scholarly journals Growing Soybean Prior to Corn Increased Soil Nitrogen Supply and N Fertilizer Efficiency for Corn in Cold and Humid Conditions of Eastern Canada

2012 ◽  
Vol 1 (2) ◽  
pp. 257
Author(s):  
Adrien N. Dayegamiye ◽  
Judith Nyiraneza ◽  
Johann K. Whalen ◽  
Michèle Grenier ◽  
Anne Drapeau
Keyword(s):  
N Uptake ◽  
N Fertilizer ◽  
Crop Rotations ◽  
Fertilizer Efficiency ◽  
Corn Yield ◽  
Soil N ◽  
Eastern Canada ◽  
Continuous Corn ◽  
N Fertilizer Efficiency ◽  
Corn Grain

<p>Growing soybean (<em>Glycine max L.)</em> prior to corn (<em>Zea mays</em> L) can enhance corn grain and nitrogen (N) use efficiency compared to continuous corn. This two year study (2007-2008) was conducted at 62 sites in Quebec (Eastern Canada) to assess the effect of crop rotations [soybean-corn, soybean-wheat (<em>Triticum aestivum</em> L.,)-corn and corn-corn] on corn yield, N uptake, N fertilizer efficiency (NFE), and the economic optimum N rate (EONR). Plots within each crop rotation received N fertilizer rates from 0 to 250 kg N ha<sup>-1</sup> to assess the N contribution from the preceding soybean crop. Corn grain yields ranged from 8.4 to 10.8 Mg ha<sup>-1</sup> and were lower in continuous corn than in the crop rotations. Corn N uptake and NFE varied from 89 to 164 kg N ha<sup>-1</sup> and from 45 to 80 kg grain per kg N fertilizer, respectively. A significant interaction of crop rotation and year on corn N uptake and NFE was obtained implying that annual variations influenced soil N supply. The EONR for corn was lower under crop rotations than continuous corn in 2008 only. No difference in corn yield, NFE and EONR was observed for soybean-corn and soybean-wheat-corn crop sequences. In conclusion, crop rotations including soybean increased soil N availability and reduced EONR from 32 to 45 kg ha<sup>-1</sup> for corn grown in 2008.</p>

Fertilizer response of barley silage in southern and central Alberta

2004 ◽  
Vol 84 (1) ◽  
pp. 133-147 ◽  
Author(s):  
R. H. McKenzie ◽  
A. B. Middleton ◽  
J. DeMulder ◽  
E. Bremer
Keyword(s):  
N Uptake ◽  
N Fertilizer ◽  
Fertilizer Efficiency ◽  
N Availability ◽  
Soil N ◽  
Fertilizer Response ◽  
Southern Alberta ◽  
Soil N Uptake ◽  
Barley Silage ◽  
N Demand

Barley (Hordeum vulgare L.) silage is the foundation for cattle production on the Canadian prairies, but few studies have evaluated fertilizer requirements for the range of cultivars, soil types and environmental conditions in which it is grown. The objectives of this study were (1) to determine optimum N fertilizer rates for a range of barley cultivars when used for silage in southern and central Alberta and (2) to determine the frequency and impact of P, K and S deficiencies. Thirty-two field experiments were conducted from 1994 to 1996; 20 in southern Alberta under irrigated (8) or dryland (12) conditions and 12 in central Alberta under dryland conditions. Two semi-dwarf (CDC Earl, Tukwa) and three conventional (AC Lacombe, Leduc and Seebe) cultivars were tested. Fertilizer treatments included six rates of N (0 to 200 kg ha-1) and one rate each of P (13 kg ha-1), K (50 kg ha-1) and S (20 or 30 kg ha-1), compared to an appropriate unfertilized control. Optimum rates of N fertilizer ranged from 0 to 172 kg N ha-1. Irrigated sites had the highest N demand but the lowest economic optimum rate of N fertilizer (NFopt) due to high fertilizer N efficiency and high soil N availability. Dryland sites in southern Alberta had a lower N demand than irrigated sites, but NFopt was higher due to lower soil N availability. Sites in central Alberta had the least demand for N, but NFopt was similar to irrigated sites due to low N fertilizer efficiency. Nitrogen fertilizer efficiency frequently exceeded 80% in southern Alberta, particularly under irrigation. Soil N uptake increased with optimum barley yield, indicating that factors that increased crop growth also increased net mineralization and/or efficiency of soil N uptake. A good fit of NFopt was obtained in southern Alberta based on spring soil NO3-N levels and optimum yield. The best estimate of NFopt in central Alberta was the mean due to the lack of a relationship between soil N uptake and spring soil NO3-N. Barley response to P fertilizer was greatest in central Alberta and least in southern Alberta under irrigation. Few responses to K or S fertilizer were observed due to the generally adequate levels of these nutrients in Alberta soils. Fiber concentrations were not strongly affected by fertilizer treatment, while protein concentrations varied with the availability of N relative to demand. Improvements in prediction of fertilizer response for barley silage require better predictors of N fertilizer efficiency and soil N uptake, particularly in central Alberta. Key words: Hordeum vulgare, nitrogen fertilizer use efficiency, protein, fiber

scholarly journals Effect of Winter Cover Crops on Soil Nitrogen Availability, Corn Yield, and Nitrate Leaching

2001 ◽  
Vol 1 ◽  
pp. 22-29 ◽  
Author(s):  
S. Kuo ◽  
B. Huang ◽  
R. Bembenek
Keyword(s):  
Cover Crops ◽  
Cover Crop ◽  
N Fertilizer ◽  
N Leaching ◽  
Corn Yield ◽  
N Availability ◽  
Soil N ◽  
Soil N Availability ◽  
N Concentration ◽  
Fertilizer Rates

Biculture of nonlegumes and legumes could serve as cover crops for increasing main crop yield, while reducing NO3leaching. This study, conducted from 1994 to 1999, determined the effect of monocultured cereal rye (Secale cereale L.), annual ryegrass (Lolium multiflorum), and hairy vetch (Vicia villosa), and bicultured rye/vetch and ryegrass/vetch on N availability in soil, corn (Zea mays L.) yield, and NO3-N leaching in a silt loam soil. The field had been in corn and cover crop rotation since 1987. In addition to the cover crop treatments, there were four N fertilizer rates (0, 67, 134, and 201 kg N ha-1, referred to as N0, N1, N2, and N3, respectively) applied to corn. The experiment was a randomized split-block design with three replications for each treatment. Lysimeters were installed in 1987 at 0.75 m below the soil surface for leachate collection for the N0, N2, and N3treatments. The result showed that vetch monoculture had the most influence on soil N availability and corn yield, followed by the bicultures. Rye or ryegrass monoculture had either no effect or an adverse effect on corn yield and soil N availability. Leachate NO3-N concentration was highest where vetch cover crop was planted regardless of N rates, which suggests that N mineralization of vetch N continued well into the fall and winter. Leachate NO3-N concentration increased with increasing N fertilizer rates and exceeded the U.S. Environmental Protection Agency’s drinking water standard of 10 mg N l�1 even at recommended N rate for corn in this region (coastal Pacific Northwest). In comparisons of the average NO3-N concentration during the period of high N leaching, monocultured rye and ryegrass or bicultured rye/vetch and ryegrass/vetch very effectively decreased N leaching in 1998 with dry fall weather. The amount of N available for leaching (determined based on the presidedress nitrate test, the amount of N fertilizer applied, and N uptake) correlated well with average NO3-N during the high N leaching period for vetch cover crop treatment and for the control without the cover crops. The correlation, however, failed for other cover crops largely because of variable effectiveness of the cover crops in reducing NO3leaching during the 5 years of this study. Further research is needed to determine if relay cover crops planted into standing summer crops is a more appropriate approach than fall seeding in this region to gain sufficient growth of the cover crop by fall. Testing with other main crops that have earlier harvest dates than corn is also needed to further validate the effectiveness of the bicultures to increase soil N availability while protecting the water quality.

Water and Nitrogen Budget Dynamics for a Maize-Peanut Rotation in Florida

2020 ◽  
Vol 63 (6) ◽  
pp. 2003-2020
Author(s):  
Maria I. Zamora Re ◽  
Sagarika Rath ◽  
Michael D. Dukes ◽  
Wendy Graham
Keyword(s):  
Crop Rotation ◽  
Root Zone ◽  
N Uptake ◽  
Irrigation Scheduling ◽  
N Fertilizer ◽  
N Leaching ◽  
Soil N ◽  
Fertilizer Rate ◽  
Irrigation Treatments ◽  
Fertilizer Rates

HighlightsDSSAT simulations of final N uptake, biomass, and yield for a maize-peanut rotational field experiment with three irrigation treatments and three N fertilizer rates had good performance for the irrigated treatments (average nRMSE of 9%) but greater error for the rainfed treatments (average nRMSE of 15%).Experiments and DSSAT simulations demonstrated that N fertilizer and irrigation applications were reduced by 26% and 60%, respectively, when using a 247 kg N ha-1 fertilizer rate and a sensor-based irrigation schedule rather than conventional practices of 336 kg N ha-1 and a calendar-based irrigation method, with no impact on yield.Simulations demonstrated that N leaching during the crop rotation was reduced by 37% when an N fertilizer rate of 247 kg N ha-1 and sensor-based irrigation scheduling were used versus conventional practices.Soil N increased (=15 mg kg-1) when maize and peanut residues decayed and then leached during the fallow season. Cover or cash crops planted immediately after the maize and peanut harvests have potential to take up this N and reduce leaching.Abstract. Nitrogen (N) is an essential element for crop growth and yield; however, excessive N applications not taken up by crops can result in N leaching from the root zone, increasing N loads to waterbodies and leading to a host of environmental problems. The main objective of this study was to simulate water and N balances for a maize-peanut (Zea mays L. and Arachis hypogaea L.) rotational field experiment with three irrigation treatments and three N fertilizer rates. The irrigation treatments consisted of mimicking grower irrigation practices in the region (GROW), using soil moisture sensors to schedule irrigation (SMS), and non-irrigated (NON). The N fertilizer rates were low, medium, and high (157, 247, and 336 kg N ha-1, respectively) for maize with a constant 17 kg ha-1 for all peanut treatments. DSSAT maize genetic coefficients were calibrated using the SMS-high treatment combination under the assumption of no water or N stress. The other eight treatment combinations were used as independent data for model validation of the crop coefficients. All soil hydrologic parameters were specified based on measured values, and default DSSAT peanut genetic coefficients were used with no calibration. For the irrigated treatments, DSSAT models had good performance for N uptake, biomass, and yield (average nRMSE of 8%) and moderate performance for soil water content (average nRMSE of 18%). Soil nitrate RMSE was 21% lower than the standard deviation of the observed data (5.8 vs. 7.2 mg kg-1). For the rainfed treatments, DSSAT had greater error (average nRMSE of 15% for N uptake, biomass, and yield, and average nRMSE of 31% for soil water). Soil nitrate RMSE was 11% greater than the standard deviation of the observed data (8.0 vs. 7.2 mg kg-1), and nRMSE was &gt;30% during the crop rotation. Simulations estimated that N leaching over the crop rotation was reduced by 24% on average when using the 247 kg N ha-1 fertilizer rate compared to 336 kg N ha-1 across the irrigation treatments. Furthermore, N leaching was reduced by 37% when using SMS to schedule irrigation and the 247 kg N ha-1 fertilizer rate for maize and 17 kg N ha-1 for peanut compared to conventional practices (GROW and 336 kg N ha-1 for maize and 17 kg N ha-1 for peanut). Moreover, this management practice reduced N fertilizer use by 26% and irrigation water use by up to 60% without negative impacts on yield. Observed and simulated soil N increased during maize and peanut residue decay, with simulations estimating that this soil N would leach below the root zone during the fallow season. This leaching could potentially be reduced if a cover crop or cash crop were planted between the maize and peanut crops to take up the mineralized N. Keywords: Agricultural best management practices, Bare fallow, BMPs, Maize-peanut rotation, N balance, N fertilization, N leaching, Sandy soils, Sensor-based irrigation scheduling, Water balance.

scholarly journals Inhibition of N2 Fixation by N Fertilization of Common Bean (Phaseolus vulgaris L.) Plants Grown on Fields of Farmers in the Eastern Cape of South Africa, Measured Using 15N Natural Abundance and Tissue Ureide Analysis

2021 ◽  
Vol 3 ◽  
Author(s):  
Simon J. Habinshuti ◽  
Sipho T. Maseko ◽  
Felix D. Dakora
Keyword(s):  
South Africa ◽  
Single Dose ◽  
Phaseolus Vulgaris ◽  
N Uptake ◽  
N Fertilizer ◽  
Double Dose ◽  
Soil N ◽  
Eastern Cape ◽  
Bean Plants ◽  
Soil N Uptake

Inhibition of N2 fixation in N-fertilized common bean (Phaseolus vulgaris L.) plants growing on the fields of farmers in the Eastern Cape of South Africa was measured using 15N natural abundance and tissue ureide analysis. The N-fertilized bean plants revealed greater soil N uptake, higher concentrations of nitrate in organs, low tissue ureide levels, and much lower percent relative ureide-N abundance when compared with unfertilized plants. In contrast, the unfertilized plants showed greater nodule fresh weight, higher N derived from fixation (e.g., 84.6, 90.4, and 97.1% at Lujecweni fields 2, 3, and 4, respectively), increased amount of N-fixed (e.g., 163.3, 161.3, and 140.3 kg ha−1 at Lujecweni fields 2, 3, and 4, respectively), greater ureide concentration in stems and petioles, higher % relative ureide-N abundance, and low soil N uptake. We also found that the percent N derived from fixation (%Ndfa) was very high for some bean plants receiving a double dose of N fertilizer [e.g., Lujecweni field 1 (51.8%) and Tikitiki field 1 (53.3%], and quite high for others receiving a single dose of N fertilizer [e.g., Tikitiki field 2 (50.1%), Mfabantu fields 1 and 2 (45.5 and 79.9%, respectively), and St. Luthberts field 1 (58.9%)]. Though not assessed in this study, it is likely that the rhizobia that effectively nodulated the N-fertilized bean plants and fixed considerable amounts of symbiotic N had constitutive and/or inducible nitrate reductase genes for reducing nitrate in nodules and bacteroids, hence their ability to form root nodules and derived high %Ndfa in bean with added N. While single- and double-dose N fertilizer applications increased plant growth and grain yield compared to unfertilized bean plants, the single-dose N fertilizer application produced much greater grain yield than the double dose. This indicates that farmers should stop using a double dose of N fertilizers on bean production, as it decreases yields and can potentially pollute the environment. This study has however shown that government supply of free N fertilizers to resource-poor farmers in South Africa increased bean yields for food/nutritional security.

scholarly journals Drainage Conditions Influence Corn-Nitrogen Management in the US Upper Midwest

Agronomy ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 2491
Author(s):  
Gabriel Dias Paiao ◽  
Fabián G. Fernández ◽  
Seth L. Naeve
Keyword(s):  
Grain Yield ◽  
N Uptake ◽  
N Fertilizer ◽  
Residual Soil ◽  
Soil N ◽  
Soil Drainage ◽  
Upper Midwest ◽  
The Us ◽  
Glycine Max L ◽  
N Management

Soil drainage is not considered in the N fertilizer guidelines for corn (Zea mays L.) in the US Midwest. This study investigated the influence of soil drainage on corn grain yield, N requirement, and residual soil N, and evaluated the utility of in-season soil N measurements to guide N application. This 6-year study in Minnesota, US on a corn–soybean (Glycine max [L.] Merr.) rotation had drained and undrained conditions and six at planting (PL) (0–225 in 45 kg N ha−1 increments) and four split (SP) N fertilizer rates (at planting/V6-V8—45/45, 45/90, 45/135, 45/179 kg N ha−1). The drained compared to undrained soil produced 8% more grain yield (12.8 vs. 11.9 Mg ha−1), 12% more N uptake (169 vs. 151 kg N ha−1), 16% lower optimal N rate (ONR) (160 vs. 193 kg N ha−1), 3.1% greater grain yield at ONR (13.5 vs. 13.1 Mg ha−1), and similar in season and residual soil N. Compared to SP, PL lowered ONR (151 vs. 168 kg N ha−1) in drained soils, and the opposite occurred for undrained soils (206 vs. 189 kg N ha−1). These results substantiate the agronomic benefits of artificial drainage and the need to incorporate drainage conditions into N management guidelines.

scholarly journals Impact of Danish Livestock and Manure Management Regulations on Nitrogen Pollution, Crop Production, and Economy

2021 ◽  
Vol 2 ◽  
Author(s):  
Sven G. Sommer ◽  
Leif Knudsen
Keyword(s):  
Crop Production ◽  
N Fertilizer ◽  
Fertilizer Efficiency ◽  
Mineral Fertilizers ◽  
Regulation System ◽  
Agricultural Practice ◽  
Pig Slurry ◽  
Catch Crops ◽  
Manure Application ◽  
N Fertilizer Efficiency

Reduction of nitrate (NO3) and ammonia (NH3) emission to the environment has, since the 1980s, been targeted by Danish environmentally friendly regulations. Nitrate pollution of aquifers and surface waters caused by farming was observed at the start of the 1980s, and in the mid-1980s, NH3 emission was known to contribute reactive nitrogen (N) to the environment. Manure is a significant source of plant nutrient loss, because there might be a lack of economic incentives and knowledge for the farmers to obtain a high nutrient utilization of the manure. This article gives a presentation of the initiatives and regulations intended to reduce the emission, the actual reduction in emission achieved, and the effect of the regulation on farmers' economy, which is considered important in the discussion about how we can reduce pollution of the environment and at the same time have an economically sustainable agriculture. In the 1980s, the Ministry of Environment and the farmers' union agreed on launching a “good agricultural practice” program, aimed at reducing N loss by increasing N use efficiency and reducing fertilizer N import. This had no or limited effect on emission, and in the late 1980s, regulations were introduced with mandatory stipulations on manure storage capacity, application of manure during the growing season, and limitation on the number of animals per hectare agricultural land (Harmony Rules). Early introduction of the Harmony Rule in 1985 has since prevented very high local surpluses of N and phosphorus. In 1993/94, legislation was introduced for a system of farm-specific N quotas and minimum requirements for utilization of N in animal manure, controlled by the Ministry of Agriculture and Environment based on fertilizer accounts for each farm. The legislation requirements for utilization of N in manure were based on research at the universities and a large number of trials on commercial farms conducted by the Danish extension service (SEGES). These convinced most farmers of the potential manure N fertilizer efficiency. From 1993/94, the N quotas were based on optimal N levels to the crops, but from 1998/99 to 2016/17, they were reduced to 10–20% below the economically optimal rate. From 2016/17, the reduced N quotas were replaced by an expansion of the catch crop requirement in the legislation. The effect is that NO3- leaching has been reduced by 45% by restricting manure application to the period with crop demand for plant nutrients, by undersupplying with N as related to the economically optimum application rate, and by compulsory cultivation of crops that take up N during most of the year. Regulation has resulted in a 51% reduction in NH3 emission from livestock buildings, manure stores, and manure application. In 2020/21, the required N fertilizer efficiency of manure N (equivalence to N in mineral fertilizers) is 75% of N in cattle slurry and 80% for pig slurry, higher than in any other countries known to us. The N quotas are based on the optimal level, and the requirement for compulsory catch crops is 40–50% for the main part of the country. The farmers can use alternatives to catch crops like a reduced N quota or early establishment of winter cereals. The revision of the “regulation system” was intended to improve the economy of the crop production, but the effect was that complexity and volume of legislation have increased significantly, without much effect on farmers' economy. It is recommended that the regulation is kept simple and that it reflects the processes leading to plant uptake and emissions.

scholarly journals Prediction of Nitrogen Responses of Corn by Soil Nitrogen Mineralization Indicators

2001 ◽  
Vol 1 ◽  
pp. 135-141 ◽  
Author(s):  
R.R. Simard ◽  
N. Ziadi ◽  
M.C. Nolin ◽  
A.N. Cambouris
Keyword(s):  
Nitrogen Mineralization ◽  
Soil Nitrogen ◽  
Sandy Loam ◽  
N Uptake ◽  
N Fertilizer ◽  
Clay Loam ◽  
Fine Sandy Loam ◽  
Soil Nitrogen Mineralization ◽  
Residual N ◽  
Corn Grain

Soil nitrogen mineralization potential (Nmin) has to be spatially quantified to enable farmers to vary N fertilizer rates, optimize crop yields, and minimize N transfer from soils to the environment. The study objectives were to assess the spatial variability in soil Nminpotential based on clay and organic matter (OM) contents and the impact of grouping soils using these criteria on corn grain (Zea mays L.) yield, N uptake response curves to N fertilizer, and soil residual N. Four indicators were used: OM content and three equations involving OM and clay content. The study was conducted on a 15-ha field near Montreal, Quebec, Canada. In the spring 2000, soil samples (n = 150) were collected on a 30- x 30-m grid and six rates of N fertilizer (0 to 250 kg N ha-1) were applied. Kriged maps of particle size showed areas of clay, clay loam, and fine sandy loam soils. The Nminindicators were spatially structured but soil nitrate (NO3–) was not. The N fertilizer rate to reach maximum grain yield (Nmax), as estimated by a quadratic model, varied among textural classes and Nminindicators, and ranged from 159 to 250 kg N ha-1. The proportion of variability (R2) and the standard error of the estimate (SE) varied among textural groups and Nminindicators. The R2ranged from 0.53 to 0.91 and the SE from 0.13 to 1.62. Corn grain N uptake was significantly affected by N fertilizer and the pattern of response differed with soil texture. For the 50 kg N ha-1rate, the apparent Nminpotential (ANM) was significantly larger in the clay loam (122 kg ha-1) than in the fine sandy loam (80 kg ha-1) or clay (64 kg ha-1) soils. The fall soil residual N was not affected by N fertlizer inputs. Textural classes can be used to predict Nmax. The Nminindicators may also assist the variable rate N fertilizer inputs for corn production.

Long-term (35 years) effects of fertilization, rotation and weather on corn yields

1995 ◽  
Vol 75 (2) ◽  
pp. 355-362 ◽  
Author(s):  
C. F. Drury ◽  
C. S. Tan
Keyword(s):  
Grain Yield ◽  
Crop Rotation ◽  
Potential Evapotranspiration ◽  
Corn Yield ◽  
Weather Factors ◽  
Grain Yields ◽  
Continuous Corn ◽  
Corn Grain ◽  
Corn Grain Yield

Long-term effects of fertilization, crop rotation and weather factors [temperature, precipitation, net radiation, maximum (potential) evapotranspiration (ET) and corn heat units (CHU)] on the sustainability of corn grain yields were investigated over 35 yr. Treatments included fertilized and unfertilized continuous com and rotation corn-oats-alfalfa-alfalfa. The fertilized rotation corn treatment produced the greatest corn grain yields (15% moisture content) with an average of 7.75 t ha−1 followed by the fertilized continuous corn treatment with 6.02 t ha−1. Fertilization increased grain yield for continuous corn treatments by 279% and increased grain yields in the rotational corn treatments by 70%. Corn grain yields increased with time with the fertilized rotation treatment, remained relatively constant with the fertilized continuous corn and decreased with the unfertilized treatments. Growing season precipitation was the only weather variable tested which was significantly related to corn grain yield. Precipitation in July was proportional to corn grain yield for all fertilized treatments. Weather variation played little role for unfertilized corn. Continuous corn production was sustained (yields did not decrease with time) when fertilizer was added. There was a considerable yield advantage with fertilized corn when grown in a rotation compared with fertilized continuous corn. Fertilization and crop rotation practices increased and buffered corn yields. Key words: Long-term, corn, yield, fertilization, rotation, weather

scholarly journals Efficiency of nitrogen fertilizer applied at corn sowing in contrasting growing seasons in Paraguay

2013 ◽  
Vol 37 (6) ◽  
pp. 1641-1650 ◽  
Author(s):  
Telmo Jorge Carneiro Amado ◽  
Enrique Oswin Hahn Villalba ◽  
Rafael Pivotto Bortolotto ◽  
Antônio Luis Santi ◽  
Enrique Asterio Benítez León ◽  
...  
Keyword(s):  
Nitrogen Fertilizer ◽  
Weather Conditions ◽  
N Fertilizer ◽  
Fertilizer Efficiency ◽  
Corn Yield ◽  
Fertilizer Rate ◽  
Growing Seasons ◽  
Use Efficiency ◽  
Fertilizer Rates ◽  
N Fertilizer Rate

In order to select soil management practices that increase the nitrogen-use efficiency (NUE) in agro-ecosystems, the different indices of agronomic fertilizer efficiency must be evaluated under varied weather conditions. This study assessed the NUE indices in no-till corn in southern Paraguay. Nitrogen fertilizer rates from 0 to 180 kg ha-1 were applied in a single application at corn sowing and the crop response investigated in two growing seasons (2010 and 2011). The experimental design was a randomized block with three replications. Based on the data of grain yield, dry matter, and N uptake, the following fertilizer indices were assessed: agronomic N-use efficiency (ANE), apparent N recovery efficiency (NRE), N physiological efficiency (NPE), partial factor productivity (PFP), and partial nutrient balance (PNB). The weather conditions varied largely during the experimental period; the rainfall distribution was favorable for crop growth in the first season and unfavorable in the second. The PFP and ANE indices, as expected, decreased with increasing N fertilizer rates. A general analysis of the N fertilizer indices in the first season showed that the maximum rate (180 kg ha-1) obtained the highest corn yield and also optimized the efficiency of NPE, NRE and ANE. In the second season, under water stress, the most efficient N fertilizer rate (60 kg ha-1) was three times lower than in the first season, indicating a strong influence of weather conditions on NUE. Considering that weather instability is typical for southern Paraguay, anticipated full N fertilization at corn sowing is not recommended due the temporal variability of the optimum N fertilizer rate needed to achieve high ANE.

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