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Advantages and Disadvantages of Subsurface Drip Irrigation

Authors:
  • Kansas State University, Colby Kansas

Abstract

The advantages and disadvantages of subsurface drip irrigation (SDI) as compared to alternative irrigation systems are conceptually discussed. Each category (advantages and disadvantages) is subdivided into three groups: 1) Water and soil issues; 2) Cropping and cultural practices, and 3) System infrastructure issues. The adaptation and adoption of SDI systems into diverse cropping systems, geographical regions, soils and climate depends, to a large extent, on how potential advantages are balanced against potential disadvantages. In some cases, just a few advantages are expressed for a given cropping system, but are expressed so strongly that they provide a good counterbalance to the potential disadvantages. Future research and development will probably add to the list of potential advantages while addressing and reducing the disadvantages. However, this current listing can be used to devise and adapt other possible uses for SDI. Specific examples of SDI use in maize (Zea mays L.), alfalfa (Medicago sativa), almonds (Prunis dulcis), cantaloupe (C. melo) and wastewater applications are discussed with respect to balancing advantages and disadvantages.
ADVANTAGES AND DISADVANTAGES
OF SUBSURFACE DRIP IRRIGATION
Dr. Freddie R. Lamm
Professor and Research Irrigation Engineer
Northwest Research-Extension Center
Kansas State University
Colby, Kansas
flamm@oznet.ksu.edu
ABSTRACT
The advantages and disadvantages of subsurface drip irrigation (SDI) as compared to alternative
irrigation systems are conceptually discussed. Each category (advantages and disadvantages) is
subdivided into three groups: 1) Water and soil issues; 2) Cropping and cultural practices, and 3)
System infrastructure issues. The adaptation and adoption of SDI systems into diverse cropping
systems, geographical regions, soils and climate depends, to a large extent, on how potential
advantages are balanced against potential disadvantages. In some cases, just a few advantages are
expressed for a given cropping system, but are expressed so strongly that they provide a good
counterbalance to the potential disadvantages. Future research and development will probably add to
the list of potential advantages while addressing and reducing the disadvantages. However, this current
listing can be used to devise and adapt other possible uses for SDI. Specific examples of SDI use in
maize (Zea mays L.), alfalfa (Medicago sativa), almonds (Prunis dulcis), cantaloupe (C. melo) and
wastewater applications are discussed with respect to balancing advantages and disadvantages.
ADVANTAGES OF SDI
The following list should be considered as potential advantages of subsurface drip irrigation (SDI)
when properly managed and/or when site conditions and cropping systems allow the advantage to be
realized. Additionally, some growers might see an aspect as an advantage, while another might see an
aspect as a disadvantage. For example, there are opportunities for improved cultural practices with
SDI, while at the same time, there might be fewer tillage alternatives. These advantages may be
further subdivided along the lines of water and soil issues, cropping and cultural practices and system
infrastructure issues.
Advantages related to water and soil issues
More efficient water use – Soil evaporation, surface runoff, and deep percolation are greatly reduced
or eliminated. Infiltration and storage of seasonal precipitation can be enhanced by drier soils with less
soil crusting. In some cases, the system can be used for a small irrigation event for use in germination,
depending on dripline depth, flow rate and soil constraints. The inherent ability to apply small
irrigation amounts can allow better water-efficient decisions about irrigation events near the end of the
cropping season. In widely spaced crops, a smaller fraction of the soil volume can be wetted, thus
further reducing unnecessary irrigation water losses.
Less water quality hazards – Runoff into streams is reduced or eliminated, and there is less nutrient
and chemical leaching due to deep percolation.
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Improved opportunities for use of degraded waters – Smaller and more frequent irrigation
applications can maintain a more consistent and lower soil matric potential that may reduce salinity
hazards. Subsurface wastewater application can reduce pathogen drift and reduce human and animal
contact with such waters.
Greater water application uniformity – Improved in-field uniformities can result in better control of
the water, nutrients and salts. Widely spaced crops may benefit from water application closer to the
crop, provided sufficient soil wetting is achieved.
Advantages related to cropping and cultural practices
Enhanced plant growth, crop yield and quality – A number of crops respond positively.
Improved plant health – Less disease and fungal pressure occurs due to drier and less-humid crop
canopies. The system can also be used for some types of soil fumigation.
Improved fertilizer and pesticide management – Precise and more timely application of fertilizer
and pesticides through the system can result in greater efficacy and, in some cases, reduction in their
use.
Better weed control – Reductions in weed germination and weed growth often occur in drier regions
Improved double cropping opportunities – Crop timing may be enhanced since the system need not
be removed at harvesting and reinstalled prior to planting the second crop.
Improved farming operations and management – Many field operations can occur during irrigation
events. Field operations result in less soil compaction, and soil crusting caused by irrigation is greatly
reduced. Variability in soil water regimes and redistribution are often reduced with SDI as compared to
surface drip irrigation (DI). Additionally, weather-related application constraints such as high winds,
freezing temperatures and wet soil surfaces are less important. Needed fertilization can be applied in a
small irrigation event even when irrigation needs are low. The ability to irrigate during freezing
conditions can be particularly beneficial where preseason irrigation is used to effectively increase
seasonal irrigation capacity. There is also less irrigation equipment exposed to vehicular damage.
Hand laborers benefit from drier soils by having reduced manual exertion and injuries.
Advantages related to system infrastructure
Automation – The closed-loop pressurized characteristic of the system that can reduce application
variability and soil water and nutrient redistribution variability make the system an ideal candidate for
automation and advanced irrigation control technologies.
Decreased energy costs – Operating pressures are often less than some types of sprinkler irrigation.
Any water savings attributable to SDI will also reduce energy costs.
System integrity issues – There are fewer mechanized parts in an SDI system as compared to
mechanical-move sprinkler irrigation systems. Most components are plastic and are less subject to
irrigation system corrosion. SDI systems do not need to be removed and installed between crops and,
thus, can experience less damage. The potential for vandalism is also reduced.
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Design flexibility – There is increased flexibility with SDI in matching field shape and field size as
compared to center pivot sprinkler irrigation systems. The SDI system can be easily and economically
sized to the available water supply. In widely spaced crops, driplines can be placed for optimum water
and nutrient uptake. Pressure compensating SDI systems have fewer slope limitations than surface
gravity irrigation.
System longevity – SDI installations can have a long economic life when properly designed and
managed. Long system life allows for amortizing investment costs over many years, thus allowing
lower-value commodity crops to be economically grown with SDI.
Less pest damage – In some cases, there may be less pest damage to SDI systems from wildlife and
insects than for DI systems. However, this must be tempered with the fact that pest damage to SDI
systems may take more effort to detect and to repair.
DISADVANTAGES OF SDI
Similarly, there are circumstances and situations that present disadvantages to selection of an SDI
system. These disadvantages also may be subdivided along the lines of water and soil issues, cropping
and cultural practices, and system infrastructure issues.
Disadvantages related to water and soil issues
Smaller wetting pattern – The wetting pattern may be too small on coarse-textured soils, resulting in
too small a crop root zone. This situation can make system capacity and system reliability extremely
critical issues as there is less ability to buffer insufficient irrigation capacity or system breakdown.
Monitoring and evaluating irrigation events – Water applications may be largely unseen, and it is
more difficult to evaluate system operation and application uniformity. System mismanagement can
lead to underirrigation and crop yield and quality reductions or overirrigation, resulting in poor soil
aeration and deep percolation problems.
Soil/Application rate interactions – Emitter discharge rates can exceed the ability of some soils to
redistribute the water under normal redistribution processes. In such cases, water pressure in the
region around the outside of the emitter may exceed atmospheric pressure, thus altering emitter flows.
Water may inadvertently “surface” (tunneling of the emitter flow to the soil surface) causing
undesirable wet spots in the field. In “surfacing” problems, small soil particles may be carried with the
water, causing a “chimney effect,” that provides a preferential flow path. The “chimney” may be
difficult to permanently remove, since a portion of the “chimney” remains above the dripline even after
tillage.
Reduced upward water movement – Using the SDI system for germination may be limited,
depending on installation depth and soil characteristics. This may be particularly troublesome on soils
with vertical cracking. Salinity may be increased above the dripline, increasing the salinity hazard for
emerging seedlings or small transplants.
Disadvantages related to cropping and cultural practices
Less tillage options – Primary and secondary tillage operations may be limited by dripline placement.
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Restricted plant root development – Smaller crop root zones can make irrigation and fertilization
more critical issues from both a timing and amount perspective. Smaller crop root zones may be
insufficient to avoid diurnal crop water stresses even when the root zone is well watered. Application
of nutrients through the SDI system may be required for optimum yields. Application of micronutrients
may also become more important as the smaller soil volume becomes depleted of these nutrients
sooner.
Row spacing and crop rotation issues – Since SDI systems are fixed spatially, it may be more
difficult to accommodate crops of different row spacing. Some crops might require a very close
dripline spacing that might be economically impractical. Additional care must be taken at the time of
annual row-crop planting to ensure crop orientation and spacing are appropriately matched to the
dripline location.
Plant development issues – Some crops may not develop properly under SDI in some soils and
climates. Peanuts may not peg properly into dry soil. Tree crops may benefit from a larger wetting
pattern.
Disadvantages related to system infrastructure
Costs – SDI has a high initial investment cost compared to some alternative irrigation systems. In
many cases, the system has no resale value or a minimal salvage value. Lenders may require a higher
equity level and more collateral before approving SDI system loans. Such large investments may not
be warranted in areas with uncertain water and fuel availability, particularly if commodity price
outlook is poor. SDI systems typically have a shorter design life than alternative irrigation systems
which means the annualized depreciation costs must increase to provide for system replacement.
Filtration issues – As with all microirrigation systems, water filtration is a critical issue in ensuring
proper system operation and system longevity. However, the issue can become more critical for long
term SDI systems where a system life of greater than ten years is desired. SDI may require more
complex water quality management than some surface microirrigation systems, since there are no
opportunities to manually clean emitters.
Other maintenance issues – Timely and consistent maintenance and repairs are a requirement. Leaks
caused by rodents can be more difficult to locate and repair, particularly for deeper SDI systems. The
driplines must be monitored for root intrusion, and system operational and design procedures must
employ safeguards to limit or prevent further intrusion. Roots from some perennial crops may pinch
driplines, eliminating or reducing flows. Periodically, the driplines need to be flushed to remove
accumulations of silt and other precipitates that may occur in the driplines.
Operational issues – Operation and management requires more consistent oversight than some
alternative irrigation systems. There are fewer visual indicators of system operation and of the system
application uniformity. Irrigation scheduling procedures are required to prevent underirrigation and
overirrigation. Monitoring of system flowmeters and pressure gages are required to determine if the
system is operating properly.
Design issues – SDI is a less-developed technology than some alternative irrigation systems. This is
particularly so in some regions where growers have little exposure and experience with these systems.
There are fewer turnkey systems available for purchase. In some regions, the lack of contractor
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capacity can result in inadequate timing of installations in wet periods. Design errors are more difficult
to resolve since most of the SDI system is below ground. There are typically more components needed
for SDI than DI systems. There is the possibility of soil ingestion at system shutdown if a vacuum
occurs, so air relief/vacuum breaker devices must be present and operating correctly. As with any
microirrigation system, zone size and length of run will be limited by system hydraulics. Compression
of the dripline due to soil overburden can occur in some soils and at some depths, causing adverse
effects on flow. SDI systems are not typically well suited for Site Specific Variable Application.
Abandonment issues – In some cases, there are concerns about waste plastic product (driplines) in
the subsoil if the SDI system is abandoned.
OVERLAP OF ISSUES
The subdivision of the advantages and disadvantages into the three categories
water and soil issues
cropping and cultural practices
system infrastructure issues
is entirely arbitrary. However, it does allow for focusing on the conceptual issues of adoption of SDI.
It is apparent that some issues also overlap between the three categories. A case could be made to look
at a different subdivision emphasizing first the importance of system infrastructure issues. In this case,
the disadvantages of SDI might break in a different manner with a preponderance of issues showing up
in this group. The revised system infrastructure group would include these nine disadvantages:
Monitoring and evaluating irrigation events
Application rate issues
Less tillage options
Costs
Filtration
Other maintenance issues
Operational issues
Design issues
Abandonment issues
Many of these nine disadvantages can be addressed through further design, research and development,
a clear indication that they are often solvable problems. However, in some cases, solving the problem
may make high investment costs become an even greater issue.
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EXAMPLE USES OF SDI AND THEIR BALANCING ACT
There have been many diverse uses of SDI around the world for a multitude of crops on multiple soil
types in various climates. The adoption and adaptation of SDI systems is not always predictable since
the expression and balancing of advantages and disadvantages can be very site specific. Additionally,
cultural differences of peoples, their traditions and their skills and perception can have a large
influence on whether SDI will be adopted. Several uses of SDI will be examined in the remainder of
this paper to show some of the diversity of SDI uses and to show how advantages and disadvantages
were balanced. No attempt is being made to show the predominate uses of SDI in the world, nor to
show a typical ideal crop for SDI since probably none exists. Rather, the purpose of this discussion is
to show some of the diverse rationale SDI has potential for wider use and to suggest that other uses
may be determined by carefully examining the advantages and balancing them against the
disadvantages.
Maize or Field Corn (Zea mays L.)
Maize (field corn) is a major irrigated crop in the United States, but traditionally has not been
considered of sufficient value to warrant the high microirrigation investment costs. Improved
microirrigation components and improved system design and management that can allow long, useful
economic SDI system life (> 10 years) are changing this situation. Amortizing the higher SDI
investment costs over many years can, in some cases, make SDI economically competitive with more
traditional center pivot sprinkler irrigation systems. SDI systems can be easily designed and
economically sized for small and irregular shaped fields not readily suited to the economic scale
factors of center pivot sprinklers (Bosch et al., 1992; O’Brien et al., 1998, Lamm et al., 2002). For
lower value crops, such as maize, important factors in making SDI economically competitive with
center pivot sprinkler irrigation systems are field size and shape, system investment costs and life,
maize yields and price and any production cost differentials between irrigation systems (Lamm et al.,
2002). Field size and shape and SDI system life are the most important factors. In the US Great Plains,
water quality from the huge Ogallala aquifer is generally high. Clogging on deeper SDI systems in this
region appears to be manageable, and long system life can be obtained. SDI research systems in
Kansas have been operating for 13 years with very little performance degradation.
Dripline spacing in maize production is generally one dripline for every two maize rows (e.g. 1.52 m
dripline spacing for 0.76 m spaced maize rows). This alternate row dripline spacing helps to reduce
SDI system costs, yet has proven acceptable in maize production in numerous locations (Camp, 1998;
Camp et al., 1989; Howell, et al., 1997; Lamm et al., 1997a). Camp (1998) concludes that this
alternate row dripline spacing can be acceptable for most uniformly spaced row crops.
Yields for maize grown with DI and SDI can be similar (Camp et al., 1989, Howell et al., 1997), but,
because of the relatively low value of maize, in the United States only SDI is considered to have any
economic competitiveness to the generally cheaper alternative systems (center pivot sprinklers and
furrow irrigation). Irrigation requirements by maize grown using SDI can be reduced by 25% or more
(Lamm et al., 1995). This is primarily attributed to reduction or elimination of soil evaporation and
drainage, elimination of irrigation-induced runoff and greater infiltration of precipitation into drier soil
surfaces. Irrigation events can be much smaller with SDI than for alternative irrigation systems, yet
can still remain very efficient. On deep soil profiles with good water holding capacity, smaller capacity
(flowrate) SDI systems can be used to provide small daily increments of water while other portions of
the maize crop water needs can be withdrawn from the soil water reserves. Limiting daily irrigation
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events to 4.3 mm/day was still effective in producing average yields of 16.1 Mg/ha in semi-arid
western Kansas (USA) where peak crop water needs can exceed 9-10 mm/day (Lamm and Trooien,
2001). On these deep soils in this climate, SDI system size can be effectively increased to provide a
larger irrigated area. SDI systems are also sometimes used to replenish deep soil water reserves during
the dormant season. The smaller irrigation events inherent to SDI are also useful in making correct
irrigation decisions at the end of cropping seasons.
Nitrogen fertigation of maize with SDI can be effective in maintaining high grain yields while
protecting the environment. In Kansas (Lamm et al., 1997b), maize yield, apparent nitrogen uptake and
water use efficiency all plateaued at the same level of total applied nitrogen (180 kg/ha nitrogen
inseason fertigation amount and 35 kg/ha nitrogen and 20 kg/ha phosphorous applied preplant
broadcast), while irrigation was scheduled to replace approximately 75% of evapotranspiration.
Average yields for the 180 kg/ha nitrogen fertigation rate was 13.4 Mg/ha. Maize yield to nitrogen
uptake ratio (kg grain/kg nitrogen) for the 180 kg/ha nitrogen fertigation rate was a high 53:1.
Although maize would not be considered a typical crop for microirrigation, the combination of these
advantages can be a large counterbalance against the primary disadvantage of high SDI investment
cost.
Cantaloupe (C. melo)
Cantaloupe has been shown to be a good crop for SDI. Multiple or double cropping of cantaloupe with
vegetables can be easily accomplished with SDI due to not having to remove the system after initial
harvest and reinstallation for the second crop (Bucks et al., 1981, Camp et al., 1993.) Yields were
similar between DI and SDI in these two studies. The useful economic life of microirrigation systems
can be prolonged with subsurface placement, provided root intrusion and emitter clogging can be
prevented or reduced to manageable levels.
The use of deep SDI (approximately 45 cm depth) on cantaloupe resulted in earlier and higher
marketable yield of cantaloupe in research in arid California (Ayars, et al., 1999). Total marketable
yield from the first four pickings from the SDI plots were 10 and 28% higher than for low frequency
and high frequency DI plots, respectively. Total marketable yields for the 8 harvest dates in the study
were not significantly different between irrigation treatments, but earlier harvest can be very important
economically. Growers often do not pick more than three times due to labor costs, decreasing harvest
quantity and cantaloupe market price fluctuations. SDI had a quality advantage by keeping the soil dry
and, thus, reducing the amount of ground-spotted and rotten cantaloupe. This advantage may be of less
importance in areas of higher rainfall.
Cantaloupe has responded well to nutrient management through drip irrigation systems. Cantaloupe
responds best when nitrogen concentration in the irrigation water is varied across plant growth stages,
with approximately 150 mg N/L for the vegetative stage and approximately 50 mg N/L in the
reproductive stage (Bhella and Wilcox, 1985.) SDI offers the potential of better management of
nutrients through more precise application in the root zone and better soil water redistribution.
Similarly, there is potential to enhance cantaloupe production and quality through application of
systemic insecticides with DI or SDI under plastic mulch. Increased cantaloupe yield and less
chemical leaching were measured when Imidacloprid insecticide was applied in a shallow SDI
placement under plastic mulch as compared to conventional irrigation practices and cultural practices
(Leib et al., 2000). The plastic mulch alone resulted in a four-fold increase in yield while the
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insecticide applied alone increased yields 2.5 times. The plastic mulch combined with the near-surface
SDI, provided an optimum soil water balance while protecting the environment from leaching of the
insecticide during high rainfall events. This demonstrates how combining other technologies with SDI
can positively affect production and reduce environmental hazards.
Alfalfa (Medicago sativa)
Alfalfa, a forage crop, has high crop water needs and, thus, can benefit from highly efficient irrigation
systems such as SDI. In some regions, the water allocation is limited by physical or institutional
constraints, so SDI can effectively increase alfalfa production by increasing the crop transpiration
while reducing or eliminating soil evaporation. Since alfalfa is such a high-water user and has a very
long growing season, irrigation labor requirements with SDI can be reduced relative to less efficient
alternative irrigation systems that would require more irrigation events (Hengeller, 1995).
A major advantage of SDI on alfalfa is the ability to continue irrigating immediately prior, during and
immediately after the multiple seasonal harvests. Continuation of irrigation reduces the amount of
water stress on the alfalfa and thus can increase forage production which is generally linearly related to
transpiration. Transpiration on SDI plots that did not require cessation of irrigation was 36% higher
during this period than plots where irrigation was stopped for the normal harvest interval (Hutmacher
et al., 1992). Yields with SDI were approximately 22% higher than surface flood-irrigated fields while
still reducing irrigation requirements by approximately 6%. Water use efficiency was increased
mainly due to increased yield, not less water use (Ayars et al. 1999). When irrigation can continue,
there is less physiological stress on the crown of the plants, and there can be less weed competition.
On some soils with some SDI designs, irrigation with SDI may need to be reduced during the harvest
interval to avoid wet spots and compaction by heavy harvesting equipment. Possible solutions to these
problems might be deeper SDI installations or closer dripline and emitter spacings, thus resulting in
more uniform water distribution (Hengeller, 1995; McGill, 1993).
Alfalfa can be very sensitive to foliar leaf burn from sprinkler irrigation of low-quality water. Yields
can also be reduced by temporary ponding of irrigation water on the soil surface during periods of hot
weather. SDI can avoid both of these issues entirely (Hengeller, 1995).
On some soils under good irrigation management, it may be possible to use a relatively wide dripline
spacing for alfalfa because of its extensive and deep root system. In arid California on a silty clay
loam, yields from driplines spaced at 2 m were nearly equal to that obtained by a narrower 1 m spacing
after the first year of operation. Yields for the wider spacing was reduced approximately 17% during
the first year when the root system was not well established. In semi-arid Kansas on a sandy loam soil,
yields were 18% lower for 1.5 m spacing as compared to the narrower 1 m spacing for the second and
third years of production (Alam and Dumler, 2002). It was concluded in this study that it was more
economical to use the 1 m spacing. However, it may be possible that irrigation applications with SDI
on this soil were too marginal to allow the alfalfa to fully develop under the wider 1.5 m spacing. SDI
applications were only approximately 50% of the average reference evapotranspiration.
In drier regions, annual weed competition can also be reduced with SDI compared to surface and
sprinkler irrigation since the soil surface is not wetted by irrigation. This advantage is difficult to
quantify in alfalfa but has been noted by numerous investigators (Hengeller, 1995; Bui and Osgood,
1990; Alam and Dumler, 2002). Fewer weeds can result in better quality hay which then can receive a
premium price in some regions.
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Almonds (Prunus dulcis)
Almonds, a tree crop, are well suited to SDI as compared to alternative irrigation systems such as DI,
microsprinklers, solid set sprinkler irrigation and border surface irrigation. Weed control with SDI on
almonds is enhanced by not wetting up the soil surface. This helps reduce herbicide applications by up
to 66% and mowing costs by 50% (Edstrom and Schwankl, 1998) resulting in easier harvest operations
(tree shaking, windrowing, drying and sweeping). Hand labor associated with raking almonds away
from irrigation components and piping was eliminated with SDI.
Growers often need to irrigate during the extended harvest period while the almonds are being allowed
to dry on the soil surface. Irrigating at this time with alternative irrigation systems without rewetting
and damaging the almonds is difficult, but can be accomplished with SDI. Irrigation during this period
helps keep the trees healthy and prevents premature senescence. This is particularly important if there
are multiple varieties in the grove having different maturity dates (Schwankl, 2002).
SDI can be a cost-effective alternative to solid set sprinkler irrigation, saving approximately 50% in
investment costs. Fertilizers can be applied near the center of the crop root zone with SDI.
The advantages of using SDI for almonds must be balanced against some disadvantages that can occur.
In some coarse or gravelly soils, the wetted area/volume may not be sufficient with SDI as compared
to microsprinklers. On these soils, almond yields may be reduced under SDI (Edstrom and Schwankl,
1998). In some cases, this problem can be alleviated by using two SDI lines for each tree row. SDI
also cannot be used for frost protection in production areas where it may be needed.
Clogging of the emitters through root intrusion is a problem with SDI on almonds. Growers have
addressed this problem by selecting trifluralin-impregnated emitters or by trifluralin applications
through the system (Schwankl, 2002). Although damage to irrigation components on the soil surface
by wildlife is eliminated, this must be balanced against the increased difficulty of SDI repairs below
the soil surface when they do occur.
A major disadvantage to almond growers is the lack of visual indicators of proper irrigation
performance (Schwankl, 2002). This tends to be a recurring issue for many high-value crops where net
returns from both yield and quality can be impaired with even slight underperformance problems.
Growers often perceive that they need to use more sophisticated and costly management procedures
with SDI. They often feel the technical capability of their laborers is insufficient to monitor the SDI
system and to detect and correct deficiencies in an appropriate timeframe. Growers can reduce some
of these uncertainties by consistent periodic monitoring of flowrates and pressures. In some cases,
small, inexpensive flowmeters can be installed on individual driplines and read weekly to determine
proper operation.
Most of the disadvantages associated with SDI on almonds can be classified as being related to system
infrastructure. The present growth of SDI for almonds is slow but is likely to increase as system
design is improved, allowing both better and more failsafe operational and management procedures.
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Wastewater application
Wastewater application through SDI is growing across the world for a number of reasons. Excellent
discussions on the advantages and disadvantages of SDI for wastewater application are available
(Gushiken, 1995; Trooien et al., 2002; Trooien et al., 2000) and will not be repeated here. However, a
few issues of particular importance from these lists will be discussed.
Irrigation is a large user of freshwater resources around the world, and in many places these resources
are being overused. The recycling of wastewater through irrigation systems can save freshwater for
higher-value uses such as domestic consumption. Wastewater from municipalities, and sometimes
even water from confined animal feeding operations, can present health hazards when humans are
exposed to them. Application of these wastewaters through SDI limits human exposure and often can
reduce the sanitary treatment requirements of the wastewater.
Reclaimed municipal wastewater has been successfully and legally applied through SDI to golf courses
in Hawaii (USA), but application constraints would have greatly reduced or eliminated the utilization
of the wastewater through sprinkler irrigation (Gushiken, 1995).
In Israel, wastewater reuse has been a part of national resource planning policy for nearly 50 years
(Oron et al., 1991). As understanding of human health issues with wastewater reuse has grown over the
years, so have the regulations and restrictions on wastewater application through irrigation systems.
Application of wastewater through SDI systems has been shown to greatly reduce pathogen transfer to
edible crops (Oron et al., 1995; Oron et al., 1991, Oron et al., 1992). It seems likely that with further
research and development, there will be even greater use of SDI for wastewater applications in edible
crops.
In the United States, there has been increasing nationwide concern about problems associated with
livestock wastewater generated by confined animal feeding operations. Three of the more significant
problems are odor, seepage into groundwater and runoff into surface water supplies. SDI is a potential
tool that can alleviate all three problems while still utilizing livestock wastewater as a valuable
resource for crop production. Research in Kansas has looked at evaluating different emitter sizes for
application of livestock wastewater. After four years of operation, it appears that molded emitter sizes
greater than or equal to 1.5 L/h are sufficient when beef lagoon wastewater is filtered to 200 mesh
(Lamm et al., 2002). Operational procedures and management of livestock wastewater reuse through
SDI are in the much earlier stages of development as compared to municipal wastewater, but are
expected to progress.
As it is with any water source in any microirrigation system, clogging is a potential concern when
wastewater is utilized. However, the problems can be exacerbated, by the particle-rich, biologically
active wastewater. Considerable research has been conducted and will continue to be conducted to
prevent, solve and remediate clogging problems associated with wastewater application (Hills and
Brenes, 2001; Ravina et al., 1992; Sagi et al., 1995; Adin and Sacks, 1991; Ravina et al., 1997; Norum
et al., 2001).
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CONCLUDING STATEMENT
SDI systems have been adopted and adapted in many diverse geographical regions for many crops
under various soil types and climates. An examination of the potential advantages and disadvantages
is a possible means of determining other new uses for SDI in addition to understanding the reasons for
and against SDI adoption in the current uses. In some cases, strong, but less obvious, advantages are
the overriding factor in adoption, providing a good counterbalance to the disadvantages.
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pp. 102-109.
Ayars, J. E., C. J. Phene, R. B. Hutmacher, K. R. Davis, R. A. Schoneman, S. S. Vail and R. M. Mead. 1999.
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Bosch, D. J., N. L. Powell and F. S. Wright. 1992. An economic comparison of subsurface microirigation and
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... Analysis of the climatic, physical and social conditions are crucial to selecting the best irrigation methods. Considering the frequent and intense water shortages in the area, sub-surface drip irrigation is the best method to use for crop growth because it conserves water as runoff is eliminated and there is less evaporation [58]. The social conditions of the northeast are such that farm management has been left in the hands of the elderly as the youth migrate for better opportunities in urban areas, hence, reducing the agricultural labor force [58]. ...
... Considering the frequent and intense water shortages in the area, sub-surface drip irrigation is the best method to use for crop growth because it conserves water as runoff is eliminated and there is less evaporation [58]. The social conditions of the northeast are such that farm management has been left in the hands of the elderly as the youth migrate for better opportunities in urban areas, hence, reducing the agricultural labor force [58]. Sub-surface irrigation requires less labor. ...
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In the study carried out in Ankara conditions, the effect of pulse (intermittent) irrigation applications in subsurface drip irrigation on yield and quality parameters of silage maize was investigated. When 30% of the available water in the soil was consumed, the irrigation water required to bring the available moisture to the field capacity was applied with F0: one irrigation, F1: one cut F2: two cuts, F3: three cuts. Irrigation time was kept equal to the interruption period in intermittent irrigation. According to the two-year average findings, the differences between the applications in terms of water use efficiency (WUE) and irrigation water use efficiency (IWUE) were found to be statistically significant (p<0.05). Accordingly, WUE and IWUE increased as the cut-off time between two irrigations increased. While irrigation practices did not have a significant effect on fresh silage yield, statistical differences were found in some quality parameters (plant height, cob weight, stem weight, crude ash). Highest and lowest fresh silage yield, plant height, number of cob per plant, stem weight, leaf weight, dry mater ratio, crude ash ratio and crude protein ratio were obtained as 8768.9-8064.9 kg da-1, 2.44-2.34 m., 1.28-1.13, 0.438-0.374 kg., 0.234-0.212 kg, 41.5%-39.0%, 7.2%-5.2% and 7.0%-6.7%, respectively. In the study, it was determined that the best water distribution was achieved in the F1 treatment, where the interval between irrigations was the longest, and this treatment was suggested
... When distribution pipes are installed below the soil surface, irrigation water is distributed directly in the root zone, with limited or absent water loss due to soil evaporation, surface runoff, and deep percolation. Moreover, SDI systems allow better management of fertilizers and pesticides, as well as the use of unconventional waters (Lamm, 2002). For these advantages, SDI systems have been receiving more attention by researchers and farmers, with applications on different crops (Ayars et al. 1999;Pisciotta et al., 2018;Martínez-Gimeno et al., 2018). ...
... Taking a more nuanced stance on irrigation techniques, where different irrigation areas employing different irrigation techniques can coexist, enables, first, avoiding designing and implementing 'one size fits all' (drip) irrigation projects (see Lopez-Gunn et al., 2012), which may lead to disappointing results in terms of water conservation (Boularbah et al., 2019). Debating the respective (dis)advantages of irrigation techniques is a sound tradition in irrigation engineering (see for instance Lamm, 2002) and it is important to maintain a critical view of the fit of different irrigation techniques (Lopez-Gunn et al., 2012). Indeed, some authors underline the pertinence of irrigation techniques other than drip irrigation, for different reasons: (1) certain field crops are better served by sprinkler or surface irrigation (Evett et al., 2019;Sezen et al., 2011); (2) certain soils such as heavy cracking clays may be better suited to furrow and sprinkler irrigation than to drip irrigation (Mandal et al., 2008); (3) the size of the plot has an impact on the cost of drip irrigation equipment: the smaller the area, the higher the cost per hectare due to the high cost of the head station (Rodrigues et al., 2013); and (4) gravity and sprinkler irrigation systems may be better suited to farmers' practices and preferences (Molle & Tanouti, 2017); for example, some farmers prefer sprinkler to drip irrigation to limit the time they have to spend in the field (Kettani et al., 2020). ...
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... Compared to the micro-sprinkler systems, traditionally used for citrus orchards, distribution pipes installed below the soil surface distribute water and fertilizers directly in the root zone, with limited or absent water loss due to soil evaporation, surface runoff, and deep percolation. Moreover, SDI systems allow better management of fertilizers and pesticides, as well as the use of unconventional waters (Lamm, 2002). ...
... Nach Schäufele (1966), Seiffert (1995), und Zattler (1936, 1956b, 1956a Auf Basis der Erkenntnisse kann die Aussage getroffen werden, dass Hopfen wie von Schäufele (1966), Seiffert (1995) und Zattler (1936, 1956b, 1956a (Graf et al., 2014;Kohlmann und Kastner, 1975 (Sne, 2006). Camp et al. (2000), Lamm (2002) (Kafkafi und Tarchitzky, 2011). In der wassergesättigten Zone direkt unter der Tropfstelle sterben Wurzeln aufgrund von Sauerstoffmangel in der Regel ab (Huck und Hillel, 1983 ...
Thesis
Stickstoff stellt bei Hopfen (Humulus lupulus L.) den mengenmäßig wichtigsten und am stärksten ertragslimitierenden Pflanzennährstoff dar, wobei überschüssiger nicht von der Hopfenpflanze aufgenommener Stickstoff unterschiedlichen Verlustprozessen unterliegt. Trotzdem ist für die aktuell in der Hallertau, dem weltweit bedeutendsten Hopfenanbaugebiet, kultivierten Hopfensorten und genutzten Anbausysteme nur wenig über die exakten Auswirkungen eines in Zeit und Höhe variierten N-Angebots bekannt. Die auszubringende Menge an Stickstoff wird in der Hallertau zum Großteil durch oberflächiges Streuen granulierter N-Düngemittel zugeführt, wohingegen in semiariden Anbauregionen der Welt hohe Anteile über das Bewässerungswasser (Fertigation) appliziert werden. Ziel dieser Arbeit war es N-Düngesysteme mit Fertigation unter den Bedingungen in der Hallertau im Hinblick auf eine bedarfsgerechtere Stickstoffernährung der Hopfenpflanze zu untersuchen. Hierzu wurden vier Forschungsfragen mit jeweils verschiedenen Teilaspekten formuliert, die nachfolgend erläutert werden. Die experimentelle Prüfung und Gewinnung empirischer Daten erfolgte im Zeitraum von 2017 bis 2019 in unterschiedlich konzeptionierten Feldversuchen in drei Versuchsserien auf verschiedenen Standorten mit den wichtigsten Hopfensorten. Dabei wurde sowohl der Zeitpunkt und die Höhe der N-Düngung variiert, als auch die Düngerapplikationsform (Oberflächige Applikation granulierter Dünger und ober- bzw. unterirdische Fertigation). Neben der Ermittlung von Ertrag, Qualität und N-Aufnahme zum Zeitpunkt der Ernte, wurden in einzelnen Feldversuchen weiterführende Untersuchungsmethoden wie die 15N-Tracer-Technik, Chlorophyllwertmessungen (SPAD-Meter) oder passive Reflexionsmessungen eingesetzt, um die N-Aufnahme und N-Verteilung in unterschiedliche Pflanzenorgane zu charakterisieren. a) Wie wirkt sich ein in Zeit und Höhe variiertes N-Angebot aus? Es wurde ermittelt, dass eine Hopfenpflanze mehr als zwei Drittel des gesamten Stickstoffs in einem 7- bis 8-wöchigen Zeitraum zwischen Anfang Juni und Ende Juli, während der Phase der Hauptbiomassebildung, aufnimmt. Obwohl vor dieser Phase relativ geringe Mengen an Stickstoff in der Pflanze akkumuliert werden, zeigte sich bei den Aromasorten Perle und Tradition, dass eine N-Unterversorgung in frühen Wachstumsphasen bis Ende Mai bereits zu einer Verringerung des Ertragspotenzials führt. Ursächlich hierfür war eine Veränderung des Habitus der Pflanzen, denn je später eine definierte Menge an Stickstoff ausgebracht wurde, desto stärker reduzierte sich die Ausbildung der Seitentriebe von unten beginnend bis in höhere Pflanzenabschnitte. Eine ausschließliche Ausrichtung des Zeitpunkts der N-Applikation an der N-Aufnahmekurve der Hopfenpflanze ist somit weder im Hinblick auf die Ertragsbildung noch die Stickstoffverwertung als sinnvoll anzusehen. Stattdessen ist bei frühreiferen Sorten wie Perle und Tradition die frühzeitige Applikation einer ersten N-Gabe bereits im April von entscheidender Bedeutung. Spätreifere Sorten wie Herkules weisen durch die verlängerte Wachstumsphase hingegen ein höheres Kompensationspotenzial auf, wodurch eine stärkere Anpassung der N-Düngung an die N-Aufnahmekurve möglich ist. Die ertragsoptimale Höhe der N-Düngung wurde vom sorten-, witterungs- und standortabhängigen Wachstumsverlauf und damit der N-Aufnahme des Pflanzenbestands sowie dem Vorrat an mineralischem Stickstoff im Boden und dem standortspezifischen N-Nachlieferungspotenzial bestimmt. Erfolgte eine Reduktion der N-Düngung auf ein Niveau deutlich unter dem N-Entzug der Pflanze, führte dies im selben Anbaujahr nicht zwingend zu einer Einschränkung der Biomasse- und Ertragsbildung, jedoch zu einer beschleunigten Reife und einer Verschlechterung der äußeren Doldenqualität. Darüber hinaus zeigte sich bei einem stark reduzierten N-Düngeniveau, dass die N-Einlagerung in die Speicherwurzeln abnimmt, wodurch die Pflanzen im Frühjahr des Folgejahres eine geringere Vitalität aufwiesen und die Entwicklung wie auch Ertragsbildung limitiert waren. Hinsichtlich der perennierenden Eigenschaften einer Hopfenpflanze und dem Ziel einer möglichst bedarfsgerechten Stickstoffernährung des Hopfens besteht somit die Notwendigkeit auch die Speicherwurzeln ausreichend mit Stickstoff zu ernähren. Im Hinblick auf den wertgebenden Inhaltsstoff Alphasäure wurde ermittelt, dass ein hohes N-Versorgungsniveau während der Phase der Alphasäuresynthese (ab Anfang August) bei der Sorte Herkules zu einer Reduktion des Alphasäuregehalts führen kann. Dazu führen kann sowohl eine späte und übermäßige N-Düngung, als auch ein hoher Vorrat an mineralischem Stickstoff im Boden und ein erhöhtes N-Nachlieferungspotenzial. Bei den untersuchten Aromasorten Perle und Tradition wurde dieser Effekt hingegen nicht beobachtet. b) Kann der aktuelle N-Ernährungszustandes nicht-invasiv erfasst werden? Die Messung des Chlorophyllwertes mit einem SPAD-Meter an den unteren Blättern des Haupttriebs bildete den N-Gehalt und N-Versorgungszustand der Hopfenpflanze grundsätzlich ab. Kurzfristige Änderungen des N-Ernährungszustandes konnten jedoch, vor allem während der Phase der Hauptbiomassebildung, an diesem Messpunkt nicht hinreichend genau erfasst werden, da erhöhte Anteile des ausgebrachten Stickstoffs in höher liegende Pflanzenabschnitte transportiert wurden, wie sich im Rahmen des 15N-Einsatzes zeigte. Hinsichtlich der Festlegung von Schwellenwerten wird unabhängig vom Messpunkt eine Unterteilung der Pflanzenentwicklung in vor, während und nach der Hauptbiomassebildung als sinnvoll erachtet, da eine Abhängigkeit des Chlorophyllwertes vom Entwicklungszustand der Pflanze besteht. Vegetationsindices, berechnet auf Basis von Reflexionsspektren, bilden neben dem N-Gehalt auch die tatsächliche N-Aufnahme des Pflanzenbestands ab, weshalb passive Reflexionsmessungen im Vergleich zu Chlorophyllwertmessungen eine höhere Aussagekraft hinsichtlich des aktuellen N-Versorgungszustandes der Pflanze haben. Diese Technologie könnte deshalb zukünftig genutzt werden, um eine standortspezifische Optimierung von Höhe und Zeitpunkt der N-Düngung und dadurch eine bedarfsgerechtere Stickstoffernährung der Hopfenpflanze zu erreichen. c) Welche Effekte hat eine ober- bzw. einer unterirdischer Tropfbewässerung? Im Untersuchungszeitraum von 2017 bis 2019 führte die zusätzliche Bewässerung der Aromasorte Perle auf einem sandigen Boden in jedem Anbaujahr zu einer Stabilisierung der agronomischen Kennzahlen Doldenertrag und Alphasäuregehalt. Darüber hinaus wurde durch Bewässerung auch die Stickstoffverwertung verbessert. Bei einer aufgrund hydraulischer Bodeneigenschaften limitierten horizontalen Verteilung des ausgebrachten Wassers erreichte die oberirdische Tropfbewässerung eine höhere Effizienz als die unterirdische. Ursächlich hierfür ist, dass sich das Feinwurzelwerk einer Hopfenpflanze zu hohen Anteilen im aufgeschütteten Bifang und in den darunter liegenden Bodenschichten befindet. d) Welche Auswirkungen hat eine Stickstoffernährung über das Bewässerungswasser? Es wurde ein Systemvergleich zwischen N-Düngesystemen mit Fertigation und ausschließlicher N-Applikation in granulierter Form angestellt. Dabei führte die Nutzung von Fertigation nicht nur zu einer Verbesserung des Doldenertrags und Alphasäuregehalts, sondern auch zu einer Steigerung des Stickstoffentzugs und Reduktion des Nmin-Gehalts im Boden, wodurch auch eine Verringerung des Risikos einer Nitrat-Auswaschung ins Grundwasser einhergeht. Düngesysteme mit Fertigation erreichten vor allem bei einem niedrigen N-Düngeniveau eine höhere Stickstoffverwertung. Bei Applikation von zwei Drittel der gesamten N-Menge über das Bewässerungswasser erwies sich unter Bedingungen eines limitierten N-Angebots die Konzentration des über Fertigation auszubringenden N-Anteils auf einen 6-wöchigen Zeitraum sortenunabhängig als positiv, da ein höherer N-Anteil während der Hauptbiomassebildung und der Phase des Seitentriebwachstums appliziert wurde. Für eine effiziente Düngung mit Fertigation sollte die Applikation zwischen Mitte Juni und Ende Juli stattfinden und ab Anfang August keine wesentlichen Mengen an Stickstoff mehr ausgebracht werden. Bei frühreiferen Sorten wie Perle und Tradition besteht die Gefahr einer nicht rechtzeitigen N-Applikation, da eine Verlegung des Tropfschlauches vor KW25 kaum zu realisieren ist. Deshalb sollte bei diesen Sorten ein höherer N-Anteil in früheren Wachstumsphasen ausgebracht werden und die über Fertigation ausgebrachte N-Menge kleiner zwei Drittel der Gesamt-N-Düngermenge sein. Als wesentlicher Vorteil von Düngesystemen mit Fertigation konnte belegt werden, dass über das Bewässerungswasser ausgebrachter Stickstoff von den Pflanzen unmittelbar aufgenommen wird, wodurch kurzfristig und effektiv in die Stickstoffernährung der Hopfenpflanze eingegriffen werden kann. Auf Basis einer zuverlässigen Erfassung des aktuellen N-Versorgungszustands während der Hauptwachstumsphase könnte durch Fertigation eine Korrektur der N-Düngung erfolgen und somit eine standortangepasste bedarfsgerechte Stickstoffernährung des Hopfens erreicht werden.
Chapter
Today, the world’s agricultural and water resources enterprises are facing formidable challenges of optimizing crop yields with reducing water inputs while minimizing environmental degradation. The key strategy to increase food security should be through the increase of production per unit resources, i.e., the combined increase of crop production per unit land and the increase of crop production per unit water consumed, i.e., increase in crop water productivity (CWP). Depending on the socioeconomic structure, policies, and climatic patterns, several strategies are available to optimize CWP. The chapter provides a description of the basic concept and methodology of CWP and discusses the current challenges and opportunities to improve CWP. The main focus will be on (i) the review of available best management techniques such as irrigation scheduling and accurate quantification of crop evapotranspiration (ETc) to enhance the efficient use of water resources and protect water quality and (ii) review of emerging technologies such as wireless communication with soil moisture and plant canopy sensors to increase CWP. Furthermore, the adoption of other sustainable farming practices such as the adoption of conservation tillage management practices, diversifying crops, and varieties that are more appropriate to thermal time with increased resistance to extreme heat and drought will be discussed briefly. Adoption of these management practices will provide valuable information and scientific and practical framework that will allow farmers and resource managers to design and implement effective water management practices in a way that is both effective for enhancing productivity and environmentally responsible.
Chapter
Agriculture is very important to human beings because it is the sole provider of basic human food. However, agricultural process requires constant energy resources in machinery’s operation, pumping water for irrigation, greenhouse heating, and so on, conventionally operated with fossil fuel energy sources that release greenhouse gases. It is, therefore, essential for farmers to adopt innovative eco-friendly techniques in various operations of food production, including agricultural farming, to meet the growing consumption of the growing population and also to save energy and water usage so as to reduce the emission of greenhouse gases from using fossil fuel energy. This made scientists to find alternative environmentally sustainable and cost-efficient agricultural farming, using innovative eco-friendly energy technology, that is, green renewable energy technology to mitigate the environmental problem and also to solve the alarming fear of exhaustion of fossil fuel energy. The authors present this chapter by reviewing literature from various available sources and is organized on the following objectives: (1) the importance of innovative eco-friendly energy technologies for sustainable agricultural farming; (2) application of different eco-friendly energy technology in agricultural farming; (3) how innovative eco-friendly energy technology is used for sustainable agricultural farming; (4) the advantages and disadvantages of using eco-friendly technology and recommendation as an innovative solution. The chapter is finally concluded with the need to promote and optimize the combination of eco-friendly energy technology application and agricultural cultivation among the agricultural farmers due to its environmental as well as economic feasibility.
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The contribution of wastewater irrigation with the improvement of irrigation practices to the productivity of silage maize is a priority issue to investigate considering the saving of scarce freshwater resources and the necessity to dispose wastewater. The aim of this study was to evaluate the effect of different irrigation levels (L100, L67 and L33) of recycled municipal wastewater (RW) compared to freshwater (FW) using subsurface drip (SSDI), surface drip (SDI) and furrow irrigation (FI) methods on yield and some physiological traits of silage maize in semi-arid conditions at a high altitude. When the total daily reference evapotranspiration value reached 50 ± 5 mm, irrigation quantities corresponding to 100%, 67% and 33% of soil moisture deficit based on field capacity in fully irrigated plots with freshwater were applied in different irrigation levels. Crop actual evapotranspiration (ETa) values were found close in both water types. SSDI reduced ETa by 18.5% and 45.6% in L100 level, 15.2% and 38.9% in L67, and 11.6% and 32.6% in L33, respectively compared to SDI and FI. The highest fresh biomass yield was determined in the SSDI-RW-L100 combination as 77.55 t ha-1, and resulted in 5% and 12.9% higher values than in SDI and FI. Leaf relative chlorophyll and water contents, leaf area index and electrolyte leakage showed strong linear correlations with yield and evapotranspiration values. The highest water productivity was determined in the SSDI-RW-L100 combination as 21.48 kg m-3 and it was higher by 28.2% and 99.4% than those in SDI and FI, respectively. Improvement of productivity with increased irrigation quantities in SSDI delivered the high yield response factor of 1.70–1.77. Therefore, it is concluded that the SSDI method can be a successful practice to improve productivity by alleviating the need for water for silage maize especially under full irrigation with RW.
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A two-year study was initiated in the spring of 1990 on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine the optimum dripline lateral spacing for irrigated corn (Zea mays L.) using subsurface driplines installed at a depth of 40-45 cm in a direction parallel to the corn rows. Average corn yields were 13.6, 12.8, and 12.2 Mg/ha for dripline spacings of 1.5, 2.3, and 3.0 m, respectively, for a seasonal-irrigation amount of 462 mm. Yields decreased to 10.8 and 9.3 Mg/ha when irrigation was reduced by 33 and 50% for the wider 2.3- and 3.0-m dripline spacings, respectively. The wider dripline spacings resulted in nonuniform horizontal distribution of available soil water. As a result, yields decreased with horizontal distance from the dripline. The highest yield, highest water use efficiency, and lowest year-to-year variation were obtained with the 1.5 m dripline spacing. An economic analysis indicated that because yield reduction were so great, the wider dripline spacings would be justified only at very high dripline costs and or very low corn grain prices.
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Irrigation development during the last 50 years has led to overdraft in many areas of the large Ogallala aquifer in the central United States. Faced with the decline in irrigated acres, irrigators and water resource personnel are examining many new techniques to conserve this valuable resource. A three-year study (1989 to 1991) was conducted on a Keith silt loam soil (Aridic Argiustoll) in northwest Kansas to determine the water requirement of corn (Zea mays L.) grown using a subsurface drip irrigation (SDI) system. A dryland control and five irrigation treatments, designed to meet from 25 to 125% of calculated evapotranspiration (ET) needs of the crop were examined. Although cumulative evapotranspiration and precipitation were near normal for the three growing seasons, irrigation requirements were higher than normal due to the timing of precipitation and high evapotranspiration periods. Analysis of the seasonal progression of soil water reveled the well-watered treatments (75 to 125%) of ET treatments) maintained stable soil water levels above approximately 55 to 60% of field capacity for the 2.4-m soil profile, while the deficit-irrigated treatments (no irrigation to 50% of ET treatments) mined the soil water. Corn yields were highly linearly related to calculated crop water use, producing 0.084 Mg/ha of grain for each millimeter of water used above a threshold of 328 mm. Analysis of the calculated water balance components indicated that careful management of SDI systems can reduce net irrigation needs by nearly 25%, while still maintaining top yields of 12.5 Mg/ha. Most of these water savings can be attributable to minimizing nonbeneficial water balance components such as soil evaporation and long-term drainage. The SDI system is one technology that can make significant improvements in water use efficiency by better managing the water balance components
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Field experiments were conducted to evaluate the reuse of domestic, secondary treated wastewater for irrigation of edible crops. Corn was irrigated under on-surface and subsurface trickle systems with effluent and compared with on-surface trickle irrigation applying fresh water. The results indicate that under sub-surface trickle irrigation fruit contamination is minimal.
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Field studies were undertaken in recent years to confirm the hypothesis that treated secondary wastewater can be disposed by using it in drip systems for irrigation of edible crops. This hypothesis was examined in field experiments conducted with the treated domestic wastewater of the city of Beer-Sheva, Israel. The results indicated that contamination of the soil surface and plants was minimal when subsurface drip irrigation was applied, but maximal when sprinkler irrigation was utilized.
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The paper describes an investigation made to evaluate the potential for producing high-value horticultural crops irrigated with surface and subsurface trickle systems; to evaluate irrigation frequencies and water quantities in terms of energy-conserving trickle systems; and determine the possibility of using the same inplace subsurface trickle irrigation system for several successive row crops.
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Four different types of manufactured drip tapes were evaluated for use with secondary effluent from an activated sludge wastewater treatment plant. Additional treatment within the irrigation system included sand media filtration, continuous chlorination to a free chlorine residual concentration of O.4 mg/L emitting from the drip tapes, and screen filtration to 100μm. Drip tapes used in this study had design discharge rates between 0.9 and 1.4 L/h/emitter at 60 kPa, emitter spacings of O.2 m, and wall thicknesses of 0.20-0.22 mm. During the first two-month phase of continuous operation, none of the drip tapes suffered flow reductions of more than 5%. One of the drip tapes, however, increased its flow by 30%, which was attributed to a fault in its design. During the six-month second phase, one of the better performing drip tapes was used for additional assessment. The statistical uniformity of emitter discharge for this latter drip tape ranged between 92.7 and 98.0% (mean value of 94.8%) during the second phase. This study indicates that drip tape technology has significantly improved in recent years. Despite its low operating pressure and emission rate, relative to other micro-emitters, drip tape appears to be a suitable product for use with activated sludge secondary effluent.
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