Least Limiting Water Range Research Articles

Cover crops influence the physical hydric quality of a tropical sandy soil under no-tillage cotton cropping

ABSTRACT Reduced stability and structural resilience expose sandy soils to physical degradation under intensive production systems. This study aimed to evaluate the influence of different cover crops (CC) under no-tillage system (NTS) cotton cropping, grown either individually or in combination, on the soil physical quality (SPQ) of a sandy loam Oxisol (Latossolo) in southeastern Brazil. To quantify the effects of CC on soil physical quality indicators, an experiment in randomized blocks design was implemented with the treatments: CC1: single cultivation of Ruzi grass; CC2: Intercropping of Pearl Millet + Ruzigrass; CC3: Intercropping of Pearl Millet + Velvet bean; CC Mixture : Intercropping of Ruzi grass, Pearl Millet and Velvet bean; and Control: maintenance of spontaneous plants. Undisturbed samples were taken from layers 0.00-0.10, 0.10-0.20, 0.20-0.40 and 0.40-0.60 m, in which were determined the soil bulk density (Bd), total porosity (TP), available water (AW), soil penetration resistance (PR) and the least limiting water range (LLWR). According to the multivariate analyses, the CC 2 treatment resulted in better SPQ compared to the other treatments. The LLWR, air-filled porosity (θ AFP ), and AW were responsible for differentiating the CC 2 treatment compared to the other treatments evaluated. Regardless of treatments, values of Bd> 1.75 Mg m -3 result in loss of SPQ due to the significant increase in PR and decreases in AW and LLWR. In the CC 3 and Control, there was a physical impediment caused by the increase in Bd in the 0.10-0.20 m layer, which could result in the confinement of cotton roots to the surface, making them more susceptible to water stress. Soil PR reached values greater than 2.5 MPa for water contents lower than the θ PWP in most treatments. In treatment CC3, for water contents equivalent to the θ PWP , the PR did not exceed 6 MPa, while for the other treatments, the PR reached values greater than 10 MPa. Only the PR was influenced using CC. Soil moisture is considered crucial to maintain PR below impeding values, determining the control of the physical quality of this sandy soil.

Sugarcane bagasse derived biochar potential to improve soil structure and water availability in texturally different soils

Low organic matter content is one of the main constraints in arid and semiarid regions. This constraint and its negative influences on soils and plant growth may be alleviated by biochar (BC). Furthermore, improving soil physical and hydraulic attributes by application of biochar has received increased attention. Therefore, in the present study, the effects of sugarcane bagasse-derived biochar on the structural stability, water availability, and pore-size distribution (PSD) of three texturally different calcareous soils collected from different agro-climatologically regions were examined during a long-term experiment. Low and high-temperature biochars, produced in a muffle furnace by the traditional slow pyrolysis method at 300 °C (BC300) and 600 °C (BC600) were evaluated. Pots (15 kg) were filled with three different silty-clay Inceptisols (SCInc), silty-clay-loam Alfisols (SCLAlf), and loam Aridisols (LArid) soils mixed with 0 (control), 1, 2, and 3 w/w% of BC300 and BC600 during 540 days of incubation. The high energy moisture characteristic (HEMC) data was modeled using a modified van Genuchten function to quantify aggregate stability through stability ratio (SR) and structural stability index (SSI). The plant available water (PAW), least limiting water range (LLWR), and integral water capacity (IWC) were calculated with two matric suctions (h) of 330 cm for field capacity (FC) and 15,000 cm for permanent wilting point (PWP). Then the integral energy (EI) values were calculated (EIIWC). Results indicated that the incorporation of 3 w/w% biochar significantly (p < 0.01) increased SR (35 to 100%) and SSI (21 to 28%) indices in all three soils. Biochar significantly increased modal suction (MS) in LArid soils (5 to 158%); whereas, decreased MS of the other soils (3 to 43%). MS, SR, and SSI of BC300 and BC600-treated soils were not significantly different. PAW, LLWR, and IWC significantly decreased in the SCInc (18 to 61%, 8 to 44%, and 6 to 35%) and SCLAlf (8 to 44%, 18 to 35%, and 20 to 47%) soils and increased in LArid (4 to 54%, 3 to 61%, and 24 to 111%) soil with increasing biochar doses. There were no changes in EIIWC in biochar-treated LArid soil where PAW, LLWR, and IWC increased. Biochar increased EIIWC across the studied soil from 1% to 3.38 folds, thereby increasing the gradient of water potential to absorb the available water. Soil and soil-biochar mixtures exhibited heterogeneous and multimodal pore-size distribution (PSD). Biochar promoted the PSD peaks related to water-transmitting pores in SCInc and SCLAlf soils while decreased in LArid soil. In conclusion, results indicated that among the applied levels of biochar, the application of 3 w/w% biochar is suggested as a suitable way to improve soil physical behavior and structural stability.

Effect of water salinity and sodicity on soil least limiting water range

AbstractThis study aimed to evaluate the effects of water salinity and sodicity on the least limiting water range (LLWR) of two clay loam and sandy loam soils. The undisturbed soil samples were subjected to different water qualities, including three levels of sodium adsorption ratio (SAR, 1, 5, and 12) and electrical conductivity (EC, 1, 6, and 10 dS m−1). Our findings indicate that increasing EC at each SAR led to greater soil water retention. This was attributed to salinity affecting pore size distribution toward smaller pores by altering the diffuse double layer and causing soil particle flocculation. With increasing SAR levels at each EC level, soil water content at the wilting point also rose due to structural changes, clay swelling, and dispersion, resulting in more micropores and increased adsorptive surfaces in the soil. Additionally, soil volumetric water content at a 10% air‐filled porosity decreased, while values at a critical penetration resistance of 2 MPa increased with higher bulk density across all treatments. The LLWR showed a negative correlation with bulk density in clay loam soil across all SAR and EC treatments. The LLWR increased with higher water EC but decreased with increasing water SAR. The highest LLWR was observed at SAR = 1 and EC = 10 dS m−1, while the lowest occurred at SAR = 12 and EC = 1 dS m−1. The results revealed that elevated values of SAR in irrigation water reduced soil water accessibility for plants. However, as irrigation water salinity increased, the detrimental effects of SAR diminished.

The Least Limiting Water Range to Estimate Soil Water Content Using Random Forest Integrated with GIS and Geostatistical Approaches

In this study, as a result of the determination of the Least limiting water range (LLWR) contents of alluvial lands with different soils, which are distributed in the Bafra Plain where intensive agricultural activities are carried out, the compression and aeration problems in the area are revealed with distribution maps. In addition, the predictability of LLWR was evaluated with the random forest (RF) algorithm, which is one of the machine learning algorithms, and the usability of the prediction values distribution maps was revealed. The LLWR contents of the soils varied in the range of 0.049- 0.273 cm3 cm-3 for surface soils. While there were aeration problems in 6.72%, compaction problems in 20.16%, both aeration and compaction problems in 0.8% of the surface soils examined in the study area, 72.32% were determined under optimal conditions. For the 20-40 cm depth, an aeration problem in the 5.88%, a compaction problem in the 28.57%, and both an aeration and a compaction problem in the 2.52% of the points were detected. In the estimation of LLWR with the random forest algorithm, the RMSE value obtained for 0-20 cm depth was determined as 0.0218 cm3 cm-3, and for 20-40 cm it was determined as 0.0247 cm3 cm-3 . In the distribution maps of the observed and predicted values obtained, the lowest RMSE value was determined by Simple Kriging interpolation methods for 0-20 cm depth and Ordinary Kriging interpolation methods for 20-40 cm. While the distribution of obtained and predicted values in surface soils was similar, variations were found in the distribution of areas with low LLWR below the surface. As a result of the study, it has been revealed that LLWR can be obtained with a low error rate with the RF algorithm, and distribution maps can be created with lower error in surface soils.

Effectiveness of narrow tyne and double-discs openers to overcome shallow compaction and improve soybean yield in long-term no-tillage soil

Compaction adversely affects the soil physical quality and crop yields in no-tillage (NT) systems. No-tillage seeders equipped with narrow tyne openers may be a cost-effective option to overcome shallow compaction in NT soil and reduce the reliance on tillage for seedbed preparation and crop establishment. This study was conducted to: (1) quantify changes in soil physical quality indicators and determine the crop response to the use of a NT seeder equipped with either narrow tyne or double-disc openers, and (2) evaluate the potential of seeding tynes to overcome shallow compaction in NT soils of southern Brazil. Soil compaction was induced by applying 0, 3, 6, and 9 tractor passes equivalent to 84 %, 89 %, 94 %, and 99 % of the degree of compactness. In each treatment, a narrow tyne opener was used for the deposition of fertilizers compared to double discs. Undisturbed soil samples were taken from the 0–0.10 and 0.10–0.20 m depths and used to measure soil bulk density, soil water and air storage capacity, and the Least Limiting Water Range (LLWR). Soil penetration resistance and soybean (Glycine max L., Merr.) yield were also measured during the 2014/2015 cropping season. Soil bulk density and soil water storage capacity increased while air storage capacity and the LLWR decreased with an increase in the degree of compactness. The use of narrow tyne openers reduced soil penetration resistance in the 0.0–0.10 m layer by up to 66 % compared with the use of discs, and increased soybean yield by an average of 600 kg ha-1 (or US$ 227 per ha). By contrast, the use of double-discs on previously compacted soil resulted in yield penalties of up to 1200 kg ha-1. Soybean yield was more strongly correlated with LLWR (r = 0.97) than with any other measured soil physical quality indicator. Overall, these results supported the hypothesis that the use of NT seeders equipped with narrow tyne openers was effective in overcoming shallow compaction in NT soil.

Least limiting water range in Oxisol under two conservation tillage systems in sugarcane farming

The Least Limiting Water Range (LLWR) is an indicator of soil physical quality, contributing in information to propose soil management systems in agricultural farming process. This work aimed to assess the usage of LLWR and critical soil bulk density for physical-water quality evaluations, as well as its effect on sugarcane farming under no-tillage and reduced-tillage, in Oxisol. Undisturbed soil samples were collected in 0.00-0.10 and 0.10-0.20 m soil layers, to determine the following attributes: soil bulk density, soil penetration resistance (PR), volumetric water content at field capacity and permanent wilting point and minimum aeration porosity. The LLWR proved to be a good soil physical water quality indicator in sugarcane farming under conservation tillage system. No-tillage presented a greater range of the LLWR when compared to the reduced-tillage, regardless to the PR value adopted as restrictive for sugarcane roots development, increasing the yield of stalks and sugars contents. The critical soil bulk density under no-tillage is between 1.48 and 1.53 Mg m-3 at the RP of 2 and 4 MPa, while under reduced-tillage it is between 1.44 and 1.51 Mg m-3.

Soil tillage and machinery traffic influence soil water availability and air fluxes in sugarcane fields

Intensive soil disturbance by conventional tillage and heavy machinery traffic for planting, cultivation, and harvesting operations are the main causes of soil compaction and degradation of soil physical quality in sugarcane fields. However, the adoption of conservation soil tillage practices, such as no-till and reduced tillage associated with traffic control have been proposed as a key strategy to preserve soil physical quality, enhancing water availability and air fluxes. Nevertheless, the effects of reduced tillage associated with traffic control in sugarcane fields are still not well documented. A study was carried out to quantify soil water availability and air flux indicators in two soils with contrasting textures (named Sandy Loam and Clayey soil) under conventional and reduced tillage practices associated with and without controlled machinery traffic in central-southern Brazil. Soil physical parameters such as bulk density, total porosity, air-filled porosity, air permeability, pore continuity index, and the least limiting water range (LLWR) were measured. In both soils, there was no difference between conventional and reduced tillage in bulk density, air permeability, and LLWR. However, reduced tillage with non-traffic decreased bulk density and increased macroporosity, air-filled porosity, air permeability, pore continuity, and LLWR in Sandy Loam soil. In Clayey soil, the bulk density and LLWR did not change between tillage practices, but air permeability and pore continuity index were larger under reduced tillage with non-traffic. These results highlighted that soil disturbance by conventional tillage does not improve the water availability and air permeability during the crop cycle. However, the traffic control is essential to support the adoption of reduced tillage in sugarcane fields, preserving soil water availability and air fluxes for the subsequent ratoons. Reduced tillage and traffic control are two of the most important pillars for reducing soil compaction and promoting sustainability of sugarcane production in Brazil.

Changes of soil structure under different tillage management assessed by bulk density, penetrometer resistance, water retention curve, least limiting water range and X-ray computed tomography

Soil structure influences the soil hydraulic properties, aeration and resistance to root penetration. Many indicators can be used to investigate the changes of soil structure, but using a single indicator or method has limitations. This study evaluates the effects of 15-years tillage management on soil structure with soil bulk density (BD), penetrometer resistance (PR), soil water retention curve (SWRC), least limiting water range (LLWR) and X-ray computed tomography (CT). The treatments include no-tillage (NT), rotary tillage (RT), and mouldboard plough (MP). Soil bulk density of the 0–30 cm soil profile was measured after the establishment of tillage treatments for 7, 9, 12 and 14-years. The values of PR, SWRC, LLWR, and 3-D pore geometry of the 5–10 and 15–20 cm layers were determined in the 15th year of the experiment. The greater BD in the 0–5 cm layer of NT was not observed after 9 years, but an increased BD in the 5–20 cm layer was found in most years. Tillage had no effect on PR in wet soil. When soil had dried, the NT treatment had a greater PR and it was the lower limiting factor of LLWR, ultimately leading to a narrower LLWR of NT. Both NT and RT showed lower proportions of structural but higher textural pores. The macroporosity (> 50 µm) from X-ray CT was greater than that estimated from SWRC of the 15–20 cm layer. The characteristics of pore morphology were similar under three tillage treatments. Therefore, NT resulted in a narrower LLWR due to the denser soil layer, yet similar macropores may alleviate the negative impacts on crop growth caused by lower LLWR. It was suggested that using LLWR and characteristics of macropores from X-ray CT at the same time is a suitable way to assess soil structure under various tillage practices.

Estimating Least Limiting Water Range (LLWR) of Soil Using Artificial Neural Networks and Genetic Algorithms

Estimating Least Limiting Water Range (LLWR) of Soil Using Artificial Neural Networks and Genetic Algorithms

Long-term straw rather than manure additions improved least limiting water range in a Vertisol

Least limiting water range (LLWR) is a range in soil water content not limiting root growth, which integrates the effect of soil water retention, aeration, and penetration resistance. This study aimed to assess the effect of different long-term fertilization treatments on LLWR in the surface layer of a Vertisol. Soil samples were taken from six long-term fertilization treatments including no fertilization (Control), inorganic fertilization (NPK), inorganic fertilization plus low amount of straw (NPKLS), inorganic fertilization plus high amount of straw (NPKHS), inorganic fertilization plus pig manure (NPKPM) and inorganic fertilization plus cow manure (NPKCM) for measuring LLWR. Results showed that in comparison with the Control, the manure treatments (NPKPM and NPKCM) increased soil organic carbon content (SOC) more pronounced than the straw treatments (NPKLS and NPKHS). However, the water stable aggregates (WSA0.25) in the manure treatments was much smaller than the straw treatments. Soil water content at field capacity (θFC) was significantly higher in the manure treatments (NPKPM and NPKCM) than the other treatments. However, soil water content at soil penetration resistance of 3 MPa (θPR) was significantly lower in the straw treatments than in the manure treatments. The LLWR in the manure treatments had sharper decline with bulk density than the other treatments. In comparison with the Control and NPK treatments, the straw treatments significantly increased the LLWR, but manure treatments did not, probably resulting from positive relation between SOC and penetration resistance at a given soil water content and less favorable effect of the manures on soil aggregation than the straw. The S index was significantly increased by the NPKCM treatment relative to the Control, and positively correlated with the SOC. The variation of WSA0.25 instead of SOC could explain the change of LLWR under different fertilization treatments effectively. These observations imply that the LLWR could assess the effect of organic fertilizations on soil physical quality more comprehensively.

Evaluation of tillage effect on maize production using a modified least limiting water range approach

AbstractThe objective of this research was to identify the mechanism of how tillage methods affect maize (Zea mays L.) production using a modified least limiting water range (LLWR) method. The LLWR is the range of soil water content within which the water and O2 are sufficiently supplied, the root growth is not restricted by penetration resistance, the root is fully contacted with the soil, and the crop is steadily hold by the soil. A 5‐yr field experiment was conducted with five treatments: no tillage, rotary tillage, conventional plow, subsoiling, and soil compaction after rotary tillage. Soil bulk density, water content, and penetration resistance were monitored annually. The soil water retention curve and penetration resistance curve were measured to determine the LLWR. Excessive soil looseness was included in the determination of the LLWR. The maize yield would be high and stable when the tillage treatment was under an optimal bulk density range with the highest LLWR. At this experimental site, the maize yield was high and stable with the relative yield of 98.3–100% when the bulk density was within 1.43–1.51 g cm–3 and the LLWR reached 0.07 g g–1 in the tillage treatments. The yield fluctuated with the relative yield of 86.3–100% when the LLWR was less than 0.035 g g–1 and the bulk density was not in the optimal range. The optimal bulk density range with high LLWR was a useful parameter for the evaluation of tillage methods.

Computational intelligence applied to the least limiting water range to estimate soil water content using GIS and geostatistical approaches in alluvial lands*

AbstractThe use of machine learning methods in pedotransfer functions has attracted considerable attention in recent years. These methods are fast and effective in solving complex events. The least limiting water range (LLWR) feature is very important in terms of water uptake by the plant and root development in agricultural production. In this study, the predictability of the LLWR feature was investigated with artificial neural networks, deep learning (DL) and the k‐nearest neighbour (k‐NN) algorithm from machine learning methods. Estimated values obtained from the model with the best estimation accuracy and observed values were evaluated through a geostatistical method from which their spatial distribution maps were created. In the present study, which was carried out on alluvial lands with different soil properties, the LLWR values of soils vary between 5.5% and 25.9%. Field capacity, bulk density, clay, organic matter, and lime content properties, which have a high correlation with the LLWR, were taken into consideration in the estimation methods. DL was determined as the best estimation method (mean absolute error [MAE]: 0.94%; root mean square error [RMSE]: 1.45%; coefficient of determination [R2]: 0.93), and the worst was k‐NN (MAE: 2.00%; RMSE: 2.55%; R2: 0.77) for the LLWR. In addition, the LLWR can be estimated with high accuracy by using ReLU and softmax functions in the DL method. The study shows that distribution maps created with LLWR values obtained by observed data and the DL method have a very similar pattern.

Corn seedling root growth response to soil physical quality

AbstractPlant available water content or matric potential, particle size (texture), aeration, and penetration resistance are soil physical properties that influence soil structure, bulk density, aggregation, and several metabolic plant processes. Collectively they influence productivity and sustainability of agricultural practices, primarily through their impact on root development and growth. To simplify use of these parameters for assessing soil physical condition, the least limiting water range (LLWR) was developed as an integrated, comprehensive soil physical quality indicator. Our objective was to use the LLWR to evaluate corn (Zea mays L.) seedling root growth in soils with clay, sandy clay loam, or sand texture. Overall, root growth was affected by soil water content, aeration, and penetration resistance. Upper and lower LLWR boundaries were defined by a minimum air‐filled porosity and maximum soil penetration resistance for water contents between field capacity and permanent wilting point. Herein, the LLWR was calculated using a range of minimum air‐filled porosity (0.117–0.146 m3 m−3), field capacity (–2.2 to –5.3 kPa), and permanent wilting point or matric potential values (–461 to –6,516 kPa), and a restrictive penetration resistance value of 1.6 MPa as boundaries. The LLWR was sensitive to soil texture, decreasing from fine to coarse soils. The highest and lowest relative root growth measurements fell inside and outside the LLWR boundaries, proving that this index can successfully predict the optimum soil physical conditions for seedlings root growth and can therefore be used as a sensitive soil physical quality.

Land-use change affects soil hydro-physical properties in Mollisols of semiarid Central Argentina

The objective of the present study was to describe the relationships between soil physical properties and to identify variables that determine the pore system and hydrological functions which are specifically important in drought prone semiarid marginal croplands. We compared Mollisols under natural vegetation (NV) with their agriculture (AG) pairs in the central Argentinean Dry Pampas to obtain the range of values for variables that characterize the soil pore system. These were total carbon (OC), bulk density (BD), structural instability index (SII), volumetric weight of aggregates (VAW), total porosity (TP), macropores (Ma), saturated hydraulic conductivity (K), infiltration rate (IR), Dexter's S index (S), and least limiting water range (LLWR). To a depth of more than 23 cm, TP and Ma were considerably lower (~ 35% and 50% less, respectively) in AG versus NV. The changes in porosity and pore size resulted in 74% smaller IR and 65% lower K. The S index had mean values of 0.16 and 0.14 for the upper and middle layer respectively in NV; while for AG, these values were significantly lower (0.09 and 0.10, respectively). The LLWR was also lower in AG (21 and 59% less in the upper and middle layer, respectively), due to high soil resistance even at non-limiting BDs (1.17 and 1.32 g cm−3 for AG2 and AG1, respectively). Soil OC was positively correlated with TP, Ma, and S, and negatively correlated with BD and SII. Multiple regression models for S included SII, TP, and clay contents, while for LLWR the variables were OC, TP, and clay plus silt. Thus, these complex soil quality indices can be predicted by using simpler physical parameters, but texture and organic matter also have a strong effect on them. Moreover, our results contribute to a better understanding of the role of texture and organic matter in controlling soil physical quality and for maintaining soil-based ecosystem services.

Evaluation of Intelligence Models to Estimate the Least Limiting Water Range Using Conveniently Measurable Soil Properties

Direct measurement of the least limiting water range (LLWR) is costly and time-consuming. In this study, genetic algorithm-based neural network (ANN-GA), artificial neural network (ANN) and stepwise multivariate regression (SMR) were used to estimate the LLWR of soil using easily measurable soil properties in the Khanmirza Plain. Then, depending on the location of each area, a total of 250 points were randomly identified as approximate sampling sites. Results showed that the accuracy of the SMR model with the percentage of clay, organic carbon and fine sand had a coefficient of determination of 0.42. The ANN-GA and ANN models with the highest coefficient of determination (R2 = 0.98) and mean square error (MAE = 0.0538) were suitable for estimating the least limiting water range. Therefore, the efficiency of models showed that the ANN and ANN-GA predicted the LLWR more accurate compared to the SMR and their results were close to the measured ones.

Evaluating soil physical quality indicators of a Vertisol as affected by different tillage practices under wheat-maize system in the North China Plain

Soil physical quality (SPQ) is an important parameter for crop growth. Tillage management is widely recognized to affect SPQ remarkably, but such an effect is complicated in Vertisols by shrinking and swelling soil structure. The objectives of this study were to (i) investigate how tillage practices affected SPQ as indicated by the S index, least limiting water range (LLWR) and water stress percentage (WSP); and (ii) determine the relationship between these SPQ indicators and crop yield. A 4-year field experiment, which was conducted in a Vertisol under wheat-maize rotation system in the North China Plain, consisted of four tillage treatments: no tillage (NT), rotary tillage (RT), subsoiling (SS), and deep ploughing (DP). Soil water retention curve (SWRC), soil shrinkage curve (SSC), penetration resistance (PR), and bulk density (BD) of the 0−10 and 10−20 cm layer were measured during wheat and maize seasons, and soil water content was continuously monitored in situ. The S index, LLWR and WSP were determined. Our results showed that SSCs were parallel to each other among four tillage treatments, indicating that tillage did not impact shrinkage capacity (P > 0.05). Relative to NT and RT treatments, the SS and DP treatments improved soil physical quality (higher S index and larger LLWR), particularly in the 10−20 cm layer. The S index presented a poor relation with wheat (P > 0.05) and maize yields (P > 0.05), while LLWR had a significant correlation with wheat yield (P < 0.05) but not with maize yield (P > 0.05). A new proposed SPQ indicator, WSP, is defined as the percentage of the period when the soil water content is above the field water capacity (waterlogging stress percentage, WLP) or below the wilting point (drought stress percentage, DSP) to the entire crop season period. The WLP presented a significantly negative relation with maize yield (P < 0.01) but not with wheat yield (P > 0.05), whereas the DSP had no relation with wheat and maize yield (P > 0.05). Moreover, the WSP was observed to be independent of the volume change in the Vertisol. Our results demonstrate that LLWR and WLP can be regarded as suitable indicators for evaluating SPQ in wheat and maize seasons, respectively, but the latter is more conveniently applied in a Vertisol.

Effects of long-term tillage systems on soil physical quality and crop yield in a Brazilian Ferralsol

Long-term soil tillage trials can provide important knowledge about sustainable changes in soil physical quality and crop yield. This study evaluated soil physical quality indicators under different long-term tillage systems and examined the relationships between quality indicators and crop yield. The study was carried out on a Rhodic Ferralsol with three tillage systems established in 1989: conventional tillage (CT), strategic tillage (ST), and no-tillage (NT). All treatments had long-term crop rotation. The soil parameters evaluated were total organic carbon (TOC), bulk density (ρs), macro and microporosity (Mac and Mic), relative gas diffusivity (D/D0), pore tortuosity (τ), relative field capacity (RFC), structural stability index (SSI), least-limiting water range (LLWR), and degree of compactness (DC, taking as reference the soil bulk density in which LLWR = 0). Soybean and maize yields in two consecutive summer seasons were measured. Conventional and strategic tillage provided higher ρs in the 0.15–0.30 m layer depth, leading to higher DC in CT. Using soil bulk density at LLWR = 0 as reference proved useful to assess soil DC and plant response. No-tillage provided lower DC in the 0–0.15 m (86 %) and 0.15–0.30 m (78 %) layers than CT (91 % and 94 %, respectively). The maize yield had a negative linear relationship to DC, with the lower values at DC > 87 %. All tillage systems affected D/D0, even at similar porosity values. The better soil physical quality under NT provided 1211 kg ha−1 higher maize yield compared with CT. The differences in soybean yield between treatments were not significant, but NT provided 381 kg ha−1 more than CT. These findings indicate that NT is the best system studied. Our results strongly suggest that ST does not improve physical properties of soils under NT with crop rotation, and that a diversified crop rotation in NT was efficient to avoid soil physical degradation.

Limiting water range: Crop responses related to in‐season soil water dynamics, weather conditions, and subsoil compaction

AbstractThe least limiting water range (LLWR) has been used as a soil structural quality indicator for identifying in‐season water dynamics, yet studies focusing on its use for detecting in‐season water stresses and their effect on crop response on severely compacted subsoils are scarce. The objectives of this study were, therefore, to examine the in‐season water dynamics on a tile‐drained soil with compacted subsoil in the light of two different approaches for calculating LLWR (standard LLWR by da Silva et al. [1994] and refined LLWR by Pulido‐Moncada &amp; Munkholm [2019]) and to evaluate the crop response to aboveground and belowground conditions. Information on LLWRs was obtained from soil sampling in the most contrasting treatments of a compaction experiment: with and without compaction. In‐season water dynamics were measured from 2017 to 2019. The refined LLWR approach defined a wider range of water content nonlimiting for plant growth compared with the da Silva et al. approach. Compaction affected the LLWRs (p &lt; .05), yet no significant effect of subsoil compaction on crop yield was found. Cumulative aeration and water stress day indicators identified from the refined LLWR were significantly related to grain yield (p &lt; .05). The lower winter wheat yield in 2018 compared with 2019 seemed to be related to the direct impact of weather factors on aboveground growth and to aeration and water stresses. The apparent lack of compaction effect suggests further studies are needed to determine if in‐season stresses derived from the LLWRs can be related to crop development and yield under different soil and weather conditions.

Are the yield of sunflower and Paiaguas palisadegrass biomass influenced by soil physical quality?

Soil compaction affects physical soil properties, which in turn influence crop growth, development and yield. The present study tested the hypothesis that the yield of sunflower achenes and Paiaguas palisadegrass biomass are influenced by soil physical properties. The effects of compaction were measured by the least limiting water range (LLWR), and its relationship with crop yield were studied. The experiment was conducted in the Rio Verde municipality, south-western Goias State, Brazil, on a Latossolo Vermelho Acriférrico típico (Typic Haplustox) soil and in accordance with a randomized complete block design, in which the treatments consisted of compaction levels established by zero, two, 10, and 30 passes of an agricultural tractor (with four replicates each). In the subplots, sunflower and Paiaguas palisadegrass were grown as monocropping and intercropping systems. The following indicators of soil physical quality were determined: bulk density (Bd), the LLWR, the Bd/alert bulk density of the LLWR (Bdalert) ratio, and the Bd/critical bulk density of the LLWR (Bdc) ratio. The correlations of these indicators with crop yield were calculated to define critical resistance values specific to each crop. The LLWR adequately described the physical quality of the soil resulting from compaction and was significantly correlated with crop yield. The relationship between sunflower and Paiaguas palisadegrass yield was modelled by a second-order equation featuring Bd and the Bd/Bdalert ratio (R2 = 0.77, ** and 0.74 **, respectively), with the greatest yield recorded when the Bd/Bdalert ratio was 1.0. Sunflower cultivation was extremely sensitive to soil compaction: when sunflower was grown as a monoculture or intercropped with palisadegrass, its yield decreased by 50 % or 80 %, respectively. However, the Paiaguas palisadegrass yield was influenced little by soil compaction. The limiting penetration resistance values for sunflower and Paiaguas palisadegrass were 1.5 MPa and 4.2 MPa, respectively.

Influence of corn residue biochar on water retention and penetration resistance in a calcareous sandy loam soil

Biochar can be potentially used as an amendment to beneficially enhance the physicochemical qualities of agricultural soils. In this study the effects of corn (Zea mays L. cv. Maxima) residue and its biochar on the soil–water characteristic curve (SWCC), the soil penetration resistance curve (SPRC, penetration resistance versus matric suction), plant available water (PAW) content, least limiting water range (LLWR) and integral water capacity (IWC) were examined in greenhouse experiments. Indices of soil physical quality and hard-setting (soil compaction during the drying processes) behavior were also measured. Pots (5 kg) were filled with a calcareous sandy loam mixed with raw corn residue or its biochars at rates of 1, 2, and 4 percent (w/w). Low and high temperature biochars, produced by slow pyrolysis process at 350 and 650 °C were evaluated. Both biochar amendments significantly ameliorated soil physical properties such as bulk density, total porosity, water retention and penetration resistance (Q) compared to the un-amended soil. Pore size distribution was significantly altered in favor of a greater fraction of wider pores (i.e. macro and mesoporosity) in the biochar amended soils. The lowest Q value was observed for the unmodified corn residue at a 4% application rate (CR 4%) in all of the matric suctions. The increase in Q with drying was attributed to Q’s strong relationship with the effective stress which originated from the matric suction. The hard-setting indices inferred from the SWCC and SPRC and shown by the slope of power model b (0.709), ΔQ (3.31 MPa), ΔQ/Q3000 (1.98), hard-setting index related to structural pores, H1 (789 hPa) and hard-setting index proposed by Dexter (2004b), HDexter (1163 hPa), were more pronounced in the untreated compared to the treated soils. Overall the changes in soil available water (SAW) for plants following biochar application was compared using three different indices, PAW, LLWR and IWC. Applying biochar could increase soil water availability such that PAW increased from 0.100 in the control to 0.156 cm3 cm−3 in BC-650 4%, LLWR100 increased from 0.079 in CR1% to 0.122% cm3 cm−3 in BC-350 2% and IWC increased from 0.072 in the control to 0.166 cm3 cm−3 in CR4%. The positive correlations between PAW, LLWR and IWC with soil physical quality indices like S1 and S2 (slopes of SWCC at first and second inflection points, related to structural and matrix pores, respectively) indicated these quantities were a potentially useful tool for evaluating soil physical quality.