Keywords
Crop residue, Crop rotation, Soil erosion, Soil water infiltration, Sustainable agriculture
This article is included in the Agriculture, Food and Nutrition gateway.
Crop residue, Crop rotation, Soil erosion, Soil water infiltration, Sustainable agriculture
The Introduction was restructured enough to explain the importance of this research and was simplified; in addition, we pointed out that the relation with root mass was an unexpected result of which suitable for the "Research Note" of F1000Research.
The overview was added in Methods.
The summary of Methods was added in the Result section
The sentences were improved to the readability.
See the authors' detailed response to the review by Kae Miyazawa
See the authors' detailed response to the review by Bingcheng Xu
Soil degradation is a major constraint of food security (Gomiero, 2016; Lal, 2015), and soil erosion represents one of the crucial intervention points for reversing soil degradation (Karlen & Rice, 2015). The Universal Soil Loss Equation (USLE) (Wischmeier & Smith, 1978), the standard for estimating erosion, shows that the risk of erosion is drastically reduced when a crop has covered soil surface. This emphasizes the importance of preventing erosion in the early stage of crop growth. There are two aspects to preventing erosion; the one is to fix soil, another is to increase the water infiltration rate. Especially, increasing infiltration rate has an additional benefit for water harvesting and reducing the surface runoff. Therefore, technologies increasing the water infiltration rate are critical to prevent soil erosion in tillage systems.
Tillage makes soil porous, but physical properties are rapidly lost (Strudley et al., 2008); however, organic matter application increases the stability of soil pores (Turmel et al., 2015). Interestingly, Potter et al. (1995) reported that water infiltration of soil was higher under no-tillage than tillage conditions when the residue input was low, but the opposite result was shown when the residue input was high. All in all, the soil erosion decreased according to the degree of water infiltration (Potter et al., 1995). However, the relation between the quantity of applied residue and infiltration rate has been less studied. Although a previous study reported that surface water runoff under normal subtillage reduced up to the applied wheat straw quantity, as the water infiltration increased with the quantity of applied straw (Russel, 1940), to our knowledge, whether the relation between the quantity of applied residue and the infiltration holds under crop rotation, has not been studied.
Therefore, we investigated the relation between the quantity of crop residue of the prior crop and the water infiltration rate in a crop rotation of corn, rose grass, and okra. Though the data supported the relation, unexpectedly, the data also suggested that the relation between the quantity of remaining underground root mass of the prior crop and the infiltration rate was stronger.
The experiment was conducted in greenhouses to prevent the rainwater. We grew corn as a cleaning crop, then grew rose grass, and okra sequentially under different nitrogen application levels and mulch conditions. All the crop residues were collected in each greenhouse, and the equal amount was returned each plot but different amount between the greenhouses. The water infiltration rate was measured on the ridge at similar soil moisture conditions, on the day incorporating the prior crop residue.
We conducted the experiment in two greenhouses at the Japan International Research Center for Agricultural Sciences experimental field (24.38°N and 124.19°E) on Ishigaki Island. The climate is subtropical. The soil type was Ultisol (Soil Survey Staff, 2014) and the texture was sandy clay loam. The greenhouse was 5 m wide and 18 m long. We made three ridges (0.2 m high and 1 m wide) with a 0.5 m path on each side. We divided these ridges into three plots with 0.8 m paths between each plot. In this way, we created nine plots (1 m × 5.2 m) in each greenhouse and randomly assigned them with nine treatments (3 × 3 factorial design). These treatments comprised three nitrogen levels (0, 10, and 40 kg N ha−1; slow-release-type urea only, no other fertilizers were used) and three mulching treatment (unmulched, weed barrier fabric, and black plastic film mulch). Although both nitrogen application and mulch treatment have impacts on the biomass, the treatments were expected to make differences on top-root ratios.
We replicated the treatments using two greenhouses (A and B). We cropped corn (Zea mays) without fertilizer as a cleaning crop and collected the residue, then chopped the residue into approximately 3 cm pieces using a chopper and dried it for two months under a roof. We adjusted the soil moisture of the greenhouse at a suitable level for tillage by irrigating (25–40 mm) with mist irrigation tubes (Kiriko; Mitsubishi Chemical Agri Dream Co., Ltd., Tokyo) and then removed the tubes. We scattered 2 Mg ha−1 of the corn residue, tilled by a rotary tiller, made the ridges, measured the soil water infiltration, set the irrigation tubes again, set the mulch films, transplanted rose grass (Chloris gayana) seedlings with fertilizer, and irrigated up to the field capacity. Additional irrigation was not provided. After harvesting rose grass, the crop residues were collected in each greenhouse then evenly returned to the plots (each plot received the same amount of residue but the amount was different between the greenhouses). We grew okra (Abelmoschus esculentus) by the same way. The growing season of corn, rose grass, and okra were 7 June to 10 August 2016, 14 October 2016 to 11 January 2017, and 12 January to 14 April 2017, respectively. An interval of 65 days was provided between the corn harvesting and the rose grass planting. There was no interval between rose grass harvesting and okra planting. (Supplementary Figure 1).
We measured the soil water infiltration rate with Mariotte's bottle (20 cm high, 10 cm in diameter), with two holes in the bottom. Mariotte’s bottle is a device that delivers a constant rate of flow. We inserted a plastic ring of the same diameter into the ridge to a 10 cm depth and then watered from a 1 m height to the ring at a 60 mm min−1 rate. We recorded the time needed to waterlog 50% of the soil surface area. We measured infiltration on the ridge at the initial stage (before the rose grass; with incorporated corn residue), after the rose grass (with incorporated rose grass residue), and after the okra (with incorporated okra residue).
The effect of the soil moisture difference treatment was determined at the end of okra cropping by extracting soil core samples from 0 to 5 cm soil depth on the ridge. Aboveground biomass was calculated by multiplying the plot’s whole fresh biomass weight to the average moisture content of the air-dried samples’ in each greenhouse. We performed Pearson’s product moment correlation analysis of the infiltration rate for the quantity of incorporated residue or for the aboveground biomass (dry weight) using the “CORREL” function of MS Excel 2016. The correlation coefficients were calculated for the mean values of nitrogen levels and for that of the mulch levels. The mean values of nitrogen levels show the effects of aboveground biomass, which averaged out the effect of soil moisture. By contrast, the mean values of mulch levels show the effect of soil moisture.
We grew corn as a cleaning crop, then grew rose grass, and okra sequentially under different nitrogen application levels and mulch conditions. All the crop residues were collected in each greenhouse, then the equal amount was inputted to each plot. The water infiltration rate was measured on the ridge at similar soil moisture conditions, on the day incorporating the prior crop residue.
There was a strong correlation between the incorporated residue dry weight and soil water infiltration rate (r = 0.953) in terms of nitrogen level treatment, even though initial corn residue showed outliers (Figure 1a). Although, our result is in line with a previous study (Russel, 1940), the outliner is not negligible because the almost same infiltration rate was observed for a 2.5-fold different input. By contrast, aboveground biomass of the prior crop showed a higher correlation with soil water infiltration rate (r = 0.965), without outliers (Figure 1b). Since the crop biomass is generally proportional to the crop root biomass when the top-root ratio is stable; however, the absence of the outlier supports that the infiltration is essentially based on the root mass. Additionally, it is well known that soil moisture strongly affects to top-root ratio. The soil moisture range of mulch treatment (6.5–9.7 %) was larger than that of nitrogen treatment (7.2–8.3 %). This means that the top-root ratio is more unstable in mulch treatment; as a result, the correlation coefficient of the infiltration rate and the aboveground weight must decrease. Actually, the rate decreased to r = 0.872 for the mulch level treatment (Figure 1c).
We should consider the duration of the “after-effect” of the prior crop (Wischmeier & Smith, 1978), such as the roots of rose grass on the soil water infiltration rate measurement of after okra. We conclude that the effect of the prior crop root mass almost disappears within the next crop growth period under the experimental conditions because the correlation between the aboveground biomass and the infiltration rate was stable and less was affected by a prior crop.
The previous study reported the correlation between the quantity of applied crop residue and the water infiltration rate for wheat (Russel, 1940), and the degree of water infiltration was related to the level of soil erosion (Potter et al., 1995).
We found a strong correlation between the incorporated prior crop residue and the infiltration rates in crop rotation. The result seems to indicate the relation between applied crop residue and soil erosion decrease is more common. However, the aboveground biomass of the prior crop showed a higher correlation to the infiltration rate more than the applied residue and that suggests the essence of the relation is based on the root mass. A previous study has shown that the decrease in water erosion rates with increasing root mass is exponential, although infiltration was not mentioned (Gyssels et al., 2005). Our data show a positive relationship between resistance to erosion and root mass when assuming that aboveground biomass is proportional to the underground biomass.
Finally, the key finding of this study is that the effect of aboveground residue quantity, more precisely root mass, was stronger than the incorporated residue. From a physical viewpoint, the area of residue surface is far smaller than that of the root surface and the gap is easily clogged by sediment caused by rainfall. Therefore, the improvement of soil water infiltration probably comes from root mass (Gyssels et al., 2005). In addition, our result also showed that the effect of the prior crop root mass disappears within the next crop period. This suggests that maintaining a large root mass is crucial for reducing soil erosion. Our results were obtained in greenhouses of the sub-tropical environment so the further study should be conducted in other conditions.
Raw data of this article are presented in figshare: https://doi.org/10.6084/m9.figshare.6741890.v1 (Oda et al., 2018).
Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).
We thank Masato Shimajiri, Yasuteru Shikina, Masashi Takahashi and Masahide Maetsu for their assistance with experiment. We thank Akiko Sawa for her assistance with the sample analysis.
Supplementary Figure 1. Timeline of the experiment. Cropping days and the residue input.
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Is the work clearly and accurately presented and does it cite the current literature?
No
Is the study design appropriate and is the work technically sound?
No
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
I cannot comment. A qualified statistician is required.
Are all the source data underlying the results available to ensure full reproducibility?
Partly
Are the conclusions drawn adequately supported by the results?
No
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Plant water use; Agronomy
References
1. Johnson J, Strock J, Tallaksen J, Reese M: Corn stover harvest changes soil hydrology and soil aggregation. Soil and Tillage Research. 2016; 161: 106-115 Publisher Full TextCompeting Interests: No competing interests were disclosed.
Reviewer Expertise: soil science, vegetable cultivation
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: soil science, vegetable cultivation
Is the work clearly and accurately presented and does it cite the current literature?
Partly
Is the study design appropriate and is the work technically sound?
No
Are sufficient details of methods and analysis provided to allow replication by others?
Partly
If applicable, is the statistical analysis and its interpretation appropriate?
No
Are all the source data underlying the results available to ensure full reproducibility?
Partly
Are the conclusions drawn adequately supported by the results?
No
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: soil science, vegetable cultivation
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