ABSTRACT Regosols (Neossolos) are soils with use limitations mainly related to effective depth, abundant presence of rock and saprolite fragments, and frequently high slope gradients; besides that, they represent a new agricultural frontier for grain production in southern Brazil. This study evaluated soil saturated hydraulic conductivity (Ksat) and water retention and availability in Regosols and saprolites derived from volcanic rocks in southern Brazil and the relationship of these variables with porosity in saprolithic horizons characterized by mineralogical weathering. The study was carried out on eight profiles derived from basic and acidic volcanic rocks of the Serra Geral Formation. We evaluated soil morphology, granulometry, porosity, bulk density (BD), Ksat, water retention, electronic/ optical microscopy and chemical composition of parent materials, and soil mineralogy. Soil Ksat ranged from 0.0 to 6.40 cm h-1 in the evaluated horizons, without significant difference between the A and Cr horizons. Seven soil profiles showed BD equal to or less than 1.28 Mg m-3 for the Cr samples. Total porosity in the Cr horizons was above 0.5 m3 m-3 and not significantly different from A horizons. In five of the eight soil profiles, one or more Cr horizons presented greater available water than A horizons. Electronic and optical microscopy evidenced abundant cracks and mineralogical weathering in the rock samples. X-rays diffraction data also indicated advanced degree of weathering of Cr horizons, evidencing abundant formation of pores in the saprolite. and justifying the high-water retention in Regosols profiles in southern Brazil. Neossolos (Neossolos depth fragments gradients that (Ksat Formation morphology granulometry BD, , (BD) electronic materials mineralogy 00 0 0. 640 6 40 6.4 h1 h 1 h- 128 28 1.2 m 3 m- samples 05 5 Xrays X rays highwater (BD 64 4 6. 12 2 1.

ABSTRACT In hydrological modeling and for the development of projects related to soil and water conservation and civil engineering, determination of water infiltration variables into the soil plays a key role. However, measuring infiltration with manual infiltrometers is work-intensive and requires several people, which casts doubts on the consistency of the process description. Our objective was to develop automated and compact systems for data acquisition by double-concentric-ring and Cornell infiltrometers. The systems are based on air differential pressure sensors and microcontrollers using open-source software and a simple construction. We developed ten sets of automatic infiltrometers for each method that were properly calibrated. The equipment was validated in the field, and the alignment of the automatically measured with the hand-measured infiltration data was considered satisfactory. The proposed systems make data records of infiltration and associated variables possible, with less operator dependence than manual measurement strategies. In addition, the enhanced resolution resulting from infiltrometer automation makes the infiltration curve more representative, especially in the initial infiltration stage. engineering role However workintensive work intensive people description doubleconcentricring double concentric ring opensource open source construction calibrated field handmeasured hand satisfactory possible strategies addition representative stage

ABSTRACT Soil steady water infiltration rate (SIR) is a key variable in hydrological modeling, but its relationship to antecedent soil moisture is not yet well understood. We tested the hypothesis that the SIR decreases with the increase in antecedent moisture, and that this relationship depends on permeability to water on the soil surface, the measurement method, and the measurement period. We conducted an experiment in an Argissolo Vermelho-Amarelo Distrófico abrúptico (Psammentic Paleudult – Soil Taxonomy), measuring infiltration in up to 14 antecedent moisture conditions under two soil structural conditions (no-till and no-till with subsoiling), with two measurement methods (double ring and Cornell infiltrometers), and for up to 48 h, with ten replications. In addition, vertical effective hydraulic conductivity of the saturated profile (Kef) was determined with Darcy’s equation for N layers. Crop succession used in the area was black oats and ryegrass in the winter and soybean in the summer. The SIR decreased to as little as 7.7 % of its original value with the increase in antecedent moisture; it was ~200 % greater in the treatment with subsoiling compared to no-till alone, and ~80 % greater when measured with the Cornell infiltrometer than with the double ring infiltrometer. Nevertheless, the effects of the method and the soil structural condition declined with the increase in antecedent moisture, confirming our hypothesis. In soil initially nearly saturated (degree of saturation ~90 %), the SIR drew near Kef (12.7 mm h-1) under the two soil structural conditions, especially when measured with the double ring infiltrometer. In contrast, increasing the time for measuring infiltration (>2 h) did not generate a new lower SIR level. The SIR decreases with the increase in antecedent soil moisture, and this relationship depends on the permeability to water of the surface layers and the measurement method. The SIR determined with infiltrometers better corresponds to vertical infiltration the nearer the soil is to saturation before beginning measurement. (SIR modeling understood period VermelhoAmarelo Vermelho Amarelo Psammentic Taxonomy, Taxonomy , Taxonomy) 1 notill no till subsoiling, subsoiling) infiltrometers, infiltrometers) 4 h replications addition (Kef Darcys Darcy s summer 77 7 7. 200 ~20 alone 80 ~8 Nevertheless degree 90 ~9 %, %) 12.7 127 12 (12. h1 h-1 contrast >2 2 (> level 20 ~2 8 ~ 9 12. (12 h- > ( (1

ABSTRACT A widespread assumption among researchers and technicians is that stony soils are more susceptible to degradation. However, the role of rock fragments in the hydrology of stony soils, especially in regard to infiltration, is still a research gap. The aim of this study was to test the hypothesis that an increase in rock fragments in the soil profile increases the water infiltration rate. Infiltration tests using a double-ring infiltrometer were conducted on February 11, 2021, and December 11, 2022, at three sites of Entisols with different fractions of rock fragments. The results supported the hypothesis of this study. The infiltration rate was up to sixteen times greater in profiles whose horizons had at least 60 % rock fragments in relation to profiles with a lower fraction of rock fragments. These findings provide evidence that some stony soils may not be as susceptible to degradation by water erosion as it was suposed. However gap doublering double ring 11 2021 2022 6 suposed 1 202 20 2

ABSTRACT Stony soils have been increasingly used for agriculture production; however, little is known about their hydraulic properties due to problems, such as sample deformation and hydraulic continuity between samples and suction devices when the sampling and measurements are accomplished with traditional techniques. In this study, the traditional ring sampling technique was replaced by the sampling of undisturbed soil blocks coated with paraffin wax to preserve their structure. A saturated paste of fine-grained mineral particles was used to ensure contact and hydraulic continuity between samples and suction devices (sand table and ceramic plates). This allowed us to determine 30 water retention curves for three stony soils with coarse particle contents (> 2 mm) ranging from zero to 69 %. The van Genuchten model was fitted to the measured retention data and the root mean square errors were between 0.0034 and 0.0331 m3 m–3, with no outliers or odd behavior in the retention curves. These results showed that consistent water retention curves for stony soils can be determined with the technique proposed. Fine-grained minerals sandwiched between the surface of suctions sources and sampled blocks improve hydraulic continuity between them. These techniques can be applied to determine water retention properties in structured soil samples with coarse particles where it is unfeasible to collect structured soil samples with metal sampling rings. production however problems study structure finegrained fine grained sand plates. plates . plates) 3 > ( mm 6 % 00034 0 0034 0.003 00331 0331 0.033 m m–3 proposed Finegrained Fine them rings 0003 003 0.00 0033 033 0.03 m– 000 00 0.0 03 0.

ABSTRACT The naturally fragile sandy soils of the Pampa Biome (PB) may be degraded with the introduction of poorly managed agricultural crops. Anthropic use can markedly decrease vegetation cover on sandy soils, leaving them more exposed to erosive agents. Decreases in organic matter content, biodiversity, and nutrient availability, increased soil compaction, and decreased water availability are also some of the impacts caused on PB soils by implementing poorly managed agricultural crops. In Rio Grande do Sul, in areas with sandier soils, the intense replacement of PB with commercial crops that has occurred in recent years (2000-2020) may be starting a disastrous cycle of degradation of these soils. However, it is not yet known how much these soils are degraded by recent anthropic use. There are no local scientific publications dedicated to the diagnosis of the degradation of these soils by anthropic use. Therefore, the need for this study was based on the objective of evaluating the physical and hydraulic properties of sandy PB soils with the insertion of agricultural crops. The study was conducted on three different soils, where soil samples were collected under three systems of use (extensive cattle raising on native grassland, eucalyptus afforestation, and soybean crop). Our results show that it can take more than nine years for soybean and ten years for eucalyptus land-use change to indicate some level of degradation in soil physical and hydraulic properties after replacing PB with these cultivated crops. (PB agents content biodiversity compaction Sul 20002020 2000 2020 (2000-2020 However Therefore extensive grassland afforestation crop. crop . crop) landuse land 2000202 200 202 (2000-202 200020 20 (2000-20 20002 2 (2000-2 (2000- (2000 (200 (20 (2 (

Resumo O objetivo deste trabalho foi obter uma metodologia de cálculo do balanço hídrico sequencial que estime com acurácia a ocorrência de excesso hídrico na soja em terras baixas. Foram testadas quatro estratégias de cálculo do balanço hídrico associadas à simulação do desenvolvimento da soja, as quais se diferenciaram em função da forma de cômputo da chuva e do tempo de drenagem da água dos macroporos do solo. Como referência foram utilizados os dados de umidade volumétrica monitorada em três camadas de solo ao longo do ciclo da soja no ano agrícola 2014/15. A microporosidade foi utilizada como limite inferior da ocorrência de excesso hídrico na área. Assim, o excesso hídrico foi considerado sempre que a umidade volumétrica diária do solo na camada 0-100 mm foi maior que 0,39 mm³ mm-3. Ao longo dos 111 dias de medição, a umidade do solo indicou a presença de excesso hídrico em 38 dias. A estratégia de cálculo tradicional do balanço hídrico subestimou a ocorrência de excesso hídrico, assim como as demais estratégias que consideraram a precipitação efetiva na sua metodologia. A estratégia de cálculo que considera que toda a chuva infiltra no solo e que a água dos macroporos é removida somente pela evapotranspiração da cultura apresentou bom desempenho e indicou 35 dias de excesso hídrico, sendo a mais adequada e recomendada para a determinação do excesso hídrico na soja em terras baixas.

Abstract The aim of this study was to derive a methodology for calculating a sequential water balance that accurately estimates the occurrence of excess water in soybeans cultivated in lowlands. We tested four calculation strategies of water balance associated with the simulation of soybean development, which differed on the calculation of rainfall and time of water drainage from the soil macropores. Data of volumetric moisture monitored in three soil layers throughout the soybean cycle in the 2014/15 agricultural year were used as a reference. Microporosity was used as a lower limit for the occurrence of excess water in the area. Excess water was considered to be whenever the daily volumetric soil moisture in the 0-100 mm layer was greater than 0.39 mm3 mm-3. Over the 111 days of measurement, soil moisture indicated the presence of excess water in 38 days. The traditional calculation strategy of water balance underestimated the occurrence of excess water, as well as the other strategies that considered effective precipitation in their formulas. The calculation strategy that considers that all the rainfall infiltrates in the soil and that the water from macropores is removed only by crop evapotranspiration exhibited good performance and indicated 35 days of excess water, being the most appropriate and recommended for determining excess water in lowland soybeans.

ABSTRACT The steady infiltration rate of soil profiles is commonly determined for irrigation and soil conservation planning, but the divergence of methods reduces the reliability of measurements. In this study, the steady infiltration rate measured with a double ring infiltrometer (isr-dri) in different layers of a soil profile was compared between layers and with the steady vertical saturated flow rate estimated by the Richards equation (isr-hy). The measurements of isr-dri at the top of the A, E, and Bt horizons were compared to each other and also compared with the isr-hy to detect the occurrence of lateral flow in double ring infiltrometer measurements. The isr-dri in the A horizon (236 mm h-1) was around 10 times higher than in the Bt horizon (20 mm h-1), which implies in a lateral flow of almost 90 % in the surface horizon. The occurrence of lateral flow in double ring infiltrometer measurements was also shown by comparing isr-dri with the vertical saturated flow rate estimated with the Richards equation, isr-hy. The main conclusion is that isr-dri measured at the soil surface overestimates the steady infiltration rate of soil profiles when underlying horizons are less permeable and more restrictive to water flow. In these cases, the use of an effective saturated hydraulic conductivity of the soil profile would imply inaccurate planning of drainage, irrigation, and soil conservation designs.

ABSTRACT The relation between water content and water potential is a key soil hydraulic property. The presence of rock fragments in soils can affect this property in bulk soil. In this study, we focused on the relation property determined with a WP4 dew point potentiometer. The objective was to evaluate the hypothesis that breaking large gravel-size particles into smaller fragments is a suitable strategy for accurate WP4 measurements in coarse materials without affecting the retention properties. Ten initial samples of basalt rock fragments with different weathering degrees were collected from the A horizon of an Entisol (Neossolo). Rock fragments initially sized between 38 to 4 mm were successively fractured into smaller fragments (size classes of 4-2, 1-0.25, and <0.25 mm). For each size class, the retention properties (water content versus water potential) were determined with WP4 equipment. No significant effect of fragment size was detected on the determined retention properties. Using supplementary water retention data from a previous study, we found an overestimation of water retention at -1.5 MPa ranging from 0.08 to 0.12 g g-1 when rock fragments were removed, which is of the order of magnitude to the available water capacity of several soils. This study showed that fragments larger than the diameter of the WP4 sample cup could be broken to sizes smaller between 4 and 0.25 mm without affecting the retention properties. This is a suitable strategy to allow accurate WP4 measurements in coarse materials while considering the effect of such coarse material on retention properties.

ABSTRACT Strategies to mitigate degradation and ensure food and water security are among the main challenges in agricultural development. Unconsolidated information about the positive impact of conservationist practices on productivity increase is fundamental for their adoption by farmers. This study evaluated if the saved rainfall excess in catchment with terrace generates higher soybean and corn yield due to greater water availability in the crop rooting zone. Experiments were conducted in southern Brazil during the agricultural years of 2016/17 (soybean) and 2017/18 (corn) in two paired zero-order catchments (~2.4 ha) with similar topography and soil properties. One catchment has no terraces, while the other has five broad-based terraces as a complementary practice to control runoff. Soybean and corn yield was compared between catchments through five paired transects, totaling 47 sampling points. The fraction of available water (FAW – the current in relation to the total available water) was monitored at two points in each catchment, one at the base and the other at the top, considering the elevation. The FAW was monitored with CS616 probes at eight soil layers (from 0.00 up to 1.60 m) at each point during the crop growth cycle. The FAW was higher in the terraced catchment than the non-terraced catchment during the soybean (14 %) and corn (8 %) cycles. The terraced area provided higher soybean (12 %) and corn (10 %) than the non-terraced area. These results highlight the importance of terraces to increase productivity by managing runoff on hillslopes, indicating the potential of terraces to mitigate water deficits.

ABSTRACT Finding the proper shaking setting to ensure total particle dispersion without altering the content of sand, silt and clay in soils composed of fragile particles such as saprolite fragments is still a research gap. This study aimed to identify the best shaking setting to optimize particle dispersion and minimize particle change in samples of Entisol (Neossolos). Samples were dispersed using an electric mixer at 12,000 rpm for 5, 15, 30 and 60 min, a horizontal shaker at 150 cycles min-1 for 1, 2, 4, 8 and 16 h with and without the use of nylon spheres, and an ultrasonic shaker at 70 and 110 J mL-1 for approximately 20 and 30 min, respectively. All the treatments affected particle distribution. Coarse sand reduced up to 14 % and clay content increased up to 18 % with the horizontal shaker with nylon spheres and the electric mixer. These changes were attributed to the breakdown of saprolite fragments, which represented around 1/3 of the coarse sand. Our results showed that the best setting was the horizontal shaker at 150 cycles min-1 for 1 to 2 h without using nylon spheres. This option allowed optimizing particle dispersion and minimizing changes in particle size distribution.

ABSTRACT Several management practices can increase soil water storage capacity, but their effectiveness to minimize the adverse effects of drought depends on their potential to increase the soil available water to plants. Terracing is an effective option to increase soil water storage, but its effect on available water to plants in no-tillage system is still a knowledge gap. In this study, we monitored soil water content at eight layers down to 1.6 m in two zero-order paired catchments for 16 months. Presence of five broad-based terraces in one of the catchments was the main difference between the two. Water availability to plants over time was expressed as a fraction of available water capacity (FAW). Positive differences of FAW between the terraced and non-terraced catchments were noticed over periods of rainfall shortage, but they were barely perceptible in periods of abundant rainfall. Over the 16 months, the frequency of FAW higher than 0.75 was between 46 and 50 % in the non-terraced catchment, and between 67 and 75 % in the terraced catchment. This benefit of terracing is more noticeable in thicker upper-section of the soil profile evaluated and with greater number of terraces upstream from the point of observation. We concluded that terracing in no-tillage turn excess rainfall into noticeable positive increases in available water to plants in the following periods of rainfall shortage.

ABSTRACT The least limiting water range (LLWR) has been extensively determined, but evaluating if LLWR can indeed indicate soil physical stress on plant growth is still a controversial issue. In this study, we used the Hydrus-1D hydrological model to simulate root water uptake (RWU) to analyze if RWU and LLWR are correlated under stress conditions. The LLWR was determined in a sandy-loam Ultisol and a clayey Oxisol. In both soils, RWU extracted by plants (leaf area index set as 3) from a rooted layer of 0.4 m was simulated over 20 days under a potential evapotranspiration rate of 6 mm day-1. For each soil, RWU was simulated over the same range of soil compaction in which LLWR was determined. The cumulative RWU over the 20 days varied between 23 to 58 mm in the Ultisol and 20 to 48 mm in the Oxisol, indicating that plants were able to take up only a small part of the cumulative potential transpiration (93 mm) and experienced severe water stress in some soil conditions. However, RWU under water stress was poorly correlated with both bulk density and LLWR. The correlation between RWU and LLWR was 0.5 (p<0.01) for the Ultisol and 0.22 (p<0.19) for the Oxisol, suggesting that LLRW has little (for Ultisol) or almost no (for Oxisol) ability to indicate soil quality related to plant water availability. Our simulations suggest that RWU in the water availability range (between field capacity and wilting point) may be little affected or even improved by light soil compaction. Studies to elucidate this phenomenon would contribute to the understanding of the compaction effect on RWU and the weak correlation between RWU and LLWR.

ABSTRACT Soil physical properties can be changed after vehicle traffic, especially by heavy military tracked vehicles. The Santa Maria military Instruction Field, where the experiment was carried out, is currently the most used area for armored tracked vehicles training in Brazil, with the M113 BR being the main equipment. The aim of this study was to determine the effect of the straight line and pivoted traffic intensity of the M113 BR on the physical properties and advancement of the compaction state of an Abruptic Alisol (Argissolo Vermelho-Amarelo Ta Distrófico abrúptico) with military vehicle traffic history. The study was conducted in a completely randomized design, independently evaluating the effect of straight and pivoting traffic in three soil layers (0.00-0.04, 0.10-0.14, and 0.20-0.24 m). For the straight-line traffic, traffic intensities (TI) with one (TI1), two (TI2), and five (TI5) passes on the same trail were evaluated. For the pivoting traffic, TI with one (TI1P) and two (TI2P) pivots was evaluated. Both studies had two non-traffic treatments (NT). The soil bulk density, total porosity, macroporosity, microporosity, saturated soil hydraulic conductivity, soil penetration resistance, soil bearing capacity, preconsolidation pressure, and gravimetric water content were analyzed in this study. In the straight-line traffic, cases with no significant differences in TP, Ma, Mi, and Ks prevailed. The highest TP, smallest Bd and largest Mi were observed in the 0.10-0.14 m layer. In the pivoting traffic, one pass was sufficient to increase Bd and decrease TP, Ma, Mi, and Ks in the 0.00-0.04 m layer and the increase from one to two pivotings had a significant difference only in Mi in this same layer. Both types of traffic intensity did not affect the PR in any layer. The Abruptic Alisol, pre-compacted from long-term military training, supported the loads applied by the M113 BR when additional traffic occurred in straight line mode, but not when in pivoting mode. The preconsolidation pressure parameter was not appropriate to assess the ability of the soil to support loads applied by pivoting traffic.

ABSTRACT: Quantification of runoff rate is an onerous task with non-automated devices; it requires a lot of manual labor to perform measurements. In this study, an automatic device to quantify the surface runoff rate from plots with a small area was developed and tested. The prototype was based on the tipping bucket technique and built with reused materials. Its performance was tested in the laboratory and a calibration curve was developed to improve measurement accuracy. The device can be used for automatic quantification of surface runoff in small plots, with a flow rate of less than 750 × 103 mm3 min-1. The device can be built with different dimensions to measure different flow rates. In that case, the error measurements and calibration curve must be recalculated.