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Article

Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area

by
Zhimeng Zhao
1,*,
Jiabin Deng
1,
Jin Zhang
2,3 and
Youxin Shen
3,4
1
Guizhou Provincial Key Laboratory of Geographic State Monitoring of Watershed, School of Geography and Resources, Guizhou Education University, Guiyang 550018, China
2
School of Mathematical Sciences, Chinese Academy of Sciences, Beijing 100049, China
3
University of Chinese Academy of Sciences, Beijing 100049, China
4
CAS Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Menglun 666303, China
*
Author to whom correspondence should be addressed.
Water 2024, 16(2), 254; https://doi.org/10.3390/w16020254
Submission received: 27 November 2023 / Revised: 6 January 2024 / Accepted: 8 January 2024 / Published: 11 January 2024
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Abstract

:
Film-mulched rock outcrops are a proven way to effectively prevent preferential flow at the rock–soil interface in rocky karst areas, but the impact on rainwater redistribution and maize growth in farmland areas has never been studied. This paper used the dye tracer method at a sprinkling intensity of 1 mm min−1 to study the rainwater redistribution in soils for three different treatments: away from rock (AR), close to rock (CR), and close to film-mulched rock (CFMR). The growth situation of maize (Zea mays L.) according to the different treatments was also studied. It was shown in the study that the rainwater gathered by rock outcrops was mainly confined only within a narrow flow path at the rock–soil interface in the CR treatment, with a preferential flow fraction of 35.78~55.54% and dyeing depth of 15.37~20.00 cm across the three dye application amounts (850 mL, 1700 mL, and 3400 mL) in contrast to the uniform distribution of the rainwater in the soil of the AR treatment, with a preferential flow fraction of 12.31~37.15% and dyeing depth of 6.93~14.00 cm. Interestingly, in the CFMR treatment, there was no preferential flow at the rock–soil interface benefiting from the film’s blocking action, and the redistribution of rainwater was mainly based on the matrix flow, with a preferential flow fraction of 24.93~39.62% and dyeing depth of 10.27~18.00 cm, indicating that the film-mulched rock outcrops improved the rock’s output capability for gathering rainwater into the surrounding soil. In addition, film-mulched rock outcrops can promote the growth of maize, as indicated by the results for plant height, stem diameter, maximum leaf area, SPAD value, and floral development of maize, which increased in order from AR, CR, to CFMR. Our study suggests that film-mulched rock outcrops have important implications for the efficient use of rainwater and the growth of crops in rocky karst areas, as well as in regions with similar geological characteristics.

1. Introduction

The karst area in southwest China is characterized by low crop productivity because most of the cropland is facing a serious problem of rocky desertification [1,2,3]. The bedrock is being gradually exposed to the surface due to soil erosion, and the rocks and soil are becoming interspersed, leading to the rocky desertification of the landscape [4,5]. The process of rocky desertification creates specific hydrogeological structures in this area, which lead to the obvious transfer of natural precipitation from the surface to the underground and the serious loss of water resources [6,7]. Preferential flow at the rock and soil interface is an extraordinarily important mechanism of soil water loss to the subsurface in this karst region, which is significantly different from that in nonkarst areas [8,9]. Therefore, preventing the preferential flow at the rock–soil interface and reducing soil water loss through this technique can alleviate agricultural soil drought and increase crop yields in karst areas.
Water is a fundamental limitation for plant survival in karst areas [10,11]. Under natural conditions, the interconversion process between various links in the water cycle and precipitation recharges in karst areas is relatively complex, and this, along with the increasing influence of human activities on the regional water cycle, has resulted in contradictions between the supply and demand of water resources becoming increasingly prominent [12,13,14,15]. For traditional agriculture, soil water, as an important limiting factor for vegetation growth, regulates the cultivation environment, planting time, and planting mode, and it often affects regional farmland productivity and economic development [16,17]. The karst area in Southwestern China, which has a subtropical monsoon climate, in fact, is rich in precipitation, but because of the limited quantity and poor water storage ability of the surface soil, the water loss is serious, and crops often struggle to make full use of the precipitation resources, leading to severe karst drought stress [18,19]. Therefore, soil water loss is an important and serious ecological and environmental problem in karst areas, which also becomes a key factor limiting the water use efficiency of karst farmland [7,20]. Relevant studies in this field can help to not only raise awareness of the spatial and temporal distributions of water resources in the unsaturated zone but also to provide a reference for the protection and optimization of the farmland ecosystem in this area [21].
The infiltration process and redistribution of rainwater in rocky karst environments are strongly affected by rock outcrops [8,22,23]. The rocks extend from the surface to the underlying bedrock and will strongly induce the vertical infiltration of soil water and then inevitably reduce the soil’s water-holding capacity due to their role in accelerating the conversion of surface water and groundwater [24,25,26]. More importantly, preferential flow at the rock–soil interface can greatly affect water infiltration and cause water to move into the bedrock along narrow flow paths even if the soil does not reach water saturation during a rainfall event [27,28]. On the other hand, in addition to the impact on rainwater infiltration, rock outcrops can affect the redistribution of rainwater due to their large intercept area on the ground [29,30]. To a certain degree, rock outcrops help improve soil moisture during rainfall when they collect and output rainwater for the surrounding soil, despite this effect varying markedly among karst ecosystems for some influencing factors, for example, the rock–soil interface, soil properties, and vegetation type [31,32,33]. In addition, rocks are an extensive landscape element of karst landforms, and changing the distribution of natural rainfall will inevitably affect plant growth [23,34,35]. In summary, rock outcrops can have positive and negative influences on the hydrology of karst areas. Significantly, a method to control the preferential flow at the rock–soil interface can change the infiltration process and redistribution of rainwater and is expected to maximize the rock’s output capability for gathering rainwater toward the surrounding soil, but there are few studies that have particularly explored this [36].
Agricultural production in a rocky karst environment is a challenging task that requires a series of special agricultural techniques and management measures. In karst areas, people choose some drought-tolerant, barren crops, such as beans, tubers, and corn. These crops can be grown in rock crevices or shallow layers of soil, making the most of limited resources. The groundwater reserves in karst areas are limited, so it is necessary to use water resources rationally and adopt water-saving irrigation measures, such as drip irrigation and seepage irrigation. At the same time, it is also necessary to pay attention to the collection and utilization of rainwater to improve the utilization efficiency of water resources [18,25,31]. Agrotechnical measures that improve soil properties can help increase water retention, such as mulching (i.e., leaving crop residues) and the introduction of practices that increase the humus content of the soil [36,37,38]. Recently, an in situ rainwater gathering measure, plastic film-mulched rock outcrops, has proven to be an effective method of preventing preferential flow at the rock–soil interface [37]. It has been proved that by applying this technique, rainwater that has gathered on film-mulched rock outcrops converges and infiltrates into the surrounding soils and then increases the soil moisture. However, the effects of film-mulched rock outcrops on rainwater redistribution and crop growth in the farmland of rocky karst areas have never been reported in the literature. In this study, tracer material (Brilliant Blue FCF) was applied to the soil/rock surface under three different treatments—away from rock (AR, at least 1 m), close to rock (CR, within 0.5 m), and close to film-mulched rock (CFMR, within 0.5 m)—to visualize the path of the rainwater’s redistribution in the soil. In addition, the growth characteristics of the maize in the jointing stage, tasseling stage, and filling stage among the different treatments were compared to preliminarily assess the impact of the film-mulched rock outcrops on the crops. The research objectives were as follows: (i) to prove that the film-mulched rock outcrops were able to stop the water loss at the rock–soil interface and transfer the rainwater collected by the rock outcrops to the surrounding soil to improve the soil moisture; and (ii) to prove that film-mulched rock outcrops can promote the growth of the corn plants around them. The experiment can further deepen the understanding of efficient water resources use and increase crop yields in farmland ecosystems in karst areas.

2. Material and Methods

2.1. Experimental Design

The experiment was conducted on a farmland plot (26°57′23″ N, 106°6′21″ E) characterized by severe rocky desertification in Makan village, Lvhua township, Qianxi city, Guizhou province, China. The area has a humid subtropical monsoon climate, with a mean annual precipitation of 1049 mm and air temperature of 13.8 °C. Most precipitation falls between June and September. The soil properties are shown in Table 1. Cone-shaped or pyramidal rocks approximately 1 meter in height cover most of the plot.
The study had a randomized complete block design, with 9 treatment combinations of dye application (i.e., 3 plot types × 3 application amounts) and 3 replicates for each treatment combination (altogether 27 dye plots, selected using the parallel line sampling method, each of which was 5 m long and 5 m wide, with rocks randomly distributed). The three plot types were AR, CR, and CFMR, and the three dye application amounts were 850 mL, 1700 mL, and 3400 mL. We randomly selected 18 rock outcrops and divided them into two groups (CR and CFMR). In the CFMR plots, plastic film (0.014 mm thick) was used to mulch a rock outcrop, and care was taken not to scratch the film with rocks when mulching. The edge of the film was vertically embedded 10 cm deep into the soil and kept 5 cm away from the mulched rock to avoid the rock–soil interface’s disturbance of the infiltration of applied water. A slit (0.1 cm width and 10 cm depth), for the film’s embedding, was cut into the soil around the mulched rock using a knife so as to minimally disturb the soil and maintain the soil’s natural condition.

2.2. Dye Tracer Tests

On 12–15 March 2023, dye tracer tests were conducted before the maize was sown, during which no rainfall occurred in this area. The dye tracer solution was made from brilliant blue, an environmentally friendly food-grade dye, which is nontoxic, odorless, and characterized by high solubility and low adsorption in soil, at a concentration of 4.0 g L−1. A press-type sprayer was used to apply the dye solution on the 27 plots, one by one, at a sprinkling intensity of 1 mm min−1. The projected area of the soil of each dye plot for the AR plot was 2500 cm2 (50 cm in length × 50 cm in width), and the projected area for each of the CR and CFMR plots was also designed to be 2500 cm2 (1250 cm2 of soil and 1250 cm2 of rock).
The four steps in the dye tracer test were as follows: (1) to ensure good staining results, carefully remove debris from the surface before dye tracer application while avoiding excessive damage to the soil structure; (2) spray the dye tracer solution on the soil/rock surface, and the durations of spraying are 3.4 min for the 850 mL, 6.8 min for the 1700 mL, and 13.6 min for the 3400 mL; (3) 24 h after the dye application, dig a soil profile to a 20 cm depth within the center of each dye plot, and the profiles are 50 cm in width for the AR plot and 25 cm for the CR and CFMR plots and perpendicular to the selected rock; (4) photograph the soil profiles with a stick of known length placed alongside as a reference, and cover the entire profile with an umbrella for soft lighting conditions.

2.3. Image Analysis

Image processing using Adobe Photoshop CS6 consisted of the following steps [38]: geometric correction, graphics clipping, background removal, and color replacement. The opacity of the images was set to 50%, and the images of the three replicates of each treatment combination were superimposed into a single picture to present the distribution pattern of the dye tracer solution. To clearly show the details of the distribution pattern in the superimposed picture, the dyed areas covered by three, two, or one original image(s) were set as blue, purple, and green, respectively. Then, the resolution of the image of each dye plot was set to 1 pixel mm−1, which allowed for the measurement of the dyeing depth, dyeing area, dyeing coverage, and preferential flow fraction with millimeter precision.

2.4. Soil Volumetric Water Content Measurement

The volumetric soil water content in each photographed soil profile of the dyed plots was measured in the AR, CR, and CFMR treatments 24 h after the dye tracer test for the different application amounts of the dye tracer solution (850, 1700, and 3400 mL). The measurements were conducted using a soil water meter (ML2-UM-3.0, Delta-T Devices Ltd., Cambridge, UK), and the values were determined based on the average of three measuring points in a soil profile, from top to bottom.

2.5. Growth Index Determination

The growth index of the maize (plant height, stem diameter, maximum leaf area, and SPAD value) in the jointing stage, tasseling stage, and filling stage among the different treatments was recorded in 2023. Crops were planted in rows for the AR and at random in the CR and CFMR plot types. Thirty samples of maize and Chinese chives were randomly selected in each treatment, and all samples were grown within 0.5 m from the rocks for CR and CFMR. The determination methods were as follows:
Plant height (cm): a meter stick was used to measure the height, from the ground to the top first leaf cushion of the maize.
Stem diameter (cm): a vernier caliper was used to measure the stem diameter of the first, second, and third internodes from the bottom of the maize, and the results were then averaged.
Area of the maximum leaf (cm2): A meter stick was used to measure the length and width of the maximum leaf of the maize. The leaf area was calculated according to the following formula:
leaf area = length × width × 0.75
SPAD value: an SPAD chlorophyll meter (SPAD-502 plus, Konica Minolta Co. Ltd., Tokyo, Japan) was used to measure the SPAD value of the fourth leaf from the bottom of the maize, and the results measured on the tip, middle, and end of the leaf were averaged.
Floral development: the development status of the maize’s male and female flowers were surveyed and the numbers counted.

2.6. Statistical Analysis

One-way analysis of variance (ANOVA) was applied to assess the effects of the plot type on the dyeing characteristics (e.g., dyeing depth, dyeing area, dyeing coverage, and preferential flow fraction) and growth index of crops. The preferential flow fraction (%) was calculated according to the following formula:
P r e f e r e n t i a l   f l o w   f r a c t i o n = 1 − U n i f o r m   d y e i n g   d e p t h × S o i l   p r o f i l e   w i d t h D y e i n g   a r e a × 100
where the uniform dyeing depth is the depth at which the dyeing coverage decreases below 80%, indicating the depth to which the matrix flow is prevalent.
The dyeing coverage (%) was calculated according to the following formula:
D y e i n g   c o v e r a g e = D y e i n g   a r e a S o i l   p r o f i l e   a r e a × 100
where the soil profile area was 1000 cm2 for the AR and 500 cm2 for the CR and CFMR plots. Two-way ANOVA was applied to assess the effect of the plot type and the dye application amount on the dyeing characteristics. All statistical procedures were performed with an α = 0.05 threshold for significance in IBM SPSS Statistics 25.0.

3. Results

3.1. Results of the Dye Tracer Test

In the dye tracer test, dyed water had a good dyeing effect on the soil, and images of the vertical soil profiles of the dyed plots clearly show the distribution patterns of colored water (Figure 1). In the AR plots, the colored water was mainly uniformly distributed with a preferential flow fraction of 12.31~37.15% under different application amounts of dye tracer, and preferential flow occasionally appeared with an increase in dye application. In the CR plots, the dyeing soil profiles showed obvious preferential flow at the rock surface with a preferential flow fraction of 35.78~55.54%, and lateral routing flow of the subsurface soil water was occasionally observed at the interface between the A horizon and B horizon (hereafter referred to as the AB horizon). In the CFMR plots, preferential flow did not exist at the rock–soil interface with a preferential flow fraction of 24.93~39.62%, and lateral flow at the AB horizon was visible in the soils near the rock outcrops.
With the increase in the dye application amount, the dyeing depth and dyeing coverage were different among the three treatments (Figure 2). In general, an increase in the dyeing depth augmented the dyeing coverage in the AR, CR, and CFMR plots. Despite the CR plot having the greatest dyeing depth, the dyeing coverage was largest for the CFMR plot. In the AR plot, the dyeing depths were 6.93~14.00 cm and the dyeing coverages were 9.83~27.43% across the three dye application amounts. Compared with the AR, the dyeing depth increased by 42.86~121.63% and the dyeing coverage increased by 31.22~115.94% in the CR plot, and increased by 28.57~48.08% and 85.57~131.50% in the CFMR plot, respectively.

3.2. Soil Water Content in Dyeing Plots

Before the dye tracer test, the initial soil volumetric water content of the study plot was approximately 11%, and after the dyeing, it increased to different degrees among the three treatments in the dyeing plots (Table 2). The plot type and application amount significantly affected the soil water content in the dyeing plots (p < 0.001). Compared with the initial soil water content, the values across the three dye application amounts increased by 110.30~243.03% in the AR, 142.12~264.54% in the CR, and 176.97~318.48% in the CFMR plots, respectively. Compared with the soil water content after the dye tracer test in the AR plot, the values increased by 6.27~15.12% in the CR and 20.24~31.70% in the CFMR plots. The soil water content in the CFMR plot was close to the value in the AR plot for double the dye tracer application amount.

3.3. Crops Growth

The growth indicators of maize under the three experimental groups in the jointing stage, tasseling stage, and filling stage are shown in Figure 3. For these three growth stages, the plant height, stem diameter, maximum leaf area, and SPAD value of the maize increased in the order of AR, CR, and CFMR, in general, and there were statistically significant differences in the comparison of all of the above indicators (LSD0.05). The exceptions were the nonsignificant differences in the leaf area and SPAD value of the maize between CR and CFMR in the tasseling stage and filling stage. Compared with the above indicators for maize in the AR plot for the three growth stages, the values for CR were higher as follows: 3.52~56.98% for plant height, 10.15~38.55% for stem diameter, 30.29~43.24% for maximum leaf area, and 3.73~7.91% for SPAD value, respectively. And for the values for CFMR, they were 12.63~72.68%, 20.27~52.23%, 33.56~66.51%, and 9.02~13.52%, respectively. In the tasseling stage, maize flowers in the CR and CFMR plots developed better compared to the AR plot. The average numbers of individual maize plants in the AR plot were 0.87 and 1.20, and the values were 1.00 and 1.67 in the CR plot and 1.00 and 2.20 in the CFMR plot, respectively. Similarly, the average number of female flowers (i.e., ears) in the CR plot (2.17) and in the CFMR plot (2.50) was higher than in the AR plot (i.e., 1.77) for the filling stage, but there was no difference in the number of male flowers among the three treatments.

4. Discussion

4.1. Effects on Rainwater Redistribution and Maize Growth

This study demonstrated that film-mulched rock outcrops can greatly change the rainwater infiltration and redistribution in the soils around the rocks and has positive effects on increasing the soil water content and then on the growth of crops. It is widely known that soil water loss is serious in karst areas, and the water loss at the rock surface is one of the most important pathways for soil water loss [27,39]. The dye tracer test revealed that a large quantity of the rainwater gathered by the rock outcrops would infiltrate into the ground along this flow path, greatly limiting the water compensation effect on the surrounding soil matrix, which was undoubtedly a loss for the water’s use by plants. Interestingly, film-mulched rock outcrops can effectively stop the preferential flow at the rock surface (Figure 1); therefore, this method is of great practical significance for regulating the spatial redistribution of soil water and increasing the efficiency of precipitation use in plants, thereby improving cropland productivity in the karst area of southwest China.
The dyeing test clearly showed that soil water movement was sharply different among the treatments in the AR, CR, and CFMR plots. In the AR plot, the water was mainly distributed in the surface soil and spread as a matrix flow, and most of the water failed to penetrate into the deep soil due to lack of a preferential flow path. Infiltration occurred at the scale of the entire soil profile in the CR and CFMR groups, whereas it was mostly confined within narrow pathways at the rock–soil interface in the CR treatment, especially at the beginning of the simulated rainfall. For karst rocky desertification (especially severe rocky desertification), widely exposed bedrock combined with shallow soil leads to extremely serious water loss, and water in the soil can easily pass through the clay-rich illuvial horizon to underground space along the rock–soil interface [40]. It has been suggested, in fact, that this preferential flow around rocks is more intense than the matrix and macropore flow and provides a fast channel for surface water loss, reducing the compensation effect of soil for rainwater trapped by rocks during rainfall [22,30,41], which makes it very unfavorable for plants to make full use of the rainfall in karst areas. In this study, rock outcrops were fully mulched with film to partially prevent preferential flow, and it was experimentally validated that this method can change the infiltration and redistribution of water in the nearby soil. The results indicate that the covered film effectively blocked the preferential flow path, to some extent, curbing water loss in the CFMR treatment and transferring the gathered rainwater to nearby soil patches, where it combined with natural rainwater on the soil surface and penetrated downward uniformly as matrix flow from the soil surface, allowing for the full replenishment of soil water by precipitation (Figure 1 and Table 2). On the other hand, film-mulched rock outcrops prompted lateral flow at the AB horizon on a far larger scale than the CR treatment, and redistributed the gathered rainwater more fully in the soil layers, which can ensure that available water reaches plant roots more effectively.
Aboveground rocks increase the soil moisture of nearby root environments resulting in the improved growth and development of agricultural crops, and as the experimental results indicate, this beneficial effect can be enhanced when they are covered with plastic film. Soil water in karst areas is mainly recharged by rainwater that falls on the soil surface and partly by the gathered water from rock outcrops [42,43]. Areas characterized by rocky desertification have a large proportion of soil that is occupied by rocks, and these rocks can direct a large quantity of rainwater to the surface soil, improving the surrounding soil conditions [29,33], as shown, for example, in the higher soil moisture in the CR plot than that in the AR plot. Even though the ability of rocks to intercept rainfall (also called the funnel effect) varies among karst ecosystems and is often related to the rocks’ characteristics (such as surface roughness and cracks) [31,32], film-mulched rock outcrops can ensure that aboveground rocks exert the funnel effect to the greatest extent, because the film can partially prevent the loss of rainwater due to the rock–soil interface, cracks, and other factors, thereby improving the supply of water from aboveground rocks to nearby plants. As shown in this study, compared to the AR treatment, the maize in the CR treatment and especially in the CFMR treatment exhibited good growth throughout the whole growth period (Figure 3). Under film-mulched rock outcrop conditions, maize growth indicators increased rapidly at first and then tended to become stable, and they were higher than that for the CR and AR treatments during the whole growth period. The appearance of the maize showed that the plant height, stem diameter, area of the maximum leaf, and SPAD value increased in the jointing stage, and the floral development improved in the tasseling stage and filling stage. The plants grew rapidly from the jointing stage to the tasseling stage but changed slowly in the filling stage as the maize transitioned from vegetative growth to reproductive growth. The fact that there was more maize in the tasseling stage in the CFMR and CR treatments than in the AR treatment shows that an increase in soil moisture accelerated the transition from vegetative to reproductive growth, and this is in good agreement with previous theoretical and experimental studies [44,45,46].

4.2. Implication of Film-Mulched Rock Outcrops

In previous literature, rock outcrops were often considered negative environmental factors in karst farmland, because in areas of severe rocky desertification, where rocks and soil become interspersed, the land has only a few remaining soil patches, which undoubtedly limits the water-storage capacity of the soil layer [30]. In addition, the rocks cover a great proportion of the surface area, and those rocks hinder soil layer continuity and reduce the use efficiency and productivity of the land [47,48,49]. Despite these factors, evidence still shows that the funneling effect of rock outcrops is expected to change the distribution pattern of rainwater and help alleviate the problem of crop water stress in karst farmland with scarce water resources [9,23,37]. Therefore, it is necessary to retain the rainwater intercepted by the rock outcrops to the maximum extent through film-mulched rock outcrops, as implemented in this study, which can effectively improve the soil water content of karst farmland and the utilization efficiency of precipitation by crops.
Water is crucial for the growth and development of maize in karst areas [50], and film-mulched rock outcrops can be a powerful means of water conservation and yield increases in agricultural production. The study showed that film-mulched rock outcrops can increase soil water content by changing the soil water redistribution and can help improve the precipitation utilization efficiency of rain-fed agricultural systems. Firstly, by transferring the collected extra rainwater to the surrounding soil, the film covering on the rocks can improve the soil water condition of root environments. And, secondly, the use of a film can reduce the loss of water by blocking preferential flow pathways, thereby providing the possibility for crops to obtain more water (as demonstrated in Figure 4). In addition, the CFMR plots highlight the crucial role of vertical matrix flow and lateral flow on water distribution in soil, since the two flow behaviors became more pronounced when the rocks were covered with film. The water infiltration process determines the spatial distribution of water in the surface soil in areas of rocky desertification, and film-mulched rock outcrops can change the infiltration characteristic by guiding the lateral movement of water into soil patches without soil water loss along the rock–soil interface. Especially for farmland with serious rocky desertification, where rocks occupy a large proportion of the land area and strongly affect the soil water distribution pattern, this measure is crucial for the effective utilization of rainwater resources by crops and their production value, although it could have less of impact on farmland characterized by less or nonrocky desertification. We believe it is an important practice for the effective use of this water resource by reducing soil water loss and can play a significant role in the ecological and economic benefits of artificial enrichment of natural precipitation in situ.

5. Conclusions

This paper used the dye tracer method at a sprinkling intensity of 1 mm min−1 to study rainwater redistribution in soils under three different treatments: away from rock (AR), close to rock (CR), and close to film-mulched rock (CFMR). In addition, the growth situation of maize (Zea mays L.) among the different treatments was also studied.
The results show that the rainwater gathered by the rock outcrops was wholly transferred to the surrounding soil in the CFMR plots without any preferential flow at the rock–soil interface, indicating that film-mulched rock outcrops can improve the rock’s output capability of gathering rainwater into the surrounding soil and crops. In addition, film-mulched rock outcrops promote the growth of maize, as indicated by the results for the plant height, stem diameter, maximum leaf area, SPAD value, and floral development of the maize, which increased in the order from AR, CR to CFMR. The present study demonstrates that rainwater in soil has the greatest likelihood of being used by crops in a CFMR plot among the three cropping systems.
In this study, film-mulched rock outcrops were proven to be effective at stopping preferential flow at the rock–soil interface and at regulating rainwater redistribution in karst rocky farmland, which may be of global significance, and, more importantly, they had positive effects on the soil moisture and growth of maize. The observed results are not specific to the studied karst area, because this practice has broader applicability to regions with similar geological characteristics.

Author Contributions

Conceptualization, Z.Z.; Methodology, Z.Z., J.D. and J.Z.; Software, Z.Z. and J.Z.; Validation, Z.Z.; Investigation, Z.Z., J.D. and Y.S.; Resources, Z.Z.; Data curation, Z.Z., J.D., J.Z. and Y.S.; Writing—Original draft preparation, Z.Z.; Writing—Review and editing, Z.Z.; Project administration, Z.Z.; Funding acquisition, Z.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Guizhou Province Colleges and Universities Young Science and Technology Talents Growth Projects (grant number: QJHKY[2022]296) and the Guizhou Provincial Basic Research Program (Natural Science) (grant number: QKHJC-ZK[2023]YB281).

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Acknowledgments

We thank the anonymous reviewers for their valuable comments. All of the authors especially appreciate the experimental equipment provided by the Guizhou Provincial Key Laboratory of Geographic State Monitoring of Watershed, School of Geography and Resources, Guizhou Education University.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 16 00254 g001
Figure 1. Rainwater distribution patterns under different treatments 24 h after simulated rain of 850, 1700, and 3400 mL. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: interface between A horizon and B horizon. Each picture is composed of three overlapping images from the respective triplicate plots, and the color is divided into dark blue, light blue, light green according to the degree of overlap.
Figure 1. Rainwater distribution patterns under different treatments 24 h after simulated rain of 850, 1700, and 3400 mL. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: interface between A horizon and B horizon. Each picture is composed of three overlapping images from the respective triplicate plots, and the color is divided into dark blue, light blue, light green according to the degree of overlap.
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Water 16 00254 g002
Figure 2. Dyeing coverage under different treatments 24 h after simulated rain of 850, 1700, and 3400 mL. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: the interface between A horizon and B horizon. The dashed and blue lines in figure are the measured values and mean of three replicate tests, respectively.
Figure 2. Dyeing coverage under different treatments 24 h after simulated rain of 850, 1700, and 3400 mL. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: the interface between A horizon and B horizon. The dashed and blue lines in figure are the measured values and mean of three replicate tests, respectively.
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Water 16 00254 g003
Figure 3. Multiple comparisons of the growth indicators of the maize under the different treatments. Jointing stage (mid-May), tasseling stage (mid-June), and filling stage (mid-July). Data are expressed as the mean ± SE. ns, not significant at p < 0.05,* p < 0.05, ** p < 0.01, and *** p < 0.001.
Figure 3. Multiple comparisons of the growth indicators of the maize under the different treatments. Jointing stage (mid-May), tasseling stage (mid-June), and filling stage (mid-July). Data are expressed as the mean ± SE. ns, not significant at p < 0.05,* p < 0.05, ** p < 0.01, and *** p < 0.001.
Water 16 00254 g003
Water 16 00254 g004
Figure 4. Redistribution patterns of rainwater under different cropping systems. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: the interface between the A horizon and B horizon. This image shows that the rainwater gathered by rock outcrops was mainly confined only within a narrow flow path at the rock–soil interface in the CR treatment, in contrast to the uniform distribution of rainwater in the soil of the AR treatment. Interestingly, in the CFMR treatment there was no preferential flow at the rock–soil interface, and the redistribution of rainwater was mainly based on matrix flow, indicating that film-mulched rock outcrops improve the rock’s output capability for gathering rainwater into the surrounding soil.
Figure 4. Redistribution patterns of rainwater under different cropping systems. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks; AB horizon: the interface between the A horizon and B horizon. This image shows that the rainwater gathered by rock outcrops was mainly confined only within a narrow flow path at the rock–soil interface in the CR treatment, in contrast to the uniform distribution of rainwater in the soil of the AR treatment. Interestingly, in the CFMR treatment there was no preferential flow at the rock–soil interface, and the redistribution of rainwater was mainly based on matrix flow, indicating that film-mulched rock outcrops improve the rock’s output capability for gathering rainwater into the surrounding soil.
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Table 1. Soil physical properties of the study site.
Table 1. Soil physical properties of the study site.
Soil HorizonDepth (cm)Soil Particle Composition (%)Soil Texture (USDA System)Bulk Density (g·cm−3)Initial Water Content (% vol.)
2~0.05 mm0.05~0.002 mm<0.002 mm
A0~1417.3247.6035.08Silty clay loam1.18 ± 0.07 b10.05 ± 0.74 b
B>145.1246.4048.48Silty clay1.26 ± 0.06 a12.13 ± 1.66 a
Notes: Data are expressed as the mean ± SE. Different lowercase letters within rows indicate significant differences among plot types (p < 0.05). A: eluvial horizon; B: illuvial horizon.
Table 2. The dyeing characteristics and soil water contents under different treatments 24 h after simulated rain.
Table 2. The dyeing characteristics and soil water contents under different treatments 24 h after simulated rain.
Application Amounts (mL)Dyeing Depth (cm)Dyeing Coverage (%)Preferential Flow Fraction (%)Soil Water Content (%vol.)
ARCRCFMRARCRCFMRARCRCFMRARCRCFMR
8506.93 ± 1.64 c15.37 ± 1.46 a10.27 ± 2.32 b9.83 ± 0.41 c17.88 ± 1.76 b22.75 ± 3.17 a12.31 ± 4.26 c35.78 ± 6.54 a24.93 ± 2.13 b23.13 ± 1.85 c26.63 ± 0.80 b30.47 ± 1.35 a
170010.83 ± 2.38 c18.97 ± 0.54 a15.90 ± 1.77 b16.32 ± 3.95 c35.23 ± 9.31 b36.30 ± 2.14 a22.73 ± 4.95 c45.18 ± 5.89 a34.84 ± 2.87 b30.30 ± 1.86 c33.13 ± 1.27 b36.43 ± 2.04 a
340014.00 ± 0.76 c20.00 ± 0.00 a18.00 ± 1.06 b27.43 ± 3.32 c35.99 ± 2.82 b50.90 ± 2.76 a37.15 ± 7.64 c55.54 ± 3.19 s39.62 ± 3.40 b37.73 ± 1.19 c40.10 ± 0.81 b46.03 ± 0.99 a
Summary of ANOVA (F values)
PT18.24 ***16.604 ***14.684 ***59.324 ***
AA14.044 ***21.034 ***12.384 ***64.924 ***
PT × AA0.35 ns1.20 ns0.35 ns0.18 ns
Notes: Data are expressed as the mean ± SE. Different lowercase letters within rows indicate significant differences among plot types (p < 0.05). PT: plot type; AA: application amount. AR: away from rocks; CR: close to rocks; CFMR: close to film-mulched rocks. ns, not significant at p < 0.05. *** p < 0.001.
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Zhao, Z.; Deng, J.; Zhang, J.; Shen, Y. Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area. Water 2024, 16, 254. https://doi.org/10.3390/w16020254

AMA Style

Zhao Z, Deng J, Zhang J, Shen Y. Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area. Water. 2024; 16(2):254. https://doi.org/10.3390/w16020254

Chicago/Turabian Style

Zhao, Zhimeng, Jiabin Deng, Jin Zhang, and Youxin Shen. 2024. "Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area" Water 16, no. 2: 254. https://doi.org/10.3390/w16020254

APA Style

Zhao, Z., Deng, J., Zhang, J., & Shen, Y. (2024). Effects of Film-Mulched Rock Outcrops on Rainwater Redistribution and Maize Growth in the Cropland of a Rocky Karst Area. Water, 16(2), 254. https://doi.org/10.3390/w16020254

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