Effects of Erosion Control Methods on Bean Growth Parameters

Objectives: To find out the method which could effectively control erosion to improve the crop growth parameters at Buhoro hill. Methods/Statistical Analysis: The experiments have considered three plots with three different erosion control methods such as the traditional plowing methods (M1) which was the control, anti-erosive hedges planting (M2) and anti-erosive hedges coupled with anti-erosive ditches (M3). The experiments were carried out in 2016 and 2017. Data were recorded at three homogeneous regions (upstream, middle and downstream) by choosing two lines at each region and analyzed through SPSS at P<0.05 for significative difference. Finding: The results showed lowest value for the control and the plot with hedges, especially for the lines near the hedges. Moreover, these outcomes highlighted the method M3 (anti-erosive hedges coupled with anti-erosive ditches) as the effective method in improving the studied parameters although the significance was not apparent in the first year. The method (M3) has effectively enhanced the leaf number; leaf area and root length than other methods, especially in the second year with a general significance difference among the treatments. Furthermore, the outcomes revealed significance effects of combining hedge and ditches method (M3) in improving stem girth and plant height for both years. Although many results reported positive effects of anti-erosive hedge planting only than the control, especially in Burundi, where the use of hedge plantation only is more frequent, to couple hedges and ditches is more effective as revealed in the present study. Application/Improvements: These results suggest M3, as the most effective method in improving bean growth parameters at Buhoro hill in Gashikanwa commune. *Author for correspondence


Introduction
Soil erosion is a natural process in which rocks, soil or dissolved material are moved from one location to another 1 . Increased soil loss due to erosion of about 200 to 400tones/ erosion decreases agricultural productivity due to upper nutrient loss 6 and a reduction in organic matter 7 . Erosion reduces the productivity of all natural ecosystems as well as agricultural, forest, and pasture ecosystems 8 . It generally increases runoff, resulting in decreased available soil water and reduced plant growth 9,10 . A study conducted at Iowa State University on 40 soil associations, reported reduced crop productivity due to soil erosion 8 . Previous researches affirmed plant growth inhibition by erosion and confirmed the difficulties of yield restoration on eroded soil 11,12 . Furthermore, decreased crop production on eroded soil and reduced root-zone depth due to erosion were highlighted by foregoing researches 13,14 . Overall soil erosion is an important barrier for crop growth and soil fertility. In Burundi, although previous researches have been done, they have put much emphasis on soil loss. However, information is scanty on erosion effects on crop growth. This study is a contribution; it intends to analyze the effects of different soil erosion control methods on plant bean growth parameters.

Site Description and Soil Properties
The experimentation site was located in Gashikanwa Ngozi province at Buhoro, a hill more prone to erosion with 1690 m of altitude, characterized by a humid tropical climate. The recorded precipitation was 1046mm with 20.5°C as mean temperature and a slope of 41%.

Experiment Design
The experiments were carried out in 2016 and 2017. Three separated plots (P1, P2 and P3) with three different erosion control methods (M1, M2 and M3) were considered. The first method, M1, was the traditional plowing method on P1, set as a control; the second, M2, was the anti-erosive hedges planting method on P2, and the third method, M3, constituted by the anti-erosive hedges coupled with anti-erosive ditches; was implemented on P3.
Before sowing, these plots were divided in four sub plot (S1, S2, S3, and S4) separated by the anti-erosive hedges on P2; anti-erosive hedges coupled with antierosive ditches on P3, while for plot P1 the separation considers just the virtual lines of these anti-erosive hedges (Photos 1). Moreover, the fertilizers were applied as recommended, while during the growth period, diseases and pests were normally controlled.

Sampling and Data Collection
For sampling, three homogeneous regions: upstream, middle and downstream were considered for each subplot, while two lines were chosen at each region. During the study, plant height, stem girth and leaves number were determined, as well as the leaf area and the root length.

Statistical Analysis
All data were processed with Applied Excel 2007 and SPSS. Figures were made by using Excel, while comparisons between treatments were conducted through LSD (least significant difference) and SPSS at P<0.05.

Effects of Erosion Control Method on Leaves Number (LN)
Results on leaves number for the two years were shown in the following Figures 1  Considering S1 (Upstream Sub plot) in 2016, the highest LN was recorded for M1 method for all tested date comparatively to M2 and M3. But in 2017, it changed, the results analysis highlighted M3 as the most effective method with maximum LN for all tested dates.
Regarding to S2 (middle Sub plot toward Upstream) in 2016 on the 2 nd December, the maximum LN of 7 leaves per plant was observed for both methods M3 and M2, while M1 got the minimum by 6 leaves per plant. On 9 th December, the highest value of LN was obtained for M3 with 9 leaves per plant, followed by M2 of 8 leaves, whereas M1 got the small value of 7 leaves per plant. The same trend was observed on 16 th December where the maximum leaves number was recorded for M3 (11 leaves per plant) followed by M2 (10 leaves per plant), and the minimum on M1 (9 leaves per plant). In 2017, the method M3 was the most effective with higher LN for all tested date by 8, 13, and 16 leaves for the tested date respectively.
Considering S3 in 2016, the maximum LN, on the 2 nd December, was observed for M3, 9 leaves per plant, followed by M2, 8 leaves per plant, while M1, 7 leaves per plant, got the minimum. On December 9 th , the optimum LN of 9 leaves per plant was observed for M3, followed by M2 with 9 leaves per plante, while the minimum of 7 leaves per plant was obtained for M1. Similarly, on 16 th December, the method M3 of 11 leaves per plant was the first having higher leaves, M2 method with 10 leaves per plant was the second while M1 of 9 leaves per plant was the last. In 2017, the results highlighted M3 as the most effective methods comparatively to M1 and M2 as shown Even though the difference was not significant, it is apparent that the implemented method M3 (the anti-erosive hedges coupled with anti-erosive ditches) was the effective method in enhancing leaves number.

Effects of Erosion Control Methods on Leaf Area (LA)
Leaf area evolution is summed up in Figures 3 and 4. As  for the leaves number, leaf area (LA) changed with the sub plot location, implemented method and the tested date. On S1, except for the first time where the highest LA was recorded for M2 (38.37 cm 2 ), the optimum leaf area in 2016 was recorded for M1 and vary from 29 to 63cm 2 . Regarding S2, the maximum LA in the first days (2 nd December) was observed for M2 method (23.57 cm 2 ), followed by M3 (17.8 cm 2 ), while the minimum of 16.75 cm 2 was recorded for M1. Considering S3, the first highest LA of 23.57 cm 2 was observed for M2, the second for M1 with 22.06 cm 2 , and the last of 17.66 cm 2 for M3 method. The same LA evolution trend was observed on S4, where the optimum LA was recorded for M2 method with 23.61 cm 2 , followed by M3 of 21.87 cm 2 , and minimum for the method M1 of 21.71 cm 2 . On the 9 th December, as it can be seen on Figure 3, the trend change, with a maximum leaf area evolution on M3 method recorded for S 2 with 65.17 cm 2 , followed by M1 and M2 with 65.03 cm 2 for both methods. Regarding S3, M1 showed higher leaf area (73.77 cm 2 ), while M2 and M3 showed little discrepancy with 67.06 cm 2 and 65.03 cm 2 respectively. On S4, the maximum leaf area was observed for M3 (111.31 cm 2 ) and significantly differed (p<0.05) from the method M2 ( 83.29 ) which was the following and M1 ( 77.74), the last one. On the last date (16 th December) of recording data in 2016, the maximum leaf area was recorded for M3 (76.71 cm 2 ), followed by M1 (71.6 cm 2 ) and minimum for M2 (55.73 cm 2 ). The same trend was observed for S3 where the first biggest plant of 73.78 cm 2 was obtained by M3, the second by M1 with 73.74 cm 2 and lowest for M2 of 55.58 cm 2 . On S4, the optimum leaf area was still recorded for method M3 with 123.66 cm 2 and significantly differed (p<0.05) to M1 and M2 which obtained 79.38 cm 2 and 77.71 cm 2 respectively.
In 2017 the maximum LA on S1 was recorded for M3 (over 34 up to 86 cm 2 ) for all tested date, followed by M1 and minimum for M2. Likewise, the same trend was observed for other sub plots (S2, S3, and S4) in general. Like in 2016, no significant difference was observed in the first time but observed later especially on S4.

Effects of Erosion Control Methods on Stem Girth (SG)
The outcomes on stem girth were shown in Figures 5 and   6. Considering S1 in 2016, the method M3 recorded the highest SG of 0.37cm in the first days, followed by M2 of 0.35 cm, while M1 method got the minimum with 0.25  cm. For S2, the first highest SG was still observed for M3 (0.48cm) and presented significant difference from the control M1. The second highest value was recorded for M2 (0.45cm) which also significantly differed from the control M1, the method with the minimum value of 0.28 cm. The same trend was observed on S3, where the highest SG value was observed for M3, 0.56cm, followed by M2, 0.46cm, and the minimum for M1 of 0.33cm. Considering S4, significance difference between methods was observed. The SG was maximum for implemented method M3 (0.62 cm), and significantly differed from the control M1 (0.35 cm) which got the minimum value.
In the second year (2017), the SG evolution on S1 was not apparent, with a little discrepancy from a used method to another. Specifically, higher value of 0.45 cm was recorded for M3 on the 16 th November 2017, followed by M1 of 0.43cm and minimum for M2 with 0.39cm. The same SG evolution was observed on S2 and S4 where the maximum SG was recorded for M3, M1 and M2 respec-tively. Considering S3, the optimum SG of 0.51cm was still observed for M3 method, followed by method M2 with 0.50cm, and minimum for M1 method of 0.47cm. For other tested date and each sub plot, the Optimum was observed for M3 which recorded highest value of SG with significant difference on S4 at the 14 th December 2017. Although significance difference was not observed for all sub plot, these outcomes revealed the effectiveness of M3 in improving plant SG than the control M1 and method M2.

Influences of Different Erosion Control Methods on Plant Height (PH)
The results on Plant Height (PH) were summarized in and 16 th , the maximum PH on S1 was observed for M1 comparatively to others, but there was no significance difference.
Regarding to S2, the maximum plant height on the 2 nd December 2016 was observed for the implemented method M3 with 12.8cm, followed by the method M1 of 12.5 cm, while the minimum of 10.7cm was observed for M2 method. The same trend was observed on the 9 th and the 16 th December, 2016 where M3 method got the optimum PH of 18.4cm and 31.8cm respectively.
Considering S3, the PH was changing from a sub plot to another. Clearly, on the 2 nd December, the maximum of 15.4cm was recorded for M2 method, followed by M3 with 14.2cm, and minimum for M1 of 11.6cm. On the 9 th December, the highest plant was observed for M3 with 21.8cm, whereas the methods M2 and M1 got almost the same plant height of 20.2 cm and 20cm respectively.
On the 16 th December, the highest PH value of 32.8 cm was observed for M3 method, followed by the one recorded for M2 (30.4 cm), while the minimum was obtained for M1 of 28.2 cm. Regarding S4, the optimum PH on each tested date was observed for M3, followed by M2 and minimum for method M1.
In 2017 (Figure 8), the used erosion control methods effectively affect plant height with M3 the most effective method than M2 and M1. For all tested date and each sub-plot, the highest plant height was recorded for M3 method which significantly differed from the control especially on S4 in the last days of recording data.

Influences of Erosion Control Methods on Root Length (RL)
The roots length (RL) was effectively influenced by erosion control methods (Figure 9 and 10). In 2016 ( Figure 9) on S1, the method M1 recorded the highest RL with 11.22 cm per plant comparatively to M2 and M3 which got 10.13 cm and 9.57 cm respectively. Considering S2, the maximum RL was observed for  M3 (14.43 cm) which significantly differed from others with p<0.05, followed by M1 (10.92 cm) and minimum for M2 (10.91 cm) respectively. Regarding S3, although there was no significance difference, the optimum RL per plant was still observed for M3 of 11.94 cm, followed by M2 and M1 with 11.75 cm and 11.05 cm respectively. On S4, the highest RL was observed for plot with M3 (15.94 cm), followed by the plot with M2 (13.32 cm), whereas the one with method M1 (12.14 cm) got the shortest roots.
In 2017, as can be seen in Figure 10, the results highlighted M3 method as the most effective method in enhancing the RL per plant comparatively to others. Although it did not differ significantly from others, M3 method recorded the highest value ranged from 11.55 cm to 15.95 cm on each sub plot. On S1, the reduced LN and LA observed for M3 and M2 (Figures 1 and 3) was due to the reduced leaves number on the lines near the anti-erosive hedges. Moreover, it was due to the reduced root length (Figure 9) on this S1 (with applied M2 and M3) caused by the presence of more small stones which limit the root extension resulting in reduced nutrients assimilation and plant growth parameters as well.  23 . However further studies are needed in this area for more clarification and conclusion.

Conclusion
The outcomes highlighted better effects of M3 method (anti-erosive hedges planting coupled with anti-erosive ditches) especially in the second year. It has played an important role in plant growth by effectively increasing the leaf area, plant height and leaves number. Furthermore, this implemented method M3 could improve plant roots length and stem girth. This study suggested M3 method as the effective method which can be used to control erosion and reduce its aggressiveness whence enhancement of crop growth. Nowadays, erosion is a major problem worldwide, to find a method that may reduce this latter is a significant issue all over the world.