Average Volumetric Water Content Research Articles

Effects of drip irrigation coupled with controlled release potassium fertilizer on maize growth and soil properties

Drip irrigation and the application of controlled-release fertilizers are two effective and important technical measures to conserve water and fertilizer resources and promote the growth and development of maize. However, the underlying physiological mechanism of how drip irrigation combined with controlled release potassium chloride affects maize production and soil properties remains unknown. In different soil water conditions, pot experiments were conducted during the summer maize growing season in 2022 and 2023 to measure maize grain yield, irrigation water productivity, apparent recovery efficiency of potassium, plant physiological characteristics, and soil enzyme activities under the coupling of two irrigation methods (flood irrigation and drip irrigation) and three potassium fertilizer types (potassium chloride (KCl), controlled release potassium chloride (CRK), and 70% CRK mixed with 30% KCl). The results revealed that drip irrigation had 6.5-8.1% and 6.7-9.4% higher average soil volumetric water content and 3.8-8.1% and 4.5-13.0% higher irrigation water productivity than flood irrigation in the two maize growth seasons, respectively. Under the drought conditions, the treatments of 70% CRK-30% KCl application led to a significant increase in maize yield by 9.5-10.7% and 12.2-16.8% and apparent recovery efficiency of potassium by 8.3-14.2% and 10.7-10.8% compared to CRK application treatments in 2022 and 2023, respectively. Compared with the other treatments, the treatment of drip irrigation coupled with 70% CRK-30% KCl application under drought conditions (DIDMK) resulted in 4.5-28.7% and 1.1-31.9% higher grain yield, 8.2-64.4% and 8.6-66.8% higher irrigation water productivity, and 5.9-28.0% and 6.7-18.9% higher apparent recovery efficiency of potassium in 2022 and 2023, respectively. Meanwhile, the leaf net photosynthetic rate, rubisco, catalase, peroxidase, and soil enzyme activities of DIDMK treatment were also maintained at a high level. Our results indicated that drip irrigation coupled with 70% CRK-30% KCl application were the optimal water and potassium supply modes for maize production. This study can provide useful information regarding summer maize sustainable production and provide theoretical and technical support for summer maize irrigation and potassium fertilizer application technologies in water-scarce regions of China and other similar regions around the world.

Effects of gravel-sand and plastic film mulching on soil water and temperature retention in cold and arid regions without irrigation

Gravel-sand mulch (GSM) and plastic film mulch (PFM) are important ways of farming in cold and arid regions without irrigation. Nevertheless, there has been a lack of studies of the system response to live weather conditions. To quantify the effects of GSM and PFM on soil moisture and temperature retention, in-situ monitoring experiments were carried out in the arid belt of central Ningxia, China, using continuous monitoring of the field soil water and meteorological conditions at a 30-mimute time-step under three treatments: a bare soil (CK), soil covered by a layer of GSM, and soil covered by GSM and a layer of plastic film (i.e., GSM + PFM). Results show that: (1) With a limited precipitation of 221 mm during the growing season, the average volumetric soil water content (SWC) in the top 30-cm soil layer was lowest for CK, medium high for GSM, and highest for GSM + PFM. Compared to CK, the soil water storage increased by 54 % under GSM and 75.2 % under GSM + PFM; (2) The most frequently occurring low-intensity rainfalls are more efficiently stored in soil under GSM + PFM; (3) Similarly, the soil temperature was significantly increased under GSM and GSM + PFM conditions. Compared to CK, the average soil temperature in the top 5-cm layer increased by 2.5 °C under GSM and 4.8 °C under GSM + PFM during the germination period, which had effectively extended the growing season for about 30 and 50 days, respectively; (4) Although dewfall is only 4 % of rainfall, the total number of dew day was more than twice that of rain day. Thus, dewfall is a more frequent and dependable source of water for native plants and animals. Our results demonstrate that the benefits of GSM and PFM can be applied globally where either insufficient rainfall or low temperatures are limiting factors.

Bark and crown morphology drive differences in rainwater distribution in an upland oak forest

Throughout the central and eastern US, the composition and structure of upland oak (Quercus) forests are changing. These changes are in part due to fire exclusion, whereby shade-tolerant, often fire-sensitive tree species are gaining a competitive edge over relatively shade-intolerant, fire-adapted oaks. This shift has been hypothesized to occur via a positive feedback termed mesophication, whereby encroaching tree species (‘mesophytes’) create dense, shaded understory conditions that limit oak regeneration and create cooler and wetter microclimates that decrease forest flammability. The change in canopy composition and structure may also impact hydrologic inputs by redistributing rainfall via throughfall and stemflow. To assess the extent of this redistribution by mesophytes compared to oaks and the net impact to forest floor moisture availability, we monitored throughfall, stemflow, and surface soil moisture at depths of 7.6 cm, 12.0 cm, and 20.0 cm near the bole, mid-crown, and crown edge monthly over a 14-month period. Measurements were made across seasons in both the midstory and overstory canopy strata, including oak (Q. alba, Q. falcata) and non-oak species that are increasing in relative abundance in midstory canopy strata in northern Mississippi (Carya tomentosa, Acer rubrum, Ulmus alata). Non-oak species in the midstory (A. rubrum, U. alata) had smoother bark that led to more than three-times larger stemflow generation and more than two-times larger throughfall generation per basal area compared to oak species. However, there was mixed response to soil moisture, with both non-oak (A. rubrum) and oak (Q. falcata) species having wetter than average volumetric water content compared to all other midstory species. Overstory C. tomentosa generated 2.7-times larger stemflow volume than Q. alba while Q. alba generated the largest throughfall volume. Although overstory A. rubrum generated intermediate volumes of throughfall and stemflow, the cumulative effect led to wetter than average soils compared to all other overstory species. These findings suggest that the hydrologic partitioning by mesophyte crowns may serve as an additional mechanism by which encroaching non-oak species act to reduce forest flammability and promote conditions favorable for their own regeneration. This differential rainwater redistribution mechanism may ultimately compromise long-term oak regeneration and our ability to restore fire to fire-dependent forest ecosystems.

Substrate moisture variations of extensive green roofs with different structural configurations in a semi-arid region: Observational data and dynamic simulation

Substrate moisture condition is crucial for hydrological performance, water management and plant survival of green roofs. To date, the behaviour of long-term substrate moisture of green roofs in various climate regions has not been well understood. In this study, 24 months continuous field monitoring of substrate moisture content within nine extensive green roof modules with varies structural configurations was conducted to investigate the impacts of structural configurations and meteorological factors on substrate moisture content, and identify the key parameters for simulating the long-term substrate moisture dynamics. Results showed that green roofs planted with SedumSpectabilehave the highest mean volumetricwater content (VWC) (0.12–0.15 m3/m3) compared to other plant species considered. Green roofs with 5-cm substrate depth had lower mean VWC (0.07–0.08 m3/m3) than other substrate depths. The average substrate moisture loss rate of green roofs in summer and autumn seasons was 1.35 and 1.22 mm/day, respectively, which was higher than the spring (0.73 mm/day) and winter (0.64 mm/day) seasons for 2021. There were significant differences in mean VWC of green roofs among substrate material types. The mean VWC of green roofs was gradually enhanced from 0.12 to 0.14 m3/m3 as the substrate depth increased from 5 cm to 15 cm. The differences of mean VWC among vegetation types were all extremely significant (p < 0.001). The relative humidity was the most significant influencing factor on the average VWC level (correlation coefficient r = 0.42), with antecedent dry weather period (ADWP) had less significant effects on substrate VWC (r = 0.33), and followed by precipitation depth (r = 0.27). However, there was no significant relationship between air temperature and average VWC level of green roofs as well as total solar radiation. Nash-Sutcliffe efficient (NSE) values of the model simulations ranged from 0.70 to 0.81, and the mean absolute relative error (MAE) values ranged from 1.25 to 2.36, which indicated the model can adequately simulate the long-term substrate moisture content dynamics of green roofs. The crop coefficient and maximum water holding capacity of the substrate were the key parameters affecting long-term moisture content simulation of green roofs. These results could provide scientific suggestions for selecting suitable structural configuration to enhance water holding capacity of extensive green roofs in arid climates.

Interseeded cover crops did not reduce silage corn performance in the sandy loam soils of South Carolina

AbstractA major concern with interseeding summer cover crops alongside cash crops is the possibility of cover crops competing with the main crop for water and nutrients and thus, reducing the main crop yields. We conducted on‐farm trials in the sandy loam soils of the upstate of South Carolina in 2020 and 2021 to evaluate the effect of white clover (Trifolium repens L.), buckwheat (Fagopyrum esculentum Moench), and pigeon pea (Cajanus cajan (L.) Millsp.) and their mixture interseeded at V4, V7, and V10 corn growth stages on silage corn performance and soil moisture content. We found that none of the cover crops affected silage corn height and aboveground biomass production regardless of the interseeding time. Further, the volumetric water content in the upper 20‐cm soil profile was not decreased by cover crops irrespective of their interseeding time. At physiological maturity, corn height, aboveground biomass, and volumetric water content ranged between 131 and 163 cm, 9 and 23 Mg ha−1, and 10% and 22%, respectively, in season‐1 and between 181 and 216 cm, 0.48 and 1.03 Mg ha−1, and 10% and 17%, respectively, in season‐2 when interseeded with cover crops. When cover crops were not interseeded, the average corn height, aboveground biomass, and volumetric water content values were 152 cm, 13 Mg ha−1, and 13%, respectively, in season‐1 and 204 cm, 0.7 Mg ha−1, and 14%, respectively, in season‐2. These results would encourage farmers who want to consider cover crop interseeding with corn in the regional production systems.

Water Budget of Urban Turf Field and Optimal Irrigation Schedule Simulation in an Ecotone between Semi-Humid and Semi-Arid Regions, Northern China

Water security in the ecotone between semi-humid and semi-arid regions (EHA) is very vulnerable and sensitive to climate change and human interferences. Urban turf irrigation is a primary consumer of urban water resources in the EHA, which places huge pressures on water security by substantial irrigated water use due to the expansion of urban turf planting. Based on a 2-year (2020–2021) turf experiment in Zhangjiakou City, a typical water-deficit city in the EHA of northern China, the water budget for turf was measured and analyzed. Furthermore, the Root Zone Water Quality Model (RZWQM2) was employed to evaluate the optimal irrigation scheme for turf. The results showed that the average volumetric water content in the 0–40 cm soil layer was maintained above 23% in 2020–2021. The evapotranspiration in growth period of turf accounted for more than 70% of the annual evapotranspiration, and the deep seepage in turf soil accounted for 49.67% and 60.28% of the total precipitation and irrigation in 2020 and 2021, respectively, during the vigorous growth period of the turf from May to September. The calibrated RZWQM2 showed a robust ability to simulate the water changes in turf. The d-values (consistency index) between the simulated and observed volumetric water contents and evapotranspiration were both greater than 0.90. In the aspects of irrigation scenarios, the T60%-12 scenario (TA-B, where A is 100%, 80%, 60% or 40% of the total irrigation amount and B is the number of irrigation events corresponding to A) was determined as the best irrigation schedule in our study area because of lower evapotranspiration, seepage and higher turf soil water storage under this irrigation scenario, also resulting from the comparison of different irrigation scenarios using the entropy-weight-TOPSIS method. In such an optimal scenario, T60%-12 irrigation treatment reduced the irrigated water requirement of turf by 40% (142.06 mm) and the seepage amount by 28.07% (39.05 mm), and had the lowest negative impacts on the turf growth.

A Novel Lithium Foil Cosmic-Ray Neutron Detector for Measuring Field-Scale Soil Moisture

During the past decade, cosmic-ray neutron sensing technology has enabled researchers to reveal soil moisture spatial patterns and to estimate landscape-average soil moisture for hydrological and agricultural applications. However, reliance on rare materials such as helium-3 increases the cost of cosmic-ray neutron probes (CRNPs) and limits the adoption of this unique technology beyond the realm of academic research. In this study, we evaluated a novel lower cost CRNP based on moderated ultra-thin lithium-6 foil (Li foil system) technology against a commercially-available CRNP based on BF3 (boron trifluoride, BF-3 system). The study was conducted in a cropped field located in the Konza Prairie Biological Station near Manhattan, Kansas, USA (325 m a.s.l.) from 10 April 2020 to 18 June 2020. During this period the mean atmospheric pressure was 977 kPa, the mean air relative humidity was 70%, and the average volumetric soil water content was 0.277 m3 m−3. Raw fast neutron counts were corrected for atmospheric pressure, atmospheric water vapor, and incoming neutron flux. Calibration of the CRNPs was conducted using four intensive field surveys (n &amp;gt; 120), in combination with continuous observations from an existing array of in situ soil moisture sensors. The time series of uncorrected neutron counts of the Li foil system was highly correlated (r2 = 0.91) to that of the BF-3 system. The Li foil system had an average of 2,250 corrected neutron counts per hour with an uncertainty of 2.25%, values that are specific to the instrument size, detector configuration, and atmospheric conditions. The estimated volumetric water content from the Li foil system had a mean absolute difference of 0.022 m3 m−3 compared to the value from the array of in situ sensors. The new Li foil detector offers a promising lower cost alternative to existing cosmic-ray neutron detection devices used for hectometer-scale soil moisture monitoring.

Fiber Optic Measurements of Soil Moisture in a Waste Rock Pile.

The design and construction of a waste rock pile influences water infiltration and may promote the production of contaminated mine drainage. The objective of this project is to evaluate the use of an active fiber optic distributed temperature sensing (aFO-DTS) protocol to measure infiltration and soil moisture within a flow control layer capping an experimental waste rock pile. Five hundred meters of fiber optic cable were installed in a waste rock pile that is 70 m long, 10m wide, and was covered with 0.60 m of fine compacted sand and 0.25 m of non-reactive crushed waste rock. Volumetric water content was assessed by heating the fiber optic cable with 15-min heat pulses at 15 W/m every 30 min. To test the aFO-DTS system 14 mm of recharge was applied to the top surface of the waste rock pile over 4h, simulating a major rain event. The average volumetric water content in the FCL increased from 0.10 to 0.24 over the duration of the test. The volumetric water content measured with aFO-DTS in the FCL and waste rock was within ±0.06 and ±0.03, respectively, compared with values measured using 96 dielectric soil moisture probes over the same time period. Additional results illustrate how water can be confined within the FCL and monitored through an aFO-DTS protocol serving as a practical means to measure soil moisture at an industrial capacity.

Effect of Mulching and/or Watering on Soil Moisture for Growth and Survival of the Transplanted Tree Seedlings in Dry Period

Dry mulch, as soil moisture conservation techniques, is seldom practiced for growth and survival of transplanted tree seedlings in dry period in Eritrea. Field experiment was conducted at Halhale, Eritrea with Dry Hyparrhenia rufa, as a mulch, on a flat basin for growth and survival of seedlings of Grevillea robusta and Acacia polyacantha subspecies Campylacantha by involving four management practices: 1) mulching and watering basins (MW); 2) no-mulching but watering basins (NMW); 3) mulching but no-watering basins (MNW); 4) no-mulching and no-watering basins (NMNW). The experimental design was CRD with three replications. MW and NMW were watered 180 litters (20 litters/month) but MNW and NMNW were not watered at all. Parameters such as soil moisture content of the basin, early growth performance of seedling and survival rate of the seedlings were studied. The result indicated that there were statistically significant differences (p 0.05) among the treatment for soil moisture content and early growth performance of the seedlings. The average volumetric water content (VWC%) on 0 - 20 cm soil depth at the end of dry period of MW, NMW, MNW, and NMNW were 10.08%, 7.7%, 6.3% and 3.9% respectively. Mean height increment of seedlings of G. robusta of MW (100 cm), NMW (83.3 cm), MNW (31.5 cm) and NMNW (9 cm) were recorded, while the mean height increments of seedlings of A. polyacantha subsp. Campylacantha of MW (48 cm), NMW (25 cm), MNW (4.5 cm) and NMNW (3 cm) were recorded. The mean survival rate of G. robusta was 91.8% of which the highest (100%) survival rate was recorded under MW, NMW and MNW, but the lowest (66.7%) was recorded by NMNW. All seedlings of A. polyacanth subsp. Campylacantha were survived, irrespective of the treatments. The study concluded that soil moisture content, early growth performance of seedlings, and survival rate of transplanted tree seedling was improved by application of mulch.

Maintaining a constant soil moisture level can enhance the growth and phenolic content of sweet basil better than fluctuating irrigation

Although soil moisture sensor-based automated irrigation systems enable researchers to grow plants efficiently and quantify drought stress via constant control of volumetric water content (VWC), growers, in practice, typically irrigate plants using excessive amounts of water based on their own experience. Herein, we investigated the effects of four different irrigation strategies on the growth, physiological responses, and phenolic content of sweet basil (Ocimum basilicum). Three-week-old seedlings were grown using an automated irrigation system incorporating a soil moisture sensor and datalogger. Treatments comprised two irrigation strategies: (i) maintaining a constant VWC of 0.30, 0.45, or 0.60 m3·m-3 by applying small amounts of tap water over time; and (ii) providing a fluctuating VWC (0.30 F), in which a large amount of tap water was applied when the VWC decreased to below 0.30 m3·m-3. Growth parameters were measured at 0, 5, 10, and 15 days after reaching a set point (DAS), and the total irrigation amount was measured at the end of the experiment. Shoot growth differed significantly among treatments, with the highest values being recorded under the 0.60 treatment, followed by the 0.45, 0.30 F, and 0.30 treatments. Physiological responses decreased under the 0.30 treatment but recovered with increasing DAS. Higher constant VWC treatments (0.45 and 0.60) were conducive to higher phenolic content, with the lowest content obtained under the 0.30 F treatment. Although we detected no significant difference in average VWCs between the 0.45 and 0.30 F treatments, 0.30 F treatment showed lower growth, physiological responses, and phenolic content. Collectively, our findings indicate that basil plants with a higher yield and phenolic content can be obtained by maintaining a constantly high VWC (0.60 m3·m-3) than when they are provided with a lower or fluctuating VWC.

Straw layer burial to alleviate salt stress in silty loam soils: Impacts of straw forms

Salt stress can be alleviated by straw layer burial in the soil, but little is known of the appropriate form of the straw layer for optimal regulation of soil water and salinity because of the uncontrollability of field tests. Here, the following four straw forms with compaction thickness of 5 cm buried 40–45 deep were studied: no straw layer (CK), segmented straw (SL, 5 cm in length), straw pellet (SK), and straw powder (SF). The three straw forms (SL, SK and SF) significantly delayed the infiltration of irrigation water down the column profile by 71.20–134.3 h relative to CK and the migration velocity of the wetting front under SF was the slowest. It took longer for the wetting front to transcend SK than SL but shorter for it to reach the bottom of soil column after water crossed the straw layer. Compared with CK, the average volumetric water content in the 0–40 cm soil layer increased by 6.45% under SL, 1.77% under SK and 5.39% under SF. The desalination rates at the 0–40 and 0–100 cm soil layers increased by 5.85 and 3.76% under SL, 6.64 and 1.47% under SK and 5.97 and 4.82% under SF. However, there was no significant difference among straw forms in the 0–40 cm soil layer. Furthermore, the salt leaching efficiency (SLE, g mm−1 h−1) above the 40 cm layer under SL was 0.0097, being significantly higher than that under SF (0.0071) by 37.23%. Salt storage under SL, SK and SF in the 40–45 cm layer accounted for 4.50, 16.92 and 7.43% of total storage in the 1-m column profile. Cumulative evaporation under SL and SF decreased significantly by 41.20 and 49.00%, with both treatments having the most significant inhibition of salt accumulation (resalinization rate being 36.06 and 47.15% lower than CK) in the 0–40 cm soil layer. In conclusion, the different forms of straw layers have desalting effects under high irrigation level (446 mm). In particular, SL and SF performed better than SK in promoting deep salt leaching and inhibiting salt accumulation on the soil surface. However, SL was simpler to implement and its SLE was higher. Therefore, the segmented 5 cm straw can be recommended as an optimum physical form for establishing a straw layer for managing saline soils for crop production.

Effects of Different Rollers and Rye Termination Methods on Soil Moisture and Cotton Production in a No-Till System

In the southern U.S., rollers/crimpers are used to terminate cover crops approximately 3 weeks before planting cotton when the cover crop reaches &gt; 90% termination. When spring is wet or cold, the 3-week period is reduced to keep recommended planting dates. A 3-year experiment was initiated in Alabama to determine the effectiveness of a 4-stage roller/crimper in increasing termination rates for cereal rye compared to 2-stage and spiral rollers/crimpers in rolling 1, 2, and 3 times over rye along with a single-pass smooth roller with glyphosate application. Effects of rye termination at 7, 14, and 21 days after rolling were assessed as were the effects on soil water conservation, cotton population, and yield. Seven days after rolling, the 4-stage, 2-stage, and spiral rollers rolling 3 times generated 96, 92, and 81% termination, respectively. Termination with the smooth roller with glyphosate was 94% and the control (no rolling) was 37%. At 14 days, termination among rollers was 91 to 98% and at 21 days no differences were found among rollers (99-100%). The 4-stage roller 3 times had the highest average soil volumetric water content (VWC) of 16.1%, whereas the spiral roller 1 time had the lowest (13.6%). Rolled rye had higher VWC content averaging 14.7% (12-cm surface layer) compared to the control (12.7%). Rolling treatments affected cotton emergence only in 2015; cotton population and yield were not affected. Seven days after rolling, the 4-stage and 2-stage roller/crimpers exceeded 90% rye termination making earlier cotton planting possible if required by climatic conditions.

Estimating evapotranspiration parameters by inverse modelling and non-linear optimization

The use of models like HYDRUS in planning irrigation and fertigation scheduling is increasingly researched. Simulation of the root zone processes using HYDRUS largely depends on characterizing parameters related to unsaturated hydraulic conductivity, root growth and water uptake dynamics. A methodology for estimating evapotranspiration parameters for drip irrigated paddy is developed in the present work. The methodology involves soil moisture logging of root zone followed by modelling the dynamics of soil water movement in the root zone by inversely solving the Richards’ equation and evapotranspiration parameters estimation by non-linear programming. All the computer programming was done with MS-EXCEL and it is found that this tool is versatile for this purpose. The results of this work are very useful for using HYDRUS in developing optimal irrigation and fertigation schedule. A threshold level of soil water suction pressure for irrigation scheduling of paddy was also obtained through this work. Temporal changes in the location of the average volumetric water content and average evapotranspiration in the root zone were evaluated. These data are useful for developing guidelines for soil water sensor placement in automatic irrigation triggers.

Effects of three in-field water harvesting technologies on soil water content and maize yields in a semi-arid region of Zimbabwe

Climate change and recurring mid-season dry spells have resulted in perennial droughts and poor yields in most smallholder farming areas located in marginal arid to semi-arid lands (ASAL) of Zimbabwe where they are dependent on rainwater for agricultural crop production. One approach that can be used to adapt to changing climatic pattern is in-field water harvesting. This study evaluated the soil profile water content and maize yields of 3 infield water harvesting technologies namely infiltration pits (IF), fanya juus (FJ) and contour ridges with cross ties (CRCT) in comparison to standard contour ridges (SC). The three systems are currently the focus of extension recommendations for water conservation in semi-arid regions of the country. Soil water content was measured on a regular basis using gravimetric methods at locations upslope and down slope of each structure. The average volumetric water content was signifcantly different between treatments, and it varied with increasing distance from the water harvesting structures. The average profile soil moisture content, over the three seasons were 8.3, 8.2, 8.1 and 7.8% for CRCT, FJ, IF and SC repectively. CRCT, FJ and IF retained more water for a greater distance from the harvesting structures compared to the SC. Maize yields were significantly higher in the water harvesting technologies compared to SC. Maize yields were 1196, 1164, 1250 and 749 kg ha−1 for CRCT, FJ, IF and SC respectively. There as a good correlation between water content and maize yields (R2 = 0.80). It was concluded that improved water harvesting structures when compared to SC have the potential to increase maize yields in areas with water shortages, hence they can be a useful strategy for climate change adaptation.

Miscanthus Biochar had Limited Effects on Soil Physical Properties, Microbial Biomass, and Grain Yield in a Four-Year Field Experiment in Norway

The application of biochar to soils is a promising technique for increasing soil organic C and offsetting GHG emissions. However, large-scale adoption by farmers will likely require the proof of its utility to improve plant growth and soil quality. In this context, we conducted a four-year field experiment between October 2010 to October 2014 on a fertile silty clay loam Albeluvisol in Norway to assess the impact of biochar on soil physical properties, soil microbial biomass, and oat and barley yield. The following treatments were included: Control (soil), miscanthus biochar 8 t C ha−1 (BC8), miscanthus straw feedstock 8 t C ha−1 (MC8), and miscanthus biochar 25 t C ha−1 (BC25). Average volumetric water content at field capacity was significantly higher in BC25 when compared to the control due to changes in BD and total porosity. The biochar amendment had no effect on soil aggregate (2–6 mm) stability, pore size distribution, penetration resistance, soil microbial biomass C and N, and basal respiration. Biochar did not alter crop yields of oat and barley during the four growing seasons. In order to realize biochar’s climate mitigation potential, we suggest future research and development efforts should focus on improving the agronomic utility of biochar in engineered fertilizer and soil amendment products.

A cost-effective and customizable automated irrigation system for precise high-throughput phenotyping in drought stress studies.

The development of high-yielding crops with drought tolerance is necessary to increase food, feed, fiber and fuel production. Methods that create similar environmental conditions for a large number of genotypes are essential to investigate plant responses to drought in gene discovery studies. Modern facilities that control water availability for each plant remain cost-prohibited to some sections of the research community. We present an alternative cost-effective automated irrigation system scalable for a high-throughput and controlled dry-down treatment of plants. This system was tested in sorghum using two experiments. First, four genotypes were subjected to ten days of dry-down to achieve three final Volumetric Water Content (VWC) levels: drought (0.10 and 0.20 m3 m-3) and control (0.30 m3 m-3). The final average VWC was 0.11, 0.22, and 0.31 m3 m-3, respectively, and significant differences in biomass accumulation were observed between control and drought treatments. Second, 42 diverse sorghum genotypes were subjected to a seven-day dry-down treatment for a final drought stress of 0.15 m3 m-3 VWC. The final average VWC was 0.17 m3 m-3, and plants presented significant differences in photosynthetic rate during the drought period. These results demonstrate that cost-effective automation systems can successfully control substrate water content for each plant, to accurately compare their phenotypic responses to drought, and be scaled up for high-throughput phenotyping studies.

Canopy transpiration of Larix principis-rupprechtii plantation and its impact factors in diffe-rent slope locations at the south side of Liupan Mountains, China.

Based on a continuous field observation in the Larix principis-rupprechtii plantation plots, located at the upper (P1), middle-upper (P2), middle (P3), middle-lower (P4), and lower (P5) positions, in a southeast-facing slope of the Xiangshuihe watershed of Liupan Mountains, China, the stem sap flow was observed with the thermal diffusivity probe method. The soil water potential and meteorological factors were monitored from May to October, 2014. We found significant differences among slope positions in the daily forest transpiration (Tr, mm·d-1), with an order of P2 (0.975)＞P4 (0.876)＞P3 (0.726)＞P1 (0.653)＞P5 (0.628). Tr was significantly positively correlated with the daily maximum temperature (Tmax), daily mean solar radiation (SR), daily mean saturated vapor pressure deficit (VPD), potential evapotranspiration (PET), and daily mean soil water potential (Ψ), but negatively correlated with the daily mean air relative humidity (RH), daily precipitation (P), and daily minimum temperature (Tmin). According to the upper boundary line ana-lysis, significant differences were found in the degree of Tr responding to each single environmental factor among slope positions. The degree of its responses gradually decreased for average daily air temperature (T), RH, VPD, PET and Ψ, whereas increased for the SR and daily average volumetric soil water content (VSM) from the upper position to the lower. Results from regression and partial correlation analysis showed that variation of Tr was mainly controlled by VPD, PET and RH in different slope positions. Tr was also strongly affected by Ψ and T in the upper-slope positions and by SR, Tmin and VSM at the lower-slope positions. Generally, the Tr difference among slope positions was a consequence of joint contributions of soil water and meteorological factors. It is necessary to consider the changes of soil water and meteorological factors in different positions along the slope when examining slope-scale or watershed-scale forest transpiration with sap flow estimated from xylem sap flux density measurements of a particular plot.

Soil Moisture Sensor-based Systems are Suitable for Monitoring and Controlling Irrigation of Greenhouse Crops

Sensor-based feedback control irrigation systems have been increasingly explored for greenhouse applications. However, the relationships between microclimate variation, plant water usage, and growth are not well understood. A series of trials were conducted to investigate the microclimate variations in different greenhouses and whether a soil moisture sensor-based system can be used in monitoring and controlling irrigation in greenhouse crop productions. Ocimum basilicum ‘Genovese Gigante’ basil and Campanula portenschlagiana ‘Get Mee’ bellflowers were monitored using soil moisture sensors for an entire crop cycle at two commercial greenhouses. Significant variations in greenhouse microclimates were observed within the two commercial greenhouses and within an older research greenhouse. Evaporation rates were measured and used as an integrated indicator of greenhouse microclimate conditions. Evaporation rates varied within all three greenhouses and were almost double the lowest rates within one of the greenhouses, suggesting microclimates within a range of greenhouses. Although these microclimate variations caused large variations in the growing substrate water contents of containers within the greenhouses, the growth and quality of the plants were unaffected. For example, no significant correlations were observed between the growth of bellflower plants and the average volumetric water content (VWC), minimum VWC, or maximum VWC of the growing substrate. The change in VWC at each irrigation (ΔVWC), however, was positively correlated with the fresh weight, dry weight, and growth index (GI) of the bellflowers. For basil, no significant correlations were observed between plant growth and ΔVWC. This suggests that sensor-based feedback irrigation systems can be used for greenhouse crop production when considerations are given to factors such as the magnitude of microclimate variation, crop species and its sensitivity to water stress, and growing substrate.

Rainfall Intensification Enhances Deep Percolation and Soil Water Content in Tilled and No‐Till Cropping Systems of the US Midwest

Core Ideas Rainfall intensification increased deep percolation in tilled and no‐till systems. Rainfall intensification increased deep soil water content in both cropping systems. A bromide tracer was detected at 1.2‐m depth sooner in no‐till than tilled systems. The effect of rainfall intensification on surface soil moisture varied seasonally. Globally, the proportion of total rainfall occurring as extreme events is increasing, which may have consequences for agriculture. In the US Midwest, we conducted a 234‐d manipulative experiment in 16 paired plots where we increased the proportion of rain falling in extreme events on tilled and no‐till cropping systems. We compared the effects of larger, less frequent rain events (“intensified” rainfall) vs. smaller, more frequent rain events (“normal” rainfall) on soil water content and deep percolation. The effect of intensified rainfall on the volumetric water content (VWC) of soil at the 10‐cm depth during the experiment varied seasonally: in spring, intensified rainfall decreased the average VWC at the 10‐cm depth by 0.05 ± 0.01 cm3 cm−3 compared with normal rainfall, but in summer and fall, it had no effect. In soil at the 100‐cm depth, VWC declined during the summer in normal but not intensified plots. A surface‐added Br− tracer was detected and peaked earlier in soil water at 120 cm under intensified rainfall vs. normal rainfall (by 6 ± 3 and 74 ± 33 d, respectively) regardless of tillage, although it was detected sooner in no‐till than tilled systems (by 9 ± 3 d). Also, less Br− was recovered in soil under intensified (8 ± 8% of total Br− added) vs. normal rainfall (21 ± 3%). Our results suggest that rainfall intensification will increase deep percolation and deep soil water content in cropping systems regardless of tillage. Such changes to soil water dynamics may alter plant water and nutrient availability.

Volumetric Water Content Measurements as Obtained from Remote Sensing and In Situ Instrumentation

A single-polarization, vertical wave propagation transmitted-vertical wave propagation received (VV), terrestrial imaging radar and time domain reflectometry (TDR) equipment were used to monitor the fluctuations of water content within two thin (15.24 centimeters) compacted clay test sections (each 30.48-m long, by 15.34-m wide). Radar imagery was obtained in 2013 on March 22, June 26, July 7 and July 10 using a Gamma Remote Sensing Portable Radar Interferometer version II (GAMMA Remote Sensing and Consulting AG, Bern, Switzerland). In situ observations were acquired hourly using TDR probes. The background, methodology, and comparison of the results of the remote sensing and in situ measurements are presented. Specifically, two remote sensing data reduction algorithms were considered. The water content results obtained from these algorithms were compared with the water content values derived from correlations with the dielectric permittivity values measured by the TDR probes. Key findings include: 1) there were differences between the values obtained from the data reduction methods, 2) there were differences between the values obtained from the remote sensing methods and the values obtained from the in situ method, and 3) the identification of additional avenues of research. The remotely sensed measurements were, on average, higher than the in situ measurements (the average volumetric water content values were 0.2 and 0.5 depending on the method, as obtained via the remotely sensed methods; the average volumetric water content value in the compacted native soil test sections was 0.22, as obtained via the in situ method).