## 4 Discussion
With the continuous grain-filling process of winter wheat, the dry matter content of grains increased, whereas the relative water content decreased. Through the comprehensive comparison of the monitoring models of the three indicators, it was found that the dry thousand-weight is the most ideal indicator to reflect the grain-filling process of winter wheat, with the reason being that the crop grain-filling process is the accumulation process of dry matter. However, the measurement of the fresh thousand-grain weight is greatly affected by the environment, such as temperature and humidity. The reason why the simulation effect of the fresh thousand-grain weight is worse than that of the dry thousand-grain weight in this study may be due to weather factors (precipitation, temperature and humidity) in different sampling periods, differences in the time period of sampling in a day, the duration of threshing at the laboratory and so on, which can lead to an error in the acquisition process of the measured data. Therefore, under the influence of these factors, the simulation effect of grain water content was worse than that of the dry and fresh thousand-grain weight. The use of non-destructive methods, such as remote sensing, to predict winter wheat maturity could increase the management accuracy at harvest time, especially in countries or regions with more than one crop per year. For instance, winter wheat is used in a crop rotation with rice in most parts of Jiangsu Province, China, and this crop rotation system causes a tight time between the harvest of winter wheat and the planting of rice. The determination of the harvest point of winter wheat is very important in agriculture production, but generally, early harvest means lower yields, whereas delaying the harvest can imply more loss and damage, such as through the impact of the rainy season and lodging. Thus, the grower must identify the moment close to the ideal maturity of grains to start harvesting. It is known that, naturally, there is soil variability, among other environmental components, which leads to the uneven development of plants [25; 56]. Hence, plants in more favorable locations will potentially be able to grow faster and mature earlier (Figure 8). Because the winter wheat growing around the field has the advantage of a marginal benefit, the overall growth and maturity are better than those in other locations, and the growers have limitations in judging the overall maturity of winter wheat in the field without an in-depth field investigation. Overall, the results suggested that the application of time-series high-spatial/temporal-resolution satellite imagery can directly and practically help growers to identify which field is more developed and should be harvested first. The results provide directions and applications to improve winter wheat cultivation and production through better management and conduction of the crop. From a practical point of view, farmers, researchers and government agencies could use high-resolution satellite imageries to monitor crop growth and generate yield formation maps. This may be an interesting strategy to support decision-making in harvest and postharvest operations, such as deciding the optimal moment to start harvesting, when areas of the field should be harvested first, and product logistics and storage. In addition, it is possible to obtain the surface information of the uniformity of the maturity stage between varieties and within varieties based on an accurate description of the grain-filling process of winter wheat by high-resolution satellite imageries. This could be used to speed up plant breeding programs focused on increasing winter wheat population uniformity. The dynamic monitoring model of the wheat grain-filling process for the mature period was constructed in this study and performed well in predicting the grain indicators. Some potential applications and extensions can be considered based on this conclusion, although more development in the following areas is still needed.