3.3. Runoff and soil loss under different rainfall intensities
The erosive rainfalls contained two categories (Fig. 5) with different intensities (> 2.75–≤ 5 mm h− 1 and > 5 mm h− 1). Analyses of variance were performed to determine whether the two categories have different impacts on the runoff and soil loss. As the three rainfalls with intensity > 5 mm h− 1 (Fig. 6) accounted for 83% and 99% of the total runoff and total soil loss over the observation period, respectively, it was expected, that the results related to this category (Table 4) are similar to those related to the totals of the observation period (Table 3). The only exception is that the runoff on grasslands was higher than on forestlands (contrast V4 in Table 4 and Fig. 8, which represents the proportion of the runoff and soil loss on the different combinations of the vegetation cover and slope gradient). The situation was different for the runoff induced by the rainfalls with low intensity (> 2.75–≤ 5 mm h− 1). The runoff on forestlands was significantly higher than on grasslands (contrast V4 in Table 4 and Fig. 8). In addition, the contrasts V1 and V3 in Table 4 were non-significant, as, exclusive of tea plantations at steep slopes, forestlands had generated even equal or a bit higher runoff than maize and tea fields (Fig. 8). The rainfalls with intensity > 2.75–≤ 5 mm h− 1 had slightly reduced tendency than the rainfalls with intensity > 5 mm h− 1 to induce higher runoff at steep slopes than at slight and moderate slopes (contrast S2 in Table 4). The only dissimilarity of the impact of both categories with different intensities on the soil loss is that the hypothesis related to the equality of the soil loss in tea and maize fields was rejected for the rainfalls with lower intensity (contrast V2 Table 4).It can be said, as indicated in Fig. 8, that, except forestlands, the highest proportion of the runoff and soil loss of the other vegetation covers was always generated at the steep slope gradient and the lowest at the slight slope gradient. Forestlands had also the highest proportion of soil loss at steep slopes. An extreme case is represented by the tea plantations, where at slopes > 30° the highest proportion among all combinations of the vegetation cover and slope gradient over the period July 15th–October 30th were produced: 27% of the total runoff (31% and 24% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and 59% of the total soil loss (63% and 56% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively). The tea plantations contributed to 48% of the total runoff (60% and 41% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and to 84% of the total soil loss (82% and 85% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) generated on all studied vegetation covers over the observation period in 2008.
3.3 การไหลบ่าและดินขาดทุนภายใต้ปริมาณน้ำฝนแตกต่างปลดปล่อยก๊าซThe erosive rainfalls contained two categories (Fig. 5) with different intensities (> 2.75–≤ 5 mm h− 1 and > 5 mm h− 1). Analyses of variance were performed to determine whether the two categories have different impacts on the runoff and soil loss. As the three rainfalls with intensity > 5 mm h− 1 (Fig. 6) accounted for 83% and 99% of the total runoff and total soil loss over the observation period, respectively, it was expected, that the results related to this category (Table 4) are similar to those related to the totals of the observation period (Table 3). The only exception is that the runoff on grasslands was higher than on forestlands (contrast V4 in Table 4 and Fig. 8, which represents the proportion of the runoff and soil loss on the different combinations of the vegetation cover and slope gradient). The situation was different for the runoff induced by the rainfalls with low intensity (> 2.75–≤ 5 mm h− 1). The runoff on forestlands was significantly higher than on grasslands (contrast V4 in Table 4 and Fig. 8). In addition, the contrasts V1 and V3 in Table 4 were non-significant, as, exclusive of tea plantations at steep slopes, forestlands had generated even equal or a bit higher runoff than maize and tea fields (Fig. 8). The rainfalls with intensity > 2.75–≤ 5 mm h− 1 had slightly reduced tendency than the rainfalls with intensity > 5 mm h− 1 to induce higher runoff at steep slopes than at slight and moderate slopes (contrast S2 in Table 4). The only dissimilarity of the impact of both categories with different intensities on the soil loss is that the hypothesis related to the equality of the soil loss in tea and maize fields was rejected for the rainfalls with lower intensity (contrast V2 Table 4).It can be said, as indicated in Fig. 8, that, except forestlands, the highest proportion of the runoff and soil loss of the other vegetation covers was always generated at the steep slope gradient and the lowest at the slight slope gradient. Forestlands had also the highest proportion of soil loss at steep slopes. An extreme case is represented by the tea plantations, where at slopes > 30° the highest proportion among all combinations of the vegetation cover and slope gradient over the period July 15th–October 30th were produced: 27% of the total runoff (31% and 24% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and 59% of the total soil loss (63% and 56% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively). The tea plantations contributed to 48% of the total runoff (60% and 41% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and to 84% of the total soil loss (82% and 85% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) generated on all studied vegetation covers over the observation period in 2008.
การแปล กรุณารอสักครู่..
3.3. Runoff and soil loss under different rainfall intensities
The erosive rainfalls contained two categories (Fig. 5) with different intensities (> 2.75–≤ 5 mm h− 1 and > 5 mm h− 1). Analyses of variance were performed to determine whether the two categories have different impacts on the runoff and soil loss. As the three rainfalls with intensity > 5 mm h− 1 (Fig. 6) accounted for 83% and 99% of the total runoff and total soil loss over the observation period, respectively, it was expected, that the results related to this category (Table 4) are similar to those related to the totals of the observation period (Table 3). The only exception is that the runoff on grasslands was higher than on forestlands (contrast V4 in Table 4 and Fig. 8, which represents the proportion of the runoff and soil loss on the different combinations of the vegetation cover and slope gradient). The situation was different for the runoff induced by the rainfalls with low intensity (> 2.75–≤ 5 mm h− 1). The runoff on forestlands was significantly higher than on grasslands (contrast V4 in Table 4 and Fig. 8). In addition, the contrasts V1 and V3 in Table 4 were non-significant, as, exclusive of tea plantations at steep slopes, forestlands had generated even equal or a bit higher runoff than maize and tea fields (Fig. 8). The rainfalls with intensity > 2.75–≤ 5 mm h− 1 had slightly reduced tendency than the rainfalls with intensity > 5 mm h− 1 to induce higher runoff at steep slopes than at slight and moderate slopes (contrast S2 in Table 4). The only dissimilarity of the impact of both categories with different intensities on the soil loss is that the hypothesis related to the equality of the soil loss in tea and maize fields was rejected for the rainfalls with lower intensity (contrast V2 Table 4).It can be said, as indicated in Fig. 8, that, except forestlands, the highest proportion of the runoff and soil loss of the other vegetation covers was always generated at the steep slope gradient and the lowest at the slight slope gradient. Forestlands had also the highest proportion of soil loss at steep slopes. An extreme case is represented by the tea plantations, where at slopes > 30° the highest proportion among all combinations of the vegetation cover and slope gradient over the period July 15th–October 30th were produced: 27% of the total runoff (31% and 24% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and 59% of the total soil loss (63% and 56% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively). The tea plantations contributed to 48% of the total runoff (60% and 41% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) and to 84% of the total soil loss (82% and 85% by the rainfalls with intensity > 5 mm h− 1 and > 2.75–≤ 5 mm h− 1, respectively) generated on all studied vegetation covers over the observation period in 2008.
การแปล กรุณารอสักครู่..