Predicting deep drainage in the soil from soil properties and rainfall

Abstract. Simple predictions of deep drainage in the soil profile are often required for preliminary planning of land management where the cost of direct measurement is not warranted. Soil hydraulic conductivity and drainage of water below the root zone can be related to the salt content at the bottom of the root zone, assuming steady-state balances of water and salt. A physically based empirical model uses readily measured soil properties to predict the quantity of drainage below the root zone under varying regimes of water management and shows a good relationship with ponded infiltration rate.     

The effect of soil surface slope on raindrop detachment

The effect of slope angle on splash detachment has been a matter of discussion for long because it has not always been clearly observed in experiments. In this paper a model, based on the physics of the drop impact, is developed.The theoretical model indicates that a wide slope effect exists. Data collected by different authors were compared with the theoretical trends showing a satisfactory agreement. Some experiments showed that small changes in soil surface characteristics may hide the slope effect.     

Effects of cover on soil particle and associated soil nutrient redistribution on slopes under rainfall simulation

Journal of Soils and Sediments - Sediment detachment, transportation, and deposition occurred alternately along slope during erosion process. Nutrients were mobilized with sediment movement. In...     

不同降雨模式下石灰土坡地地表侵蚀特征

采用人工模拟降雨的方法,研究不同降雨模式下石灰土坡地的地表侵蚀特征.结果表明：1）降雨总量为102mm,降雨强度为2.03 mm/min时,地表累积产沙量多达1 201.86 g,降雨强度为0.37 mm/min时,产生的地下土流失量最多为6.563 g;2）降雨时间均为90 min,降雨强度由强变弱时地表产沙量最多为796.7 g,降雨强度由弱变强时产生的延续产沙量最多为41.38 g,此时产生的地下土流失量仅为4.923 g;3）影响地表产沙量的主要因素是降雨强度,影响延续产沙量最显著的因子是降雨后期降雨强度,而降雨时间的长短决定了地下土流失量.     

模拟降雨条件下保水剂对沙质土壤水分的影响

为了探究保水剂对沙质土壤水分的影响,采用室内重建土柱,在人工模拟降雨条件下研究不同用量保水剂对沙质土壤(0~30 cm)含水率的影响。结果表明:土壤含水率随着保水剂用量的增加而增加,保水剂用量为0.2%时不但省时省力,而且0~10 cm、10~20 cm、20~30 cm 3个土层土壤含水率分别为45.42%、48.48%、46.16%,既能满足植物的生长需要,又能节省经济成本,可为干旱、半干旱区节水造林及保水剂的合理使用提供理论依据。     

Residue cover and rainfall intensity effects on runoff soil organic carbon losses

Soil cover and rainfall intensity (RI) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity (RI) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h^− 1) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h^− 1 of rain, while under RI of 65 mm h^− 1, the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ER_SOC) in the sediment. The amount of runoff sediment rather than the ER_SOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ER_SOC were high and positively correlated with the ER values of particles smaller than 20 µm (p < 0.01). Although the sediment contained substantially more fine fractions (fine silt and clay, < 20 µm), the original soil and runoff sediment were still of the same texture class, i.e. silt clay loam.     

Effects of a one-year rainfall manipulation on soil nematode abundances and community composition

Soil nematodes play a crucial role in the terrestrial nitrogen cycle by accelerating the release of ammonium from microorganisms (bacteria and fungi). As aquatic organisms, nematodes are likely to be affected by predicted changes in precipitation patterns and soil moisture during the 21st century. The objective of this study was to measure the response of soil nematodes to a one-year rainfall manipulation in the sandy, forest soils of the New Jersey Pinelands (USA). We excluded all rain from four replicate field plots and applied double the amount of natural rainfall to four additional plots. We then assessed the impact of these precipitation treatments on nematode abundance and community composition. We found that total nematode abundance increased with more precipitation, and were highly sensitive to annual precipitation amount. This is in contrast to microbial biomass which was previously found to be insensitive to precipitation change. We suggest that any increased microbial growth in high rainfall plots was consumed by microbivorous nematodes. We further suggest that nematodes in the freely draining, sandy soils we studied may be unsuccessful at surviving drought because few water-filled pore spaces remain, as compared to more aggregated soils. All nematode families were sensitive to drought, but the effect was greatest on the Plectidae, while no significant effects were found for the Cephalobidae and Qudsianematidae. While not directly measured, these results provide insight into the relative anhydrobiotic abilities of these families. We found that bacterial-feeding nematodes were most sensitive to drought, suggesting that grazer-induced alterations to the nitrogen cycle are possible if precipitation patterns change in the future.     

Influence of simulated rainfall on physical properties of a conventionally tilled loess soil

Rainfall simulations were conducted on a loess derived silt loam soil (Henan province, P.R. China) under conventional tillage. This tillage practice is widespread and involves the turning of the plough layer and the wheat stubble in July (primary tillage), followed by a secondary tillage operation in October. Soil samples were collected and in situ measurements were done before each rainfall simulation in order to analyse soil physical properties after successive simulated rainfall events. The purpose of this study was to determine rainfall induced changes in saturated hydraulic conductivity, bulk density, penetration resistance, water retention and soil erodibility. The results only showed significant differences in soil bulk density and erodibility when applying successive rainfall events. Penetration resistance and water retention (at matric potentials ≤ − 3 kPa) were not significantly affected and soil surface sealing was not observed. This was also confirmed by the infiltration measurements, where no significant differences in saturated hydraulic conductivity were found. From a soil conservation point of view, this study indicated that the primary tillage operation (i.e. ploughing at the beginning of July) is rather disadvantageous: the saturated hydraulic conductivity is not significantly affected, but the soil erodibility is considerably higher in comparison to a consolidated soil. Furthermore, the beneficial effects of the wheat stubble on soil and water conservation are lost by the tillage operation.     

Soil management effects on runoff and soil loss from field rainfall simulation

Soil erosion from agricultural lands is a serious problem on the Chinese Loess Plateau. In total, 28 field rainfall simulations were carried on loamy soils under different management practices, namely conventional tillage (CT), no till with mulch (NTM), reduced tillage (RT), subsoiling with mulch (SSM), subsoiling without mulch (SS), and two crops per year (TC), to investigate (i) the effects of different soil management practices on runoff sediment and (ii) the temporal change of runoff discharge rate and sediment concentration under different initial soil moisture conditions (i.e. initially dry soil surface, and wet surface) and rainfall intensity (85 and 170 mm h^− 1) in the Chinese Loess Plateau. NTM was the best alternative in terms of soil erosion control. SSM reduced soil loss by more than 85% in 2002 compared to CT, and its effects on runoff reduction became more pronounced after 4 years consecutive implementation. SS also reduced considerably the runoff and soil loss, but not as pronounced as SSM. TC resulted in a significant runoff reduction (more than 92%) compared to CT in the initial ‘dry’ soil, but this effect was strongly reduced in the initial ‘wet’ soil. Temporal change of runoff discharge rate and sediment concentration showed a large variation between the different treatments. In conclusion, NTM is the most favorable tillage practices in terms of soil and water conservation in the Chinese Loess Plateau. SSM can be regarded as a promising measure to improve soil and water conservation considering its beneficial effect on winter wheat yield.     

Comments on the regulatory gate hypothesis and implications for C-cycling in soil

The paper by Kemmitt et al. [2008. Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass - a new perspective. Soil Biology and Biochemistry 40, 61-73] proposing the existence of an abiotic regulatory gate that controls the rate-limiting step of stabilised soil organic matter (SOM) mineralization, has initiated a fundamental and far-reaching debate. In this contribution the implications of a functioning abiotic regulatory gate are considered in the context of microbial community diversity and soil carbon cycling. I argue that although the evidence presented in support of the regulatory gate is strong, abiotic routes for SOM-mineralization function in parallel with biologically mediated mechanisms. Evidence is now accumulating that, in the presence of plant-inputs to soil, enhanced microbial mobilisation of SOM into biomass is a quantitatively important and ubiquitous process. I argue that this mineralization of SOM is fuelled by energy-rich substrates and is driven by microbial nutrient-demand. This implies that the mineralization of stabilised SOM and the turnover of C-inputs from current vegetation are intimately linked through the functioning of microbial communities associated with plants. This suggests that the microbial ‘eye of the needle’ is a crucial control-point in determining the carbon balance of soils. Fortunately, there are now excellent methods that allow quantification of SOM- and plant-derived C-fluxes through the members of soil microbial communities, and will also allow quantification of the relative importance of the abiotic and biotic routes of SOM-mineralization.     

The selective soil covering mechanism of weed harrows on sandy soil

Improvement of intra-row mechanical weed control is important to reduce the reliance on herbicides in arable crops and vegetables. Covering weeds by soil is an important weed control mechanism of weed harrows. A shallow post-emergence harrow cultivation controls weeds but also damages the crop to some extent. This paper explores how plants get covered by soil and how a plant’s resistance against being covered is related to its height, flexibility and shape of leaves. Seedlings of two contrasting species were sown in bins filled with a sandy soil and harrowed by a small model harrow in the laboratory. Covering selectivity (percentage covered ryegrass/percentage covered garden cress) could be influenced by soil moisture content, working depth and working speed. Differences in covering were related to spatial patterns of plant downward bending and soil surface level upheaval. These patterns are associated with soil failure patterns near tines and soil flow patterns, connected with different effects of plant height and plant flexibility. This study indicates that relationships between weed control and crop covering may not only depend on weed and crop characteristics but also on soil conditions and implement settings. As less than 10% of the covered plants were buried deeper than 15 mm, covering would mainly cause growth reduction and little killing. Limited burial depth may be an important cause for limited weed control effectiveness of harrowing.     

人工模拟降雨条件下花岗岩红壤坡面侵蚀过程与特征分析简

通过室内人工模拟降雨试验,研究降雨强度、坡度及地表覆盖3因素对花岗岩红壤坡面侵蚀过程的影响.结果表明：1）起始产流时间随降雨强度和坡度的增加而有所提前,而地表覆盖能延缓起始产流时间;2）在不同降雨强度和坡度条件下,径流率从产流初期开始都快速增加,7 ～ 10 min后达到稳定,且随着降雨强度和坡度增加,径流率也显著增加;3）随着降雨强度的增大,产沙率明显增大,且降雨强度越大,坡度对产沙率的影响越明显;4）降雨强度和径流总量、产沙总量之间相关性极显著,其相关系数分别为0.892和0.799;5）地表覆盖具有良好的减沙作用,其减沙效益超过90％.     

The effect of initial soil water content and rainfall intensity on near-surface soil hydrologic conductivity: A laboratory investigation

This paper investigates the influence of rainfall intensity and initial soil water content on changes in the near-surface soil hydraulic conductivity. While numerous papers have examined surface sealing, this paper outlines two important innovations: the design and application of time-domain reflectometry probes with the ability to measure and record soil water content at very short time and length scales; the design and application of stainless steel tensiometers to measure soil water potential at the same, very short, time and length scales. These permit the Richards Equation to be applied and the near-surface hydraulic conductivity computed. An exponential curve was fitted to the temporal changes in hydraulic conductivity, as both a function of water potential or soil water content, with a high degree of fit. As rainfall intensity increased, the degree of scatter about the best-fit line increased, probably due to the ability of high intensity rainfall to disrupt the near-surface soil structure. While utilising deterministic models, such as the Richards Equation, may be appropriate at the column scale there are practical difficulties due to the very small length scale variability in each of the input variables. The experimental results detailed here indicate that even with data at very short time and length scales it is still not possible to utilize the Richards Equation, or at least, it may be difficult to transfer the laboratory results to the field due to the effect of the specific laboratory experimental conditions on the results.     

Effects of rainfall intensity and slope gradient on the dynamics of interrill erosion during soil surface sealing

Soil erosion during rainfall is strongly affected by runoff and slope steepness. Runoff production is drastically increased when a seal is formed at the soil surface during rainfall. Therefore, a complex interaction exists between soil erosion and surface sealing. In this study, the dynamics of interrill erosion during seal formation is studied under different simulated rainfall and slope conditions. A sandy soil was exposed to 70 mm of rainfall at two intensities, 24 mm h^− 1 and 60 mm h^− 1, and five slope gradients, from 5% to 25%. Infiltration, runoff and soil loss rates were monitored during rainfall. Final infiltration rates increased with slope gradient at both rainfall intensities, this effect being stronger for the higher intensity. Cumulative runoff at the end of the rainfall event was lower as slopes were steeper, while an opposite trend was obtained for soil loss. For the 5% and the 9% slopes, the sediment concentration in runoff reached quickly a stable value during the whole rainfall event, while it reached a peak value before declining for the higher slopes. The peak value and its timing were rainfall intensity dependent. Soil erodibility during seal formation was evaluated using two empirical multiplication-of-factors type models. It seems that slope and rainfall erosivity are accounted for only partly in these models. For mild slope gradients below 9%, the value of K_i estimated by means of the two expressions becomes practically constant shortly after runoff apparition. Consequently, the estimates resulting from this type of expressions remain valuable from the practical point of view.     

The influence of the soil conditioner ‘Agri-SC' on splash detachment and aggregate stability

The influence of the soil conditioner ‘Agri-SC' on splash detachment and water-stable aggregation of an erodible clay Vertisol from Oahu, HI, was assessed. Laboratory rainfall simulation was used to assess splash detachment from soil treated with 0 (untreated control), 0.3, 3.0, 30, and 300 l ha⁻¹ of Agri-SC. Results indicated that the quantity of sediment splashed was significantly lower for Agri-SC application rates of 0.3 and 3.0 l ha⁻¹ (rates are equivalent to 1 and 10 times the manufacturer's recommended rates, respectively), than for the control, or for Agri-SC applied at 30 and 300 l ha⁻¹ (100 and 1000×, respectively). A second experiment was designed to test the influence of Agri-SC on water-stable aggregation of the Vertisol. Aggregates were subjected to rapid immersion in solution, shaken and washed through a series of sieves. Data indicated that there were no statistically significant differences in geometric mean aggregate diameter between the untreated and treated aggregates. The effect of the active ingredient, ammonium laureth sulfate (an anionic surface active agent) on splash and erodibility are discussed. These preliminary results indicate that further testing of Agri-SC is warranted on a variety of soils with different textures and mineralogies.     

Determining the depth of mixing layer in which soil solute releasing from soil to surface runoff on the unsaturated loess slope under artificial rainfall condition

Journal of Soils and Sediments - The mixing zone depth is a critical parameter in many popular agricultural non-point source pollution (NPS) models. Its variation for some special soil conditions...     

Relationships among rainfall, runoff and soil loss for the design of soil and water conservation works in submontane Punjab

Abstract. Linear, exponential and power function regressions were compared for rainfall, runoff and soil loss data. The power function performed better (R²= 0.77) than exponential or linear functions for estimating runoff from daily rainfall. However, this relationship was improved (R²= 0.96) by inclusion of a random component to the deterministic part of the function. A linear relationship between runoff and soil loss data performed better (R²= 0.77) than exponential or power functions. These relationships help in designing soil and water conservation works for supplemental irrigation in the area.     

The effects of slope and fertilizer rates on nitrogen losses in runoff from red soil and paddy soil during simulated rainfall

Journal of Soils and Sediments - Runoff and soil erosion reflect the interactions of soil properties and rainfall. However, few researchers have investigated the forms of nitrogen lost, the first...