Furrow-irrigated Fields Research Articles

Evaluating whole field irrigation performance using statistical inference of inter-furrow infiltration variation

Inter-furrow infiltration variability is often ignored during the evaluation and optimisation of furrow irrigation. Existing techniques for estimating infiltration parameters are generally too intensive in measurement and computation for routine application at the field scale and have therefore primarily been used to study the behaviour of single furrows. This paper identifies the inter-furrow infiltration variation within typical furrow-irrigated fields and determines that this variation can be adequately described using a log-normal distribution. A procedure to predict whole field furrow infiltration characteristics using minimum field measurements is then presented. The technique uses a single advance measurement for single furrows and the log-normal probability distribution to predict the statistical distribution of infiltration functions across the field based on the measured infiltration curve for one or more fully evaluated furrows. This technique also considers the infiltration curve over appropriate ranges of opportunity time. Simulations using the predicted infiltration parameters demonstrate more accurate estimates of the whole field efficiency and uniformity than those extrapolated from infiltration measurements on a limited number of furrows as sampled in a conventional evaluation.

Infiltration, Runoff, and Export of Dissolved Organic Carbon from Furrow-Irrigated Forage Fields under Cover Crop and No-Till Management in the Arid Climate of California

Development of best management practices (BMPs) such as conservation tillage and winter cover crop to mitigate runoff and reduce dissolved chemicals in irrigation runoff is an important objective for controlling surface water pollution attributable to agricultural activities. In this study, the effect of standard tillage (ST), STwith winter cover cropping (STCC), and no-till (NT) management practices on infiltration, runoff, and dissolved organic carbon (DOC) export from furrow-irrigated fields of 244-m length was investigated for summer 2007 and 2008 irrigations. The practices were implemented for 2 years. The average surface residue cover was 11, 44, and 32% for ST, STCC, and NT, respectively, for 2007 and 11, 59, and 61%, respectively, in the following year of the study. Two irrigations in each year were considered for the analysis. The runoff samples were collected from each tillage treatment using ISCO autosamplers at regular time intervals. The infiltration and runoff were estimated using a volume balance model (VBM) by considering a 0.2-m irrigation requirement. Converting from ST to STCC increased the infiltration by 14 and 43% and reduced the runoff by 48 and 43% in 2007 and 2008 irrigations, respectively; whereas, converting ST to NT enhanced the infiltration by 4% in both years and decreased the runoff by 19 and 23% in 2007 and 2008 irrigations, respectively. The authors observed only slightly higher DOC concentrations in STCC, but there was a 24% increase for NT in 2007 irrigations, and both compared to with ST ranged from 3.98 to 5:46 mg=L. The DOC concentration was not significantly different among the treatments in 2008 irrigations (3.48 to 4: 6m g=L). Combining the runoff and DOC concentration effects, the DOC export for STCC was decreased by 55% in both years; whereas, it was decreased by 4 and 27% for NT in 2007 and 2008 irrigations, respectively, compared with ST. Although STCC and NT have higher concentrations, the reduction in export in these treatments is attributable to lower runoff. These results suggest that DOC export can be controlled with STCC practice. No-till showed the same trend, although these results must be confirmed after extended implementation of this practice. DOI: 10.1061/(ASCE)IR.1943-4774.0000385. © 2012 American Society of Civil Engineers.

Agronomic and economic evaluation of various furrow irrigation strategies for corn production under limited water supply

It is commonly known that furrow irrigation is a less efficient method of irrigation than a sprinkler center pivot system, but many fields9 irregular shapes prevent the use of center pivot irrigation. Restricted water allocations of surface and subsurface water are forcing farmers to implement irrigation strategies that will reduce water application on furrow-irrigated fields. The study site was located in south central Nebraska. The objective of this study was to evaluate two irrigation scheduling scenarios: (1) the every-furrow irrigation method with 50% (0.5), 70% (0.7), and 90% (0.9) field capacity (FC) treatments and (2) the every-furrow (EF) irrigation method compared to the every-other-furrow (EOF) method with both using the 75% field capacity (0.75 FC) treatment effects on corn (Zea mays L.) yield, net economic return, and residual soil nitrate-nitrogen. The experimental design was a randomized complete block with three replications. Grain yield showed no significant difference in both years for all irrigation treatments. Irrigation water application with the 0.5 FC strategy reduced the amount of applied water by approximately 70% and 200% compared to 0.7 FC and 0.9 FC, respectively, in both years. The water savings with the EOF method over the EF method was 23%. The economic return with 0.5 FC was 6% to 13% and 36% to 69% over 0.7 and 0.9 FC irrigation treatments, respectively. The 0.5 FC strategy showed no significant reduction in nitrate-nitrogen loss over 0.7 FC and 0.9 FC, while the EOF method reduced soil nitrate-nitrogen loss by 11% to 26% over the EF irrigation method in both years. The average economic return over two years with the 0.5 FC strategy was 9.5% and 52.5% over 0.7 FC and 0.9 FC irrigation treatments, respectively, while the average economic return with the EOF method over the EF method was 9.5%. Findings demonstrated that economic and environmental benefits of using 0.5 FC or the EOF method is much superior to other furrow irrigation strategies, especially in areas with limited water resources where less efficient irrigation methods may lead to significant water loss.

UV - visible spectroscopic properties of dissolved fulvic acids extracted from salined fluvo-aquic soils in the Hetao Irrigation District, China

The elemental composition and the UV–visible spectroscopic properties of dissolved fulvic acids (FA) extracted from salined fluvo-aquic soils in the Hetao Irrigation District were examined to evaluate the humification degree of FA and salinisation processes of soils. Composite soil samples of different depths (0–20, 20–40, 40–60, 60–80 cm) were collected from four native halophyte soils [communities Salicornia europaea (CSE), Suaeda glauca (CSG), Kalidium foliatum (CKF), Sophora alopecuroides (CSA)] and two furrow-irrigated fields [corn (CFD), wheat (WFD)] along a saline impact gradient. Seven humification indices (HIXs: C/N, SUVA, E2/E3, E2/E4, S275–295, S350–400, and S250–400), deduced from elemental analysis and UV–visible spectroscopy of FAs, were used to evaluate the humification degree. The humification degree of FA from the WFD soil was the highest, followed by CFD, CSA, CKF, CSG, and CSE. There were significant relationships between the seven HIXs (P < 0.05). The exchangeable sodium percentage (ESP) exhibited close correlations with the seven HIXs, and the humification degree increased with decreasing ESP. The HIX can not only indicate the humification degree of soil organic matter but also characterise the salinisation processes of soils.

Acrylamide Monomer Leaching from Polyacrylamide‐Treated Irrigation Furrows

Water-soluble anionic polyacrylamide (WSPAM), which is used to reduce erosion in furrow irrigated fields and other agriculture applications, contains less than 0.05% acrylamide monomer (AMD). Acrylamide monomer, a potent neurotoxicant and suspected carcinogen, is readily dissolved and transported in flowing water. The study quantified AMD leaching losses from a WSPAM-treated corn (Zea mays L.) field using continuous extraction-walled percolation samplers buried at 1.2 m depth. The samplers were placed 30 and 150 m from the inflow source along a 180-m-long corn field. The field was furrow irrigated using WSPAM at the rate of 10 mg L(-1) during furrow advance. Percolation water and furrow inflows were monitored for AMD during and after three furrow irrigations. The samples were analyzed for AMD using a gas chromatograph equipped with an electron-capture detector. Furrow inflows contained an average AMD concentration of 5.5 microg L(-1). The AMD in percolation water samples never exceeded the minimum detection limit and the de facto potable water standard of 0.5 microg L(-1). The risk that ground water beneath these WSPAM-treated furrow irrigated soils will be contaminated with AMD appears minimal.

Mitigation techniques reduce sediment in runoff from furrow-irrigated cropland

Irrigation tailwater can transport sediments and sediment-associated agricultural pollutants to nearby waterways. To help protect the biota of surface waters, we evaluated the use of polyacrylamide (PAM, a synthetic material that flocculates sediments when added to water), vegetated ditches and sediment traps to mitigate sediment losses from furrow-irrigated fields. In a 2-year study, liquid PAM injected into irrigation source water most effectively reduced suspended-sediment concentrations in runoff from different soil types. Dry tablet and granule PAM formulations were also effective, as long as their placement in the furrows promoted their dissolution in irrigation water. Vegetated ditches resulted in intermediate reductions in suspended sediments in tailwater. The sediment traps were limited in their effectiveness by insufficient holding time for fine-grained particulates to settle out of the runoff.

Effects of a New Polysaccharide-Based Amendment on Furrow Irrigation Infiltration and Erosion

Controlling soil erosion on furrow-irrigated fields is essential to maintain productivity and reduce off-site impacts. Identifying effective alternatives to polyacrylamide (PAM) is desired for continued, affordable irrigation erosion control. We compared the effectiveness of a new polysaccharide/PAM amendment with water-soluble, high molecular weight, anionic PAM in two furrow-irrigated field tests in southern Idaho. Test 1 evaluated three rates of the polysaccharide/PAM amendment (6, 12, and 18 mg L-1 of polysaccharide/PAM), two rates of PAM (2 and 10 mg L-1 of PAM), 10 mg L-1 polysaccharide, and a control during two irrigations in a fallow field. Treatments were applied as a solution with furrow inflow water during irrigation advance. Test 1 results indicated that polysaccharide/PAM amendment could improve infiltration and reduce sediment loss compared to untreated furrows, but its effectiveness seemed to diminish when amendment application stopped. Polysaccharide alone did not significantly effect infiltration, runoff, or sediment loss compared to the control for either irrigation, whereas the polysaccharide/PAM amendment significantly increased infiltration and reduced sediment loss for one irrigation. Test 2 compared polysaccharide/PAM amendment and PAM, both applied at either 2 mg L-1 (active ingredient) continually during irrigation (dissolved treatments) or as a 20 g per furrow of dry material near the furrow inflow point (patch treatments), during four irrigations on a dry bean field. Both amendments significantly increased cumulative infiltration and decreased cumulative runoff and sediment loss compared to untreated furrows. Dissolved polysaccharide/PAM increased cumulative infiltration 19% compared to the control, while dissolved PAM, patch polysaccharide/PAM, and patch PAM treatments increased cumulative infiltration 13%, 11%, and 7%, respectively, compared to the control. Dissolved and patch PAM and dissolved and patch polysaccharide/PAM treatments significantly reduced cumulative sediment loss 98%, 90%, 65%, and 49%, respectively, compared to the untreated furrows. These test results indicate that the polysaccharide/PAM amendment can be used as an alternative, albeit less effective, to PAM for reducing sediment loss from furrow-irrigated fields.

Evaluating the Surface Irrigation Soil Loss (SISL) Model

The SISL (surface irrigation soil loss) model was developed by the Idaho Natural Resources Conservation Service (NRCS) in 1991 to estimate annual soil loss from furrow irrigated fields to assess benefits of conservation practices, such as converting from furrow to sprinkler irrigation. This empirical model was based on over 200 field-years of data from southern Idaho, but it has not been independently evaluated. Data collected in 2003 from six production fields near Kimberly, Idaho, along with previously published furrow irrigation erosion data from Kimberly, Idaho and Prosser, Washington, were used to evaluate the SISL model. Predicted soil loss correlated reasonably well with measured soil loss for all three data sets (r2= 0.73, n = 30). The model predicted the relative effects of conservation tillage practices, straw mulching, and surge irrigation reasonably well, however, the absolute differences between measured and predicted soil loss were sometimes large. Number of irrigations is embedded in the base soil loss so SISL cannot be applied when irrigation application varies significantly from typical southern Idaho conditions. The limited number of conservation practice factors included in SISL also did not represent all types and frequencies of tillage operations that occurred in the field. A better approach may be to calculate the base soil loss from field length, slope, soil, and some estimate of runoff rather than selecting base soil loss from slope and crop categories in the current model.

Using Polyacrylamide (PAM) for Reducing Sediment and Nutrient Losses from Cool Season Vegetable Fields

Agricultural runoff is a source of nutrients and sediments in surface water on the central coast of California. Treating soils with high molecular weight anionic polyacrylamide (PAM) may reduce sediments and P lost from furrow and sprinkler irrigated fields by maintaining infiltration and stabilizing soil aggregates. We conducted column and field studies to quantify the effect of PAM on infiltration rate, run off, and sediment and nutrient (ortho and total P, NO3, K) loss from cool season vegetable fields. Column studies demonstrated a reduction in infiltration for 10 soil types when PAM was continuously applied in the irrigation water at 10 ppm. Recirculating infiltrometer studies showed that in furrow systems, PAM, applied only in the initial water at 10 ppm, had no significant effect on infiltration at four of six sites evaluated. Turbidity and total suspended solids were significantly reduced in the PAM treated water. Across all sites, treatment with PAM reduced suspended solids by 85% compared to the untreated control. Additionally, soluble and total P, and total N were reduced in the PAM treated water. PAM had no effect on nitrate or salt levels in the runoff. PAM applied through sprinklers at a 5 ppm concentration was able to significantly reduce the turbidity and the suspended solids in the tailwater. Similar to the results obtained with the recirculation infiltrometer trials, PAM reduced soluble and total P and total N in the runoff, but had no significant effect on NO3-N. Total sediment loss under sprinklers was reduced by as much as 95% using PAM.

Occurrence and measurement of salinity stratification in shallow groundwater in the Murrumbidgee Irrigation Area, south-eastern Australia

Capillary upflow from shallow groundwater is a significant contributor of soil salinisation in irrigated areas and is highly dependent on water table position and salinity. Lysimeters have traditionally been used to quantify capillary upflow from shallow water tables and the potential salinisation risk. However, water table position and salinity are usually controlled to remain constant in lysimeter studies, while short-term variations in these parameters may exist under surface irrigated agriculture. Consequently, the extrapolation of calculated crop water uptake and potential soil salinisation processes from lysimeter studies to field conditions may be misleading in selected cases. A multilevel sampler was designed to collect water samples at 20 cm intervals to investigate changes in water table position and salinity stratification of a shallow fluctuating water table under furrow irrigated fields. Water samples were taken from the upper 20 cm of the shallow groundwater (the water table zone, WTZ) as it rose and fell following irrigation events at three farms in the Murrumbidgee Irrigation Area, in south-western New South Wales, Australia. The water table was within 2 m of the ground surface at all sites and irrigation events resulted in large fluctuations in water table position over the irrigation season. Salinity stratification of the shallow groundwater was found to exist with low salinity water overlying more saline groundwater and a zone of variable salinity extending up to 2 m. The salinity generally increased with depth. In addition to changes in shallow groundwater salinity with depth, salinity fluctuated at specific depths over the irrigation season. The salinity of the WTZ also varied with changes in water table position. Following an irrigation event, a rising water table is associated with lower salinity at the WTZ. At each depth interval sampled, the salinity increased between water table rise and fall. The water table position and salinity are important determinants of salinity risks since they are the foundation for capillary upflow. Consequently, short-term variations in the position and salinity of shallow water tables under field conditions will affect capillary upflow and salt movement into the root zone. Therefore, where variations in these parameters exist at the field scale, detailed measurements should be taken to accurately predict crop water uptake and assess potential soil salinisation hazards.

SEDIMENT POND EFFECTIVENESS FOR REMOVING PHOSPHORUS FROM PAM-TREATED IRRIGATION FURROWS

Polyacrylamide (PAM) greatly reduces erosion on furrow-irrigated fields and sediment ponds can be constructedto remove suspended sediment from irrigation runoff. Both practices are approved for reducing phosphorus (P) loading inthe Lower Boise River Pollution Trading Project in southwest Idaho, but information is not available about using bothpractices on the same field. The objective of this study was to measure the combined effects of PAM application and sedimentponds on sediment and P losses from a furrow-irrigated field. Small sediment ponds (5.8 m2) with a 60-min design retentiontime were installed on two fields to receive runoff from PAM-treated or control furrows. Pond inflow and outflow weremonitored during a total of 11 irrigations on the two fields. Three crop years of data showed that applying PAM to furrowsreduced sediment and total P mass transport to the ponds 50% to 80%, which reduced the mass of sediment and total P retainedin the ponds. However, PAM application did not change the percentage of sediment (86%) and total P (66%) retained. ThePAM-sediment pond combination reduced average total P loss by 86% to 98%, based on the difference between untreatedinflow and PAM-treated outflow. PAM and sediment ponds had little or no effect on dissolved reactive P (DRP)concentrations. The mass of DRP retained in sediment ponds was directly related to the amount of water that infiltrated withinthe ponds. Applying PAM to irrigation furrows and installing sediment ponds at the end of the field can be an effectivecombination for reducing sediment and total phosphorus losses from furrow-irrigated fields, but these practices only reducedsoluble P losses by decreasing the volume of water that ran off the fields.

Water flow and solute transport in furrow-irrigated fields

Field-scale solute transport experiments are not easily implemented because of the overwhelming problems of soil heterogeneity and variability in subsurface hydraulic and solute transport properties. In this paper, the results of four field-scale furrow irrigation experiments designed to investigate the effect of flow depth and solute application time on bromide distribution along and below the furrows are presented. One experiment was conducted under free-draining (FD) conditions in which bromide was applied during the entire irrigation event. Three experiments were carried out in blocked-end furrows in which bromide was injected either during the entire irrigation event (100%), the first half of the irrigation (FH), or the second half of the irrigation (SH). The FD experiment was equipped with neutron probe tubes for measuring soil water contents at different times and locations in furrow cross-section whereas soil samples for bromide analysis and gravimetric soil water contents from all the experiments were collected at different depths up to 1.80 m, 5 days after the irrigation at three locations near the inlet, in the middle, and close to the outlet of the furrows. Overland flow depths along the furrows were also recorded using staff gauges at the inlet, middle, and outlet sites every few minutes during the entire irrigation. Results showed substantial non-uniformity in solute movement along the monitored furrows, with the degree of non-uniformity depending upon flow depth and solute application time. Non-uniform distributions were observed especially at the outlet sites, compared with those at the inlet and middle sites. Solute application efficiencies for the FD, 100%, FH, and SH experiments were 50, 100, 64, and 93%, respectively. The effects of flow depth and irrigation/solute application time on soil water contents were more pronounced in the soil surface layers and were found to be relatively minor at deeper depths. Water and solute deep percolation rates also showed dependency to flow depth and solute application/opportunity time and gradually decreased along the furrows.

Effects of irrigation-induced salinity and sodicity on soil microbial activity

The effects of irrigation-induced salinity and sodicity on the size and activity of the soil microbial biomass in vertic soils on a Zimbabwean sugar estate were investigated. Furrow-irrigated fields were selected which had a gradient of salinity and sugarcane yield ranging from good cane growth at the upper ends to dead and dying cane at the lower ends. Soils were sampled under dead and dying cane, poor, satisfactory and good cane growth and from adjacent undisturbed sites under native vegetation. Electrical conductivity (EC) and sodium adsorption ratio (SAR) of saturation paste extracts was measured, as well as the exchangeable sodium percentage (ESP). There was a significant negative exponential relationship between EC and microbial biomass C, the percentage of organic C present as microbial biomass C, indices of microbial activity (arginine ammonification and fluorescein diacetate hydrolysis rates) and the activities of the exocellular enzymes β-glucosidase, alkaline phosphatase and arylsulphatase but the negative relationships with SAR and ESP were best described by linear functions. By contrast, the metabolic quotient increased with increasing salinity and sodicity, exponentially with EC and linearly with SAR and ESP. Potentially mineralizable N, measured by aerobic incubation, was also negatively correlated with EC, SAR and ESP. These results indicate that increasing salinity and sodicity resulted in a progressively smaller, more stressed microbial community which was less metabolically efficient. The exponential relationships with EC demonstrate the highly detrimental effect that small increases in salinity had on the microbial community. It is concluded that agriculture-induced salinity and sodicity not only influences the chemical and physical characteristics of soils but also greatly affects soil microbial and biochemical properties.

POLYACRYLAMIDE FOR SURFACE IRRIGATION TO INCREASE NUTRIENT-USE EFFICIENCY AND PROTECTWATER QUALITY

Furrow irrigation systems have a greater application capacity, are less costly, and use less energy than sprinkler systems but furrow irrigation produces greater runoff, erosion, and deep percolation losses. Phosphorus (P) and nitrogen (N) losses are associated with runoff sediment, and can be minimized by eliminating irrigationinduced erosion. Excessive leaching of inorganic and organic solutes commonly occurs at the inflow region of furrow irrigated fields where infiltration opportunity times are longer. In one conservation practice, a high molecular weight, anionic polyacrylamide (PAM) is applied to advancing furrow stream flows at a concentration of 10 mg L−1. Because PAM stabilizes furrow soil and flocculates suspended sediment, we hypothesized that this treatment would reduce runoff losses of sediment, molybdate reactive P (MRP), total P, NO3-N, and chemical oxygen demand (COD). Polyacrylamide treatment may increase furrow infiltration in some soils. However, we hypothesized that because it permits higher initial inflows, PAM would not increase NO3-N or Cl leaching relative to conventional, constant inflow irrigation. To test the first hypothesis, all treatments had the same inflow regime. For hypothesis two, control inflows were a constant 15 L min−1; PAM treated in- flows were cut back from 45 to 15 L min−1 after furrow advance. Irrigation runoff and percolation waters were sampled and analyzed. Polyacrylamide increased infiltration and decreased runoff, particularly early in the irrigations. Mean cumulative runoff sediment loss over 12 h was 11.86 kg for each control furrow vs 1.15 kg for PAM-treated furrows. The PAM reduced 12-h cumulative sediment losses in runoff by 90%, MRP by 87%, total P by 92%, and COD by 85%, relative to control furrows. Polyacrylamide had no field-wide, season-long effect on cumulative amounts of water, NO3-N or Cl leached. The PAM-technology effectively prevented soil nutrient losses, increased nutrient-use efficiency, and decreased N and P loads in irrigation return flows and receiving surface waters.

Furrow Irrigation Erosion and Sedimentation: On-field Distribution

Erosion created by furrow irrigation is a serious problem in some states and has resulted in reduced crop yields. Most furrow erosion assessments have been based on measured sediment discharge from the field, which results in an average erosion rate for the whole field. However, erosion theory predicts that the erosion rate should decrease with distance from the head (inflow) end of the furrow. The purpose of this study was to quantify soil erosion and deposition distribution within furrow irrigated fields. Within-field sediment discharge measurements on two silt loam fields in southern Idaho showed that over half of the soil that eroded from the head end of the furrows deposited on the lower portions of the field as furrow flow rates decreased. Erosion rates on the upper quarter of uniformly-sloped furrows were 6-20 times greater than average rates from the field. The measurements demonstrate the need to measure erosion rates on the head ends as well as for the whole field, and explain visible erosion damage from head ends where field average erosion rates are not high.

Comparative Study of Microclimate and Downy Mildew Development in Subsurface Drip- and Furrow-Irrigated Lettuce Fields in California

Microclimates and downy mildew (caused by Bremia lactucae) disease progress were monitored in neighboring lettuce fields with subsurface drip or furrow irrigation during five trials in 1992 to 1993. The trials included a total of ten irrigation events during which soil moisture, soil temperature, canopy air temperature and humidity, leaf wetness duration, wind speed, and solar radiation were recorded. Disease intensity was assessed at intervals, beginning at thinning of the crop and ending just before harvest. Wilcoxon's Signed Rank Tests were computed to compare microclimates between drip- and furrow-irrigated fields, separately for days before or after irrigation. There were no significant differences in microclimate between the two irrigation methods before irrigation. Within 3 days after irrigation, there were significantly longer overall leaf wetness periods (P ≤ 0.0025) and a trend toward higher daytime humidity (P ≤ 0.1254) and longer morning leaf wetness periods (P ≤ 0.0863) in fields with furrow irrigation. Air temperature and nighttime humidity were not consistently different between the two irrigation methods. Downy mildew developed in four of the five trials, and disease intensity was always lower under drip irrigation than under furrow irrigation. The magnitude of the differences in disease was small, however. It appears that, on most days in coastal California, mesoclimatic variations outweigh microclimatic modifications that could potentially influence disease development

Nitrogen Fertilization of Wheat No-Till Planted in Alfalfa Stubble

Conservation tillage practices significantly reduce soil erosion, improve water distribution, and decrease environmental concerns in furrow-irrigated fields. Developing optimum N fertilization practices after legumes in these systems will help their adoption. We conducted three field studies on a silt loam soil to determine if N fertilizer is required for furrow-irrigated wheat (Triticum aestivum L.) planted in herbicide killed alfalfa (Medicago sativa L.) stubble. Fall regrowth of alfalfa was sprayed with a mixture of 1 qt glyphosphate and 2 qt 2,4-D/acre. `Stephens', a soft white winter wheat was planted with a double disk opener drill in two experiments and 'Bronze Chief', a hard red spring wheat in a third experiment. Nitrogen fertilizer (ammonium nitrate) was spring broadcast at four rates from 0 to 200 or 240 lb N/acre. The buried plastic bag technique estimated available N (EAN); above ground whole plant samples estimated root zone nitrate-N; and grain plot yields estimated with a combine. Nitrogen fertilization increased grain yield in all experiments because sufficient N had not mineralized from soil and legume residues before uptake needs of the wheat. The wheat plant at the soft dough growth stage contained about 109 lb N/acre from N mineralized from soil and legume residue sources. The apparent N fertilizer recovery calculated by a combined regression relationship between N uptake and fertilizer rates was 76%. The average plant recovery of mineralized N at maximum grain yields was calculated at 78%. Crops planted in herbicide killed alfalfa should be selected so sufficient nitrate-N can accumulate from mineralization before maximum crop uptake and for N uptake ability in late summer. Nitrogen fertilizer applications should be based on a spring soil test for nitrate-N in this no-till system. Both practices will reduce the potential for nitrate-N leaching losses.

Zone-subsoiling effects on infiltration, runoff, erosion, and yields of furrow-irrigated potatoes

Soil compaction is a problem in many Pacific Northwest fields. We hypothesized that zone subsoiling would improve potato ( Solanum tuberosum L., cv. ‘Russet Burbank’) yield or grade, increase infiltration, and decrease bulk density, runoff, and erosion of furrow-irrigated fields, while maintaining trafficability and irrigability of furrows. A 2 year study was established on a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthids). In the fall, plots were in wheat stubble (1988) or bean stover (1989), and were either disked (10–12 cm), chiselled (25–30 cm), or moldboard plowed (20–25 cm). Fall tillages were split in spring, half of each plot receiving in-row zone subsoiling (46 cm) after planting potatoes. The effect of zone subsoiling on infiltration in 1989 was small because of variation across fall tillages. In 1990, zone subsoiling increased infiltration by 10% across fall tillages. Erosion decreased up to 278% with zone subsoiling. Zone subsoiling reduced erosion more effectively than it increased infiltration, shown by a two- to three-fold decrease in the sediment loss to water infiltrated ratio. Zone subsoiling increased infiltration and reduced erosion more in 1990 when the study was conducted on a slightly steeper slope with higher water application rates than in 1989. In 1989, zone subsoiling increased the yield of grade 1 tubers by 3.8 t ha −1 (4.6%), but the total yield was not significantly increased. In 1990, zone subsoiling increased the total yield by 4.2 t ha −1, and the yield of grade 1 tubers by 5.6 t ha −1 (7.7%). With zone subsoiling, the percentage of large grade 1 market-grade tubers increased by 3.3% in 1989 and 5.7% in 1990. Zone subsoiling requires some extra attention by the irrigator early in the season to insure uniform furrow irrigation, but it can potentially conserve both soil and water while improving grade and yield.

Effects of crop and surface irrigation method on water intake rate of soil

Two surface irrigation methods on three crop fields (border irrigated alfalfa and small grain and furrow-irrigated potatoes) in southeast Idaho were tested to determine their effects on the parameters of the Kostiakov equation. A double-ring infiltrometer was used to measure the water intake rate of soil for the border irrigated fields. The furrow-irrigated fields were tested by both double-ring infiltrometer and inflow-outflow methods. The border-irrigated fields showed higher values of the intercept of the Kostiakov equation than the furrow-irrigated fields for a given soil. This means that the border-irrigated fields have a higher initial intake rate than that of the furrow-irrigated fields. The intercepts obtained by the inflow-outflow method were lower than that by the double-ring infiltrometer but the exponents were statistically not different.

Nitrate-Nitrogen Accumulation In Furrow Irrigated Fields and Effects of Sugarbeet Production

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