To test the hypothesis that lead (Pb) content of rice grain may be related to its transport and subcellular distribution in rice plant, the present study was conducted with six rice cultivars of different types under different soil Pb levels. The results showed that grain Pb concentrations were correlated positively and significantly (P<0.05 or 0.01) with distribution ratios (DRs) of Pb from shoots to ears/grains, but insignificantly (P>0.05) with the DR from roots to shoots. The DR from shoots to ears/grains was correlated positively and significantly (P<0.05 or 0.01) with subcellular distribution ratios (SDRs) of Pb in soluble fraction of shoots, but negatively and significantly (P<0.05 or 0.01) with the SDR in cell wall fraction of shoots. In conclusion, Pb transportation from the shoot to the grain is the key factor in determining Pb content of rice grain. The Pb distributed in soluble fraction of shoot tissue is the key source of Pb for transferring into the grain. The Pb precipitated in cell wall fraction is the key sink of Pb in shoot tissue that restricts the transport of Pb from the shoot to the grain.
To reduce the missing rate caused by the arching phenomenon of seed potatoes in the traditional seed boxes of cup-belt potato planters, a conical-shaped seed box comprising a seed-metering box and a reseeding box connected together was proposed. The method in this paper combined the discrete-element-analysis method and response-surface method and took the movement of the seed-potato group in the seed box as the research object. First, by analyzing the force and speed of seed potatoes, the main structural parameters affecting the seed-box seed-metering performance were determined, and the indices for evaluating the seed-box seed-metering performance were established. Additionally, a single-factor simulation test and orthogonal test were carried out for the main structural parameters of the seed box. Using the optimized structural parameters of the seed box, a trial conical seed box was produced, and bench-verification tests were carried out. The results showed that the multiple rate, missing rate and coefficient of the variation of the plant distance for the conical seed box were reduced by 4.76%, 4.0% and 9.18%, respectively. The research results have practical significance as guidance for improving the sowing performance of cup-belt potato planters. At the same time, the research results have reference value for solving the arching problem for granular materials in the box.
HighlightsThe structural parameters of the seed box of a cup-belt potato planter were optimized.The arching phenomenon of seed potato in the reseeding box was reduced.The qualified rate of cup-belt potato planters in field operation was improved.Abstract. To solve the problem of missed sowing caused by the arching phenomenon of seed potato in the reseeding box of a cup-belt potato planter, this study used the discrete element method to analyze the seed potato movement in the seed box. The analysis revealed unreasonable structural parameters of the seed box. Therefore, the discrete element method was used to optimize the structural parameters of the seed box. First, the structural parameters of the seed box were analyzed by single-factor analysis, and then quadratic rotation orthogonal combination simulation tests of three factors and five levels were performed. Two evaluation indexes were established to evaluate the flow performance of the seed box: the amount of seed taken minus the amount of seed replenishment (CD), and the coefficient of variation of the average seed-population velocity in the reseeding box (CV). The best factor combination was found through optimization. With a 42° inclination angle of the bottom surface of the seed box (a), 145 mm reserved height of the seed isolation baffle (h), and 100° inclination angle of the seed isolation baffle (ß), the CD was 2.622 grains, and the CV was 22.887%. With these parameters, the mobility of seed potato in the reseeding box was good, and there was no arching in the reseeding box. To verify the accuracy of the optimized results, a cup-belt potato seeding test bench was built to conduct verification tests. The bench test verified the rationality of the model and the optimized parameters. Field tests showed that the arching phenomenon in the reseeding box was solved by optimizing the structural parameters of the seed box. The purpose of improving the sowing performance of the cup-belt potato planter was achieved. Keywords: Agricultural machinery, Discrete element method, Parameter optimization, Potato planter, Seed box.
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