Drainage water management via controlled drainage (CD) and subirrigation (SI) has shown positive effects on water quality. To determine the impact of CD and SI in the Red River Valley (RRV), data from two fields, each with CD and SI, were analyzed. Water samples taken during SI from a North Dakota field during 2012-2018 were significantly different from those taken during CD and free drainage (FD). This was likely due to the SI water source of marginal quality, which also impacted soil quality near the drain tile. Three Minnesota fields were compared during 2013-2019, each with differing drainage practices. Results from a rainfall event showed an intermediate water table depth in the CD and SI field, along with a higher phosphate but lower nitrate concentration in surface runoff samples compared to subsurface drainage samples. Despite differences found between these fields, correlation between drainage practice and crop yield was not present.

<p>Controlled drainage is a management strategy designed to mitigate water quality issues caused by subsurface drainage. To improve controlled drainage system management and better understand its hydrological and environmental effects, this study analyzed water table recession rate, as well as drain flow, nitrate and phosphorus loads of both free and controlled drainage systems, and simulated the hydrology of a free drainage system to evaluate surface runoff and ponding at the Davis Purdue Agricultural Center located in Eastern Indiana. </p> <p>Statistical analyses, including paired watershed approach and paired t-test, indicated that controlled drainage had a statistically significant effect (<i>p</i>-value <0.01) on the rate of water table fall and reduced the water table recession rate by 29% to 62%. The slower recession rate caused by controlled drainage can have negative impacts on crop growth and trafficability by causing the water table to remain at a detrimental level for longer. This finding can be used by farmers and other decision-makers to improve the management of controlled drainage systems by actively managing the system during storm events. </p> <p>A method was developed to estimate drain flow during missing periods using the Hooghoudt equation and continuous water table observations. Estimated drain flow was combined with nutrient concentrations to show that controlled drainage decreased annual nitrate loads significantly (p<0.05) by 25% and 39% in two paired plots, while annual soluble reactive phosphorus (SRP) and total phosphorus (TP) loads were not significantly different. These results underscore the potential of controlled drainage to reduce nitrate losses from drained landscapes with the higher level of outlet control during the non-growing season (winter) providing about 70% of annual water quality benefits and the lower level used during the growing season (summer) providing about 30%. </p> <p>Three different methods including monitored water table depth, a digital photo time series and the DRAINMOD model simulations were used to determine the generation process of surface ponding and runoff and the frequency of incidence. The estimated annual water balance indicated that only 7% of annual precipitation contributed to surface runoff. Results from both simulations and observations indicated that all of the ponding events were generated as a result of saturation excess process rather than infiltration excess.</p> <p>Overall, nitrate transport through controlled drainage was lower than free drainage, indicating the drainage water quality benefits of controlled drainage, but water table remained at a higher level for longer when drainage was controlled. This can have negative impacts on crop yields, when water table is above a detrimental level, and can also increase the potential of nutrient transport through surface runoff since the saturation excess was the main reason for generating runoff at this field.</p>

<p>Daily nitrate-N, soluble reactive phosphorus and total phosphorus loads in subsurface drainage were quantified in an agricultural farm field in eastern Indiana (Davis Purdue Agricultural Center).</p> <p><b>Site description:</b> The data was collected from the field W at Davis Purdue Agricultural Center (DPAC) located in eastern Indiana. Field W is relatively flat (slope < 1%), with 0.16 km2 total area, divided into four plots, northwest (NW), southwest (SW), northeast (NE), and southeast (SE) with areas ranging from 3.5 ha to 3.7 ha. The four soil series at the site range from very poorly to somewhat poorly drained, with a small portion of moderately well drained series. The subsurface drainage system was installed in 2004, with 10-cm laterals having an approximate depth of 1 m and spacing of 14 m, resulting in a drainage intensity of 1.1 cm day-1 and drainage coefficient of 1 cm day-1. Drainage in the SE and NW plots was controlled at two different levels during some periods depending on the season, while the SW and NE were allowed to drain freely. This field has been in a corn-soybean rotation since 2011 and in continuous corn before that, and was managed using chisel-plow tillage in the fall and field cultivator tillage in the spring during the study period. Nitrogen (N) and phosphorus (P) fertilizers were applied at different rates prior to and after planting corn. Phosphorus was also applied prior to soybean planting in two of the three soybean years. The rate and timing of fertilizer applications were uniform for all plots and were based on Purdue Extension recommendations. Further details of the site management and data are available in Abendroth et al. (2017). More information about this site and fertilizer application can be found in Saadat et al., 2018.</p> <p><b>Sampling strategy and load calculation:</b> Automated water samplers (ISCO) were used to draw samples from the drainage outlet flow of each plot. Samples were collected every hour when flow was present except during winter, and combined into weekly composite samples varying in length from twice a week to biweekly. During the winter, water samples were collected manually to avoid freezing problems, approximately every week whenever flow was present. Samples were kept frozen until analysis and then analyzed on a SEAL Analytical AQ2 auto-analyzer to be tested for nitrate+nitrite-N (referred to nitrate-N), soluble reactive phosphorus (SRP) and total phosphorus (TP) according to US EPA methods.</p> <p>Daily nitrate-N, SRP and TP concentration values needed for the load calculations were estimated using linear interpolation. After estimating daily concentrations, daily loads were calculated by multiplying the daily drain flow by estimated daily concentrations.</p> <p><b>References: </b>Saadat, S., Bowling, L., Frankenberger, J. and Kladivko, E., 2018. Nitrate and phosphorus transport through subsurface drains under free and controlled drainage. <i>Water research, 142: </i>196-207.</p><br>

No description available.

The fate of the carbon and nitrogen in dairy farm effluent (DFE) applied onto soil was investigated through laboratory experiments and field lysimeter studies. They resulted in the development and testing of a complex carbon (C) and nitrogen (N) simulation model (CaNS-Eff) of the soil-plant-microbial system. To minimise the risk of contamination of surface waters, regulatory authorities in New Zealand promote irrigation onto land as the preferred treatment method for DFE. The allowable annual loading rates for DFE, as defined in statutory regional plans are based on annual N balance calculations, comparing N inputs to outputs from the farming system. Little information is available, however, to assess the effects that these loading rates have on the receiving environment. It is this need, to understand the fate of land-applied DFE and develop a tool to describe the process, that is addressed in this research. The microbially mediated net N mineralisation from DFE takes a central role in the turnover of DFE, as the total N in DFE is dominated by organic N. In a laboratory experiment, where DFE was applied at the standard farm loading rate of 68 kg N ha⁻¹, the net C mineralisation from the DFE was finished 13 days after application and represented 30% of the applied C, with no net N mineralisation being measured by Day 113. The soluble fraction of DFE appeared to have a microbial availability similar to that of glucose. The low and gradually changing respiration rate measured from DFE indicated a semi-continuous substrate supply to the microbial biomass, reflecting the complex nature and broad range of C compounds in DFE. The repeated application of DFE will gradually enhance the mineralisable fraction of the total soil organic N and in the long term increase net N mineralisation. To address the lack of data on the fate of faecal-N in DFE, a ¹⁵N-labelled faecal component of DFE was applied under two different water treatments onto intact soil cores with pasture growing on them. At the end of 255 days, approximately 2% of the applied faecal ¹⁵N had been leached, 11 % was in plant material, 11 % was still as effluent on the surface, and 40% remained in the soil (39% as organic N). Unmeasured gaseous losses and physical losses from the soil surface of the cores supposedly account for the remaining ¹⁵N (approximately 36%). Separate analysis of the total and ammonium nitrogen contents and ¹⁵N enrichments of the DFE and filtered sub-samples (0.5 mm, 0.2µm) showed that the faecal-N fraction was not labelled homogeneously. Due to this heterogeneity, which was exacerbated by the filtration of DFE on the soil surface, it was difficult to calculate the turnover of the total faecal-N fraction based on ¹⁵N results. By making a simplifying assumption about the enrichment of the ¹⁵N in the DFE that infiltrated the soil, the contribution from DFE-N to all plant available N fractions including soil inorganic N was estimated to have been approximately 11 % of the applied DFE-N. An initial two-year study investigating the feasibility of manipulating soil water conditions through controlled drainage to enhance denitrification from irrigated DFE was extended a further two years for this thesis project. The resulting four-year data set provided the opportunity to evaluate the sustainability of DFE application onto land, an extended data set against which to test the adequacy of CaNS-Eff, and to identify the key processes in the fate of DFE irrigated onto soil under field conditions. In the final year of DFE irrigation, 1554 kg N ha⁻¹ of DFE-N was applied onto the lysimeters, with the main removal mechanism being pasture uptake (700 kg N ha⁻¹ yr⁻¹ removed). An average of 193 kg N ha⁻¹ yr⁻¹ was leached, with 80% of this being organic N. The nitrate leaching decreased with increasing soil moisture conditions through controlled drainage. At the high DFE loading rate used, the total soil C and N, pH and the microbial biomass increased at different rates over the four years. The long-term sustainability of the application of DFE can only be maintained when the supply of inorganic N is matched by the demand of the pasture. The complex simulation model (CaNS-Eff) of the soil-plant-microbial system was developed to describe the transport and transformations of C and N components in effluents applied onto the soil. The model addresses the shortcomings in existing models and simulates the transport, adsorption and filtration of both dissolved and particulate components of an effluent. The soil matrix is divided into mobile and immobile flow domains with convective flow of solutes occurring in the mobile fraction only. Diffusion is considered to occur between the micropore and mesopore domains both between and within a soil layer, allowing dissolved material to move into the immobile zone. To select an appropriate sub-model to simulate the water fluxes within CaNS-Eff, the measured drainage volumes and water table heights from the lysimeters were compared to simulated values over four years. Two different modelling approaches were compared, a simpler water balance model, DRAINMOD, and a solution to Richards' equation, SWIM. Both models provided excellent estimation of the total amount of drainage and water table height. The greatest errors in drainage volume were associated with rain events over the summer and autumn, when antecedent soil conditions were driest. When soil water and interlayer fluxes are required at small time steps such as during infiltration under DFE-irrigation, SWIM's more mechanistic approach offered more flexibility and consequently was the sub-model selected to use within CaNS-Eff. Measured bromide leaching from the lysimeters showed that on average 18% of the bromide from an irrigation event bypassed the soil matrix and was leached in the initial drainage event. This bypass mechanism accounted for the high amount of organic N leached under DFE-irrigation onto these soils and a description of this bypass process needed to be included in CaNS-Eff. Between 80 and 90% of the N and C leached from the lysimeters was particulate (> 0.2 µm in size), demonstrating the need to describe transport of particulate material in CaNS-Eff. The filtration behaviour of four soil horizons was measured by characterising the size of C material in a DFE, applying this DFE onto intact soil cores, and collecting and analyzing the resulting leachate using the same size characterisation. After two water flushes, an average of 34% of the applied DFE-C was leached through the top 0-50 mm soil cores, with a corresponding amount of 27% being leached from the 50-150 mm soil cores. Most of the C leaching occurred during the initial DFE application onto the soil. To simulate the transport and leaching of particulate C, a sub-model was developed and parameterised that describes the movement of the effluent in terms of filtering and trapping the C within a soil horizon and then washing it out with subsequent flow events. The microbial availability of the various organic fractions within the soil system are described in CaNS-Eff by availability spectra of multiple first-order decay functions. The simulation of microbial dynamics is based on actual consumption of available C for three microbial biomass populations: heterotrophs, nitrifiers and denitrifiers. The respiration level of a population is controlled by the amount of C that is available to that population. This respiration rate can vary between low level maintenance requirements, when very little substrate is available, and higher levels when excess substrate is available to an actively growing population. The plant component is described as both above and below-ground fractions of a rye grass-clover pasture. The parameter set used in CaNS-Eff to simulate the fate of DFE irrigated onto the conventionally drained lysimeter treatments over three years with a subsequent 10 months non-irrigation period was derived from own laboratory studies, field measurements, experimental literature data and published model studies. As no systematic calibration exercise was undertaken to optimise these parameters, the parameter set should be considered as "initial best estimates" and not as a calibrated data set on which a full validation of CaNS-Eff could be based. Over the 42 months of simulation, the cumulative drainage from CaNS-Eff for the conventionally drained DFE lysimeter was always within the 95% CI of the measured value. On the basis of individual drainage bulking periods, CaNS-Eff was able to explain 92% of the variation in the measured drainage volumes. On an event basis the accuracy of the simulated water filled pore space (WFPS) was better than that of the drainage volume, with an average of 70% of the simulated WFPS values being within the 95% CI for the soil layers investigated, compared to 44% for the drainage volumes. Overall the hydrological component of CaNS-Eff, which is based on the SWIM model, could be considered as satisfactory for the purposes of predicting the soil water status and drainage volume from the conventionally drained lysimeter treatment for this study. The simulated cumulative nitrate leaching of 4.7 g NO₃-N m⁻² over the 42 months of lysimeter operation was in good agreement to the measured amount of 3.0 (± 2.7) g NO₃-N m⁻². Similarly, the total simulated ammonium leaching of 2.7g NH₄- N m⁻² was very close to the measured amount of 2.5 (± 1.35) g NH₄- N m⁻² , however the dynamics were not as close to the measured values as with the nitrate leaching. The simulated amount of organic N leached was approximately double that measured, and most of the difference originated from the simulated de-adsorption of the dissolved fraction of organic N during the l0-month period after the final DFE irrigation. The 305 g C m⁻² of simulated particulate C leached was close to the measured amount of 224 g C m⁻² over the 31 months of simulation. The dissolved C fraction was substantially over-predicted. There was good agreement in the non-adsorbed and particulate fractions of the leached C and N in DFE. However, the isothermic behaviour of the adsorbed pools indicated that a non-reversible component needed to be introduced or that the dynamics of the de-adsorption needed to be improved. Taking into account that the parameters were not calibrated but only "initial best estimates", the agreement in the dynamics and the absolute amounts between the measured and simulated values of leached C and N demonstrated that CaNS-Eff contains an adequate description of the leaching processes following DFE irrigation onto the soil. The simulated pasture N production was in reasonable agreement with the measured data. The simulated dynamics and amounts of microbial biomass in the topsoil layers were in good agreement with the measured data. This is an important result as the soil microbial biomass is the key transformation station for organic materials. Excepting the topsoil layer, the simulated total C and N dynamics were close to the measured values. The model predicted an accumulation of C and N in the topsoil layer as expected, but not measured. Although no measurements were available to compare the dynamics and amounts of the soil NO₃-N and NH₄-N, the simulated values appear realistic for an effluent treatment site and are consistent with measured pasture data. Considering the large amount of total N and C applied onto the lysimeters over the 42 months of operation (4 t ha⁻¹ of N and 42 t ha⁻¹0f C), the various forms of C and N in dissolved and particulate DFE as well as in returned pasture, and that the parameters used in the test have not been calibrated, the simulated values from CaNS-Eff compared satisfactorily to the measured data.