Figures 6(a), 6(b), and 6(c) show that, from the early sowing season to the end of the early growing season (the detectable period), the DMSR of band 1 for PML are obviously greater than that of non-PML (winter wheat and spring corn fields). The reason is that, from the time the farmers put the new transparent plastic mulch on the fields in the sowing season, the plastic mulch, which has a higher spectral reflectance in band 1, is visible in the early growing season. By further analyzing Figs. 6(a), 6(b), and 6(c), we find that the PML DMSR curves of band 1 fluctuate around 0.2, while non-PML 0.15, and this pattern of difference was the same for all the three years. Figures 6(d), 6(e), and 6(f) illustrate that the NDVI values of non-PML are above that of the PML in three years, since cotton phenology differs from that of winter wheat, namely winter wheat is in the green-up stage, while cotton is in sowing and emerging stages. Figures 6(d), 6(e), and 6(f) also show that NDVI values for non-PML in the three years of study fluctuated between 0.2 and 0.5, but generally went up with the progress of the growing season. However, the NDVI values for PML can be divided into two stages. The first stage is from the 90th day to the 125th day when the NDVI fluctuated between 0.1 and 0.25, and the second stage is from the 126th day to the 150th day when the NDVI went up with the progress of the season. Therefore, it is clear that we can use NDVI values from the 90th to 125th day (a total of 31 days), which includes the sowing and seedling emergence periods of cotton, to discriminate PML and non-PML.