**3.2. Leached nitrate**

In **Tables 6** and 7, the nitric N leached in the periods comprehended between the beginning of the sampling period until harvest and between the beginning of the sampling period until it finished are, respectively, shown. Statistically significant differences were only observed between treatment 80 + 140 and the rest of treatments at the period of time comprehended between the beginning of the campaign and harvest in year 2003 and all the sampling period in year 2004. Although Webster et al. [44] reported some 19 kg ha−1 of N leached for the non-fertilized treatment, a similar figure to that reported in this work in year 2004 (**Table 7**), the 32 kg N ha−1 obtained for treatment 80 + 140 is minor to the 50 kg N ha−1 quantities reported by the same authors for treatments with similar dosages, presumably due to variables such as different kinds of soils, etc. By the deduction of nitric **N** leached at the non-fertilized treatment, the nitric N quantities leached in years 2003 and 2004 were assessed in the other treatments. Until harvest, those quantities ranged between the 4 and the 6% of the applied N and, when all the sampling periods were considered, they comprehended N quantities that ranged between the 8 and the 14% of the N fertilized.

Concurring with the results obtained for treatment 80 + 140, in a study performed in Denmark, Kjellerup and Kofoed [24] observed that N fertilizer dosages around 200 kg N ha−1 significantly raised the leached nitrate in drained waters for they exceeded the adsorbing capacity of the crop; the assessed losses were approximately 40 kg N ha−1. In the neighbor community of Navarra, Arregui [7] also described the augmenting N leaching trend for dosages larger than 110 or 120 kg N ha−1.

In **Tables 6** and 7, the average nitric N in the total quantity of drained water is also shown. It was calculated as the product of the drained total N (kg ha−1) throughout all the drainage

**Table 5.** Nitric origin N percentage in relation to Nmin in the soil at different depths, moments, and treatments.

period was 7 ppm N in the year 2003 and 14 ppm in the year 2004 for treatment 80 + 140,

rest in years 2003 and 2004 except for treatment 40 + 60 + 40 in year 2004 when all the sampling period was considered. The average concentrations in treatments 40 + 60 + 40 and 80 + 140 in year 2004 when all the periods were considered were larger than the allowed

−

0 40 + 100 40 + 60 + 40 80 + 140

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**N-NO3 − /Nmin (%)**

−

concentration in the sampling

, statistically differentiated from the

period and the drained water (mm) in the same period.

**Moment Depth (mm) Treatment**

30–60 96

30–60 85

30–60 43

After harvest 0–30 75 89 94 81

Before harvest 0–30 82 86 79 88

After harvest 0–30 92 90 86 92

Before harvest 0–30 79 84 86 83

End of winter 0–30 77 87 83 89

After harvest 0–30 88 88 94 93

30–60 83 89 94 84

30–60 90 89 89 85

30–60 89 89 84 87

30–60 79 83 83 88

30–60 79 83 82 91

30–60 80 90 85 84

Before harvest 0–30 82

End of winter 0–30 78

End of winter 0–30 67

2002

2003

2004

which was the treatment that regards average N-NO<sup>3</sup>

11.3 mg L−1 N-NO<sup>3</sup>

− limit.

Thus, it can be observed that the maximum average N-NO<sup>3</sup>

Approximately 50% of the leached N-NO<sup>3</sup> − in all the samples in 2004, leached in the period comprehended between the moments after harvest and the end of sampling in September for all treatments (**Table 7**).


**2.8. Statistics**

88 Global Wheat Production

**3.1. Mineral N**

referred to in this work.

than 110 or 120 kg N ha−1.

all treatments (**Table 7**).

Approximately 50% of the leached N-NO<sup>3</sup>

**3.2. Leached nitrate**

**3. Results and discussion**

PROC GLM [39] procedure was used to carry out the variance analysis and then determine

Through the Nmin analysis, it was observed that about the 80–95% of the Nmineral (Nmin) analyzed in the floor of the assay was of nitric origin (**Table 5**). The non-fertilized treatment had the least nitric N percentages at every moment and depth in comparison to the percentages in the fertilized treatments. The nitric N percentage was constant or increased with depth, (i.e., from 0–30 to 30–60 cm) except in the moments after harvest in years 2003 and 2004, when the percentage of nitric N was somewhat inferior in the 30–60 cm layer due to the deep and recent extraction of the culture until harvest, close to the moment "after harvest"

In **Tables 6** and 7, the nitric N leached in the periods comprehended between the beginning of the sampling period until harvest and between the beginning of the sampling period until it finished are, respectively, shown. Statistically significant differences were only observed between treatment 80 + 140 and the rest of treatments at the period of time comprehended between the beginning of the campaign and harvest in year 2003 and all the sampling period in year 2004. Although Webster et al. [44] reported some 19 kg ha−1 of N leached for the non-fertilized treatment, a similar figure to that reported in this work in year 2004 (**Table 7**), the 32 kg N ha−1 obtained for treatment 80 + 140 is minor to the 50 kg N ha−1 quantities reported by the same authors for treatments with similar dosages, presumably due to variables such as different kinds of soils, etc. By the deduction of nitric **N** leached at the non-fertilized treatment, the nitric N quantities leached in years 2003 and 2004 were assessed in the other treatments. Until harvest, those quantities ranged between the 4 and the 6% of the applied N and, when all the sampling periods were considered, they comprehended N quantities that ranged between the 8 and the 14% of the N fertilized.

Concurring with the results obtained for treatment 80 + 140, in a study performed in Denmark, Kjellerup and Kofoed [24] observed that N fertilizer dosages around 200 kg N ha−1 significantly raised the leached nitrate in drained waters for they exceeded the adsorbing capacity of the crop; the assessed losses were approximately 40 kg N ha−1. In the neighbor community of Navarra, Arregui [7] also described the augmenting N leaching trend for dosages larger

−

comprehended between the moments after harvest and the end of sampling in September for

in all the samples in 2004, leached in the period

the differences between averages with the Duncan procedure.

**Table 5.** Nitric origin N percentage in relation to Nmin in the soil at different depths, moments, and treatments.

In **Tables 6** and 7, the average nitric N in the total quantity of drained water is also shown. It was calculated as the product of the drained total N (kg ha−1) throughout all the drainage period and the drained water (mm) in the same period.

Thus, it can be observed that the maximum average N-NO<sup>3</sup> − concentration in the sampling period was 7 ppm N in the year 2003 and 14 ppm in the year 2004 for treatment 80 + 140, which was the treatment that regards average N-NO<sup>3</sup> − , statistically differentiated from the rest in years 2003 and 2004 except for treatment 40 + 60 + 40 in year 2004 when all the sampling period was considered. The average concentrations in treatments 40 + 60 + 40 and 80 + 140 in year 2004 when all the periods were considered were larger than the allowed 11.3 mg L−1 N-NO<sup>3</sup> − limit.


**Table 6.** N-NO<sup>3</sup> − leached from January to harvest in year 2003.

#### *3.2.1. Gaseous losses*

Through the integration in time of the daily emission and production rates, losses due to N<sup>2</sup> O emitted to atmosphere and N<sup>2</sup> O + N<sup>2</sup> due to denitrification in 2002 and 2003 were assessed (**Table 8**). In spite of the fact that N fertilization has a key role in N<sup>2</sup> O emissions (Bouwman, 1996), no statistical differences were observed between fertilizing treatments for the emission or the N2 O cumulated production, as described by Menéndez [32] in an essay carried out in Mediterranean climatic conditions. However, when the N<sup>2</sup> Oem quantity corresponding to the non-fertilized treatment is deducted from the other treatments, the N<sup>2</sup> O emitted quantities range from 1.8 to 2.9% of the N broadcast as a fertilizer, superior numbers to those cited by the IPCC [20] when estimating the winter house effect caused by agriculture [21].

Although Hussain et al. [19] report in their review, that the emission of greenhouse gases is fre-

Oem) in all the sampling period in year 2002.

O production rates (N<sup>2</sup>

(Ndeni) from the beginning of the sampling period until harvest and until the end of the sampling period is shown;

Nitrogen balances for the different campaigns are shown in **Tables 9**–**11**. The yield and thus the extraction of the non-fertilized treatment in year 2002 was larger than in the latter two campaigns, due to the fact that in the first year, the field preceding the essay was thoroughly

O em) 2 ±0 2 ±0 6 ±3 5 ±2

Nmin after harvest (NminAH) 17 ±5 33 ±1 45 ±14 17 ±3 NTOTAL OUTPUTS 160 ±8 254 ±15 280 ±21 254 ±25 N not computed 0 ±14 46±19 19 ±24 126 ±27 Fertilizer use efficiency (NUE) 0.49 ±0.12 0.60 ±0.14 0.35 ±0.12 N harvest index 0.84 ±0.08 0.90±0.04 0.81 ±0.05 0.87 ±0.06

**Table 9.** N balance (kg N ha−1) during the 2002 campaign; average values ± standard errors are reported.

Dosage (kg N ha−1) 0 140 140 220 Splitting 0 40 + 100 40 + 60 + 40 80 + 140 Nmin initial (NminS) 40±3 40±3 40 ±3 40 ±3 N mineralized (MIN) 120±11 120 ±11 120 ±11 120 ±11 N fertilized (F) 0 140 140 220 NTOTAL INPUTS 160±11 300 ±11 300 ±11 380 ±11 N absorbed by the aerial part (Nab) 113±6 177 ±15 185 ±15 188 ±24 N absorbed by the roots (Nabr) 28 ±2 42 ±3 44 ±3 44 ±5

O, Ndeni, or Nprod.

due to denitrification

91

quently favored by tilling, such a fact was not observed in this work for N<sup>2</sup>

**Treatment 2002\* 2003 until harvest\*\* 2003 in all the sampling period\*\*\***

**Oem Ndeni Nprod N2**

**Oem**

Oprod) and N<sup>2</sup>

From March 5 until May 17, 2002.

O + N<sup>2</sup>

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**3.3. Nitrogen balance**

N gas (N2

40 + 60 + 40 6 a

\*\*From January 21 to July 4, 2003.

\*\*\*From 2003, January 21 to 2004, February 4.

In the year 2003, N<sup>2</sup>

**Table 8.** Cumulated N<sup>2</sup>

**N2**

**Oem N2**

0 2 a 5 a 4 b 7 a 10 a 40 + 100 2 a 4 a 5 b 10 a 9 a

80 + 140 5 a 8 a 9a 11 a 14 a

Oem accumulation, from the N<sup>2</sup>

statistically different values are marked with different letters.**\***

O emissions (N2

In 2003, in spite of the fact that applied N dosage had no effect on the N<sup>2</sup> O emissions to the atmosphere or on its production in the arable layer, it did affect the N<sup>2</sup> O+ N<sup>2</sup> production due to total denitrification—it was larger for the treatment with the largest N dose, i.e., 80 + 140. As mentioned before, N<sup>2</sup> O+ N<sup>2</sup> peaks due to denitrification were only observed until April 2; thus, these largest losses due to denitrification are imputable to the denitrification peaks after fertilization. Due to the same reason, the cumulated values of N<sup>2</sup> O+ N<sup>2</sup> rates due to denitrification until harvest and after it are similar.


Statistically different values (α ≤ 0.05) are identified with different letters.\* from January 9, 2004 to July 1, 2004. \*\*from January 9, 2004 to September 27, 2004.

**Table 7.** N-NO<sup>3</sup> − leached from January until harvest in all the sampling period of year 2004.


In the year 2003, N<sup>2</sup> Oem accumulation, from the N<sup>2</sup> O production rates (N<sup>2</sup> Oprod) and N<sup>2</sup> O + N<sup>2</sup> due to denitrification (Ndeni) from the beginning of the sampling period until harvest and until the end of the sampling period is shown; statistically different values are marked with different letters.**\*** From March 5 until May 17, 2002.

\*\*From January 21 to July 4, 2003.

O

O emissions (Bouwman,

O emitted quantities

O emissions to the

rates due to denitrifica-

**[N-NO3 − ] average** 

**(mg L−1)**

production due

Oem quantity corresponding to the

O+ N<sup>2</sup>

*3.2.1. Gaseous losses*

−

**Table 6.** N-NO<sup>3</sup>

**Treatment N-NO3**

90 Global Wheat Production

**−**

 14 b 350 4 b + 100 14 b 4 ab + 60 + 40 12 b 3 b + 140 23 a 7:00 AM

Statistically different values (α ≤ 0.05) are identified with different letters.

leached from January to harvest in year 2003.

or the N2

emitted to atmosphere and N<sup>2</sup>

As mentioned before, N<sup>2</sup>

**Treatment Period**

**Table 7.** N-NO<sup>3</sup>

Through the integration in time of the daily emission and production rates, losses due to N<sup>2</sup>

 **(kg ha−1 ) Drainage (mm) [N-NO3**

1996), no statistical differences were observed between fertilizing treatments for the emission

range from 1.8 to 2.9% of the N broadcast as a fertilizer, superior numbers to those cited by the

to total denitrification—it was larger for the treatment with the largest N dose, i.e., 80 + 140.

thus, these largest losses due to denitrification are imputable to the denitrification peaks after

**2004 until harvest**\* **2004 all the sampling period**\*\*

**[N-NO3 − ] average (mg L−1)**

 19 a 371 5 a 38 b 487 8 b + 100 20 a 5 a 41 b 8 b + 60 + 40 31 a 8 a 62 ab 13 ab + 140 32 a 9 a 70 a 14 a

leached from January until harvest in all the sampling period of year 2004.

O cumulated production, as described by Menéndez [32] in an essay carried out in

due to denitrification in 2002 and 2003 were assessed

**−**

**] average (mg L−1)**

peaks due to denitrification were only observed until April 2;

**N-NO3 − (kg ha−1)** O+ N<sup>2</sup>

**Drainage (mm)**

from January 9, 2004 to July 1, 2004.

O + N<sup>2</sup>

(**Table 8**). In spite of the fact that N fertilization has a key role in N<sup>2</sup>

non-fertilized treatment is deducted from the other treatments, the N<sup>2</sup>

IPCC [20] when estimating the winter house effect caused by agriculture [21].

In 2003, in spite of the fact that applied N dosage had no effect on the N<sup>2</sup>

atmosphere or on its production in the arable layer, it did affect the N<sup>2</sup>

Mediterranean climatic conditions. However, when the N<sup>2</sup>

O+ N<sup>2</sup>

tion until harvest and after it are similar.

**N-NO3 − (kg ha−1 )**

\*\*from January 9, 2004 to September 27, 2004.

−

fertilization. Due to the same reason, the cumulated values of N<sup>2</sup>

**Drainage (mm)**

Statistically different values (α ≤ 0.05) are identified with different letters.\*

\*\*\*From 2003, January 21 to 2004, February 4.

**Table 8.** Cumulated N<sup>2</sup> O emissions (N2 Oem) in all the sampling period in year 2002.

Although Hussain et al. [19] report in their review, that the emission of greenhouse gases is frequently favored by tilling, such a fact was not observed in this work for N<sup>2</sup> O, Ndeni, or Nprod.

#### **3.3. Nitrogen balance**

Nitrogen balances for the different campaigns are shown in **Tables 9**–**11**. The yield and thus the extraction of the non-fertilized treatment in year 2002 was larger than in the latter two campaigns, due to the fact that in the first year, the field preceding the essay was thoroughly


**Table 9.** N balance (kg N ha−1) during the 2002 campaign; average values ± standard errors are reported.


**Table 10.** N balance (kg N ha−1) during campaign 2003.

fertilized while in the following two campaigns, wheat was again preceded by wheat and it was not fertilized. The extraction by the aerial part at the other treatments ranged between 134 and 188 kg N ha−1. Mineralization rate was between 93 and 123 kg N ha−1 at the three campaigns.

non-fertilized treatment received no N fertilization. NUE values that range between 0.3 and 0.6

Dosage (kg N ha−1) 0 140 140 220 Splitting 0 40 + 100 40 + 60 + 40 80 + 140 Nmin initial (NminS) 28 ± 2 35 ±2 36 ±7 36 ± 3 N mineralized (MIN) 93 ± 16 93 ± 16 93 ± 16 93 ± 16 N fertilized (F) 0 140 140 220 N TOTAL INPUTS 121 ± 16 268 ± 16 269 ± 17 349 ± 16 N absorbed by the aerial part (Nab) 56 ± 14 134 ± 7 145 ± 10 165 ± 5 N absorbed by the roots (Nabr) 14 ± 3 33 ± 2 36 ± 2 41 ± 1 N leached (Nlix) 19 ± 2 20 ± 2 31 ± 2 32 ± 2 Nmin after harvest (Nmin AH) 32 ± 1 33 ± 1 42 ± 8 53 ± 2 N TOTAL OUTPUTS 121 ± 15 220 ± 8 254 ± 13 291 ± 7 N not computed 0 ± 22 48 ± 18 15 ± 22 58 ± 18 Fertilizer use efficiency (NUE) 0.69 ± 0.18 0.79 ± 0.2 0.62 ± 0.1 Harvest index 0.77 ± 0.26 0.73 ± 0.03 0.87 ±0.04 0.74 ± 0.07

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It was observed that the NUE decreased as the fertilizer dose increased, as observed by other authors (Huggins and Pan, [18]). Fischer et al. [16] stated that depending on the quantity and the distribution of N, HI (harvest index) in wheat ranged from 0.64 to 0.85. Similarly, HI comprehended values between 0.65 and 0.87 in our experiment, the most frequent value of HI was about

1. The average Nmin values in the soils in years 2002, 2003, and 2004 ranged between 12 and

**2.** Nitrate leaching after harvest in the year 2004 accounted for 50% of the total N leached at every treatment. Thus, it was concluded that a significant mineralization took place after harvest that, together with the absence of crop in summer, causes a Nmin accumulation in

**3.** With treatment 80 + 140, more nitrate was leached than with treatments 0 and 40 + 100; losses up to 70 kg N ha−1 were assessed in all the sampling periods in 2004. In this very

as the average concentration in drained water in the sampling period. By the subtraction of the nitric N quantity leached for the non-fertilized treatment, it was assessed that the

−

limit was exceeded, calculated

are frequent at the experiments carried out by the ITGA in Navarra [23].

**Table 11.** N balance (kg N ha−1) during campaign 2004; average values ± standard error.

summer and its ulterior leaching with the rain in autumn.

treatment and treatment 40 + 60 + 40, the 11.3 mg L−1 N-NO<sup>3</sup>

0.70–0.80 (**Tables 9–11**).

**4. Conclusions**

53 kg N ha−1.

It can be observed that the non-accounted N augmented with the N fertilizer dose, as it happened with the leached N quantities and the N emitted as N<sup>2</sup> O. In general, such an effect was also observed for balances performed in Navarra and Castilla-La Mancha [34]. As Estavillo et al. [15] reported, these facts suggest an N mineralization rate different to that of the nonfertilized treatment and dependent on the broadcast N fertilizer dose. In this sense, Kuzyakova and Stahr [27] observed there was an effect on the mineralization pattern after the fertilizer application and Webster et al. [44] imputed the increasing Nc to short periods of immobilization that increased with the increasing quantity of available Nmin. Another possibility is that the increase of Nc might be due to some other kind of undetermined losses in the study such as those derived from ammonia leaching, which is presumed not to be very large since the ammonia quantity regarding nitrate is around 10% of the Nmin (**Table 5**). The losses corresponding to ammonia volatilization were not accounted for, but in posterior studies in the zone, they have proved to be dismissible (personal communication).

NUE (nitrogen use efficiency) ranged between 0.35 and 0.60 in the year 2002 and between 0.62 and 0.82 in the years 2003 and 2004 (**Tables 9–11**). This occurred due to the major extraction of the non-fertilized treatment at the first campaign as compared to the following two, since in the first campaign, the essay was preceded by a fertilized crop, while in the following two campaigns, the


**Table 11.** N balance (kg N ha−1) during campaign 2004; average values ± standard error.

non-fertilized treatment received no N fertilization. NUE values that range between 0.3 and 0.6 are frequent at the experiments carried out by the ITGA in Navarra [23].

It was observed that the NUE decreased as the fertilizer dose increased, as observed by other authors (Huggins and Pan, [18]). Fischer et al. [16] stated that depending on the quantity and the distribution of N, HI (harvest index) in wheat ranged from 0.64 to 0.85. Similarly, HI comprehended values between 0.65 and 0.87 in our experiment, the most frequent value of HI was about 0.70–0.80 (**Tables 9–11**).
