# Analysis of Maize Sowing Periods and Cycle Phases Using Sentinel 1&2 Data Synergy
## 3 Results and Discussion
### Emerging of Plants and Sowing Periods
The early sowing is mostly related to the grain maize, which requires longer periods to grow and reach the optimum water content in the final product at the end of the season, and to local insurance policies that refund maize farmers in case of late frosts in April. According to the methodology described in Section 2.4, the actual sowing dates were estimated by inverting the method for the calculation of the emerging period from the sowing date, according to daily temperatures and soil water content. Considering that emergence periods can be calculated on a 6-days interval, because of the revisiting time of Sentinel-1 data, the estimation of actual sowing dates is affected by the same uncertainty; in Figure 7, results are presented with such temporal resolution. More than 52% of maize areas are sowed in the last six days of April, especially in the northern municipalities where this percentage is higher than 70% (e.g., 78% in Fossano, 73% in Sant'Albano Stura). About 9.1% of maize fields are sowed in the remaining days  
Figure 7: Spatial distribution of sowing dates at 10 m \(\times\) 10 m resolution. The sowing periods are grouped by 6-days classes. The spatial variability confirms the SAR analysis of emergence periods: for lower elevations, maize is sowed earlier on average. of April. About 30% of maize areas were sowed in the second half of May and at least 9% during the first half of the month. The spatial distribution of maize SP highlights that, on average, the fields at lower elevations are sowed earlier (see the DTM map in Figure 1b). A statistical analysis was performed to calculate the correlation between the SP and the topographic elevation: the 6-days intervals, consistently with the Sentinel-1 revisiting time, were numbered for year 2019 (e.g., April 13 th-18 th interval is the 18 th group of 6 days from the beginning of the year); for each field, the numbered 6-days period was compared to the elevation (in terms of meters above the mean sea level). The Pearson correlation coefficient (R), which quantifies the correlation strength between two sets of variables (ranging from 0 to \(\pm\)1), shows a moderate positive correlation of 0.41 between sowing periods and topographic elevation (according to the classes of correlation proposed by [PERSON] in 1996 [57]). In fact, despite an evident gradient of sowing periods moving from lower to higher altitudes, a significant part of fields at low altitudes appears to be sown during May. This can be explained by some declarations from local farmers, stating that fields at low elevations have a higher probability to be cultivated with winter crops until April (Appendix A): this could be the main reason for the coexistence of fields sowed on early April and late May at elevations <450 m above the sea, where medium temperatures are higher. The results of sowing periods are consistent with the information collected from local farmers (interviewed by the authors in November 2021) who declared that maize is usually sowed twice per season, in April and May, according to the agronomic variety of plants and the use for which the product is intended. The maize sowed in April is usually a high-quality product for the food market, while the plants sowed in May are those to produce mash corn for farm animals. The results obtained in this study fit well with the available sowing information described by previous studies in Northern Italy. [PERSON] et al. [52] collected sowing periods over 6 sites in North-East Italy, from 2005 to 2007: local farmers declared that maize was mostly sown during late April in 2005 (sowing occurred between 27 April and 1 May in 3 of the 6 sites). Despite a slight temporal variability, this study states that most of the maize was sown in April also in 2006 and 2007. Even if the data were collected in the eastern part of Po Valley, the agricultural practices can be assumed as sufficiently uniform in the densely cultivated region of Northern Italy. Moreover, also the regional calendar provided by [PERSON] et al.