Gary A. Lehrsch

FURROW IRRIGATION AND N MANAGEMENT STRATEGIES TO PROTECT WATER QUALITY

N management under furrow irrigation is difficult because nitratenitrogen (NO3-N) is frequently leached to groundwater. Banding and sidedressing N fertilizer on a non-irrigated side of a row of corn (Zea mays L.) might increase N uptake and minimize nitrate leaching potential by reducing the NO3-N in soil profiles at harvest, thereby protecting water quality. For two years in the field, we evaluated two N placements (broadcast vs. banded), two row spacings (0.76-m vs. a modified 0.56-m), and two ways of positioning irrigation water (applying water to the same side or alternating sides of the row with successive irrigations) for their effects on N uptake in corn silage and soil profile NO3-N (to the 0.9-m depth). In southern Idaho, we grew field corn in Portneuf silt loam (coarse silty, mixed superactive, mesic Durinodic Xeric Haplocalcid) by irrigating every second furrow nine times in 1988 and seven times in 1989. We measured N uptake by harvesting whole plants at physiological maturity and NO3-N in soil samples taken at two in-row locations in selected plots after each irrigation. Where irrigating alternating sides of the row, two-year average N uptake from 0.76-m rows was 131 kg ha 1, 15% greater (P < 0.001) than from 0.56-m rows. Where irrigating the same furrow all season, N uptake from banding equaled that from broadcasting the first year but was 21% greater (P < 0.001) the second. Applying water to the same furrow decreased profile N by about 170 kg ha 1 under 0.76-m rows by seasons end in 1988. In 1989, irrigating the same furrow and banding N into an adjacent, never-irrigated furrow produced season-average profile N of a) 303 kg ha 1, the least under all fertilized 0.76-m rows, and b) 152 kg ha 1 under 0.56-m rows, half that under similarly treated 0.76-m rows. Our findings suggest that corn in 0.76-m rows should be fertilized by banding N into every second furrow and irrigated season-long using the remaining, non-fertilized furrows because those practices maintained or increased N uptake in silage and minimized residual NO3-N in 0.9-m soil profiles at seasons end.

Seasonal trends in furrow irrigation erosion in southern Idaho

Abstract A study was conducted to measure the seasonal irrigation furrow erosion pattern in the absence of cultivation and a growing crop. This erosion pattern was compared to those of previous measured plot experiments for different years in the presence of cultivation and a growing crop. Erosion for sugarbeets, corn and beans was low early in the season and increased to a maximum during the same 3-week period, from 24 June to 10 July over several years. Erosion decreased as the irrigation season progressed after the erosion peak. The erosion pattern from the uncultivated, non-cropped plots resembled the pattern from previous studies on cropped soil with the maximum erosion occurring about the same time of season. The pattern trends differed only after peak erosion. For the copped plots, there was a sudden erosion decline after peak erosion, followed by a continual gradual decrease. In contrast, for the uncultivated, non-cropped plots, there was a sudden erosion decline after peak erosion, followed by a gradual increase in erosion. Although the seasonal erosion pattern cannot be completely explained, it is important to report it because of the implication for erosion modeling. Sediment loss rates measured from these soils in southern Idaho in late June or early July would significantly overestimate seasonal erosion, whereas sediment loss rates measured in May or early June or after mid-July would underestimate seasonal erosion. These results show that researchers cannot rely upon a one-time measurement for model validation if attempting to predict irrigation furrow erosion over an entire irrigating season.

Whey utilization in furrow irrigation: Effects on aggregate stability and erosion

Improving soil structure often reduces furrow erosion and maintains adequate infiltration. Cottage cheese whey, the liquid byproduct from cottage cheese manufacture, was utilized to stabilize soil aggregates and reduce sediment losses from furrow irrigation. We applied either 2.4 or 1.9L of whey per meter of furrow (3.15 or 2.49Lm(-2), respectively) by gravity flow without incorporation to two fields of Portneuf silt loam (Durinodic Xeric Haplocalcid) near Kimberly, ID. Furrows were irrigated with water beginning four days later. We measured sediment losses with furrow flumes during each irrigation and measured aggregate stability by wet sieving about 10 days after the last irrigation. Overall, whey significantly increased aggregate stability 25% at the 0-15mm depth and 14% at 15-30mm, compared to controls. On average, whey reduced sediment losses by 75% from furrows sloped at 2.4%. Whey increased the aggregate stability of structurally degraded calcareous soil in irrigation furrows.

Compost and Manure Effects on Fertilized Corn Silage Yield and Nitrogen Uptake under Irrigation

Abstract Dairy manure increases the yields of dry bean (Phaseolus vulgaris L.) and spring wheat (Triticum aestivum L.) from eroded, furrow‐irrigated soils and may increase corn (Zea mays L.) silage yield from steeper eroded areas under sprinkler irrigation. In a 2‐year field study in southern Idaho on Portneuf silt loam (coarse silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid), the effects of a one‐time, fall application of 29 or 72 Mg ha−1 of dry manure or 22 or 47 Mg ha−1 of dry compost on subsequent silage yield and nitrogen (N) uptake from previously eroded, sprinkler‐irrigated hill slopes were evaluated. In October 1999, stockpiled or composted dairy manure was disked to a depth of 0.15 m into plots with slopes from 0.8 to 4.4%. After planting field corn in 2000 and 2001, a low‐pressure, six‐span traveling lateral sprinkler system was utilized to apply water at 28 mm h−1 in amounts sufficient to satisfy evapotranspiration to 6.4‐×36.6‐m field plots. Yields in 2000 were 27.5 Mg ha−1, similar among all rates of all amendments and a fertilized control. In 2001, compost applied at oven‐dry rates up to 47 Mg ha−1 increased yield compared to controls. Silage yield in 2001 increased initially then decreased with increasing manure applications. Where compost or manure was applied, regardless of rate, 2‐year average N uptake was 15% greater than controls. Regardless of treatment or year, yields decreased linearly as soil slope increased.

Furrow erosion and aggregate stability variation in a Portneuf silt loam

Abstract Numerous soil factors, including aggregate stability, affect erosion rates from irrigated furrows. Since aggregate stability varies within growing seasons, furrow erosion may vary as well. The study objectives were to (1) measure furrow erosion and aggregate stability periodically over two growing seasons, (2) statistically characterize the temporal variation in furrow erosion and aggregate stability, and (3) relate variation in erosion rates to changes in aggregate stability and other soil properties. Erosion rates from replicated, previously unirrigated furrows in fallow plots on a Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid ) at Kimberly, Idaho, USA, were measured every 2–3 weeks from mid-May through mid-August 1988, and from late-April to late-August 1989. During each 6.5-h irrigation, three furrows in 1988 and four furrows in 1989 were irrigated at an inflow rate of 11.3 l·min −1 . At each irrigation, soil samples were taken to a depth of 5 cm from the bottom of furrows adjacent to or near those irrigated. From these samples, soil gravimetric water content was measured and aggregate stability was determined by wet sieving. Erosion from furrows not previously irrigated varied greatly when measured throughout two growing seasons. For both years, erosion rates were significantly lower later in the growing season than earlier. For a 4.0% slope area in 1988, furrow erosion rates varied over the entire season by a factor of six or more while aggregate stability varied (increased) by only 17%. Thus, aggregate stability was not significantly correlated with furrow erosion rates.

Nitrogen Availability and Uptake by Sugarbeet in Years Following a Manure Application

The use of solid dairy manure for sugarbeet production is problematic because beet yield and quality are sensitive to deficiencies or excesses in soil N, and soil N availability from manure varies substantially depending on the year of application. Experimental treatments included combinations of two manure rates (0.33 and 0.97 Mg total N ha−1) and three application times, and non-manure treatments (control and urea fertilizer). We measured soil net N mineralization and biomass, N uptake, and yields for sprinkler-irrigated sugarbeet. On average, the 1-year-old, low-rate manure, and 1- and 2-year-old, high-rate manure treatments produced 1.2-fold greater yields, 1.1-fold greater estimated recoverable sugar, and 1.5-fold greater gross margins than that of fertilizer alone. As a group the 1-year-old, low-rate manure, and 2- and 3-year-old, high-rate-manure treatments produced similar cumulative net N mineralization as urea fertilizer; whereas the 1-year-old, high-rate manure treatment provided nearly 1.5-fold more N than either group. With appropriate manure application rates and attention to residual N and timing of sugarbeet planting, growers can best exploit the N mineralized from manure, while simultaneously maximizing sugar yields and profits.

Aggregate Tensile Strength and Friability Characteristics of Furrow and Sprinkler Irrigated Fields in Southern Idaho

Agricultural crops grown in southern Idaho are furrow or sprinkler irrigated. Therefore, the soil experiences several wetting and drying cycles each growing season that can contribute to changes in aggregate tensile strength and friability. The objective of the research was to evaluate the influence of irrigation on soil structural properties. Four furrow-irrigated fields were sampled at the top and bottom of the field, in the furrow and on the bed location of the furrow. Five sprinkler-irrigated fields were sampled at depths of 0–5 and 5–15 cm and at the top and bottom of the field. Results from this study indicate that differences in tensile strength in furrow-irrigated fields were only evident soon after irrigation; otherwise, there were few differences in tensile strength and friability. In sprinkler-irrigated fields tensile strength increased with depth in three of the five fields measured. Friability was less affected by depth.

Winter Wheat Yield, Quality, and Nitrogen Removal Following Compost- or Manure-Fertilized Sugarbeet

ABSTRACT To efficiently use nitrogen (N) while protecting water quality, one must know how a second-year crop, without further N fertilization, responds in years following a manure application. In an Idaho field study of winter wheat (Triticum aestivum L.) following organically fertilized sugarbeet (Beta vulgaris L.), we determined the residual (second-year) effects of fall-applied solid dairy manure, either stockpiled or composted, on wheat yield, biomass N, protein, and grain N removal. Along with a no-N control and urea (202 kg N ha−1), first-year treatments included compost (218 and 435 kg estimated available N ha−1) and manure (140 and 280 kg available N ha−1). All materials were incorporated into a Greenleaf silt loam (Xeric Calciargid) at Parma in fall 2002 and 2003 prior to planting first-year sugarbeet. Second-year wheat grain yield was similar among urea and organic N sources that applied optimal amounts of plant-available N to the preceding year’s sugarbeet, thus revealing no measurable second-year advantage for organic over conventional N sources. Both organic amendments applied at high rates to the preceding year’s sugarbeet produced greater wheat yields (compost in 2004 and manure in 2005) than urea applied at optimal N rates. On average, second-year wheat biomass took up 49% of the inorganic N remaining in organically fertilized soil after sugarbeet harvest. Applying compost or manure at greater than optimum rates for sugarbeet may increase second-year wheat yield but increase N losses as well. Abbreviations CNS, carbon–nitrogen–sulfur