Use of time domain reflectometry for continuous monitoring of nitrate-nitrogen in soil and water

Nitrate-Nitrogen (NO3-N) losses to ground and surface water are an environmental and agronomic concern in modern crop production systems in the Central Great Plains. Monitoring techniques for nitrogen use in agricultural production are needed to increase crop yield, optimize nitrogen use, and reduce NO3-N leaching. Time domain reflectometry (TDR) could potentially be calibrated to continuously measure NO3-N in soil and water. The objectives of this study were to: (1) evaluate the effect of different factors affecting the response of the bulk electrical conductivity (ECb) sensed by TDR, (2) compare the sensitivity and differences between vertically-installed and horizontally-installed probes for measuring NO3-N leaching in the soil profile, and (3) evaluate the feasibility of using TDR to measure changes in NO3-N concentration in an irrigated agricultural soil. Studies were conducted in the laboratory and in the field at the University of Nebraska West Central Research and Extension Center in North Platte, Nebraska. Temperature of the medium (Ts), solute concentration, TDR cable length, and volumetric soil water content (0v) all influenced and were linearly related to the bulk electrical conductivity (ECb) sensed by the TDR probes. In the field, measured soil NO3-N correlated well with values estimated using TDR measurements of ECb, corrected for changes in 0v and Ts. These results indicated that TDR, if properly calibrated for a particular soil, could be used to continuously monitor NO3-N in soil, and should also be well-suited for monitoring NO3-N in groundwater and surface water. It is, however, important to perform the calibration over a long enough period of time to include the expected range of 0v, Ts, and NO3-N values to obtain adequate accuracy

CLINOPTILOLITE ZEOLITE INFLUENCE ON INORGANIC NITROGEN IN SILT LOAM AND SANDY AGRICULTURAL SOILS

ABSTRACT Development of best management practices can help improve inorganic nitrogen (N) availability to plants and reduce nitrate-nitrogen (NO 3 -N) leaching in soils. This study was conducted to determine the influence of the zeolite mineral Clinoptilolite (CL) additions on NO 3 -N and ammonium-nitrogen (NH 4 -N) in two common Pacific Northwest soils. The effects of CL application rate (at least 12 tons/acre) either band applied or mixed with a set rate of nitrogen (N) fertilizer on masses of NO 3 -N and NH 4 -N in leachate and soil was investigated in a column study using a Portneuf silt loam (coarse-silty mixed mesic Durixerollic Caliciorthid) and a Wolverine sand (Mixed, frigid Xeric Torripsamment). All treatments for each soil received a uniform application of N from urea fertilizer, with fertilizer banded or mixed with CL. In the Portneuf soil, band application of CL and N contained 109% more total inorganic N (NO 3 -N + NH 4 -N) in the soil/leachate system compared to mixing. In both soils, CL application rate influenced the quantity of NO 3 -N and NH 4 -N in the leachate and soil. Application of CL at rates of 3 to 6 tons/acre resulted in the conservation of inorganic N in the soils. Band applying CL and N appears to conserve available inorganic N in the soil compared to mixing CL and N possibly due to decreased rates of microbial immobilization, nitrification and denitrification

Effect of Nitrogen Application Timing on Corn Production Using Subsurface Drip Irrigation

The use of subsurface drip irrigation (SDI) in row-crop agriculture is increasing because of potential increases in water and nutrient use efficiency. Research-based information is needed to manage N applications through SDI systems in field corn (Zea-mays L.) production. This study was conducted to assess the effect of different in-season SDI system N application timings on corn production and residual soil N03-N at the University of Nebraska-Lincoln West Central Research and Extension Center in North Platte, Neb, on a Cozad silt loam (fine-silty, mixed, mesic Fluventic Haplustoll). We evaluated the effect of three N application timing methods (varying percentages of the total N rate [48% of total N] applied at the VIO, VT, and R3 growth stages, in addition to uniform N applications [52% of total NJ over all treatments at preplant, planting, and V14 growth stage) at two N application rates (University of Nebraska-Lincoln [UNL] recommended rate and the UNL rate minus 20%) on corn grain and biomass yield and end-of-study distribution of residual soil N03-N. In 2006, there were no significant differences in corn grain yields between the two N application rates. In 2007, the grain yield under the UNL.recommended N rate was significantly higher (190 kg ha-1) than the UNL-minus-20%N rate. The average grain yield for this study was close to the predicted yields (based on average 5-year historic yields + a 5% yield increase), indicating that ,orn production under SDI is satisfactory. In 2006 and 2007, grain yield and biomass production for the N application timing treatments were not significantly different (P \u3e 0.05). The application of 13% of the total N at as late as R3 did not result in decreased yields. The lack of response to differentN application timing treatments indicates that there is flexibility in N application timing for corn production under SDI. The distribution of N03-N in the 0- to 0.9-m and 0.9- to 1.8-m soil profiles was not significantly different among all the treatments

Effect of Nitrogen Application Timing on Corn Production Using Subsurface Drip Irrigation

The use of subsurface drip irrigation (SDI) in row-crop agriculture is increasing because of potential increases in water and nutrient use efficiency. Research-based information is needed to manage N applications through SDI systems in field corn (Zea-mays L.) production. This study was conducted to assess the effect of different in-season SDI system N application timings on corn production and residual soil N03-N at the University of Nebraska-Lincoln West Central Research and Extension Center in North Platte, Neb, on a Cozad silt loam (fine-silty, mixed, mesic Fluventic Haplustoll). We evaluated the effect of three N application timing methods (varying percentages of the total N rate [48% of total N] applied at the VIO, VT, and R3 growth stages, in addition to uniform N applications [52% of total NJ over all treatments at preplant, planting, and V14 growth stage) at two N application rates (University of Nebraska-Lincoln [UNL] recommended rate and the UNL rate minus 20%) on corn grain and biomass yield and end-of-study distribution of residual soil N03-N. In 2006, there were no significant differences in corn grain yields between the two N application rates. In 2007, the grain yield under the UNL.recommended N rate was significantly higher (190 kg ha-1) than the UNL-minus-20%N rate. The average grain yield for this study was close to the predicted yields (based on average 5-year historic yields + a 5% yield increase), indicating that ,orn production under SDI is satisfactory. In 2006 and 2007, grain yield and biomass production for the N application timing treatments were not significantly different (P \u3e 0.05). The application of 13% of the total N at as late as R3 did not result in decreased yields. The lack of response to differentN application timing treatments indicates that there is flexibility in N application timing for corn production under SDI. The distribution of N03-N in the 0- to 0.9-m and 0.9- to 1.8-m soil profiles was not significantly different among all the treatments

Yield response of corn to deficit irrigation in a semiarid climate

Irrigation water supplies are decreasing in many areas of the US Great Plains, which is requiring many farmers to consider deficit-irrigating corn (Zea mays L.) or growing crops like winter wheat (Triticum aestivum L.) that require less water, but that are less profitable. The objectives of this study were to: (1) quantify the yield response of corn to deficit irrigation, and (2) determine which of several seasonal water variables correlated best to corn yield in a semiarid climate. Eight (T1-T8) and nine (T1-T9) deficit-irrigated treatments (including dryland), were compared in 2003 and 2004 in North Platte, Nebraska. The actual seasonal crop evapotranspiration (ETd) (calculated with procedures in FAO-56) for the different treatments was 37-79% in 2003 and 63-91% in 2004 compared with the seasonal crop evapotranspiration when water is not limited (ETw). Quantitative relationships between grain yield and several seasonal water variables were developed. Water variables included, irrigation (I), total water (W ) rain + irrigation (WR+1), evaporation (E), crop evapotranspiration (ETd) ; crop transpiration (Td), and the ratios of ETd and Td to evapotranspiration and transpiration when water is not limited (ETw and Tw). Both years, yield increased linearly with seasonal irrigation, but the relationship varied from year to year. Combining data from both years, ETd had the best correlation to grain yield (yield = 0.028ETd-5.04; R2 = 0.95), and the water variables could be ranked from higher to lower R 2 when related to grain yield as: ET d(R2=0.95) > Td(R2=0.93) > ETd/ETw(R2=0.90) = Td/Tw(R2=0.90) > Wall(R2=0.89) > E(R2 =0.75) > WR+I(R2=0.65) > I(R2=0.06). Crop water productivity (CWP) (yield per unit ETd) linearly increased with ETd/ETW (R2 = 0.75), which suggests that trying to increase CWP by deficit-irrigating corn is not a good strategy under the conditions of this study

Cumulative deficit irrigation and nitrogen effects on soil water trends, evapotranspiration, and dry matter and grain yield of corn under high frequency sprinkler irrigation

Historically feed corn has been a minor crop in south central Idaho, but over the past three decades corn production in southern Idaho has increased fourfold in response to a similar increase in the local dairy industry. Corn seasonal water use and response to water deficits in the region’s climate is lacking. A three-year field study on corn (Zea mays L.) was conducted in 2017, 2018 and 2019 to evaluate the cumulative effects of continuous water and nitrogen deficits on soil water trends, evapotranspiration, and dry matter and grain yield. Four irrigation rates, fully irrigated (FIT) and three deficit irrigation rates (75% FIT, 50% FIT, and 25% FIT) combined with two nitrogen rates (0 and 246 kg N/ha) were investigated under lateral-move irrigation. Growing season soil water depletion in 2017 in the 25% FIT and 50% FIT irrigation treatments significantly reduced soil water availability at planting in subsequent years and resulted in reduced yields relative to 2017. Nitrogen treatments had no significant effect on soil water availability, seasonal soil water depletion, or crop evapotranspiration for a given irrigation treatment. Crop evapotranspiration was significantly different between irrigation treatments in each study year and decreased as irrigation amount decreased. Dry matter yield was significantly different between irrigation treatments in each study year, but there was no significant difference between the 75% FIT and FIT irrigation treatments for a given nitrogen treatment. Differences in dry matter yield decreased between nitrogen treatments as irrigation amount decreased. Grain yield was significantly reduced by deficit irrigation in each study year, but there was no significant difference between the 75% FIT and FIT irrigation treatments for a given nitrogen treatment in study year. Grain yield was significantly different between nitrogen treatments for only the FIT irrigation treatment. The lack of significant difference in grain yield between the 75% FIT and FIT irrigation treatments resulted in a curvilinear convex downward water production response regardless of nitrogen treatment. A reduction in applied water resulted in a reduction of grain yield regardless of nitrogen availability suggesting that a reduction in irrigation application to less productive areas of a field will cause a yield reduction. The lack of significant difference in crop evapotranspiration between nitrogen treatments for a given irrigation treatment indicates that crop evapotranspiration is independent of crop productivity when soil water contents are similar under high evaporative demand and frequent sprinkler irrigation

High-Yielding Corn Response to Applied Phosphorus, Potassium, and Sulfur in Nebraska

Nutrient management recommendations may change as yield levels and efficiency of crop production increase. Recommendations for P, K, and S were evaluated using results from 34 irrigated corn (Zea mays L.) trials conducted in diverse situations across Nebraska. The mean yield was 14.7 Mg ha-1 with adequate fertilizer applied. Th e median harvest index values were 0.52, 0.89, 0.15, and 0.56 for biomass, P, K, and S, respectively. Median grain yields were 372, 49, and 613 kg kg-1 of above-ground plant uptake of P, K, and S, respectively. The estimated critical Bray-1 P level for corn response to 20 kg P ha-1 was 20 mg kg-1 when the previous crop was corn compared with 10 mg kg-1 when corn followed soybean [Glycine max (L.) Merr.]. Soil test K was generally high with only three site-years kg-1. Over all trials, application of 40 kg K ha-1 resulted in a 0.2 Mg ha-1 mean grain yield decrease. Application of 22 kg S ha-1 did not result in significant yield increase in any trial. Soil test results accounted for twice as much variation in nutrient uptake when soil organic matter (SOM) and pH were considered in addition to the soil test nutrient values. The results indicate a need to revise the current recommendation for P, to maintain the current K and S recommendations, and to use SOM and pH in addition to soil test nutrient values in estimating applied nutrient requirements for irrigated high yield corn production

High-Yielding Corn Response to Applied Phosphorus, Potassium, and Sulfur in Nebraska

Nutrient management recommendations may change as yield levels and efficiency of crop production increase. Recommendations for P, K, and S were evaluated using results from 34 irrigated corn (Zea mays L.) trials conducted in diverse situations across Nebraska. The mean yield was 14.7 Mg ha-1 with adequate fertilizer applied. Th e median harvest index values were 0.52, 0.89, 0.15, and 0.56 for biomass, P, K, and S, respectively. Median grain yields were 372, 49, and 613 kg kg-1 of above-ground plant uptake of P, K, and S, respectively. The estimated critical Bray-1 P level for corn response to 20 kg P ha-1 was 20 mg kg-1 when the previous crop was corn compared with 10 mg kg-1 when corn followed soybean [Glycine max (L.) Merr.]. Soil test K was generally high with only three site-years kg-1. Over all trials, application of 40 kg K ha-1 resulted in a 0.2 Mg ha-1 mean grain yield decrease. Application of 22 kg S ha-1 did not result in significant yield increase in any trial. Soil test results accounted for twice as much variation in nutrient uptake when soil organic matter (SOM) and pH were considered in addition to the soil test nutrient values. The results indicate a need to revise the current recommendation for P, to maintain the current K and S recommendations, and to use SOM and pH in addition to soil test nutrient values in estimating applied nutrient requirements for irrigated high yield corn production

Mycorrhizal colonization and nutrient uptake of dry bean in manure and compost manure treated subsoil and untreated topsoil and subsoil

Eroded or leveled Portneuf silt loam soils (coarse-silty mixed mesic Durixerollic Calciorthid) have been restored to topsoil productivity levels by manure application, but not by other organic sources such as cheese whey. In dry bean (Phaseolus vulgaris L. cv. Viva), only soil organic matter and Zn concentration of leaf tissue correlated with improved yields. Manure application could potentially increase or decrease mycorrhizal colonization depending on which factors dominate. Manured and unmanured soils from a long-term field experiment were sampled and mycorrhizal spores were quantified, but there was no significant manure treatment effect on spore numbers. A greenhouse study was conducted to see if manure or composted manure freshly applied to subsoils would facilitate mycorrhizal colonization in dry bean roots compared to untreated topsoil or conventionally fertilized subsoil. Low level colonization (< 5%) was observed 21 days after planting and that increased to 58% by 56 days after planting. Roots grown on subsoil treated with manure or composted manure showed higher percent colonization than roots from untreated subsoil, but roots on topsoil had highest colonization. This increase in colonization was statistically significant for the last two sampling dates. Topsoil promoted the greatest percent colonization in early bean growth and this was reflected in greater Zn uptake during early growth stages. By day 56, plants grown in manured subsoil absorbed Zn equal to topsoil and at higher levels than the subsoil control. However, this increase in Zn uptake was not seen in plants grown in compost manured subsoil. A decrease in root and shoot weight was observed in the composted manure treatment and this seemed to decrease mycorrhizal efficiency. Uptake of other nutrients was either not related or was negatively related to mycorrhizal infection. The higher percent colonization of roots by mycorrhizal fungi stimulated by manure could explain the field observations of higher bean yield and Zn contents in dry bean in manured than in untreated subsoils