Wuyunjing 30 (salinity-susceptible rice). This experiment was conducted under non-salinity (NS) and salinity (S) conditions and three drought levels from jointing to heading (CC, control condition; MD, moderate drought; SD, severe drought). Individual salinity and drought treatments and their combination shortened the total growth duration by 3–4 days and 4–6 days in Nanjing 9108 and Wuyunjing 30, respectively. Both salinity and drought treatments reduced (P < 0.01 or P < 0.05) rice yield by 12.9%−40.9% and 28.1%−35.0% across the two cultivars, respectively, and the combined salinity × drought treatment resulted in a more pronounced yield loss of 53.1%−113.3%. A greater reduction in grain yield caused by the combined salinity × drought stress was detected in Wuyunjing 30 than in Nanjing 9108. The poor grain yield performance of rice under combined salinity × drought stress was mainly attributable to the following: (1) yield components, panicle length, and single panicle weight were lower than they were under an individual stress; (2) combined stress caused greater reductions in shoot biomass, leaf area index (LAI), and nonstructural carbohydrate (NSC) content in the stem at heading and maturity, although harvest index and NSC remobilization reserve were increased; (3) each stress and especially combined stress increased Na+/K+ ratio in the leaf, while reducing leaf photosynthetic rate and SPAD values after heading, and total accumulation of nitrogen (N), phosphorus (P), and potassium (K). Our results suggested that the combined salinity × drought stress was more damaging than either stress alone, and resulted in a greater yield penalty of rice. In terms of grain yield, salinity-susceptible rice was more responsive to the combined stress than salinity-tolerant rice. • The effects of combined salinity × drought stress on rice yield and NPK uptake were evaluated. • The combined salinity × drought stress reduced rice yield more than either stress alone. • Salinity-susceptible rice was more responsive to the combined salinity × drought stress. [ABSTRACT FROM AUTHOR]

The cropping area of japonica inbred rice has expanded rapidly since the 1980 s, which occupies 90% of the total cropping area nowadays in Jiangsu, east China. In this process, information on the genetic improvement in grain yield and nutrient use efficiency of japonica inbred rice is still limited. Fifteen japonica inbred rice released from 1983 to 2014 were tested during the 2018 and 2019 rice-growing seasons. Grain yield increased yearly at 65.1 kg ha−1 (0.65%) in 2018 and 58.1 kg ha−1 (0.59%) in 2019. Panicles per m2 and filled-kernel percentage decreased (P < 0.01), while spikelets per panicle increased (P < 0.01), with year of release. Pre-heading biomass, post-heading biomass, and total biomass increased (P < 0.01 or P < 0.05) linearly with year of release; while harvest index gradually increased with year of release before 2000, thereafter remaining relatively stable. Leaf area index (LAI) at heading and maturity, plant height, specific leaf weight, and flag leaf photosynthetic rate at heading, and intercepted radiation and radiation use efficiency (RUE) from heading to maturity all increased (P < 0.01) with year of release, which was associated with the increased biomass accumulation during the breeding process. Genetic improvement has increased total N, P, and K accumulation, as well as their use efficiencies. Grain yield and harvest index correlated positively (P < 0.01) with NUEg, PUEg, and KUEg among rice cultivars. Our results suggested the impressive progress in grain yield and nutrient use efficiency of japonica inbred rice since the 1980 s in eastern China. The yield progress was mainly attributed to the increased spikelets per panicle. For rice cultivars released before 2000, an increase in harvest index contributed more to yield improvement than total biomass; while the yield improvement after 2000 resulted from total biomass. The results also indicated possible opportunities for improving use efficiency of N, P, and K through increasing harvest index in rice. • Genetic improvement has progressively increased grain yield of japonica inbred rice since the 1980s in eastern China. • The increased harvest index contributed more to yield gain before 2000, while total biomass for yield gain after 2000. • Genetic selection for rice grain yield has also improved N, P, and K use efficiencies. • Harvest index was positively (P<0.01) correlated with NUEg, PUEg, and KUEg in rice. [ABSTRACT FROM AUTHOR]

• JIH exhibited yield superiority over IH not only in non-saline fields, but also in saline fields. • Limited shoot and root growth were responsible for the yield penalty of rice under saline field conditions. • The improved agronomic and physiological traits of JIH facilitated superior grain yield over IH in saline fields. It is of great interest to utilize saline fields to promote rice production in China. Previous studies reported greater yield productivity of japonica/indica hybrids (JIH) over indica hybrids (IH) under nonsaline fields. It has still not been established how salinity stress intervenes with rice yield and whether JIH would exhibit superior grain yield than IH under saline field conditions. This study investigated three JIH and three IH cultivars grown at the two sites that differed significantly in soil salinity, namely, nonsaline (Wulie, abbreviated as WL) and saline (Tiaozini, abbreviated as TZN) fields, in Yancheng, Jiangsu, China. The panicles per m2, spikelets per panicle, filled-kernel percentage, and kernel weight of JIH and IH were reduced, and a 36.0 %–43.5 % loss in grain yield was observed with salinity stress at TZN compared with WL. For JIH and IH, the shoot biomass and leaf area index (LAI) at jointing, heading, and maturity were all reduced at TZN compared to those at WL; similar results were also detected for root biomass, root length and volume, and root bleeding rate after heading. Compared with IH, JIH produced a 24.8 % higher grain yield under saline field conditions at TZN across two years. Four agronomic and physiological traits were summarized for superior grain yield of JIH compared to that of IH with salinity stress under field conditions. First, JIH had an enlarged sink size potential of a greater number of spikelets per panicle. Second, a synergistically increased biomass accumulation and harvest index of JIH, supported by higher biomass accumulation and LAI at the main growth stages and improved NSC remobilization after heading. Third, JIH had an improved stay-green characteristic, indicated by a higher leaf area per plant, SPAD values, and leaf photosynthetic rate after heading. Fourth, JIH exhibited a better root morpho-physiology than that of IH after heading, showing a larger and deeper root structure and higher root bleeding rate. These results indicated that the limited shoot and root growth were responsible for the yield penalty of rice under saline field conditions. JIH's improved agronomic and physiological traits facilitated superior yield performance over IH with salinity stress under field conditions. [ABSTRACT FROM AUTHOR]