Fertigation Events Research Articles

Spatiotemporal variation of event related N2O and CH4 emissions during fertigation in a California almond orchard

Nitrogen fertilizer applied to soil is the primary source of the greenhouse gas (GHG) nitrous oxide (N2O). The assessment of N2O emissions, or net fluxes of the GHG methane (CH4), are lacking for upland, arid agricultural ecosystems worldwide. In California, where rates of application for nitrogen (N) can exceed 300 kg per hectare for N‐intensive fruit and nut crops (>2 million acres), liquid N fertilizers applied through microirrigation systems (fertigation) represent the predominant method of N fertilization. Little information is available for how these concentrated and spatially discrete N solution applications influence N2O emissions and net CH4 fluxes (the sum of methanogenic and methanotrophic activity). In this study we examined soil N2O‐N emissions and net CH4 fluxes for drip and stationary microsprinklers, two of the most widely used fertigation emitters, in an almond orchard where 235.5 kg N/ha were applied during the season of measurement (2009–2010). We accomplished this by modeling the spatial patterns of N2O and CH4 at the scale of meters and centimeters using simple mathematical approaches. For two applications of 33.6 kg/ha and three applications of 56.1 kg/ha targeted to the phenologic stages with highest tree N demand, the spatial patterns of N2O fluxes were similar to the emitter water distribution pattern and independent of temperature and fertilizer N form applied. Net CH4 fluxes were extremely low and there was no discernible spatial pattern, but areas kept dry (driveways between tree rows) generally consumed CH4 while it was produced in the microirrigation wet‐up area. The N2O‐N emissions for fertigation events at the scale of days, and over a season, were significantly higher from the drip irrigated orchard (1.6 ± 0.7 kg N2O‐N ha−1yr−1) than a microsprinkler irrigated orchard (0.6 ± 0.3 kg N2O‐N ha−1 yr−1). N2O emissions and net CH4 fluxes were only significantly correlated with soil water filled pore space and not with mineral‐N. The correlation was much better for N2O emissions. Our results greatly improve our ability to scale N2O production to the orchard level, and provide growers with a tool for lowering almond orchard carbon and nitrogen footprints.

Two-dimensional modeling of water and nitrogen fate from sweet sorghum irrigated with fresh and blended saline waters

The need for reducing irrigation water demand and non-point source pollution all across Europe has made sweet sorghum [Sorghum bicolor (L.) Moench], due to its lower water and nutrient requirements, an interesting alternative to other traditional summer crops in European Mediterranean regions. HYDRUS-2D was used to model the fate of nitrogen in a plot planted with sweet sorghum grown under Mediterranean conditions between 2007 and 2010, while considering drip irrigation scenarios with different levels of nitrogen and salty waters. HYDRUS-2D simulated water contents, ECsw, and NNH4+ and NNO3− concentrations continuously for the entire duration of the field experiment, while producing RMSE between simulated and measured data of 0.030 cm3cm−3, 1.764dSm−1, 0.042mmolcL−1, and 3.078mmolcL−1, respectively. Estimates for sweet sorghum water requirements varied between 360 and 457mm depending upon the crop season and the irrigation treatment. Sweet sorghum proved to be tolerant to saline waters if applied only during one crop season. However, the continuous use of saline waters for more than one crop season led to soil salinization, and to root water uptake reductions due to the increasing salinity stress. The relation found between NNO3− uptake and dry biomass yield (R2=0.71) showed that nitrogen needs were smaller than the uptakes estimated for the scenario with the highest levels of nitrogen application. The movement of N out of the root zone was dependent on the amount of water flowing through the root zone, the amount of N applied, the form of N in the fertilizer, and the timing and number of fertigation events. The simulations with HYDRUS-2D were useful to understand the best strategies toward increasing nutrient uptake and reducing nutrient leaching. In this sense, NNO3− uptakes were higher when fertigation events were more numerous and the amounts applied per event smaller.

The Effects of Drip Irrigation System Uniformity on Soil Water and Nitrogen Distributions

The effects of drip irrigation system uniformity and nitrogen application rate on the distribution of water and nitrate in the soil were investigated through field experiments to modify the current design and evaluation standards for drip irrigation uniformity. The experiments were conducted in a solar-heated greenhouse in the 2009 and 2010 growing seasons of Chinese cabbage. Three statistical uniformity coefficients (Us = 55%, 73%, and 95%) and two nitrogen application rates (150 and 300 kg ha-1) were evaluated in 2009. In 2010, three Us values (53%, 65%, and 94%) and one nitrogen application rate (225 kg ha-1) were tested. The distribution of the soil water content and bulk electrical conductivity was monitored continuously with equally spaced frequency domain reflectometry (FDR) sensors located along a dripline. Gravimetric samples of soil for each plot were collected regularly to determine the distribution of nitrate. For all of the tested system uniformities, the soil water content displayed high uniformity coefficients throughout the entire growing season. The effects of system uniformity and nitrogen application rate on the seasonal mean water content and bulk electrical conductivity (ECb) and on the seasonal mean uniformity of water content and bulk electrical conductivity were insignificant at a significance level of 0.05. The uniformity coefficient of the soil bulk electrical conductivity and nitrate content was substantially lower than that of the soil water content and was dependent on the uniformity of the initial salt and nutrient constituents in the soil. Moreover, the system uniformity and nitrogen application rate had an insignificant effect on the uniformity of the nitrate content. The results of this study showed that uniformity values that are lower than those recommended by the current standards can be used in drip irrigation systems if sufficient irrigation and fertigation events are conducted to approach a uniform distribution of water and nutrients in the soil.

Transpiração do tomateiro cultivado em substrato e sua influência na fração lixiviada e na condutividade elétrica da solução nutritiva drenada

The objective of this work was to evaluate the influence of tomato transpiration on the leaching fraction and electrical conductivity (EC) of the nutrient solution drained in the sand substrate under greenhouse growing conditions. Two fertigation techniques were used, one denoted by conventional control system and the other by computerized control system. In the conventional control system, the nutrient solution was applied by using fixed time intervals between fertigation events. In the other system, the application occurred according to transpiration estimates, which were performed by the control algorithm of the computerized system. Under cloudy conditions, the EC of the drained nutrient solution decreased in both systems as a result of low transpiration and high leaching fractions, which mitigated substrate salinization. However, under high values of solar radiation, EC increased due to low leaching fractions. The results demonstrated that, under cloudy conditions, the computerized control system reduced effluent volumes by 54% as compared to the conventional control system and, simultaneously, prevented substrate salinization by maintaining mean EC values of the drained solution in the range from 2.9 to 3.5 dS m-1.

Irrigation Water and Nitrate-nitrogen Loss Characterization in Southern Florida Nurseries: Cumulative Volumes, Runoff Rates, Nitrate-nitrogen Concentrations and Loadings, and Implications for Management

Enrichment of surface water with nitrate-nitrogen (NO3-N) is a significant problem throughout the world. In support of developing a method for removing NO3-N from water using denitrification, this project characterized runoff events at two nurseries in southern Florida to provide information needed for designing capacity. Specifically, estimates of runoff rates and volumes, NO3-N concentrations and loadings were profiled during intensively sampled fertigation events at a foliage plant nursery and a bedding plant nursery. Discharge volumes and rates varied with event, ranging from 2,487 to 20,935 L and 59.2 to 126 L·min−1, respectively, per event. NO3-N concentrations ranged from 0.7 to 386.4 mg·L−1, and event loadings ranged from 51 to 3024 g, indicating that significant losses may be realized. This project provided valuable hydraulic and chemical loading information needed for the development and design of bioremediation tools for the horticultural industry.

Impacts of management on decomposition and the litter-carbon balance in irrigated and rainfed no-till agricultural systems

The litter carbon (C) pool of a single litter cohort in an agroecosystem is the difference between net primary productivity and decomposition and comprises 11–13% of the total C pool (litter and soil 0–15 cm depth) post-harvest. This litter-C pool is highly dynamic and up to 50% can be decomposed in the first 12 months of decomposition. Thus, understanding litter-C dynamics is key in understanding monthly and annual total ecosystem carbon dynamics. While the effects of management practices such as irrigation and fertilization on productivity are well understood, the effects on decomposition are less studied. While irrigation and fertilization increase productivity, this will only lead to increased litter-C residence time and litter-C pool accretion if these techniques do not also result in equivalent or greater increases in decomposition. Management could potentially have impacts on litter-C accretion by increasing litter inputs, changing plant-C allocation, plant tissue quality, or decomposition rates. We examined carbon loss of one annual cohort of maize litter using in situ nylon litter bags for 3 years in three no-till fields with differing management regimes: irrigated continuous maize with a pre-planting fertilization application and two fertigation events, irrigated maize–soybean rotation with the same fertilization regime as the irrigated continuous maize management regime, and rainfed maize–soybean rotation with a single pre-planting fertilization event. We addressed the effects of these different management regimes on net primary productivity and litter inputs, litter nitrogen (N) concentrations and carbon quality measures, plant C allocation, decomposition rates and the potential changes in the overall litter-C balance. We found that irrigation/fertigation management increased litter inputs, led to changes in plant tissue quality, had no effect on carbon allocation, and increased decomposition rates. This balance of both greater litter inputs and outputs of C from the irrigated management regimes led to a similar litter-C balance for this litter cohort in the irrigated and rainfed management regimes after 3 years of decomposition. Our data clearly show that merely increasing litter-C inputs through irrigation/fertigation practices is not sufficient to increase litter-C residence time because decomposition rates also increase. Therefore, close monitoring of decomposition rates is essential for understanding litter-C pool dynamics.

Effect of Fertigation Strategy on Nitrogen Availability and Nitrate Leaching using Microirrigation

Injection during the middle one-third or the middle one-half of the irrigation is recommended for fertigation using microirrigation. However, short fertigation events are commonly used by growers. This project investigated the effect of fertigation practices on nitrate availability and leaching. The first phase of the project (completed) determined nitrate distributions in the root zone for four microirrigation systems, three soil types, and five fertigation strategies using the HYDRUS-2D computer simulation model. Fertigation strategies included injecting for short time periods at the beginning, middle, and end of the irrigation cycle, respectively; injecting during the middle 50% of the irrigation cycle, and continuous injection. The second phase (ongoing) is investigating the distribution of nitrate, ammonium, urea, phosphate, and potassium around the drip line for selected Phase 1 scenarios. Phase 1 results showed less nitrate leached from the root zone for a 2-h injection time at the end of a long irrigation event compared to injection at the beginning and middle of a long irrigation event for surface drip irrigation. A more continuous fertigation resulted in a more uniform distribution of nitrate in the soil. The results were less conclusive for subsurface drip lines, due to upward movement of nitrate above the drip line. Little difference in nitrate leaching occurred for short irrigation events, regardless of fertigation strategy. Data analysis of the Phase 2 modeling is under way. The HYDRUS-2D model included partition coefficients for ammonium, phosphate, and potassium, and parameters for hydrolysis (conversion of urea to ammonium), nitrification, and denitrification.

Taxa de emissão de CO2 de um latossolo fertirrigado com ácido fosfórico por gotejamento

A aplicação de fertilizantes fosfatados por meio de fertirrigação com sistemas de irrigação localizada pode causar obstrução de emissores. Para evitar esse problema, pode ser utilizado o ácido fosfórico como fonte de fósforo às plantas. Porém, têm sido pouco investigados os efeitos da irrigação relacionados às perdas de CO2 do solo para a atmosfera, em conseqüência da decomposição do carbono orgânico e da infiltração de água no solo. Neste trabalho, investigou-se, no período de um mês, o efeito da fertirrigação com ácido fosfórico nas taxas de emissão de CO2 de um latossolo desprovido de vegetação, na Área Experimental de Irrigação da UNESP, Câmpus de Jaboticabal - SP. Utilizou-se de um sistema de irrigação por gotejamento, com delineamento experimental em blocos casualizados, constando de cinco repetições e cinco tratamentos (0; 30; 60; 90 e 120 kg ha-1de P2O5), aplicados via fertirrigação com ácido fosfórico. Verificou-se que as taxas de emissão de CO2 aumentaram significativamente após as fertirrigações, porém não houve efeito da dose do ácido fosfórico sobre as taxas. A umidade do solo mostrou-se um fator importante na relação entre as variações das taxas de emissão e a temperatura do solo ao longo do período estudado.

Two-dimensional modeling of nitrate leaching for various fertigation scenarios under micro-irrigation

The regular application of nitrogen fertilizers by irrigation is likely responsible for the increase in nitrate concentrations of groundwater in areas dominated by irrigated agriculture. Consequently, sustainable agricultural systems must include environmentally sound irrigation practices. To reduce the harmful effects of irrigated agriculture on the environment, the evaluation of alternative irrigation water management practices is essential. Micro-irrigation offers a large degree of control, enabling accurate application according to crop water requirements, thereby minimize leaching. Furthermore, fertigation allows the controlled placement of nutrients near the plant roots, reducing fertilizer losses through leaching into the groundwater. The presented two-dimensional modeling approach provides information to improve fertigation practices. The specific objective of this project was to assess the effect of fertigation strategy and soil type on nitrate leaching potential for four different micro-irrigation systems. We found that seasonal leaching was the highest for coarse-textured soils, and conclude that fertigation at the beginning of the irrigation cycle tends to increase seasonal nitrate leaching. In contrast, fertigation events at the end of the irrigation cycle reduced the potential for nitrate leaching. For all surface-applied irrigation systems on finer-textured soils, lateral spreading of water and nitrates was enhanced by surface water ponding, causing the water to spread across the surface with subsequent infiltration downwards and horizontal spreading of soil nitrate near the soil surface. Leaching potential increased as the difference between the extent of the wetted soil volume and rooting zone increased.

Fertigation Frequency for Subsurface Drip-Irrigated Broccoli

Subsurface-drip irrigation and fertigation with fluid N fertilizer sources offers substantial flexibility for N fertilizer management. Fertigation events can be scheduled as often as irrigation, up to several times per day. However, because of system or management constraints very frequent fertigation may not be possible or desirable for some growers. Optimum fertigation interval for subsurface drip-irrigated crops has not been well researched. A 3-yr field experiment was conducted on a sandy loam soil in southern Arizona with subsurface drip-irrigated broccoli (Brassica olearacea L. Italica) to i) determine the effects of N rate and fertigation frequency on crop yield, quality, and crop N status, and ii) estimate a N balance. Broccoli was planted in two rows per raised bed 1.02 m apart, with one drip line buried 0.15 to 0.20 m deep within each bed. The experiment included factorial combinations of two N rates and four fertigation frequencies (intervals of 1, 7, 14, and 28 d). Broccoli marketable yield and quality were responsive to N rate, but not to increased fertigation frequency. During one of three seasons, fertigation frequency significantly (P ≥ 0.05) affected crop N uptake, but there was no trend of increasing N uptake with increasing fertigation frequency. Unaccounted fertilizer N and apparent N use efficiency (ANUE) were calculated for two seasons. Unaccounted fertilizer N averaged 20 and 75 kg ha -1 and ANUE 90 and 81% with 250 and 350 kg N ha -1 applied, respectively. Neither was significantly affected by fertigation frequency. We conclude, therefore, that for broccoli production with subsurface-drip irrigation on sandy loam or finer soils, fertigation can be applied as infrequently as monthly, without compromising crop yield or quality, or causing excessive N losses.

Solute Transport Modeling in Overland Flow Applied to Fertigation

A model of solute transport in overland flow is developed and applied to the simulation of surface fertigation. Water flow is simulated using the depth-averaged, 1D shallow water equations. Solute flow is represented by an advection-diffusion model. The resulting set of three partial differential equations is sequentially solved at each time step. First, water flow is computed using the explicit two-step McCormack method. Based on the obtained velocity field, solute transport is explicitly determined from the advection-diffusion equation using the operator split technique. Four field experiments involving fertigation events on an impervious free-draining border were performed to validate the proposed model and to obtain estimates of Kx, the longitudinal dispersion coefficient. A value of Kx = 0.075 m2 s−1 satisfactorily reproduces the field experiments. The model is also applied to the simulation of a fertigation event on a pervious border. A sensitivity analysis is performed to assess the dependence of f...

Soil acidification caused by four commercial nitrogen fertilizer solutions and subsequent soil pH rebound

Soil acidification resulting from nitrification of ammonium‐ and urea‐containing nitrogen (N) fertilizers is a management problem in tree fruit orchards, particularly where fertigation through drip irrigation systems is practiced. Anecdotal field evidence suggested that fertilizer‐induced acidification may be transitory because soil pH will increase, or “rebound,” during the following winter. We conducted a laboratory experiment to determine the influence of N fertilizer solution source [calcium nitrate (CN), calcium‐ammonium nitrate (CAN), ammonium nitrate (AN), and urea‐ammonium nitrate (UAN)] and rate (0, 100, 300, and 500 mg total N L‐1 in fertigation solution) on the pH of five Washington orchard soils, using a procedure to simulate two fertigation events followed by a water‐only leaching event. Soil pH was measured five weeks after each event. The relative ranking of the acidification potential of the four fertilizers was consistent with their published values: CN<CAN<AN=UAN. Although CN is usually stated as having a net basic soil reaction, the CN product had no or a slightly acidifying effect, consistent with the presence of the small amount of NH4 in the commercial formulation. At each simulated management stage, soil pH tended to decrease with increasing N rate for each N source. Leaching the fertilizer‐acidified soils caused pH to increase, with one‐third of all the plus‐N treatments returning to the zero‐N treatment pH. The results of the current experiment suggest a possible mechanism explaining the field observations of soil pH rebound. Furthermore, the substantial changes in soil pH induced by N fertilization or leaching suggest that the timing of soil pH assessment should be determined by its temporal relation to specific farming practices.