Increased Plant Available Water Research Articles

Widespread greening suggests increased dry-season plant water availability in the Rio Santa valley, Peruvian Andes

Abstract. In the semi-arid Peruvian Andes, the growing season is mostly determined by the timing of the onset and retreat of the wet season, to which annual crop yields are highly sensitive. Recently, local farmers in the Rio Santa basin (RSB) reported more erratic rainy season onsets and further challenges related to changes in rainfall characteristics. Previous studies based on local rain gauges, however, did not find any significant long-term rainfall changes, potentially linked to the scarce data basis and inherent difficulties in capturing the highly variable rainfall distribution typical for complex mountain terrain. To date, there remains considerable uncertainty in the RSB regarding changes in plant-available water over the last decades. In this study, we exploit satellite-derived information of high-resolution vegetation greenness as an integrated proxy to derive variability and trends of plant water availability. By combining MODIS Aqua and Terra vegetation indices (VIs), datasets of precipitation (both for 2000–2020) and soil moisture (since 2015), we explore recent spatio-temporal changes in the vegetation growing season. We find the Normalized Difference Vegetation Index (NDVI) to be coupled to soil moisture on a sub-seasonal basis, while NDVI and rainfall only coincide on interannual timescales. Over 20 years, we find significant greening in the RSB, particularly pronounced during the dry season (austral winter), indicating an overall increase in plant-available water over the past 2 decades. The start of the growing season (SOS) exhibits high interannual variability of up to 2 months compared to the end of the growing season (EOS), which varies by up to 1 month, therefore dominating the variability of the growing season length (LOS). The EOS becomes significantly delayed over the analysis period, matching the observed dry-season greening. While both in situ and gridded rainfall datasets show incoherent changes in annual rainfall for the region, Climate Hazards InfraRed Precipitation with Station data (CHIRPS) rainfall suggests significant positive dry-season trends for 2 months coinciding with the most pronounced greening. As the greening signal is strongly seasonal and reaches high altitudes on unglaciated valley slopes, we cannot link this signal to water storage changes on timescales beyond one rainy season, making interannual rainfall variability the most likely driver. Exploring El Niño–Southern Oscillation (ENSO) control on greening, we find an overall increased LOS linked to an earlier SOS in El Niño years, which however cannot explain the observed greening and delayed EOS. While our study could not corroborate anecdotal evidence of recent changes, we confirm that the SOS is highly variable and conclude that rainfed farming in the RSB would profit from future efforts being directed towards improving medium-range forecasts of the rainy season onset.

Thermal Desorption Temperature Affects Water Retention and Hydraulic Conductivity of Three Contrasting Soils

ABSTRACT Thermal desorption is an effective approach to removing petroleum hydrocarbons from soil. However, the resultant environmental function and revegetation potential of the soil can be reduced by high temperatures. This study evaluated the effect of nine temperatures of heating (60–800°C) on water retention and hydraulic conductivity in three soils of contrasting mineral and physical properties. Fredlund-Xing water release curves were developed using the HYPROP system. Features of the release curves were compared for differences: the water content (%Vol) at which air first enters the macropore volume (AEV), the slope of the rapid desorption portion of the curve, field capacity, and the residual water content. A Hearne sandy loam showed an increase in the %Vol at saturation (0.354 to 0.557 cm3 H2O cm−3 soil), but a decrease in plant available water with increasing temperature. A Rader sand showed a decrease in field capacity and plant available water. A Weswood clay showed no change in field capacity, but an increase in plant available water 10.87 to 18.39 cm3 H2O cm−3 soil through 700°C. Saturated hydraulic conductivity (Ksat) increased for both the Hearne and the Weswood soils with increasing temperature. However, the Rader soil Ksat saw an increase from 0.002 to 0.007 cm s−1 to 450°C but declined to <0.0005 cm s−1 between 500°C and 800°C. This study shows the release curve comparison approach can be effective to quantify changes or differences in soil water relationships by treatment or soil property. Additional insight is provided by electron microscope imaging.

Effect of biochar and biochar particle size on plant-available water of sand, silt loam, and clay soil

Biochar is being used as a soil amendment to improve soil hydraulic properties. It has been reported that biochar increases plant-available water, particularly in coarse-textured soils; however, effects on fine-textured soils are less pronounced. Here, we quantified the effects of biochar particle size on plant-available water in sand, silt loam, and clay soils. We amended these soils with a hydrophilic biochar, and packed soil-biochar mixtures into columns of 5.35-cm diameter and 3.0-cm height. Biochar was produced by gasification of woody forest residues. We applied the biochar at two different rates (0.5% and 2% by weight of C) and with four different biochar particle-size fractions (<4.75, <2.0, <1.0 and <0.5 mm). Our results show that biochar amendments increased the plant-available water (when expressed gravimetrically) of all three soils, particularly at the highest biochar application rate. Although the absolute increase in plant-available water was largest for the silt loam soil, the relative increase of plant-available water was greater for the sand than for the silt loam and clay. When expressed in volumetric terms, however, the effects on water retention were less pronounced: the sand showed a small increase in plant-available water with biochar amendment, and no change was observed with the silt loam and clay. Particle size of biochar had little effect on plant-available water (when expressed in gravimetric terms) in the three soils, but silt loam and clay showed increased plant-available water (when expressed in volumetric terms) with decreasing biochar particle size, while no effect was observed for the sand. While our findings corroborate many of the previously reported effects of biochar on soil-water retention, we show that the effects and their magnitude depend on whether the results are reported in terms of gravimetric or volumetric water contents. Because bulk density tends to decrease with increasing biochar application, so will the volumetric water content, and thus the magnitude of the effect on plant-available water will be smaller when expressed in volumetric water content.

Soil Nutrient Status and Cowpea Biological Nitrogen Fixation in a Maize-Cowpea Rotation Under Conservation Farming

This paper reports the impacts of a four-year maize-cowpea rotation under conservation farming on selected soil chemical, physical and biological properties with or without 100 kg/ha of Nitrogen: Phosphorus: Potassium: Sulphur (10:20:10:65) compound fertilizer. The study took advantage of an already established 4-year maize-cowpea rotation site and a maize monocrop field from which soil samples were collected for selected chemical, physical and biological analyses, and for setting up a greenhouse experiment for the determination of biological nitrogen fixation capabilities of cowpea. The results suggest that maize-cowpea rotations and addition of fertilizer influence particular chemical, physical and biological attributes of the soil in a varied manner. Rotating maize and cowpea has no influence on soil reaction, soil organic carbon, micronutrients, and exchangeable bases except for potassium. However, the addition of fertilizer to the maize-cowpea rotation reduces total nitrogen, while increasing the levels of sulphur and phosphorus in both the rotation and maize monocrop. Soil bulk density, total porosity and infiltration rate are not influenced by the maize-cowpea rotation with or without fertilizer amendment. Rotating maize with cowpea without the addition of fertilizer can result in an increase in plant available water, an observation needing further study. It can also be concluded that maize-cowpea rotations can reduce microbial biomass, regardless of fertilizer amendment, thus suggesting a need to understand maize and cowpea rhizopheric attributes affecting microbial biomass levels. Under the current conditions, the amount of biologically fixed nitrogen by cowpea is reduced by the application of fertilizer but not influenced by the rotation. Since these findings are based on four-year crop rotation, it is being recommended that further work be conducted to continue monitoring soil so as to factor in the effect of length of time.

How good is the evidence that soil‐applied biochar improves water‐holding capacity?

AbstractBiochar application to soil is suggested as a way of enhancing soil fertility by increasing the availability of nutrients and water. The former is perhaps better documented while the latter has less experimental support. This review critically investigates the recent literature which focuses on determining whether biochar induces increases in plant available water and that this provides part of the explanation for possible increases in crop yield. A number of studies suggest that biochar increases crop yields, and this is linked to the enhancement of soil water content and increased crop growth. However, many of these studies fail to fully consider if the measured biochar increases of 10–30% in soil water content were actually responsible for an increase in plant available water for crop growth. There is also limited evidence of increased crop yields when biochar is used in field experiments. While biochar soil application may increase soil water content, this appears to most likely occur with free draining coarsely textured sandy soils. As yet there is limited evidence that biochar improves soil water content in temperate soils and even less that it facilitates plant tolerance to drought stress. More recent literature shows the use of methods which quantify soil biochar changes with respect to plant water availability. However, despite some advances in our understanding of biochar's mode of action, there are still only a few studies which link increases in plant available water with increased crop yields, and particularly with respect to the longer term use and functionality of soil‐applied biochar.

Exploring the Relationships between Greenhouse Gas Emissions, Yields, and Soil Properties in Cropping Systems

Relationships between greenhouse gas emissions, yields, and soil properties are not well known. Utilizing two datasets from long-term cropping systems in Illinois, USA, our we aim to address these knowledge gaps. The objective of this study was to explore the relationships between the physical and chemical properties and greenhouse gas (GHG) emissions of soil, and cash crop yields over a four-year time-period and following 15 years of treatment implementation in Illinois, USA. The experimental layout was a split-plot arrangement involving rotation and tillage treatments in a randomized complete block design with four replications. The studied crop rotations were continuous corn [Zea mays L.] (CCC), corn-soybean [Glycine max (L.) Merr.] (CS), continuous soybean (SSS), and corn-soybean-wheat [Triticum aestivum L.] (CSW), with each phase being present for every year. The tillage options were chisel tillage (T) and no-tillage (NT). We used an array of multivariate approaches to analyze both of our datasets that included 31 soil properties, GHG emissions (N2O, CO2, and CH4) and cash crop yields. The results from our analyses indicate that N2O emissions are associated with a low soil pH, an increased Al concentration, the presence of soil nitrate throughout the growing season, an increase in plant available water (PAW) and an increased soil C concentration. Likewise, soil CO2 respiration was correlated with low pH, elevated Al concentrations, low Ca, increased PAW, higher levels of microbial biomass carbon (MBC), and lower water aggregate stability (WAS). Emissions of CH4 were associated with increased levels of MBC. Lastly, the yield index (YdI) was correlated with lower levels of soil Ca and available P and lower values of WAS. The association between high YdI and lower WAS can be attributed to tillage, as tillage lowers WAS, but increases yields in highly productive cropping systems in the Midwest.

The Different Expressions of Draft Cherry Tomato Growth, Yield, Quality under Bamboo and Rice Husk Biochars Application to Clay Loamy Soil

This study evaluated the different expressions of cherry tomato growth, yield and quality under bamboo and rice husk biochar applications to soil. The experiment was conducted under glasshouse conditions at Hakozaki campus, Kyushu University, Japan and consisted of 5 treatments, namely 1) no biochar application as a control; 2) 2% (RH2) and 3) 5% (RH5) of rice husk biochar; 4) 2% (BB2) and 5) 5% (BB5) of bamboo biochar. Bamboo biochar application significantly improved tomato growth, including number of leaves, fresh biomass yield of aboveground and underground parts for BB5; number of fruit; fresh yield from 24% - 25% for BB2 and BB5. In particular, both bamboo and rice husk biochar application at two rates 2% and 5% had positive effects on tomato quality, demonstrated by the increased total sugar content from 56% to 91%, and the enhancement of ascorbic acid content for BB2 and RH2 by 12% and 17%, respectively. Those improvements reflected the soil physiochemical property changes after biochar application, including the increase in plant available water for bamboo biochar amendment before and after cultivating by 25% - 38% and 9% - 18%, respectively, compared with those of control; and the increased total soil N for bamboo biochar treatments (11% - 14%). Generally, all data above support bamboo biochar utilization for the purpose of improving soil properties and developing crop production.

Sensitivity of soil water retention and availability to biochar addition in rainfed semi-arid farmland during a three-year field experiment

Aridity and water stress limit the productivity of rainfed dryland agriculture, and one possible solution to this problem is the application of biochar, a highly porous, pyrolysed biomass material that has been well documented to improve soil quality. The objectives of this study are to investigate whether straw-biochar can be beneficial for improving soil hydraulic properties, explore how biochar affects the temporal and spatial distributions of soil moisture, and ultimately determine whether biochar impacts soil water availability. A 3-year field experiment was conducted on the semi-arid Loess Plateau in northern China, and biochar derived from maize-straw feedstock was applied to a spring maize monoculture cropping system at rates of 0, 10, 20 and 30tha−1. The results of two sampling campaigns of undisturbed soil indicated that the incorporation of biochar reduced the soil bulk density and increased the total pore volume at depths of 0–10 and 10–20cm. In addition, a significant negative linear correlation was observed between the rate of biochar addition and the soil bulk density. The incorporation of biochar into the soil not only increased the soil permeability (higher saturated hydraulic conductivity) but also improved the water retention capacity of the mixed soil (higher saturation, readily available and estimated available water contents), particularly when biochar was added at 30tha−1. The soil water contents following rainfall in the biochar-amended plots were consistently greater than the soil water contents in the control (BC0) throughout the entire 5-day monitoring period, and both irregular precipitation and crop water utilization resulted in temporal and spatial variations in soil water contents throughout the crop growing seasons. Biochar-amended soils were more sensitive to rainfall variations, and the variations in water across the soil profile mainly occurred at depths of 0–40cm. Compared with the control, the soil permeability was obviously enhanced by the addition of 30tbiocharha−1, which resulted in water infiltration at a depth of 0–60cm. Biochar application increased the crop yields and water use efficiency (WUE). The average yields during the 3 studied years were 10.2% and 14.2% higher in BC20 and BC30, respectively, than in the control, and the average WUEs were 9.4% and 12.3% higher in BC20 and BC30 than in the control, respectively. These results indicate that biochar amendment could improve the physical and hydraulic status of semi-arid agricultural soils, thereby leading to an increase in plant available water.

Biochar increases plant-available water in a sandy loam soil under an aerobic rice crop system

Abstract. The main objective of this study was to assess the impact of biochar rate (0, 8, 16 and 32 Mg ha−1) on the water retention capacity (WRC) of a sandy loam Dystric Plinthosol. The applied biochar was a by-product of slow pyrolysis (∼450 °C) of eucalyptus wood, milled to pass through a 2000 μm sieve that resulted in a material with an intrinsic porosity ≤10 μm and a specific surface area of ∼3.2 m2 g−1. The biochar was incorporated into the top 15 cm of the soil under an aerobic rice system. Our study focused on both the effects on WRC and rice yields 2 and 3 years after its application. Undisturbed soil samples were collected from 16 plots in two soil layers (5–10 and 15–20 cm). Soil water retention curves were modelled using a nonlinear mixed model which appropriately accounts for uncertainties inherent of spatial variability and repeated measurements taken within a specific soil sample. We found an increase in plant-available water in the upper soil layer proportional to the rate of biochar, with about 0.8% for each Mg ha−1 biochar amendment 2 and 3 years after its application. The impact of biochar on soil WRC was most likely related to an effect in overall porosity of the sandy loam soil, which was evident from an increase in saturated soil moisture and macro porosity with 0.5 and 1.6% for each Mg ha−1 of biochar applied, respectively. The increment in soil WRC did not translate into an increase in rice yield, essentially because in both seasons the amount of rainfall during the critical period for rice production exceeded 650 mm. The use of biochar as a soil amendment can be a worthy strategy to guarantee yield stability under short-term water-limited conditions. Our findings raise the importance of assessing the feasibility of very high application rates of biochar and the inclusion of a detailed analysis of its physical and chemical properties as part of future investigations.

Impact of roots, mycorrhizas and earthworms on soil physical properties as assessed by shrinkage analysis

Summary Soil biota such as earthworms, arbuscular mycorrhizal fungi (AMF) and plant roots are known to play a major role in engineering the belowground part of the terrestrial ecosystems, thus strongly influencing the water budget and quality on earth. However, the effect of soil organisms and their interactions on the numerous soil physical properties to be considered are still poorly understood. Shrinkage analysis allows quantifying a large spectrum of soil properties in a single experiment, with small standard errors. The objectives of the present study were, therefore, to assess the ability of the method to quantify changes in soil properties as induced by single or combined effects of leek roots ( Allium porrum ), AMF ( Glomus intraradices ) and earthworms ( Allolobophora chlorotica ). The study was performed on homogenised soil microcosms and the experiments lasted 35 weeks. The volume of the root network and the external fungal hyphae was measured at the end, and undisturbed soil cores were collected. Shrinkage analysis allowed calculating the changes in soil hydro-structural stability, soil plasma and structural pore volumes, soil bulk density and plant available water, and structural pore size distributions. Data analysis revealed different impacts of the experimented soil biota on the soil physical properties. At any water content, the presence of A. chlorotica resulted in a decrease of the specific bulk volume and the hydro-structural stability around 25%, and in a significant increase in the bulk soil density. These changes went with a decrease of the structural pore volumes at any pore size, a disappearing of the thinnest structural pores, a decrease in plant available water, and a hardening of the plasma. On the contrary, leek roots decreased the bulk soil density up to 1.23 g cm −3 despite an initial bulk density of 1.15 g cm −3 . This increase in volume was accompanied with a enhanced hydro-structural stability, a larger structural pore volume at any pore size, smaller structural pore radii and an increase in plant available water. Interestingly, a synergistic effect of leek roots and AMF in the absence of the earthworms was highlighted, and this synergistic effect was not observed in presence of earthworms. The structural pore volume generated by root and AMF growth was several orders of magnitude larger than the volume of the organisms. Root exudates as well as other AMF secretion have served as carbon source for bacteria that in turn would enhance soil aggregation and porosity, thus supporting the idea of a self-organization of the soil–plant–microbe complex previously described.

Amelioration of dense sodic subsoil using organic amendments increases wheat yield more than using gypsum in a high rainfall zone of southern Australia

Subsoil constraints are major limiting factors in crop production in many soils of southern Australia. A field study examined effects of deep incorporation of organic and inorganic amendments in 30–40 cm on soil properties, plant growth and grain yield of wheat ( Triticum aestivum var. Ambrook) on a Sodosol with dense sodic subsoil with or without lucerne history in a high rainfall region (long-term average annual rainfall 576 mm) of Victoria. Amendments were applied at a rate of 10–20 t ha −1. Deep ripping alone and deep ripping with gypsum did not significantly affect grain yields. In comparison, application of organic materials doubled biomass production and increased grain yield by 1.7 times. Organic amendment-treated plots produced 60% more grains per area than the untreated control. The crop extracted over 50 mm extra water from below 40 cm soil in organic amendment-treated plots than the untreated control. Nitrogen uptake was almost doubled (403 kg ha −1) in the organic amendment-treated plots than the untreated control (165 kg ha −1). The improved yield with amendments was related to an increase in plant available water in the hostile subsoil, and prolonged greenness of leaves and supply of nitrogen and other nutrients.