Drip fertigation and plant hedgerows significantly reduce nitrogen and phosphorus losses and maintain high fruit yields in intensive orchards

A field experiment was carried out to evaluate the effects of drip fertigation combined with plant hedgerows on nitrogen and phosphorus runoff losses in intensive pear orchards in the Tai Lake Basin.Nitrogen and phosphorus runoff over a whole year were measured by using successional runoff water collection devices.The four experimental treatments were conventional fertilization(CK),drip fertigation(DF),conventional fertilization combined with plant hedgerows(C+H),and drip fertigation combined with plant hedgerows(D+H).The results from one year of continuous monitoring showed a significant positive correlation between precipitation and surface runoff discharge.Surface runoff discharge under the treatments without plant hedgerows totaled 15.86%of precipitation,while surface runoff discharge under the treatments with plant hedgerows totaled 12.82%of precipitation.Plant hedgerows reduced the number of runoff events and the amount of surface runoff.Precipitation is the main driving force for the loss of nitrogen and phosphorus in surface runoff,and fertilization is an important factor affecting the losses of nitrogen and phosphorus.In CK,approximately 7.36%of nitrogen and 2.63%of phosphorus from fertilization entered the surface water through runoff.Drip fertigation reduced the accumulation of nitrogen and phosphorus in the surface soil and lowered the runoff loss concentrations of total nitrogen(TN)and total phosphorus(TP).Drip fertigation combined with plant hedgerows significantly reduced the overall TN and TP losses by 45.38 and 36.81%,respectively,in comparison to the CK totals.Drip fertigation increased the vertical migration depth of nitrogen and phosphorus nutrients and reduced the accumulation of nitrogen and phosphorus in the surface soil,which increased the pear yield.The promotion of drip fertigation combined with plant hedgerows will greatly reduce the losses of nitrogen and phosphorus to runoff and maintain the high fruit yields in the intensive orchards of the Tai Lake Basin.

Growth and nitrogen productivity of drip-irrigated winter wheat under different nitrogen fertigation strategies in the North China Plain

Excessive application of nitrogen (N) fertilizer is the main cause of N loss and poor use efficiency in winter wheat (Triticum aestivum L.) production in the North China Plain (NCP).Drip fertigation is considered to be an effective method for improving N use efficiency and reducing losses,while the performance of drip fertigation in winter wheat is limited by poor N scheduling.A two-year field experiment was conducted to evaluate the growth,development and yield of drip-fertigated winter wheat under different split urea (46%N,240 kg ha^(-1)) applications.The six treatments consisted of five fertigation N application scheduling programs and one slow-release fertilizer (SRF) application.The five N scheduling treatments were N0–100 (0%at sowing and 100%at jointing/booting),N25–75 (25%at sowing and 75%at jointing and booting),N50–50(50%at sowing and 50%at jointing/booting),N75–25 (75%at sowing and 25 at jointing/booting),and N100–0 (100%at sowing and 0%at jointing/booting).The SRF (43%N,240 kg ha^(-1)) was only used as fertilizer at sowing.Split N application significantly (P<0.05) affected wheat grain yield,yield components,aboveground biomass (ABM),water use efficiency(WUE) and nitrogen partial factor productivity (NPFP).The N50–50 and SRF treatments respectively had the highest yield(8.84 and 8.85 t ha^(-1)),ABM (20.67 and 20.83 t ha^(-1)),WUE (2.28 and 2.17 kg m^(-3)) and NPFP (36.82 and 36.88 kg kg^(-1)).This work provided substantial evidence that urea-N applied in equal splits between basal and topdressing doses compete economically with the highly expensive SRF for fertilization of winter wheat crops.Although the single-dose SRF could reduce labor costs involved with the traditional method of manual spreading,the drip fertigation system used in this study with the N50–50 treatment provides an option for farmers to maintain wheat production in the NCP.

Effect of fertigation frequency on soil nitrogen distribution and tomato yield under alternate partial root-zone drip irrigation

Alternate partial root-zone drip fertigation (ADF) is a combination of alternating irrigation and drip fertigation,with the potential to save water and increase nitrogen (N) fertilizer efficiency.A 2-year greenhouse experiment was conducted to evaluate the effect of different fertigation frequencies on the distribution of soil moisture and nutrients and tomato yield under ADF.The treatments included three ADF frequencies with intervals of 3 days (F3),6 days (F6) and 12 days (F12),and conventional drip fertigation as a control (CK),which was fertilized once every 6 days.For the ADF treatments,two drip tapes were placed 10 cm away on each side of the tomato row,and alternate drip irrigation was realized using a manual valve on the distribution tapes.For the CK treatment,a drip tape was located close to the roots of the tomato plants.The total N application rate of all treatments was 180 kg ha^(-1).The total irrigation amounts applied to the CK treatment were450.6 and 446.1 mm in 2019 and 2020,respectively;and the irrigation amounts applied to the ADF treatments were 60%of those of the CK treatment.The F3 treatment resulted in water and N being distributed mainly in the 0–40-cm soil layer with less water and N being distributed in the 40–60-cm soil layer.The F6 treatment led to 21.0 and 29.0%higher 2-year average concentration of mineral N in the 0–20 and 20–40-cm soil layer,respectively and a 23.0%lower N concentration in the 40–60-cm soil layer than in the CK treatment.The 2-year average tomato yields of the F3,F6,F12,and CK treatments were 107.5,102.6,87.2,and 98.7 t ha^(-1),respectively.The tomato yield of F3 was significantly higher (23.3%) than that in the F12 treatment,whereas there was no significant difference between the F3 and F6 treatment.The F6 treatment resulted in yield similar to the CK treatment,indicating that ADF could maintain tomato yield with a 40%saving in water use.Based on the distribution of water and N,and tomato yield,a fertigation frequency of 6 days under ADF should be considered as a water-saving strategy for greenhouse tomato production.

Simulation of water and nitrogen dynamics as affected by drip fertigation strategies

The aim of drip fertigation is synchronising the application of water and nutrients with crop requirements, and maintaining the proper concentration and distribution of nutrient and water in the soil. The wetting patterns and nutrient distributions under drip fertigation have been proved to be closely related to the fertigation strategies. In order to find out the critical factors that affect the nutrient distribution under different drip fertigaiton strategies, a computer simulation model HYDRUS2D/3D was used to simulate the water and nitrate distribution for various fertigation strategies from a surface point source. Simulation results were compared with the observed ones from our previous studies. A 15° wedge-shaped plexiglass container was used in our experiment to represent one-twenty-fourth of the complete cylinder. The height of container is 40 cm, and the radius is 41 cm. The ammonium nitrate solution was added through a no. 7 needle connected to a Mariotte tube with a flexible hose. The soil water content, nitrate and ammonium concentrations were measured. The comparison of simulated and observed data demonstrated that the model performed reliably. The numerical analysis for various fertigation strategies from a surface point source showed that：（1） The total amount of irrigation water, the concentration of the fertilizer solution and the amount of pure water used to flush the pipeline after fertilizer solution application are the three critical factors influencing the distribution of water and fertilizer nitrogen in the soil.（2） The fresh water irrigation duration prior to fertigation has no obvious effect on nitrate distribution. The longer flushing time period after fertigation resulted in nitrate accumulation closer to the wetting front. From the point of avoiding the possibility of nitrate loss from the root zone, we recommended that the flushing time period should be as shorter as possible.（3） For a given amount of fertilizer, higher concentration of the fertilizer applied solution reduces the potential of nitrate leaching in drip irrigation system. While, lower concentration of the fertilizer solution resulted in an uniform distribution of nitrate band closer to the wetted front.

Cotton Response to Variable Nitrogen Rate Fertigation through an Overhead Irrigation System

Recent increases in irrigated hectares in the Southeastern US have enabled growers to obtain higher yields through applying nutrients through irrigation water. Therefore, many growers apply nutrients through irrigation systems, known as fertigation. Currently, there are no practical decision-making tools available for variable-rate application of nitrogen (N) through overhead sprinkler irrigation systems. Therefore, field tests were conducted on cotton (Gossypium hirsutum L.) during the 2016 and 2017 growing seasons to 1) adapt the Clemson sensor-based N recommendation algorithms from a single side-dress application to multiple applications through an overhead irrigation system;and 2) to compare sensor-based VRFS with conventional nutrient management methods in terms of N use efficiency (NUE) and crop responses on three soil types. Two seasons of testing Clemson N prediction algorithms to apply multiple applications of N were very promising. The multiple applications of N compared to the grower’s conventional methods (even though less N was applied) had no impact on yields in either growing season. There was no difference in cotton yields between 101 and 135 kg/ha N applications in either management zone. Also, there were no differences in yield between sensor-based, multiple N applications and conventional N management techniques. In relation to comparisons of the sensor methods only applying N in three or four applications, statistically increased yields compared to single or split applications in 2016. Applying N in four applications, statistically increased yields compared to single, split or triple applications in 2017. When the sensor-based methods were compared to the grower’s conventional methods averaged over four treatments, the sensor-based N applications reduced fertilizer requirement by 69% in 2016 and 57% in 2017 compared to grower’s conventional methods. When comparing N rates among the four sensor-based methods (three or four) applications, increased N rates by 22 kg/ha in 2016 and 26 kg/ha in 2017 compared to single or split applications but increased the cotton lint yields by 272 and 139 kg/ha, for 2016 and 2017, respectively.

Main Methods Applied in Fertigation Technology

In order to better promote extension and application of fertigation technology,this paper elaborates major technical issues. It presents pipeline diameter control and increasing the uniformity in selection of methods of irrigation system types and in the process of system design. Besides,it introduces characteristics and use methods of main fertilizer application equipment,filter,and control devices. In addition,it lists amount of fertilizer application and irrigation according to target yield of crops,and describes major attentions for selection of fertilizers,irrigation,and soil moisture control.

Fertigation for Environmentally Friendly Fertilizers Application: Constraints and Opportunities for Its Application in Developing Countries

There is an increasing concern about agriculture’s role in polluting the environment which makes farmers feel guilty about using fertilizers. Fertigation is proposed as a panacea to this dilemma, which by this practice reaffirms the principles of 4Rs which are the right source, at the right rate, right time and right place. The aim of this study was to explore constraints and opportunities for its application in developing countries for environmentally friendly fertilizers application. It is a review of literature from government reports, legislature and published material on fertilization and irrigation initiatives of developing countries which include Rwanda, Nepal, Suriname, Zambia, Panama, Tanzania, Sri Lanka and South Sudan in addition to the case presented of China during the “2016 Environmentally Friendly Fertilizer Production, Application and Demonstration from Developing Countries” training course. The study found that in developing countries there is potential to apply fertigation as a way of environmentally friendly fertilizers application as it has been adopted in China. These opportunities include the following: Abundant natural resources like land and water, less polluted environment, conducive agricultural policies, zero duties levied on imported irrigation equipment. However, a number of limitations also are highlighted including: Lack of investment, lack of infrastructure, lack of information, requires expertise on plant nutrition and management of fertigation system, require soil analysis and proper interpretation which is done by experts. This study provides relevant information for fertigation planning and application in respective developing countries.

Effect of Long-term Drip Fertigation on Root Growth of Lychee and Soil pH

Through field experiment,we explore the impact of long-term drip fertigation on growth and distribution of lychee root and changes of soil pH in different layers of soil in lychee garden.The results show that drip fertigation can significantly promote the growth of lychee roots,and increase the contact area of root and soil;if it experiences six years of drip fertigation successively,the dry weight of root,root length and surface area of root in soil in drip fertigation area,will be 2.29 times,2.17 times and 2.25 times that in non-drip fertigation area,respectively.The lychee root is mainly distributed in 0-40 cm layer of soil,but there is conspicuous difference between drip fertigation area and non-drip fertigation area in terms of root distribution in 0-20 cm and 20-40 cm layer of soil.Drip fertigation is more favorable for the root to go deep inside the soil.Under long-term drip fertigation,the soil acidification in lychee garden is prominent,and in comparison with non-drip fertigation area,there is the greatest decline in soil pH in 10-20 cm layer of soil in drip fertigation area,reaching 1.47 units.

Distribution, Enrichment and Accumulation of Heavy Metals in Soil and <i>Trigonella foenum-graecum</i>L. (Fenugreek) after Fertigation with Paper Mill Effluent

The aim of the study was to investigate distribution, enrichment and accumulation of heavy metals in soil and Trigonella foenum-graecum (var. Pusa Early Bunching) after fertigation with paper mill effluent. Doses of paper mill effluent viz. 5%, 10%, 25%, 50%, 75% and 100% were used for fertigation of T. foenum-graecum along with bore well water (control). The results revealed that paper mill effluent had significant (P +, K+, Ca2+, Mg2+, Fe2+, TKN, PO3-4, SO2-4, Cd, Cr, Cu, Mn and Zn of the soil in both seasons. Insignificant (P > 0.05) changes in WHC and bulk density of the soil were observed after irrigation with paper mill effluent. The agronomical performance of T. foenum-graecum was increased from 5% to 25% concentration and decreased from 50% to 100% concentration of paper mill effluent as compared to control in both seasons. The heavy metals concentration was increased in T. foenum-graecum from 5% to 100% concentrations of paper mill effluent in both seasons. Biochemical components like crude proteins, crude fiber and crude carbohydrates were found maximum with 25% paper mill effluent in both seasons. The enrichment factor (Ef) of various heavy metals was in order of Cd > Mn > Cr > Cu > Zn > Fe for soil and Mn > Cu > Cr > Cd > Zn > Fe for T. foenum-graecum plants after fertigation with paper mill effluent. Therefore, paper mill effluent can be used as a biofertigant after appropriate dilution to improve yield of T. foenum-graecum.

Responses of Nitrogen Uptake and Yield of Winter Wheat to Nonuniformity of Sprinkler Fertigation

Field experiments were conducted to investigate the effects of nonuniformity of sprinkler fertigation and the amount of fertilizers applied through fertigation on nitrogen uptake and crop yield during two growing seasons of winter wheat in 2002-2003 and 2003-2004 at an experimental station in Beijing. In the experiments, the seasonal averaged Christiansen irrigation uniformity coefficient （CU） varied from 72% to 84%. Except for the fertilizer applied before planting, fertilizer was applied with the sprinkler irrigation system with a seasonal averaged CU for fertigation varied from 71% to 85%. Three levels of fertilizer applied varying from 0 to 180 kg N ha^-1 were used in the experiments. The experimental results demonstrated that sprinkler fertigation uniformity had insignificant effects on nitrogen uptake and crop yield for the uniformity range tested. Also, the influence of fertilizer applied through sprinkler fertigation on crop yield was minor, while the total nitrogen content for stem and nitrogen uptake increased with increasing fertilizer applied.

Root Characters of Maize as Influenced by Drip Fertigation Levels

The efficient use of water by modern irrigation systems is becoming increasingly important in arid and semi-arid regions with limited water resources. Field experiments were conducted during 2008-2010 to study the effect of drip fertigation with water soluble fertilizer on root growth of maize under maize based intercropping system. The experiment was laid out in strip plot design with three replications. The treatment consists of nine fertigation levels in main plots and four inter crops in sub plots. Root spread and root dry mass were increased under drip fertigation practices while rooting depth was more under surface irrigation. Drip fertigation with water soluble fertilizer improved the root system by inducing new secondary roots which are succulent and actively involved in physiological responses. Drip fertigation has pronounced effect on the root architecture especially in the production of highly fibrous root system.

Introduction of Fertigation in Sugarcane Production for Optimization of Water and Fertilizers Use

A fertigation experiment was conducted during 2009/2010 and 2010/2011 seasons under com-mercial field conditions in Kenana Sugar Scheme, Sudan (latitude 13.10’N and longitude 32.40’E) in heavy clay soils, with 65% clay, 24% silt, 11% sand and pH 7.5 - 8.5. The primary objective of this study was to compare different strategies for timing of injection, to develop management practices on the efficient use of water and fertilizers in production of sugarcane, maximize yield, and improve quality. In both seasons four treatments were studied in a randomized complete block design with three replications as: Injection of the dissolved urea (46% N) during entire irrigation time (100%), during the first half of the irrigation time, during the second half of the irrigation time, and Mechanical application of urea. The first three treatments were applied with the third irrigation cycle through the irrigation water so that nitrogen fertilizer in form of dissolved urea (46% N) was injected in irrigation water by means of pressure differential tank system which is based on the principle of a pressure differential being created by a valve and flow regulator forcing and injecting a varying amount of dissolved fertilizer into the irrigation water. In the fourth treatment the fertilizer spreader and rigid tine cultivator were used for urea application just before the third irrigation event. The reference evapotranspiration (ETo) and the amount of water required for irrigating sugarcane plants were calculated according to its phenological stages using Peman-Monteith approach. The results of this study support the general finding that the injection during the entire irrigation (100% of the irrigation) produced the best distribution uniformity of added urea. In this study, injection during the first half of the irrigation was not statistically different from injection during 100% of the irrigation.

Response of maize growth and soil biological characteristics to planting density under fertigation in a semi-arid region

Increasing the planting density can exacerbate crop competition for water,nutrients and space which results in a decline in the crop yields.However,the effect of increasing planting density on crop growth and soil biological characteristics in barren sandy land in the semi-arid regions are still unclear.In this study,we investigated the effects of six planting densities(5.4×10^(4),6.45×10^(4),7.95×10^(4),9.5×10^(4),9.75×10^(4) and 10.5×10^(4) plants/hm^(2))on maize growth,photosynthesis characteristics,yield and soil biological characteristics in barren sandy soil in the semi-arid region of Ningxia,China.The results indicated that the stem diameter and spike length decreased linearly with increasing planting density.The plant height,spike weight,grain weight and 100-grain weight decreased with increasing plating density.Moreover,the root length increased with increasing planting density.The diameter,volume and activity increased and then decreased with increasing planting density.There was no significant difference(p>0.05)in the effect of planting density on transpiration rate intercellular CO_(2) concentration.As well,the soil microbial biomass carbon and microbial biomass nitrogen decreased with increasing planting density.The soil catalase activities increased and then decreased with increasing planting density.The alkaline phosphatase activity,the amounts of soil bacteria and actinomycetes increased with increasing planting density.Generally,a moderately increasing planting density can improve maize yield when water and nutrients are sufficient.The optimal planting density was 8.29×10^(4) plants/hm^(2) and the highest yield was 15.84 t/hm^(2) in barren sandy soil in semi-arid region of Ningxia,China.This study provides a theoretical basis for high yield and high efficiency of maize.

Effects of fertigation strategies on water and nitrogen distribution under water storage pit irrigation for orchards

Water storage pit(WSP)irrigation is a simple and inexpensive technology suitable for orchards in semiarid and arid regions of North China.This study compared the effects of different fertigation strategies on water and nitrogen distribution,and ammonia volatilization.A fertigation experiment was conducted using a 30°wedge-shaped plexiglass soil container,which represents one-twelfth of the complete storage pit.The height of the container was 120 cm,and a plexiglass damper for simulating the zero flux plane of adjacent water storage pits was located at the 40 cm radius.Four fertigation strategies were used for WSP irrigation:solution application during the first half(N-W),the last half(W-N),the middle half of an irrigation cycle(W-N-W),and during the entire irrigation(N-N).Surface(SF)irrigation was used as a control treatment with solution application during the entire irrigation(SN-N).The experimental results showed that the soil water and ammonium contents at 0-10 cm soil depth under WSP irrigation were only 10.51%and 18.42% of those under SF irrigation,respectively.The cumulative NH3 volatilization under WSP irrigation was 51.71%-68.72% lower compared with that under SF irrigation.The soil water distributions were similar for all four fertigation strategies.NH3 volatilization mainly occurred at the pit wall interface,and cumulative NH3 volatilization loss followed the trend N-N>W-N>W-N-W>N-W.Ammonium was adsorbed into the soil and thus mostly remained near the pit wall.Low concentrations of ammonium were found near the edge of the wetting zone under all strategies.Compared to N-W,N-N and W-N-W treatments,W-N treatment decreased the nitrate accumulation at 80-90 cm by 38.6%,19.0%and 10.3%,respectively.The W-N strategy was suggested for minimizing potential nitrate leaching.

Optimal control algorithm of fertigation system in greenhouse based on EC model

Two new control algorithms based on MSP430 microcontroller unit(MCU)were developed to improve the performance of a fertigation system controlled by the electrical conductivity(EC)value of an irrigation nutrient solution in a greenhouse.The first algorithm is incremental proportional-integral-derivative(PID),and the second one is a two-stage combination algorithm(PID+fuzzy).With an improved multi-line mixing Venturi tube,several sets of experiments were conducted for a fertilizer absorption test under two conditions,namely,various suction lines and different EC target values settings.Under the first condition,with an EC target value of 2.0 mS/cm and opening of various suction pipes,the steady-state times are 186 s,172 s,134 s,and 122 s corresponding to the opening of one to four suction pipes,respectively,for PID+fuzzy control.The corresponding values are 220 s,196 s,158 s,and 148 s for incremental PID control.Under the second condition,four suction pipes are opened with different target EC values of 1.5 mS/cm,2.0 mS/cm,and 2.5 mS/cm,and the shortest response time and the minimum overshoot were obtained for PID+fuzzy control when the target EC value is 1.5 mS/cm,which are 96 s and 0.18 mS/cm,respectively.While the corresponding values are 112 s and 0.4 mS/cm,respectively for incremental PID control.The two control strategies can adjust the EC value to the target value for real-time control,but the combination control algorithm can be implemented more rapidly,accurately,and steadily with a small overshoot compared with incremental PID control.The combination algorithm(PID+fuzzy)control strategy also possesses better properties for automatic fertigation control in greenhouses than the incremental PID control strategy,the combination algorithm provides an optimal way of water and fertilizer management for crops in greenhouses which will contribute to water and fertilizer saving.

Increasing yield and agronomic efficiency of boro rice(Oryza sativa)by fertigation with bed planting compared with conventional planting

The fertigation technique with raised bed planting for transplanted boro(winter,irrigated)rice production is a research focus nowadays.A field experiment compared two cultivation methods:the fertigation technique within raised bed planting on boro rice,and fertilizer broadcasting in the conventional planting method.Compared to conventional fertilizer broadcasting,results showed that the new fertigation technique in raised bed planting increased grain yield of transplanted boro rice by up to 17.04%.It yielded a greater number of panicles per square meter,a greater number of grains per panicle,higher 1000-grains weight,and better plant growth attributes.Sterility percentage and weed infestation were lower.Thirty six percent of irrigation water and time for application could be saved.Water use efficiency for grain and biomass production was higher.The agronomic efficiency of nitrogen(N)fertilizer was significantly higher.This study concluded that fertigation in raised bed planting for transplanted boro rice is a new approach with higher yield and higher fertilizer and water use efficiency than the existing agronomic practice in Bangladesh.

The Comparative Performance of Plug Preparation Using Different Fertilizer Sources and Concentrations

Plugs are crucial for initiating crop production in greenhouses, soil, and controlled environment agriculture (CEA). Vegetable, fruiting, ornamental, and other horticultural crops that utilize plugs for production have demonstrated superior transplant establishment rate, plant health, and total yield. The APS Laboratory for Sustainable Food at Florida Gulf Coast University investigated the quality of plugs grown based on different concentrations and fertigation sources using synthetic and organic sources. We carried out the growth of “Rex Butterhead” Lettuce (Latuca sativa) plugs with five different fertigation treatments, 1) full-strength synthetic starter fertilizer solution;2) half-strength synthetic starter fertilizer solution;3) full-strength organic starter fertilizer solution;4) half-strength organic starter fertilizer solution, and 5) no fertilizer for control. Fertilizer treatments were formulated following manufacturer recommendations. The seeds were sown in Oasis® Horticubes and saturated every day with the different fertilizer treatments. The plugs were cultivated for 15 days in a controlled environment until two leaves after the cotyledons had developed. After 15 days, we collected data which included wet weight (g), dry weight (g), leaf area (cm2), and chlorophyll concentration (mg/cm2). In addition, we derived data including the Leaf Area Index (LAI, cm2/cm2) and Specific Leaf Area (SLA, cm2/g). Descriptive statistics were used to describe the biomass data. A Tukey’s HSD test was carried out to understand the differences between the fertilizer sources. We determined there was a statistically significant difference (P = 7.34E−29) in the measured plug growth parameters due to the various fertigation sources. We found that all fertilizer treatments produced viable plugs except for the control treatment. Of all the treatments, we concluded the half-strength organic treatment produced the more vigorous plugs with the greatest wet weight (g) and largest total leaf area (cm2) which was statistically significantly different. Results from this study may inform growers about appropriate fertilizer options for plug production.

Wetting Patterns and Nitrate Distributions in Layered-Textural Soils Under Drip Irrigation

Laboratory experiments were conducted in different sequence and thickness of the soil layers to investigate the effects of layered-textural soils on wetting patterns and water and nitrate distributions from a surface point source under various combinations of application rate and applied volume. Three layered soils, including a sandy-over-sandy loam （SL）, a sandy loam-over-sandy （LS）, and a sandy loam-sandy-sandy loam （LSL）, and two uniform soils （a uniform sandy loam and a uniform sandy soil） were tested. In the experiments, the application rate was varied from 0.69 to 3.86 L h^-1 and the applied volume from 5.7 to 12.1 L. The experimental results demonstrated that the wetting patterns and water and nitrate distributions were greatly affected by the sequence and thickness of soil layers as well as the application rate and volume applied. An interface existing in the layered soils, whether a fine-over-coarse or a coarse-over-fine, had a common feature of limiting downward water movement and of increasing horizontal water movement. For the fine-over-coarse layered soils of LS and LSL, water and nitrate were uniformly distributed at a given depth in the top layer soil. For a coarse-over-fine layered soil of SL, however, water accumulated in the sublayer soil underneath the interface and a zone of lower nitrate concentration was observed. The effect of application rate on water distribution pattern was dependent upon soil layering. A minor influence of application rate on water distribution for the fine-over-coarse layered soils （LS and LSL） than for the uniform soils was found. To obtain a greater wetted depth through selecting the emitters having a smaller application rate, which is a common method in the system design for a uniform soil, may not be necessarily applied for the layered soils. Measurements of nitrate distribution showed that nitrate accumulated toward the boundary of the wetted volume for both the uniform and the layered soils. This suggests the importance of optimal management of drip fertigation because nitrate is susceptible to the movement out of the root zone by mismanagement of fertigation. The information obtained from this research is useful in the design, operation, and management of a drip fertigation system.

Water and nutrient management effects on water use and yield of drip irrigated citrus in vertisol under a sub-humid region

Scarcity of water and nutrients in orchards are the major causes of low productivity and decline of citrus in tropics. With a hypothesis that the optimal amount of water and nutrients application through drip irrigation （DI） could save substantial irrigation and fertilizers comparative to that under traditional basin irrigation （BI） with band placement of fertilizer （BPF）, this study was conducted in citrus in vertisol of central India. Three DI regimes： I1, I2 and I3 scheduled at 50% class-A pan evaporation rate （Ep）, 75% Ep, and 100% Ep atong with three fertilizer doses： F1, F2 and F3 at 50% recommended dose of fertilizer （RDF, N：P2Os：K20=600 g：200 g：100 g）, 75% of RDF and 100% of RDF were applied to mandai＇in plants respectively. BI with band placement of fertilizer （BPF） at 100% RDF was taken for comparison. All the drip-fertigation treatments （except I1F1） produced higher plant growth and fruit yield, with better quality fruits compared with BI＋BPF. The highest fruit yield （16.39t ha^-1）, water use efficiency （3.9 kg m^-3） and fertilizer use efficiency （87.3 kg kg^-1） were observed in I2F2. The concentrations of N, K and Fe in leaves were significantly higher in I2F2 compared to other treatments. The leaf photosynthesis, stomatal conductance （G） and transpiration were the highest in I3F3. However, leaf water use efficiency （LWUE, photosynthesis/transpiration） was the highest in I2F2. The overall results of this study demonstrated that the application of optimum quantity of water and fertilizers （I2F2） through DI could be a productive and water efficient option in citrus production in vertisol.

Sesame response to nitrogen management under contrasting water availabilities

Sesame is mainly cultivated under traditional,low-input agro-systems.Recent breeding developments promoted the modernization and mechanization of sesame cultivation.However,only a few articles have been published concerning fertilization requirements for both modern and traditional agro-systems.In field trials at two locations,we determined the response of irrigated sesame to nitrogen(N).Three promising sesame lines were tested combining two irrigation levels with four N levels.At a high irrigation level,N had a significant effect on growth,branching,and consequently,seed yield exceeding two-ton ha^(-1).A high N doze was accompanied by a decrease in the photosynthetic rate and leaf water potential.The δ^(13)C confirmed lower stomatal conductance under high N treatments.Under deficit irrigation,the N level had a minor effect on the monitored parameters,indicating N fertilization was not efficient.Seed oil content was negatively correlated with seed N concentration.Our results question the necessity of N application when water is limited,as N fertilization promotes vigorous development that rapidly depletes soil water.Thus,water availability should be considered when developing an N management strategy.For high-yielding agro-systems,roughly 80–120 kg ha^(-1)N is required for optimal yield,bearing in mind the negative association between seed-N and oil content.