Water Table Treatments Research Articles

Belowground plant allocation regulates rice methane emissions from degraded peat soils

Carbon-rich peat soils have been drained and used extensively for agriculture throughout human history, leading to significant losses of their soil carbon. One solution for rewetting degraded peat is wet crop cultivation. Crops such as rice, which can grow in water-saturated conditions, could enable agricultural production to be maintained whilst reducing CO2 and N2O emissions from peat. However, wet rice cultivation can release considerable methane (CH4). Water table and soil management strategies may enhance rice yield and minimize CH4 emissions, but they also influence plant biomass allocation strategies. It remains unclear how water and soil management influences rice allocation strategies and how changing plant allocation and associated traits, particularly belowground, influence CH4-related processes. We examined belowground biomass (BGB), aboveground biomass (AGB), belowground:aboveground ratio (BGB:ABG), and a range of root traits (root length, root diameter, root volume, root area, and specific root length) under different soil and water treatments; and evaluated plant trait linkages to CH4. Rice (Oryza sativa L.) was grown for six months in field mesocosms under high (saturated) or low water table treatments, and in either degraded peat soil or degraded peat covered with mineral soil. We found that BGB and BGB:AGB were lowest in water saturated conditions where mineral soil had been added to the peat, and highest in low-water table peat soils. Furthermore, CH4 and BGB were positively related, with BGB explaining 60% of the variation in CH4 but only under low water table conditions. Our results suggest that a mix of low water table and mineral soil addition could minimize belowground plant allocation in rice, which could further lower CH4 likely because root-derived carbon is a key substrate for methanogenesis. Minimizing root allocation, in conjunction with water and soil management, could be explored as a strategy for lowering CH4 emissions from wet rice cultivation in degraded peatlands.

Challenges of Including Wet Grasslands with Variable Groundwater Tables in Large-Area Crop Production Simulations

Large-scale assessments of agricultural productivity necessitate integrated simulations of cropland and grassland ecosystems within their spatiotemporal context. However, simultaneous simulations face limitations due to assumptions of uniform species distribution. Grasslands, particularly those with shallow groundwater tables, are highly sensitive to water availability, undergoing rapid species composition changes. We hypothesised that predicting above-ground biomass (AGB) remains challenging due to these dynamic responses. Ten years of data from four lysimeters at a German wet grassland site, with varying water table treatments, was utilised to test this hypothesis. Correlation analysis revealed a strong positive indirect effect of the water regime on AGB, with a one-year time lag (r = 0.97). The MONICA model initially exhibited fair agreement (d = 0.69) in simulating Leaf-Area-Index (LAI) but performed poorly in replicating AGB (d = 0.3). After removing the species composition change effect from the LAI and AGB datasets, the simulation notably improved, with the overall relative root mean square error (rRMSE) of AGB decreasing from 1.55 to 0.90 between the first and second simulations. This demonstrates MONICA’s ability to predict grass growth patterns amidst changing water supply levels for constant species composition. However, it needs a competition model to capture biomass growth changes with varying water supply.

Water table depth and plant species determine the direction and magnitude of methane fluxes in floodplain meadow soils.

Methane (CH4) is a powerful greenhouse gas with ongoing efforts aiming to quantify and map emissions from natural and managed ecosystems. Wetlands play a significant role in the global CH4 budget, but uncertainties in their total emissions remain large, due to a combined lack of CH4 data and fuzzy boundaries between mapped ecosystem categories. European floodplain meadows are anthropogenic ecosystems that originated due to traditional management for hay cropping. These ecosystems are seasonally inundated by river water, and straddle the boundary between grassland and wetland ecosystems; however, an understanding of their CH4 function is lacking. Here, we established a replicated outdoor floodplain-meadow mesocosm experiment to test how water table depth (45, 30, 15 cm below the soil surface) and plant composition affect CH4 fluxes over an annual cycle. Water table was a major controller on CH4, with significantly higher fluxes (overall mean 9.3 mg m-2 d-1) from the high (15 cm) water table treatment. Fluxes from high water table mesocosms with bare soil were low (mean 0.4 mg m-2 d-1), demonstrating that vegetation drove high emissions. Larger emissions came from high water table mesocosms with aerenchymatous plant species (e.g. Alopecurus pratensis, mean 12.8 mg m-2 d-1), suggesting a role for plant-mediated transport. However, at low (45 cm) water tables A. pratensis mesocosms were net CH4 sinks, suggesting that there is plasticity in CH4 exchange if aerenchyma are present. Plant cutting to simulate a hay harvest had no effect on CH4, further supporting a role for plant-mediated transport. Upscaling our CH4 fluxes to a UK floodplain meadow using hydrological modelling showed that the meadow was a net CH4 source because oxic periods of uptake were outweighed by flooding-induced anoxic emissions. Our results show that floodplain meadows can be either small sources or sinks of CH4 over an annual cycle. Their CH4 exchange appears to respond to soil temperature, moisture status and community composition, all of which are likely to be modified by climate change, leading to uncertainty around the future net contribution of floodplain meadows to the CH4 cycle.

Methane and nitrous oxide emissions from rice grown on organic soils in the temperate zone

Organic soils are important carbon stocks. The conventional (dry) cultivation of these soils turns them into strong sources of greenhouse gas (GHG) emissions. For situations where restoration of natural land cover is not possible, solutions to this problem include the wet cultivation of these soils, reducing CO2 and N2O emissions. One option, paddy rice cultivation, has begun in the Swiss Central Plateau, which hitherto did not provide a suitable climate for wet rice. Wet rice is however associated with high CH4 emissions. These need to be quantified for this region, as the increased CH4 fluxes might negate the expected reductions in CO2 and N2O. Here, we quantify CH4 and N2O emissions from wet rice on organic soil with chamber measurements, in an outdoor mesocosm experiment in the Swiss Central Plateau, located in the cool temperate moist zone. We apply two water treatments (a high water table (WT) treatment, − 6 cm with mid-season drainage, and two medium WT treatments, − 11 and − 17 cm without mid-season drainage) and additionally test the use of a mineral cover layer to reduce N2O emissions. Additionally, a deeply-drained grassland treatment is used as a reference treatment. Annual CH4 emissions from rice cultivation are 6.2 g CH4.m-2.a-1 for the higher WT treatment, 6.4 g CH4.m-2.a-1 for the medium WT treatment and 2.4 g CH4.m-2.a-1 for the medium WT treatment with mineral cover. The corresponding N2O emissions are 203, 190 and 56 mg N2O-N.m-2.a-1, respectively. These results show that adding a mineral cover layer reduces annual emissions from both GHGs substantially. In total, the maximum increase in CH4 and N2O emissions resulting from rice cultivation, compared to the drained grassland treatment, is 2.3 t CO2-eq.ha-1.a-1. Expected CO2 emissions savings (derived from a literature-based model) due to a higher WT are a factor of 5–9 greater than this. We thus conclude that the cultivation of these organic soils in this region with wet rice could reduce their induced warming compared to their cultivation with (deeply drained) grassland.

Evidence for older carbon loss with lowered water tables and changing plant functional groups in peatlands.

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m3 mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO2 fluxes, decomposition, and older C loss. We used Δ14 C and δ13 C of ecosystem CO2 respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic 14 C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.

Managing water table depth thresholds for potato subirrigation

Subirrigation requires precise control of the water table level to provide adequate soil water content (SWC) for promoting plant growth. Optimizing water table level management has been shown to improve soil aeration, reduce N-leaching, and reduce risk of crop losses. The objectives of this study were to: i) assess if water table level and N-fertilizer rate impact potato growth, root development, plant N uptake, or tuber yield; and ii) estimate the optimum water table level threshold that provides sufficient soil upward water flux to meet plant water requirements. The study was conducted in 2013 and 2014 in Hastings, FL, USA. Water table level was automatically controlled in three independent irrigation zones of 1.4 ha at 36, 54, and 71 cm from the top of the hilled row, termed as high (HWT), medium (MWT), and low (LWT) water table treatments, respectively, and SWC measured at 22 cm depth was used as covariate to compare treatments. A randomized complete block with three replications was used to evaluate potato cultivars ‘Atlantic’ and ‘FL1867′ under 0, 112, 224, and 336 kg ha−1 of N-fertilizer within water table treatments. Marketable yield in 2013 was lower than 2014, owing to the high precipitation (421 mm) during tuber bulking that led to high SWC and tuber decay. Total and marketable tuber yields were maximized when N fertilizer rates ranged from 243 to 336 kg ha−1. The highest yield and proportion of large tubers occurred when SWC at 22 cm ranged from 0.13 to 0.16 m3 m−3. The HWT significantly limited root length, diameter, and surface area, compared to the LWT. In 2014, variation of SWC at 22 cm depth had little effect on tuber yield. The HWT was not detrimental to tuber yield, but rather it compounded the negative effect that high precipitation rate had on fluctuating SWC in the root zone, resulting in reduced yield and tuber quality. Optimal SWC in the root zone can be achieved by adjusting the water table level and upward soil water flux throughout the season, according to the crop evapotranspiration for each crop stage, which reduces irrigation water requirements and minimizes the risks of soil water saturation and tuber yield losses.

Drainage increases species richness and density of soil macro-invertebrates in the Zoige peatland of eastern Tibetan Plateau

Soil macro-invertebrates play an important role in the decomposition process of soil organic matter. As the world’s largest alpine peatland, the Zoige peatland on the eastern Tibetan Plateau is experiencing the decline in water table level primarily because of historic drainage. However, little is known about the responses of soil macro-invertebrate communities to water table decline. To address this issue, we established a field drainage experimental platform in 2013, which consists of low (50 cm deep drainage ditch) and intermediate (20 cm deep drainage ditch) water table level treatments, and the ambient (no drainage ditch) plots. In July (warm season) and November (cold season) of 2019, we examined the species composition, richness, densities and the vertical distribution of soil macro-invertebrates. Results showed that the species composition differed significantly among treatments. Species richness and densities of overall and different trophic groups (i.e., detritivores, herbivores and predators) of soil macro-invertebrates were significantly higher in the drained treatments compared to the ambient plots. Moreover, soil macro-invertebrates moved down to deeper soil layers in the low water table treatments compared to the ambient plots. In addition, sampling season (warm vs. cold) did not affect the responses of soil macro-invertebrates to water table decline. These results indicate that soil macro-invertebrate community is sensitive to water table decline in the Zoige peatland. Given the recognized importance of soil fauna to ecosystem functioning, more attention should be paid to the conservation of peatlands.

Consequences of Increased Variation in Peatland Hydrology for Carbon Storage: Legacy Effects of Drought and Flood in a Boreal Fen Ecosystem

Globally important carbon (C) stores in boreal peatlands are vulnerable to altered hydrology through changes in precipitation and runoff patterns, groundwater inputs, and a changing cryosphere. These changes can affect the extent of boreal wetlands and their ability to sequester and transform C and other nutrients. Variation in precipitation patterns has also been increasing, with greater occurrences of both flooding and drought periods. Recent work has pointed to the increasing role of algal production in regulating C cycling during flooded periods in fen peatlands, but exactly how this affects the C sink-strength of these ecosystems is poorly understood. We evaluated temporal trends in algal biomass, ecosystem C uptake and respiration (using static and floating chamber techniques), and spectroscopic indicators of DOM quality (absorbance and fluorescence) in a boreal rich-fen peatland in which water table position had been experimentally manipulated for 13 years. Superimposed on the water table treatments were natural variations in hydrology, including periods of flooding, which allowed us to examine the legacy effects of flooding on C cycling dynamics. We had a particular focus on understanding the role of algae in regulating C cycling, as the relative contribution of algal production was observed to significantly increase with flooding. Ecosystem measures of gross primary production (GPP) increased with algal biomass, with higher algal biomass and GPP measured in the lowered water table treatment two years after persistent flooding. Prior to flooding the lowered treatment was the weakest C sink (as CO2), but this treatment became the strongest sink after flooding. The lower degree of humification (lower humification index, HIX) and yet lower bioavailability (higher spectral slope ratio, Sr) of DOM observed in the raised treatment prior to flooding persisted after two years of flooding. An index of free or bound proteins (tyrosine index, TI) increased with algal biomass across all plots during flooding, and was lowest in the raised treatment. As such, antecedent drainage conditions determined the sink-strength of this rich fen—which was also reflected in DOM characteristics. These findings indicate that monitoring flooding history and its effects on algal production could become important to estimates of C balance in northern wetlands.

Fungi are more sensitive than bacteria to drainage in the peatlands of the Zoige Plateau

The peatlands of the Zoige Plateau are an important global carbon source that is currently under threat as a result of drainage for grazing. How drainage affects the microbial diversity and activity in peatlands is unclear. This study examined the response of microbial communities at two sites to short-term drainage (3 years) and long-term drainage (48 years) in combination with three different water table treatments. Our objective was to examine the changes in the physicochemical properties of the soil, composition of bacterial and fungal communities, and microbial activity. Our results indicated that (1) both duration of drainage and water table drawdown had significant effects on the diversity and composition of the bacterial and fungal communities in the soil, and certain bacteria were replaced by fungal decomposers; (2) duration of drainage affected the structure of fungal communities more than that of bacterial communities, and interactions between microbial species were more complex in peatlands with long-term drainage; (3) drainage significantly altered concentrations of dissolved inorganic nitrogen (NH4+-N and NO3−-N), and these changes correlated with structure of bacterial and fungal communities as well as with changes in abundance of certain dominant microbial species; and (4) fungal communities explained a larger part of microbial activity than bacterial communities. Overall, these findings suggest that fungi play a much more important role than bacteria in microbial-mediated ecosystem functioning in peatlands undergoing drainage.

Tiller Size and Water Table Effects in Celery Growth on Floating Cultivation System

Jaya KK, Lakitan B, Bernas SM. 2020. Tiller size and water table effects in celery growth on floating cultivation system. Jurnal Lahan Suboptimal : Journal of Suboptimal Lands 9(2): 184-191.Riparian wetland is highly available and potential suboptimal lands for an alternative solution in extending agricultural activity, but several constrains need to be resolved. The objective of this study was to improve the diversification of vegetables for increasing riparian wetland with utilizing floating cultivation system. This study was conducted From November until December 2019 in Jakabaring (104°46’4” E; 3°01’35” S) Palembang. The design of experiments used in this study was arranged in split plot-completely randomized design with 2 factors (main plot and sub-plot). Main plot was the height of water table, namely: R1 (1 cm upper raft surface), R5 (5 cm upper raft surface), and R10 (10 cm upper raft surface). Sub-plot was the size of celery tiller, i.e., B1 (big size) and B2 (small size). Each combination treatment consisted of five replication. Results showed that there was no any significant effect on water table and tiller size combination treatments in all observed variables, such as: plant height, leaf area, number of petioles, root length, fresh weight, and dry weight of shoot and roots. But, root length was significant different in water table treatment. Therefore, cultivated celery using floating culture system from tiller of parent plants can be an alternative to increase agriculture activity by shortening the planting period to increase vegetable diversification in riparian wetland.

Effects of Water Table, Population Density and Transplanting Time on Vegetative Growth of Black Sticky Rice at Floating Seedbed Method

Ria RP, Lakitan B, Negara ZP. 2020. Effects of water table, seedling density and transplanting time on vegetative growth of black sticky rice at floating seedbed. Jurnal Lahan Suboptimal : Journal of Suboptimal Lands 9(2): 167-174.Study on black sticky rice cultivation in South Sumatera is seldom carry out. The objective of this study was to evaluate the effect of water table and population density on the growth of rice during seedling preparation at floating seedbed; furthermore, this study aimed to evaluate the effect of transplanting time on vegetative growth of black sticky rice. The research was started in May 2018 in Palembang. Black sticky variety used in this research was Toraja variety. The raft used is made from 1,5 l plastic bottles which are arranged to reach 2x1 meters in size. This study was conducted by two stages. The first stage was for water table and population density treatments laid on split plot design. The second stage was for transplanting time utilizing completely randomized factorial design. Statistically, results showed water table and population density significantly influensced root length of black sticky rice and transplanting time 14 DAS haad an effect on the leaf length , leaf width and leaf area.

Penggunaan Biochar dan Tinggi Muka Air pada Umur Satu Bulan setelah Tanam terhadap Pertumbuhan dan Hasil Tanaman Bawang Merah

Susilawati S, Irmawati I, Sukarmi S, Kurnianingsih A, Mutia A. 2019. The application of biochar and water table at one month after planting on growth and yield of shallot. Jurnal Lahan Suboptimal: Journal of Suboptimal Lands. 8(2):202-212. The success of onion self-sufficiency is the arrangement and growth of production centers that are not only concentrated in Java. The research aimed to evaluate the effect of biochar application and water table treatment on growth and yield of shallot plant. The research was conducted in Experimental Farm of Agriculture Faculty, Sriwijaya University at 2019. Materials used consisted of shallot bulb of Bima Brebes variety, oil palm shells biochar, paper bag, and plastic bag. While the tools used were hoe, gauge, pH meter, basin, scale, and oven. Factorial Randomized Block Design was used with two factors and three replicates. The first factor was biochar dosages consisting of P1 (51 g/plant) and P2 (102 g/plant) and the second factor was soil water table consisting of T0 (no water table treatment), T1 (10 cm of water table below soil surface), T2 (15 cm of water table below soil surface) and T3 (30 cm of water table below soil surface). The observed parameters included plant height, leaf number, tiller number, total bulb fresh weight, bulb fresh weight, bulb dry weight and root length. Results showed that the application of biochar and water table treatment statistically affected the growth and yield of shallot plant. The effect on both growth and yield parameters were obtained from the combination of P2T3. Correlation was found between plant height and leaf number, total bulb fresh weight and bulb fresh weight.

Optimizing rice paddies’ lower greenhouse gas emissions and higher yield with SRI management under varying water table levels

The System of Rice Intensification (SRI) is known as a climate-smart agricultural practice that increases rice production by changing the management of plants, soil, water, and nutrients. SRI water management relies on intermittent irrigation rather than on the continuous flooding of conventionally managed rice production. Different water table levels affect the soil conditions which contribute to different fluxes of greenhouse gas (GHG) emissions. This study estimated the impact on global warming potential (GWP) of GHG emissions from rice paddies when an SRI crop is managed with different water table levels. In this study, CO2 equivalence was assessed using a Simple Greenhouse Gas model, and an artificial neural network model for assessing CH4 and N2O. SRI paddy rice was grown in experimental pots under varying water table treatments, with the water table controlled by using Mariotte tubes set at + 2, 0, − 3, − 5, − 7, and − 12 cm from the soil surface. GHG emissions, which could be monitored more closely in pot trials than in fields, are a composite of the plants’ respiration, soil respiration (which is a result primarily of microbial activity), and the respiration that results from root exudates. With SRI practices, rice paddies can serve as a sink rather than a source for CH4 as seen from the negative values for CH4 emissions at all water table treatments. While there were N2O emissions with SRI practice, they were much less in terms of CO2 equivalence than the GWP reduction achieved by reducing CH4. Overall, under the experimental conditions the best water table level for SRI cultivation, with the most rice produced relative to GHG emissions, was − 5 cm from the soil surface. For each kg of grain produced, there were 0.80 kg CO2 eq of GHG emissions. By comparison, a normally flooded paddy field with usual crop management methods emits 1.97 kg CO2 eq per kg of grain produced, almost 150% more. This finding that a water table of − 5 cm is optimal will not necessarily apply for all field conditions, but the research addresses the desirability of seeking to optimize between GHG reductions and increased yield when growing paddy rice, and of developing appropriate methodology for achieving this composite objective.

Impacts of experimental alteration of water table regime and vascular plant community composition on peat mercury profiles and methylmercury production

Climate change is expected to alter the hydrology and vascular plant communities in peatland ecosystems. These changes may have as yet unexplored impacts on peat mercury (Hg) concentrations and net methylmercury (MeHg) production. In this study, peat was collected from PEATcosm, an outdoor, controlled mesocosm experiment where peatland water table regimes and vascular plant functional groups were manipulated over several years to simulate potential climate change effects. Potential Hg(II) methylation and MeHg demethylation rate constants were assessed using enriched stable isotope incubations at the end of the study in 2015, and ambient peat total Hg (THg) and MeHg concentration depth profiles were tracked annually from 2011 to 2014. Peat THg and MeHg concentrations and the proportion of THg methylated (%MeHg) increased significantly within the zone of water table fluctuation when water tables were lowered, but potential Hg(II) methylation rate constants were similar regardless of water table treatment. When sedges dominate over ericaceous shrubs, MeHg concentrations and %MeHg became significantly elevated within the sedge rooting zone. Increased desorption of Hg(II) and MeHg from the solid phase peat into pore water occurred with a lowered water table and predominant sedge cover, likely due to greater aerobic peat decomposition. Deeper, more variable water tables and a transition to sedge-dominated communities coincided with increased MeHg accumulation within the zone of water table fluctuation. Sustained high water tables promoted the net downward migration of Hg(II) and MeHg. The simultaneous decrease in Hg(II) and MeHg concentrations in the near-surface peat and accumulation deeper in the peat profile, combined with the trends in Hg(II) and MeHg partitioning to mobile pore waters, suggest that changes to peatland hydrology and vascular plant functional groups redistribute peat Hg(II) and MeHg via vertical hydrochemical transport mechanisms.

Shallow groundwater effects on evaporation and soil temperature in two windblown sands (Eutric Cambisol and Chromic Luvisol) in South Africa

The aim of this study was to investigate the effect of shallow groundwater tables on soil surface evaporation and its effect on temperature distribution on two aeolian soils in South Africa, Clovelly (Eutric Cambisol) and Hutton (Chromic Luvisol) soil forms. The study was conducted at a lysimeter under semi-arid climatic conditions. A constant groundwater tables were created at different depths (0 mm, 500 mm, 1000 mm, 1500 mm and a No WT (no water table treatment as a control) and each of the lysimeters were equipped with a 1200 mm long DFM soil moisture probe to measure the profile water content and soil temperature at 6 depths along the profile (every 200 mm depth). The research site was also equipped with a movable shelter to prevent rain water dilution during rainfall events. Finally, evaporation is calculated by the water balance approach. The ANOVA showed that there was a highly significant difference (P < .01) in rate of evaporation from the water table depths and soil types. The minimum and maximum evaporation were recorded in the deepest and shallowest water table depths. The diurnal soil water content shows that the maximum water content in the two soil profiles was recorded in the early morning times (6:00) and the minimum was in the late afternoon times (between 16:00–17:00). The diurnal variation of soil water content also increased with decreasing water table depth. Regarding the soil temperature, the ANOVA showed that the soil temperature was influenced by the interaction between water table and measurement depths. Hence, the top five minimum soil temperatures were recorded in the shallower (≤500 mm) water tables and the top 5 maximums were recorded in the deeper water table depths (1000, 1500 and No WT). Generally, as the groundwater table depth increased from the surface down the profile, the rate of evaporation decreased resulting an increase in the variation of temperature with in the diurnal cycle.

Tolerance of common bean (Phaseolus vulgaris L.) to different durations of simulated shallow water table condition

Shallow water table problem has lessened farmer’s interest in cultivating vegetables at riparian wetland in Indonesia. At present, riparian wetlands are mostly underutilized. Objective of this study was to evaluate tolerance of common bean (Phaseolus vulgaris) to shallow water table condition. Common bean variety of PV072 was used in this study. Research was conducted in Jakabaring, South Sumatra, Indonesia; from November 2016 to February 2017. Leaf and root growth or damage can be used as an indicator of stress tolerance in plants exposed to unfavorable soil conditions. Results of our study indicated that roots of common bean were unable to survive in water saturated condition below water table, but the plants were able to compensate for this constraint by increasing root biomass within aerobic substrate above water table. Moreover, after termination of shallow water table treatment, common bean was able to regrow their roots into the ex-saturated zone. Common bean plants produced marketable yield albeit limited rhizosphere space. Interestingly, the plants exposed to 24 days of shallow water table produced the highest yield. In conclusion, common bean can be considered as tolerant vegetable to shallow water table. It should be noted that bean leaf reached 90 percent and full size in less than 6 days and 9 days, respectively, after the young leaf was unfolded. Therefore, long term study on bean leaf growth and development requires measurement on sequential and multiple leaves. Also, nocturnal relative leaf expansion rate (RLER) was significantly faster than diurnal RLER.

Effect of Water Table Depth on Nutrient Concentrations Below the Water Table in a Spodosol

Water table depth manipulations as implemented in sugarcane fields of Southwestern Florida, USA, were hypothesized to influence the nutrient concentrations below the water table. Concentrations of phosphorus (P), potassium (K), nitrogen (N), and bromide (Br−) were monitored above and below the water table using a column leaching experiment. Three columns were packed with Immokalee soil (A, E, and Bh horizons) classified as a spodosol and fertilizers (NPK) were applied on the soil surface as solids using rates of 11 kg P ha−1, 166 kg K ha−1, and 200 kg N ha−1. A fourth column where fertilizer mixture and bromide were not added acted as a blank. Potassium was also applied as KBr with bromide used as tracer for water movement. Water table was maintained at 30 cm for 6 weeks and lowered to 50 cm deep for another 6 weeks. Samplers were placed in A, E, and Bh horizons and outlets were placed at 30 and 50 cm deep to obtain solutions for monitoring nutrients and tracer. Solution samplers placed in E and Bh horizons were located below the water table. Slightly elevated P, N, and K concentrations in E horizon for a 50-cm water table depth treatment were observed. For both water table treatments, minimal loss of applied N, P, and K below the water table was observed. The results of the study have shown that movement of nutrients below the water table is slow, and depends on the type of nutrients applied and the water table depth.

Effects of Water Regimes on Methane Emissions in Peatland and Gley Marsh

Core Ideas Large pulses of CH4 can be emitted during short‐duration drying–wetting episodes. Peatland soils had higher CH4 emissions than gley marsh soils under a steady water table. Accurate CH4 estimates should include weather events that cause rapid changes in soil moisture regimes. The increasing frequency of extreme drought and intense precipitation events with global warming may affect CH4 emissions from different types of wetlands by regulating drying–wetting cycles. To determine the effects of different water regimes on CH4 emissions, a mesocosm experiment was conducted. Soil cores sampled from peatland and gley marsh were subjected to two drying–wetting cycles (i.e., fluctuating between −10 and 10 cm for 7 and 15 d, respectively) and three steady water table treatments (10, 0, and −10 cm). Alternation between drying and wetting stimulated CH4 emissions (F = 16.03 for 7 d and F = 31.85 for 15 d, P &lt; 0.01). The highest emission pulses were observed between 4 and 9 d after the water table increased according to the models. Peak pulse emissions significantly increased by 41% in peatland and 109% in gley marsh after rewetting compared with that in the steady 0‐cm water table treatment. Peatland soils had higher CH4 emissions than gley marsh soils under steady water table treatments (P &lt; 0.01). This study shows that large pulses of CH4 can be emitted during short‐duration drying–wetting episodes. If these pulses are not accounted for in budgets, CH4 emissions may be incorrectly assessed when comparing with field measurements during regularly spaced sampling intervals over only a few days or weeks by the static opaque chamber technique. Accurate estimates of CH4 budgets not only depend on increased measurement frequency but by necessity should incorporate weather events that cause rapid changes in the soil moisture regime.

Muka Air Optimum Pada System Of Rice Intensification (SRI)

Pengendalian muka air merupakan cara mengelola air di sawah SRI. Petani cenderung mengaplikasikan muka air yang berbeda tergantung pada praktek pengelolaan air setempat. Hal ini dapat berimplikasi pada pertumbuhan tanaman yang dapat terlihat dari jumlah anakan. Pada penelitian ini dilakukan pengamatan pada pembentukan anakan padi SRI di berbagai perlakuan muka air. Muka air dikendalikan menggunakan tabung mariot dengan set-point -12, -7, -5, -3, 0, dan +2 cm dari permukaan tanah. Hasil penelitian menunjukkan nilai kelembaban tanah (Ɵ) berfluktuasi karena adanya penerapan irigasi berselang dan perbedaan muka air. Hal tersebut mempengaruhi jumlah anakan yang terbentuk dimana laju pembentukannya bervariasi antara 0,21-0,29 anakan/hari. Anakan pertama muncul pada 18 hari setelah tanam (HST). Jumlah anakan terus meningkat hingga mencapai nilai maksimal pada 63-72 HST. Studi empirik ini menunjukkan bahwa pengendalian muka air pada -5 cm dari permukaan tanah di budidaya padi SRI merupakan pengelolaan air terbaik dalam produksi anakan dengan produktivitas lahan dan air tertinggi daripada penerapan muka air lainnya. Konsistensi produksi anakan dari awal pembentukan anakan hingga akhir dari musim tanam terlihat pada perlakuan ini.

The effect of water table decline on soil CO2 emission of Zoige peatland on eastern Tibetan Plateau: A four-year in situ experimental drainage

Water table decline is a major threat to soil organic carbon in peatlands worldwide principally because it may largely increase soil CO2 emission (SCE). This study is to determine the response of SCE to water table decline in the Zoige peatland of Tibetan Plateau, which has experienced rapid decline of water table due to climate change and anthropogenic drainage. We conducted a field in situ drainage experiment consisting of low (plots surrounded by 50cm deep ditches), intermediate (20cm deep) and high (intact) water table levels. The experiment lasted for about four years, during which we measured SCE rate and associated variables including soil temperature and moisture with a higher frequency in the growing season (May–September) than the non-growing season (October–April). Experimental drainage decreased water table height by ca. 12cm and 15cm (relative to the intact) and soil moisture (at 5cm soil) by 6% and 12% (relative to 45% in the intact) on average in intermediate and low water table treatments, respectively, but it did not affect soil temperature during the experimental years.The effect of drainage on SCE varied with season. In the non-growing season, the drainage effect was non-significant in each measurement possibly because the low-temperature effect overrode the drainage effect on SCE. In the growing season, the drainage mostly increased the emission except for several cases, in which a negative effect was observed. The negative effect of drainage could be due to the low soil moisture (<25%) in the drained treatments. Provided that the magnitude and the duration of the SCE increase were greater than those of the decrease, it can be estimated that drainage increased SCE by 17% and 20% on average in the low and the intermediate water table treatments, respectively, over the experimental years. Our results suggest that water table decline may facilitate net carbon emission and hence decrease soil carbon storage in the Zoige peatland. We call for artificial filling of the ditches that were historically created by both human beings and storm waters to increase water table in the Zoige peatland.