Residual NO3-N Research Articles

Drip fertigation triggered by soil matric potential reduces residual soil nitrate content and improves maize nitrogen uptake and yield stability in an arid area

Effective water and fertilizer management is crucial for enhancing nitrogen (N) use efficiency and ensuring regional food security, especially in arid regions. Drip fertigation can synchronize water and fertilizer supply with crop demand, but its maximum benefits can only be achieved with appropriately designed and well-managed irrigation systems. In this study, we built on our previous work on optimizing the design of drip irrigation systems and evaluated the effect of drip fertigation regimes on soil nitrate nitrogen (NO3-N) supply, crop N uptake, yield, and yield stability. We conducted a five-year field experiment using drip fertigation to grow maize (Zea mays L.) in the Hetao Irrigation District, Northwest China, from 2016 to 2020. We implemented three water levels by controlling soil matric potential (SMP) threshold values [− 10 kPa (S1), − 30 kPa (S3), and − 50 kPa (S5)] under the same N fertilization rate (150 kg N ha−1 broadcast as basal fertilizer, 150 kg N ha−1 applied with drip fertigation). Our results indicated that soil NO3-N in 0–60 cm profile was typically distributed in the non-mulched zone at maturity. Compared with S5, S1 and S3 on average significantly decreased NO3-N accumulation in the 0–60 cm profile by 66% and 47%, and S1 and S3 significantly decreased NO3-N accumulation in the 60–120 cm profile by 31% and 30%. In addition, the S3 significantly decreased NO3-N accumulation in the 120–200 cm profile by 52% and 35% compared with S1 and S5. S3 significantly improved crop grain yield by 45%, sustainable yield index by 26%, N uptake by 28%, and N utilization efficiency by 11% compared with S5. In contrast, S3 decreased the irrigation amount by 40% compared with S1, with no significant differences in grain yield, yield stability, and N uptake in most years. We recommend using an SMP threshold value of − 30 kPa combined with a drip fertigation rate of 150 kg N ha−1 to reduce residual NO3-N and improve yield and yield stability in arid regions. Furthermore, we also recommend using drip fertigation with 208–253 mm irrigation water in wet years and > 253 mm in dry years (irrigation every four days from V6 to R3 stage), with 13.6 kg ha−1 N applied per irrigation (from VT to R3 stage) to facilitate farmer operations. Our research provides valuable technical guidance to promote a stable and sustainable agricultural production in arid regions.

Subsurface fertilization boosts crop yields and lowers greenhouse gas emissions: A global meta-analysis

The subsurface application (SA) of nitrogenous fertilizers is a potential solution to mitigate climate change and improve food security. However, the impacts of SA technology on greenhouse gas (GHG) emissions and agronomic yield are usually evaluated separately and their results are inconsistent. To address this gap, we conducted a meta-analysis synthesizing 40 peer-reviewed studies on the effects of SA technology on GHG and ammonia (NH3) emissions, nitrogen uptake (NU), crop yield, and soil residual NO3-N in rice paddies and upland cropping system. Compared to the surface application of N, SA technology significantly increased rice yields by 32 % and crop yield in upland systems by 62 %. The largest SA-induced increases in crop yield were found at low N input rates (<100 kg Nha−1) in rice paddies and medium N input rates (100–200 kg Nha−1) in upland systems, suggesting that soil moisture is a key factor determining the efficiency of SA technology. SA treatments increased yields by more at reduced fertilizer rates (~30 % less N), a shallow depth (<10 cm), and with urea in both cropping systems than at the full (recommended) N rate, a deeper depth (10–20 cm), and with ammonical fertilizer. SA treatments significantly increased NU in rice paddies (34 %) and upland systems (18 %), and NO3-N (40 %) in paddyland; however, NO3-N decreased (28 %) in upland conditions. Ammonia mitigation was greater in paddyland than in upland conditions. SA technology decreased the carbon footprint (CF) in paddyland by 29 % and upland systems by 36 %, and overall by 33 %. Compared with broadcasting, SA significantly reduced CH4 emissions by 16 %, N2O emissions by 30 %, and global warming potential (GWP) by 10 % in paddy cultivation. Given SA increased grain yield and NU while reducing NH3, CF, and GWP, this practice provides dual benefits – mitigating climate change and ensuring food security.

Combined nitrogen and phosphorus management based on nitrate nitrogen threshold for balancing crop yield and soil nitrogen supply capacity

An appropriate combined nitrogen (N) and phosphorus (P) fertilization strategy is essential for obtaining sustained higher grain yields while maintaining soil fertility. In this study, a long-term split-plot design farmland experiment (initiated in 2009) with five N fertilizer rates combined with four P fertilizer rates was established during 2016–2019 to determine an appropriate nitrate-N (NO3-N) threshold in an intensive managed wheat–maize double cropping system. A fertilization strategy was then proposed based on the NO3-N threshold to balance the crop yields and soil nitrogen supply capacity. The results showed that N fertilizer increased the accumulated NO3-N, and the combined application of phosphate fertilizer with each N rate reduced the accumulated NO3-N to different degrees. The residual soil NO3-N reached a steady-state soil N pool balance after long-term application of N at 150–225 kg ha−1 combined with P at 60–120 kg ha−1. The residual NO3-N threshold in the root zone (0–100 cm soil layer) was determined as about 100 kg ha−1 at the crop harvest to maintain the N supply capacity and prevent leaching into the deep soil (>100 cm soil layer). The fertilization guidelines are 154 kg ha−1 for N fertilizer and 106 kg ha−1 for P fertilizer in the winter wheat season, and 162 kg ha−1 for N fertilizer and 122 kg ha−1 for P fertilizer in the summer maize growing season based on the NO3-N safety threshold. The optimized fertilizer strategy reduced the fertilizer application rate by 67 kg N ha−1 per year and the residual NO3-N by 34.2 % in the deep soil, while only reducing the average yield by 3.1 % across the crops and years. These findings provide a basis for sustainably balancing grain yields and soil nitrogen supply capacity as well as preventing nitrate pollution of farmland.

Increasing yields while reducing soil nutrient accumulation by straw strip mulching in the dryland wheat (Triticum aestivum L.) cropping system of Northwest China

Surface mulching is an effective strategy to increase yields in rainfed agroecosystems. The plastic film residue and overuse of chemical fertilizer cause a serious non-point source pollution and high production input cost. With mulching, farmers typically attempt to maintain the balance of soil nutrients and reduce fertilizer use while ensuring high yields. Straw strip mulching (SM) is a new mulching technique, but the effects on nutrient uptake have not been studied yet. Therefore, 19 field comparative experiments were conducted in four growth seasons of winter wheat with three mulching treatments: (1) straw strip mulch (SM), a partial ground mulching using whole corn stalks that alternate with planting strips without mulch; (2) full-field plastic film mulching (PM); and (3) no mulching with wheat sown in rows, as a control (CK). Compared with CK, on average over all experiments, SM increased grain yield by 11.5%, biomass by 19.0%, the total aboveground uptakes of nitrogen (N), phosphorus (P) and potassium (K) by 16.1%, 18.4% and 22.9%. There were no significant differences between SM and CK in N and P requirements, the N, P and K concentrations in grain. The increased total aboveground uptake of each nutrient was closely associated with higher biomass, grain yield and straw yield (r = 0.66 −0.84, P < 0.01). Relative to CK, SM significantly decreased the total accumulation of residual NO3-N in the top 100 cm at maturity stage by 32.3% (22.7 kg ha-1) in typical fertilization (N, 120 kg ha-1; P2O5, 90 kg ha-1) and by 33.8% (45.8 kg ha-1) in high fertilization (N, 150 kg ha-1; P2O5, 120 kg ha-1), and the leaching of NO3-N into the deep soil below 40 cm. When only grain nutrients exported from the field after harvest in typical fertilization, N balance in SM, PM and CK accounted for 43.8%, 38.5% and 48.6% of N input, while P balance for 74.8%, 74.0% and 78.4% of P input, respectively, indicating possible saving potentials in fertilizer costs for all treatment, but the saving potential of P is much greater than that of N. Relative to PM, SM had similar the total aboveground nutrients uptake, similar to or slightly less grain yields, and higher economic benefit. SM is suitable for popularizing in a semiarid rainfed agroecosystem.

Comprehensive assessment of the effects of nitrification inhibitor application on reactive nitrogen loss in intensive vegetable production systems

Previous studies regarding environmental impacts of nitrification inhibitors (NIs) in intensive vegetable production systems mainly focused on the fate of individual nitrogen (N) compounds. Due to the influence of various N-dynamic pathways on one another, systematic observations, taking into account all key component processes, must be carried out to achieve practically useful recommendations. As well, the mechanisms of how NI application leads to increasing vegetable yields are not well understood. Therefore, we conducted a field experiment with three leading vegetable crops (lettuce, celery, and tomato), and two urea N input rates, without (N1, N2) or with a nitrification inhibitor, 2-chloro-6-(trichloromethyl)-pyridine (CP) (N1 + CP, N2 + CP), to evaluate the comprehensive effects of CP on reactive-N emission in these intensive vegetable production systems, with a focus on leaching, ammonia (NH3) volatilization, and nitrous oxide (N2O) emission, and to clarify the possible mechanisms by which CP affects vegetable yield. The results show that CP application significantly decreased (p < 0.05) N leaching by 36.9, 26.9, and 28.4 %, soil residual NO3-N contents by 34.1, 43.7, and 43.9 %, N2O emission by 46.4, 77.2, and 36.9 %, and significantly increased (p < 0.05) NH3 volatilization by 33.5, 56.3, and 308.1 % in the lettuce, celery, and tomato seasons, respectively, while having no significant effect on yield at the typical N-application rate (N2). Under 60 % of the typical N-application rate (N1), CP addition significantly increased (p < 0.05) yield and N-use efficiency (NUE) over the three-season period by 23.9 and 55.1 %, respectively, significantly reduced (p < 0.05) N2O emission by 43.5 %, while having no significant effect on the other three observed N processes. In a lettuce-celery-tomato rotation, compared with the typical N-application rate (N2), 60 % of the typical N-application rate with CP addition (N1 + CP) significantly increased (p < 0.05) yield and NUE by 37.1 and 214 %, and decreased (p < 0.05) soil residual NO3-N contents, N leaching, and N2O emission by 70.9, 51.1, and 69.6 %, respectively, and had no significant effect on NH3 volatilization. Furthermore, the distribution analysis of N derived from 15N-labeled urea in tomato aboveground suggested that CP application significantly decreased (p < 0.05) N allocation to stems and leaves by 12.1 and 9.7 %, and significantly increased (p < 0.05) N allocation to fruits by 31.2 %, averaged over 60 % and 100 % N treatments. Application of CP increased N storage in fruits and benefited yield.

Effects of nitrogen supply methods on fate of nitrogen in maize under alternate partial root-zone irrigation

Partial root-zone irrigation (PRI) has been practiced worldwide, but little information is available on nitrogen (N) supply methods influence on fate of applied N fertilizer for crop production under PRI. A field experiment was conducted to investigate effect of N supply methods on the uptake, residual, and loss of applied N fertilizer in maize (Zea mays L.) under alternate PRI at Wuwei, northwest China in 2014. 15N-labeled urea was used as N fertilizer. Two irrigation methods included alternate furrow irrigation (AI) and conventional furrow irrigation (CI). Two N fertilizer supply methods included conventional N supply (CN) and alternate N supply (AN), were applied in combination with each irrigation method. Grain yield, root length density (RLD), N uptake by maize at the maturity stage, and atom % of 15N excess, residual 15N and residual NO3-N in the 0-100 cm soil layer after maize harvest were determined. Results shown that compared to CI coupled with CN, AI coupled with AN or CN significantly increased the grain yield, harvest index, RLD, N uptake by maize, 15N accumulation in grain, atom % of 15N excess in the 0-60 cm soil layer, the residual 15N and 15N uptake rates; but significantly decreased the residual NO3-N in the 0-100 cm soil layers and 15N loss rate. Moreover, the synchronized rather than separation supply of N fertilizer and water enhanced the most above parameters under AI. 15N uptake rate was positively correlated with RLD in the 0-40 cm soil layer, suggesting that the enhanced RLD contributed to the improved 15N uptake rate. Therefore, alternate furrow irrigation coupled with conventional or alternate nitrogen supply (synchronized supply of N fertilizer and water) could help improve 15N uptake rate and reduce the 15N loss rate. Keywords: 15N-labeled technology, root length density, nitrogen fertilizer fate, nitrogen management, residual nitrogen DOI: 10.25165/j.ijabe.20201303.5287 Citation: Qi D L, Hu T T, Song X. Effects of nitrogen supply methods on fate of nitrogen in maize under alternate partial root-zone irrigation. Int J Agric & Biol Eng, 2020; 13(3): 129–135.

Effects of nitrogen supply methods on fate of nitrogen in maize under alternate partial root-zone irrigation

Partial root-zone irrigation (PRI) has been practiced worldwide, but little information is available on nitrogen (N) supply methods influence on fate of applied N fertilizer for crop production under PRI. A field experiment was conducted to investigate effect of N supply methods on the uptake, residual, and loss of applied N fertilizer in maize (Zea mays L.) under alternate PRI at Wuwei, northwest China in 2014. 15N-labeled urea was used as N fertilizer. Two irrigation methods included alternate furrow irrigation (AI) and conventional furrow irrigation (CI). Two N fertilizer supply methods included conventional N supply (CN) and alternate N supply (AN), were applied in combination with each irrigation method. Grain yield, root length density (RLD), N uptake by maize at the maturity stage, and atom % of 15N excess, residual 15N and residual NO3-N in the 0-100 cm soil layer after maize harvest were determined. Results shown that compared to CI coupled with CN, AI coupled with AN or CN significantly increased the grain yield, harvest index, RLD, N uptake by maize, 15N accumulation in grain, atom % of 15N excess in the 0-60 cm soil layer, the residual 15N and 15N uptake rates; but significantly decreased the residual NO3-N in the 0-100 cm soil layers and 15N loss rate. Moreover, the synchronized rather than separation supply of N fertilizer and water enhanced the most above parameters under AI. 15N uptake rate was positively correlated with RLD in the 0-40 cm soil layer, suggesting that the enhanced RLD contributed to the improved 15N uptake rate. Therefore, alternate furrow irrigation coupled with conventional or alternate nitrogen supply (synchronized supply of N fertilizer and water) could help improve 15N uptake rate and reduce the 15N loss rate. Keywords: 15N-labeled technology, root length density, nitrogen fertilizer fate, nitrogen management, residual nitrogen DOI: 10.25165/j.ijabe.20201303.5287 Citation: Qi D L, Hu T T, Song X. Effects of nitrogen supply methods on fate of nitrogen in maize under alternate partial root-zone irrigation. Int J Agric & Biol Eng, 2020; 13(3): 129–135.

Intersowing Cover Crops into Standing Soybean in the US Upper Midwest

Nutrient losses and soil erosion after soybean (Glycine max (L.) Merr.) harvest are common in the US Upper Midwest. Cover crops need to provide adequate growth and cover to prevent soil degradation throughout the winter and early spring months. The objective of this study was to determine the establishment of intersown cover crops and their impacts on a soybean-wheat rotation. Four cover crops—winter camelina (Camelina sativa (L.) Crantz), winter pea (Pisum sativum ssp. arvense (L.) Poir), winter rye (Secale cereale L.), and radish (Raphanus sativus L.)—were directly sown at the R4 and R6 stages of soybean at two locations, Prosper and Fargo, ND in 2016–2017. Cover crops above ground biomass in the fall ranged from 0.4 to 3.0 Mg ha−1 and N accumulation ranged from 28.7 to 73.2 kg ha−1. Winter camelina and winter rye reduced subsequent spring wheat yield compared with the no cover crop treatment. Fall soil residual NO3-N levels were lowest where cover crops were sown compared with the check. Spring NO3-N levels were lowest in winter camelina and winter rye compared with all the other cover crops and the check. Results indicated intersowing cover crops have no impact on soybean yield, and show potential to mitigate soil nitrate losses in areas that grow soybean as a cash crop.

Controlling cold temperature partial nitritation in moving bed biofilm reactor

Mainstream partial nitritation was studied at 10 °C in a moving bed biofilm reactor treating synthetic wastewater containing both nitrogen (≈40 mg L−1) and organic carbon at COD/N ratio ranging from 1.3 to 2.2. Three different control strategies were investigated to achieve partial nitritation. Initially, biofilm age was controlled by incorporating a media replacement strategy. Next, separately from the media replacement, oxygen limited conditions were investigated and finally pH control was incorporated together with oxygen limitation. Successful partial nitritation was achieved only by combining oxygen limitation with pH control. The average NH4-N concentration was equal to 16.0 ± 1.6 mg L−1 and average NO2-N concentration was equal to 15.7 ± 2.4 mg L−1 during steady state partial nitritation. The average residual NO3-N concentration was equal to 2.6 ± 2.2 mg L−1. The results obtained from this study prove for the first time that partial nitritation can be successfully controlled in a biofilm reactor treating wastewater with low nitrogen concentration, relatively high COD/N ratio and at low temperature. An algorithm for dynamic process control of partial nitritation has been also developed.

Responses of residual and recommended N, P, K, S nutrients and crops to six annual soil test-based fertilizer rates and seeding systems

Responses of residual and recommended nitrogen (N), phosphorus (P), potassium (K), sulfur (S) nutrient amounts and crops (yield, emergence, and height) to 0, 60, 100, and 140% soil test-based fertilizer rate applications on the same plots for six years under minimum tillage and direct seeding systems were assessed. Higher fertilizer rates increased residual nitrate (NO3)-N, extractable K, and sulfate (SO4)-S amounts after a low crop yield year, particularly NO3-N, without temporal trend. Increase in residual available P level at higher fertilizer rates showed a positive temporal trend. Lower N, P, and S fertilizer rates were recommended to crops after higher residual NO3-N, available P, and SO4-S levels. Crops effectively used the residual nutrients. Compared to 0%, the relative seed yields at 60, 100, and 140% rates increased with years of fertilization. There were no clear responses of measured soil and crop parameters to seeding systems. Testing residual nutrients can optimize fertilizer use and crop yields.

Effect of Irrigation Level and Irrigation Frequency on the Growth of Mini Chinese Cabbage and Residual Soil Nitrate Nitrogen

Nitrogen (N) fertilizer is known to improve the quality and biomass of vegetables, but it is unclear how to manage the large amount of NO3-N that accumulates in the soil after vegetable harvest. In this study, we examined the influence of irrigation level and irrigation frequency on the growth and soil residual NO3-N of the catch crop mini Chinese cabbage (Brassica pekinensis) in a greenhouse. Using conventional border irrigation with adequate water supply as a control (CK), three irrigation levels (WH: 160% crop evapotranspiration (ETc), WM: 120% ETc and WL: 80% ETc) and three irrigation frequencies (intervals of F2: 2 days, F4: 4 days, and F8: 8 days) were assessed in 2014, 2015 and 2016 in northwest China. The results showed that the weight of the leaves and leaf stalks was the primary determinant of yield, and that these are the primary N-containing vegetative organs of the plants. At the same irrigation level, the total N content of the plants increased in the order F8 &lt; F2 &lt; F4. The trend in the total N content in the mini Chinese cabbage plants among different treatments was synchronized with the yield. The highest total N content in the plants was observed in the WMF4 treatment during all three years. The three-year averages of mini Chinese cabbage aboveground biomass, yield and water use efficiency (WUE) in the WMF4 treatment were 60%, 64.5% and 119.2% higher respectively than in the CK treatment. The residual NO3-N content in the soil in the WMF4 treatment was only 1.3% higher than that in the CK treatment. The total N uptake in the WMF4 treatment was 79.2% higher than that in the CK treatment, and the N loss in the WMF4 treatment was 46.3% lower than that in the CK treatment. Under these experimental conditions, the WMF4 treatment can be recommended as an appropriate irrigation regime for mini Chinese cabbage under fallow greenhouse management in northwest China.

Effects of Different Plastic Mulching Methods on Soil Water, Temperature and Nitrate Accumulation in a Dryland Winter Wheat Field

This study has investigated the effects of two different plastic mulching methods on soil water, temperature, and nitrate (NO3-N) accumulation in a dryland winter wheat field after one-year experiment. The drought-resistant wheat (Triticum aestivum) variety Chang-8744 was grown by (i) furrow planting with ridge mulching, (ii) bunch planting with flat mulching, and (iii) conventional flat planting without mulching (or control). Results showed that dryland winter wheat effectively utilized soil water down to 2 m depth, mainly in the first 140 cm. Plastic mulching increased the evapotranspiration during wheat growing season and mostly r flat plastic mulching, by ~18% over the value recorded in the control plots. Soil temperature of the 20-40 cm-layer was higher than the one recorded at 5-10 cm depth during seedling-overwintering stages. Ridge plastic mulching and flat plastic mulching increased soil temperatures at 5 cm, 10 cm, and 40 cm depths during seedling&amp;ndash;overwintering stages with reference to the control (no mulching), then lowered them at the same depths during reviving&amp;ndash;ripening stages. Residual NO3-N was always detected in the soil after harvesting irrespective of the mulching method. It was mainly concentrated in the first -60 cm accounting for ~50% of soil NO3-N accumulation within the 2-m profile. The highest soil NO3-N accumulation occurred under flat plastic mulching, which represented ~107% of the mean value of the remaining treatments. Finally, flat plastic mulching showed the greatest effects on soil water, temperature, and NO3-N accumulation in dryland wheat field.

Effects on Selected Soil Properties of Subsurface Banding and Surface Broadcasting Pelletized Poultry Litter on Cotton

The response of soil chemical, physical, and biological properties to subsurface band and surface broadcast applications of pelletized poultry litter (PPL) to row crops has not been well documented in Mississippi agroecosystems. This study was conducted in a no-till system on Caledonia silt loam and in a conventional tillage system on Marietta loam, to determine the effects of PPL placement relative to inorganic N fertilizer on selected soil health indicators, including total C, penetration resistance, and microbial activity. The experimental design at each site was a randomized complete block with three treatments replicated four times. Treatments were PPL at the rate of 6.7 Mg ha−1, state-recommended inorganic N fertilizer, and an unfertilized control. Inorganic N fertilizer was applied as urea-ammonium nitrate (32% N). Relative to inorganic N fertilizer, applying PPL in subsurface band for 4 years (2010–2103) increased soil P by 48% and total C by 17%. Regardless of the PPL application method, soil penetration resistance was 19% lower with PPL than fertilizer N. Residual NO3-N levels in the soil layers did not differ between PPL and unfertilized control; however, levels were greatest with inorganic N fertilizer. Additionally, applying PPL in subsurface bands increased soil dehydrogenase activity and cephalothin-resistant heterotrophic plate count bacteria as compared with the control and inorganic N fertilizer. Cotton lint yield was significantly greater with PPL than with inorganic N fertilizer in 2012 in Caledonia silt loam soil (1,244 vs. 1,128 kg ha−1) and in 2013 in Marietta loam soil (1,369 vs. 1,078 kg ha−1). Subsurface band placement of PPL appeared to be very useful in improving soil chemical, physical, and biological properties.

Irrigation and Nitrogen Regimes Promote the Use of Soil Water and Nitrate Nitrogen from Deep Soil Layers by Regulating Root Growth in Wheat.

Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6–45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1–45.3% compared to the W1 treatments during the drier growing seasons (2010–2011, 2012–2013, and 2015–2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011–2012, 2013–2014, and 2014–2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO3-N from the deep soil layers. N applications increased yield by 19.1–64.5%, with a corresponding increase in WUE of 66.9–83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha−1, respectively. A N application rate of 240 kg ha−1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO3-N and also in reducing the residual NO3-N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180–240 kg ha−1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical.

Soil Carbon and Nitrogen in Response to Perennial Bioenergy Grass, Cover Crop and Nitrogen Fertilization

Cover crop and nitrogen (N) fertilization may maintain soil organic matter under bioenergy perennial grass where removal of aboveground biomass for feedstock to produce cellulosic ethanol can reduce soil quality. We evaluated the effects of cover crops and N fertilization rates on soil organic carbon (C) (SOC), total N (STN), ammonium N (NH4-N), and nitrate N (NO3-N) contents at the 0–5, 5–15, and 15–30 cm depths under perennial bioenergy grass from 2010 to 2014 in the southeastern USA. Treatments included unbalanced combinations of perennial bioenergy grass, energy cane (Saccharum spontaneum L.) or elephant grass (Pennisetum purpureum Schumach.), cover crop, crimson clover (Trifolium incarnatum L.), and N fertilization rates (0, 100, and 200 kg N ha−1). Cover crop biomass and C and N contents were greater in the treatment of energy cane with cover crop and 100 kg N ha−1 than in the treatment of energy cane and elephant grass. The SOC and STN contents at 0–5 and 5–15 cm were 9%–20% greater in the treatments of elephant grass with cover crop and with or without 100 kg N ha−1 than in most of the other treatments. The soil NO3-N content at 0–5 cm was 31%–45% greater in the treatment of energy cane with cover crop and 100 kg N ha−1 than in most of the other treatments. The SOC sequestration increased from 0.1 to 1.0 Mg C ha−1 year−1 and the STN sequestration from 0.03 to 0.11 Mg N ha−1 year−1 from 2010 to 2014 for various treatments and depths. In contrast, the soil NH4-N and NO3-N contents varied among treatments, depths, and years. Soil C and N storages can be enriched and residual NO3-N content can be reduced by using elephant grass with cover crop and with or without N fertilization at a moderate rate.

Residual soil nitrate content and profitability of five cropping systems in northwest Iowa.

Many communities in the Midwestern United States obtain their drinking water from shallow alluvial wells that are vulnerable to contamination by NO3-N from the surrounding agricultural landscape. The objective of this research was to assess cropping systems with the potential to produce a reasonable return for farmers while simultaneously reducing the risk of NO3-N movement into these shallow aquifers. From 2009 to 2013 we conducted a field experiment in northwest Iowa in which we evaluated five cropping systems for residual (late fall) soil NO3-N content and profitability. Soil samples were taken annually from the top 30 cm of the soil profile in June and August, and from the top 180 cm in November (late fall). The November samples were divided into 30 cm increments for analysis. Average residual NO3-N content in the top 180 cm of the soil profile following the 2010 to 2013 cropping years was 134 kg ha-1 for continuous maize (Zea mays L.) with a cereal rye (Secale cereale L.) cover crop, 18 kg ha-1 for perennial grass, 60 kg ha-1 for a three year oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-maize rotation, 85 kg ha-1 for a two year oat/red clover (Trifolium pratense L.)-maize rotation, and 90 kg ha-1 for a three year soybean (Glycine max (L.) Merr.)-winter wheat (Triticum aestivum L.)-maize rotation. However, residual NO3-N in the 90 to 180 cm increment of the soil profile was not significantly higher in the oat-alfalfa-maize cropping system than the perennial grass system. For 2010 to 2013, average profit ($ ha-1 yr-1) was 531 for continuous corn, 347 for soybean-winter wheat-maize, 264 for oat-alfalfa-maize, 140 for oat/red clover-maize, and -384 (loss) for perennial grass. Considering both residual soil NO3-N and profitability data, the oat-alfalfa-maize rotation performed the best in this setting. However, given current economic pressures widespread adoption is likely to require changes in public policy.

Development of Soil N Testing for Wheat Production using Soil Residual Mineral N

The effects of soil residual nitrate (NO3-N) and ammonium (NH4-4) on wheat (Triticum aestivum L.) grain yield and N uptake were evaluated in a three-year experiment from 1991 to 1993, in the province of Quebec, Canada. Soil samples were collected at harvest from the depth of 0-30 and 30–60 cm from 20 wheat sites and analyzed in the laboratory for NO3-N and NH4-N. Wheat yield and N-uptake was also determined. Using statistical analysis system (SAS) and Matlab, data were analyzed and the best-fitted regression equations were plotted. Significant amounts of soil NO3-N was found in the soil ranging from 31.6 to 61.6 kg/ha. The amount of soil NH4-N varied from 9.2 to 23.3 kg/ha. The statistical effects of model parameters indicated that soil NO3-N and soil NH4-N significantly influenced wheat yield and N uptake. It may be possible to investigate wheat behavior at harvest using soil residual NO3-N and NH4-N.

DAIRY MANURE AND NITROGEN FERTILIZER EFFECTS ON RESIDUAL NITRATE AND PHOSPHATE, AND WHEAT YIELD IN A SANDY CLAY LOAM SOIL

Dairy manure (DM) rates of [0 (DM0), 30 (DM30)), 60 (DM60) Mg ha−1] and three nitrogen (N) rates [0 (N0), 125 (N125), 250 (N250) kg ha−1] were tested in a sandy clay loam, to evaluate their effects on growth and yield of wheat crop (Triticum aestivum L.), residual nitrate nitrogen (NO3-N) and phosphorus (P) concentrations in the surface soil, and selected soil physical measurements [saturated hydraulic conductivity (Ksat), and bulk density (BD)]. Increasing N and DM rates gave higher wheat yields, increased concentrations of residual NO3-N and P in the surface soil and improved Ksat and BD. Highest grain yield of 3.8 Mg ha−1 (70.3% more than the control) was observed in DM60 × N250 treatment. Residual accumulation of N-NO3 and P in the surface soil at high N and/or DM application rates suggests the need to carefully manage N and DM inputs on farm fields to avoid environmental contamination.

Sidedressed Dairy Manure Effects on Corn Yield and Residual Soil Nitrate

Application of livestock manure to an annual crop such as corn is typically limited to relatively short periods in the fall after harvest or in the spring before planting. Direct incorporation or injection into a growing corn crop at sidedress time offers another window of time for manure application—one that avoids planting delays associated with spring application and may reduce potential for nitrate leaching. We established a 2-year field study in northwestern Vermont to compare sidedressed liquid dairy manure directly incorporated with spreader-mounted S-tine cultivators (SD-Incorp) or surface applied (SD-Surf) to preplant-incorporated manure (PP-Incorp) and sidedressed fertilizer N (SD-FertN) to assess effects on corn silage yields, N uptake, and residual soil nitrate. The PP-Incorp manure N rate was higher than SD (212 vs. 150 kg ha−1) in Year 1 but similar (270 and 256 kg ha−1) in Year 2. In Year 1, N uptake for PP and SD-Incorp was similar and greater than SD-Surf and Control (no manure or additional fertilizer N); corn silage yields showed similar but nonsignificant trends. In Year 2, yield for SD-Incorp was equal to other manure and fertilizer N treatments and greater than Control; effects on N uptake were similar except that PP-Incorp was greater than SD manure. Postharvest residual NO3-N in the 1.2-m soil profile was highest in PP-Incorp and SD-FertN treatments; over-winter decreases in profile NO3-N were greater from SD-FertN than from incorporated manure treatments, suggesting higher leaching or denitrification losses. These results show that sidedressed manure can supply adequate N to meet the needs of a corn silage crop and may reduce excess residual NO3-N and potential for N losses.

Corn (Zea mays L.) Grain and Stover Yield as Affected by Soil Residual Mineral Nitrogen

Evaluation of nitrogen (N) dynamic in soil using regression equations is important for proper determination of N fertilization. A 3-year field experiment was conducted to (1) develop the best-fitted regression model relating corn grain and stover yield to soil residual ammonium (NH4)-N and nitrate (NO3)-N for corn yield prediction and (2) evaluate how such a model can be beneficial to the health of ecosystem by predicting the appropriate rates of N fertilization for corn production. Soil NH4-N and NO3-N were determined at corn harvest at the depths of 0–30 and 30–60 cm. Nitrogen fertilizer rates and soil mineral N accounted for a maximum of 93% variation in corn grain yield. Soil mineral N enhanced corn yield more than N fertilizer. Totals of 63.1 and 14.1 kg/ha of soil residual NO3-N and NH4-N were found in the 0- to 60-cm depth, indicating the importance of performing soil N tests.