Nitrogen uptake of cereals grown on sandy soils as related to nitrogen fertilizer application and soil nitrogen fractions obtained by electro-ultrafiltration (EUF) and CaCl2 extraction

Eur. J. Agron., 1992, 1 (1), 01-09

Nitrogen uptake of cereals grown on sandy soils as related to nitrogen fertilizer application and soil nitrogen fractions obtained by electro-ultrafiltration (EUF) and CaCl2 extraction T. Appel and K. Mengel (I) Institute of Plant Nutrition of the Justus Liebig University, Sudanlage 6, 6300 Giessen, Germany.

Received 20 May 1991 ; accepted 18 September 1991.

C') To whom correspondence should be addressed. Abstract

Field trials were carried out to examine to what extent nitrogen fertilizer and various soil nitrogen fractions contribute to the nitrogen uptake of cereals. The study focused on soil N tests which are easy to handle, in order to improve their acceptance by farmers. The soil nitrogen fractions estimated were NHt, NO 3' , and organic nitrogen extracted by electro-ultrafiltration (EUF) or CaCl 2 solution, respectively, sampled at various times in early winter and spring. The investigation comprised 36 different sites; all sandy soils derived from mottled sandstone or alluvium. Nitrogen fertilizer rates were 0, 40, 80, and 120 kg N ha- 1 applied iil the form of calcium ammonium nitrate. The relationship between nitrogen fertilizer rates and nitrogen uptake was weak (r2 = 0.36). The coefficient of determination (r2) for the nitrogen uptake by the crop was improved to 73 % if, in addition to the N fertilizer rate, the inorganic N (N03' + NHt) present in the soil profile (0-90 cm) in spring was included in a multiple regression. Soil sampling to a depth of 90 cm in early spring is laborious work and therefore empirical models of « available N » were evaluated based on soil samples taken from the top soil layer (0-30 cm) in early winter. Satisfactory coefficients of determination for the relatioriship between nitrogen uptake of crops v.s. soil test were found for soil tests in which the samples were taken from the top layer (0-30 cm) in December and in which, besides inorganic nitrogen, organic nitrogen was included in the regression. The coefficients of determination thus obtained were 0.65, 0.68 and 0.73 for the EUF-Norg , the CaClz-Nor , and total soil nitrogen, respectively. We believe that such a soil test method based on soil sampling from the upper soil layer in early winter will be more readily accepted by farmers than the N min method. Key-words: Fertilizer, Soil nitrogen fractions, Availability, Cereals, Sandy soils.

INTRODUCTION Sandy soils are generally well drained with an enhanced risk of nitrate leaching into the groundwater (Strebel et al., 1985). Therefore application of excess fertilizer N should be avoided on sandy soils. The Nmin method of Wehrmann & Scharpf (1979) has been found to be a reliable soil N test, particularly on heavier textured soils. Its drawback is the need for soil sampling from three soil layers during a rather short period in spring. It is for this reason that its acceptance by farmers is poor. This is why we sought to develop a soil test method based on soil sampling from the top soil layer in late autumn and early winter. As a first step in N fertilizer recommendation the amount of « crop available» N from various sources has to be predicted precisely. In sandy soils nitrate leaching rates are generally high and in addition selectively bound NH.t is usually low. Hence in ISSN 1161-030119210110109 $ 2.901 © Gauthier-Viliars-ESAg

climatic zones where a positive water balance occurs during winter, easily mineralizable organic soil N has been assumed to playa major role in the N nutrition of crops on sandy soils. According to Mengel (1985) arable soils contain generally large amounts of organic bound nitrogen (1 000 to 20000 kg ha- 1 in the top 0-30 cm). However, usually less than 1 to 3 % of the total organic soil N becomes available to plants by mineralization during a season. The various approaches for estimating the plant available soil N were reviewed by Kohl & Werner (1989). Soil extraction by the electro-ultrafiltration (EUF) technique (Wiklicky & Nemeth, 1981) has attained practical importance for the prediction of mineralizable soil N. The EUF method extracts N03', NH.t and an organic N fraction, which is relatively small compared with the total organic soil N. The chemical analysis of the extracted organic N fractions showed that this socalled N org fraction comprises amino acids, proteins and other hydrolysable N compounds, which are

T. Appel and K. Mengel

2

assumed to be easily mineralizable in soils (Nemeth et al., 1988 ; Danneberg et al., 1989 ; Hiitsch & Mengel, 1990; Recke et al., 1990; Uischner-Peetz & Neumann, 1990). From experiments with soils containing mostly medium to high clay concentrations it was reported that the correlation between the organic N extracted by 0.01 M CaCl2 solution and N uptake of ryegrass was similar to that between EUF-N org and N uptake (Appel & Steffend, 1988). Recent investigations with sandy soils have shown that the organic N fractions measured by EUF and CaCl 2 extraction were significantly correlated with net N mineralization and N uptake by rape (Appel & Mengel, 1990). The amounts of inorganic N extracted by EUF and CaCl2 from dried soil samples were almost identical (Appel & Mengel, 1990; Appel & Steffens, 1988). According to investigations by Houba Table I. -

Cropping and selected soil characteristics (0-30 crn). Texture (%)

Site no.

1

2 3 4 5

6 7 8

9 10 11 12 13 14 15 16 17 18

19 20 21

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

et al. (1990) the inorgani~ N concentrations of dried soil samples were very close to the inorganic N concentrations extracted from fresh samples according to the N min method. The investigations cited above were carried out in pot experiments with air dried soils. For the present study, field experiments were carried out on representative sandy soils in Hessia, Germany, which derived from mottled sandstone and alluvial sands. Investigations were focused on the question how fertilizer N and the various N fractions in sandy soils contribute to the N supply of cereals, with the aim of elaborating empirical models for predicting the amount of N available for cereals during the growth period. These models, based on soil extractions by electro-ultrafiltration or CaCl2 solution, respectively, may become a useful tool for fertilizer recommendations.

Sand

Silt

Clay

55 67 72 75 81 81 87 87 88 87 78 85 88 93

35 22 20

11

19

6

11 13 7 6 7 8 17 8 6 3 5 13 16 11 35 33 30 21 34 5

8 6 6 6 5 6 6 7 6 4 4 7 8 12 10 10 8 11 6

91 78 77 81 54 58 60 71 55 88 86 82 79 73

11 8

9

7

7

11 10 14

8 11 13

66

22

11

85 87 85 88 87 88 75

8 5 8 5 6 7 17

7 8 7 7 7 6 8

pH

Total

(CaCI 2 )

N

6.6 5.5 5.9 6.6 5.2 6.6 6.8 6.4 4.7 6.2

6.6 6.9 6.8 7.1 7.0 7.4 7.1 6.7 6.4 6.8 5.4 6.1 6.4 6.0 5.9 7.1 6.3 6.4 7.3 4.4 7.0 6.9 4.6 6.7 6.3 7.0

(g kg-I)

1.19 1.98

1.19 0.65 0.93 0.66 0.73 0.73 0.48 0.64 0.88 0.65 0.47 0.54 0.55 1.20 0.50 0.70 1.06 0.93 1.04 0.88 1.00 1.11 0.73 0.61 3.99 0.59 1.40 0.65 0.59 0.82 0.43 0.55 0.54 0.54

Total C (g kg-I)

C:N

12.6 23.8 14.1 6.9 12.1 7.6 6.8 7.2 5.8 5.8 13.3 8.0 5.5 5.5 6.2 15.5 5.5 8.0 9.0 9.2 9.5 8.5 9.3 13.6 8.6 7.8 47.1 6.7 24.2 7.3 6.1 9.5 4.6 6.3 6.3 5.9

10.6 12.1 11.8 10.7 13.0 11.6 9.3 9.8 12.2

Crop

Previous crop

ratio

9.1 15.1 12.2 11.6 10.2 11.4 12.9

11.1 11.5 8.5

9.9 9.1 9.7 9.3 12.3 11.9 12.9 11.8 11.3 17.3 11.2 10.3 11.6 10.7 11.4 11.8 10.9

oats oats oats s.-barley w.-rye s.-barley s.-barley s.-barley s.-barley s.-barley oats s.-barley s.-barley s.-barley s.-barley s.-barley s.-barley s.-barley oats w.-barley oats w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye w.-rye

w.-wheat w.-rye w.-barley (rape) w.-rye (rape) rape (rape) w.-barley (rape) sugarbeet potatoes carrots sugarbeet w.-wheat maize sugarbeet maize sugarbeet w.-rye (rape) s.-wheat oats/peas w.-rye 'w.-wheat (rape) sugarbeet rape (rape) rape (rape) s.-barley w.-barley (cabbage) maize maize s.-barley maize maize onions sunflowers potatoes s.-barley w.-rye s.-barley

0= inter crop; sites I to 23 investigated in 1987/88 and sites 24 to 36 in 1988/89. Eur. J. ARron.

3

Soil nitrogen fractions

MATERIAL AND METHODS Nitrogen rate field trials were carried out as a complete block design comprising 36 blocks, each on a different field site. Each block comprised four plots of about 30 to 40 m 2 , which were fertilized with 0, 40, 80, 120 kg N ha- I (No, N 40 , N 80 , N 120) applied as calcium ammonium nitrate at the beginning of the growth period in spring. Our study was focused on the fertilizer N effect and also on the effect of soil N fractions on the N uptake of the crop. In order to obtain a wide variation in soil N fractions the blocks were established on different field sites, 23 in 1987/88 and 13 in 1988/89, on representative sandy soils of Hessia. Winter-rye was grown on 16 sites, springbarley on 13 sites, oats on 6 sites, and winter-barley on one site. Essential data on soils and cropping are given in table I. More detailed information about each field site is reported elsewere (Appel, 1991). Bulk samples were taken from the 0-30 cm layer of the soils in December, February, March/April (before the N was applied) from each site. Samples of each plot were taken in May/June (anthesis), and July/August (maturity). In addition the subsoil was sampled to a depth of 90 cm in March/April (bulk sample at each site), May/June (each plot), and July/August (each plot). Three field sites (number 6, 13, and 23) were not sampled in December. Coolboxes were used to transport the samples immediately after sampling to the laboratory, where the samples were homogenized and dried in a drying cabinet (40 T, 18 h). The dried soil was milled and sieved (~ 1 mm mesh width). Subsamples from the first sampling were used for determination of total soil N (Nt) by the Kjeldahl method and total C by a Wosthoff apparatus according to Schlichting & Blume (1966, p. 122). A fractionated soil extraction with 0.01 M CaCl2 solution was carried out according to Appel & Mengel (1990). The first fraction (20 ·C, 120 min) of this extraction is equivalent to the extraction procedure proposed by Houba et al. (1986). The second fraction was extracted at 80 ·C for 20 min. Two electro-ultrafiltration (EUF) fractions were extracted from the soil samples according to the method of Nemeth (1985): (1) 0-30 min at 20 ·C, 200 V and ~ 15 rnA ; (2) 30-35 min at 80 ·C, 400 V and ~ 150 rnA. Total N, NOrN and NH4-N were analysed in the EUF and CaCl2 extracts by a continuous flow analyser. Organic N in the extracts (N org ) was calculated from the difference between the total N and (NOr N + NH4-N). The extractable N content in a soil profile was calculated assuming a soil density of 1.3 g ml- I (topsoil) and 1.4 g ml- I (subsoil) and expressed in kg N ha- I . Vol. 1, nO 1-1992

In May/June, and July/August the aerial plant parts of 6 m 2 were clipped from each plot and a representative sample of this material was analysed for total N (by a Kjeldahl procedure). In March/April a bulk sample of autumn sown cereals taken from 4 m 2 at each site was clipped and analysed for total N. The total amount of N present in straw plus grain (kg N ha- I ) at the end of the growth period was assumed to reflect the variation of plant available N at the various field sites. Therefore the total amount of N in grain plus straw (hereafter called N uptake) was used as the dependent variable in a multiple linear regression analysis to quantify the effect of the most important factors which influenced the variation of available N. Nominal scaled factors were introduced to the regression analysis by dummy variables according to Montgomery & Peck (1982, p. 216), For example the dummy variable CR was used for the effect of crop residues; CR was coded 1 if sugarbeet leaves, residues of rape, potatoes, sunflowers, legumes, onions, carrots, peas and cabbage has remained on the field. In the case of cereal residues the dummy variable was O. Data of EUF and CaCl 2 extractable N fractions in the soils, used for regressions, and the N uptake of plants from No-plots are given in table II. The data from the other sampling dates are given as means in tables III and IV in order to show the general influence of sampling time and the general effect of fertilizer N on the soil N fractions and the N uptake. Significant change with time and also significant decrease or increase of the N content in the soils and in crops caused by fertilization were tested by at-test for pair differences (Sachs, 1978, p. 242 ; Kohler et ai" 1984, p, 97). The data set was not suitable to analyse crop or year effects separately, because crop and year were not independent (e,g. all sites in 1988/89 but only 3 sites in 1987/88 were cropped with winter rye). RESULTS The amounts of EUF and CaCl2 extractable N fractions in soils before fertilization and in No-plots are shown in table III. A significant decrease of NOr N, NH4-N was found from March/April to May/June, which was presumably due to the N uptake by the crop. Because the N uptake exceeded the decrease of inorganic N in the soils, it can be assumed that mineralization of organic N contributed to the N nutrition of plants, although no significant decrease of the extractable organic N fractions was found. On the contrary there was a slight, but significant increase of extractable organic N in the top-soil. During the grain filling period from May/June to July/August the N uptake of the crops was not reflected in a corresponding decrease in extractable

T. Appel and K. Mengel

4

Table II. -

EUF and CaCl2 extractable N in the soils (bulk samples of each site) and N uptake of plants (grain + straw, NO-plots).

December Site no.

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

March/April CaCI2 extr. 20 °C fraction topsoil (0-30 cm) (kg N ha-~)

EUF

20 T + 80°C fraction topsoil (0-30 cm) (kg N ha- 1)

CaCI 2 extr. 20 T fraction profile (0-90 cm) (kg N ha- 1)

N org

NOrN

NH4-N

N org

inorganic N

53 60 53 55

27 26 37 8 7

5 11 6 4 5

22 29 25 22 27

5 5 7 5 11 4

39 38 31 34 44 35

12 8 21 9 54 4

2 3 4 3 7 2

19 16 15 14 20 14

36 36 58 36 37 36 38 36 32

4 5 5 9 8 24

11

5 5 7 6 5 5 7 8 5

36 12

3 3 4 3 3 4 4 7 4

11 22 19 15 14 15 18 17 15

5 8 4 17 3 9 4 4 8 2 4 4 3

10 9 7 18 6 8 8 6 8 6 7 8 7

48 44 53 119 54 85 51 53 60 35 41 30 43

4 8 4 12 3 9 4 3 7 2 3 2 2

4 6 2 16 3 7 6 2 5 4 3 4 3

25 23 20 62 18 31 29 18 26 13 21 15 19

54 102 43 42 16 56 52 44 54 64 84 39 54 25 48 57 43 55 36 20 50 27 54 21 38 16 146 12 35 15 18 29 22 16 28 26

NOrN

NH4-N

26 28 36 7 7

7 14 9 8 8

11 7 22 9 53 4 6 3 4 10 7 23 12 35

77

13

inorganic N. Nitrate increased significantly in the topsoil, which indicates that mineralization of organic N exceeded crop N demand during the grain filling period. Again this N mineralization was not reflected in a corresponding decrease in the extractable organic N fractions. Table IV shows the influence of fertilizer N on the extractable N fractions in the soils and the N uptake of the crops. Nitrogen uptake increases significantly due to N application. The apparent recovery rates, however, were less than 50 % (tab. IV). The inorganic N fractions in the soils, particularly NOrN, increased

July/Aug. N in aerial plant parts (kg N ha- 1)

73 112 57 72

58 116 80 51 73 99 106 49 89 43 63 83 57 63 62 44 66 57 55 30 68 36 123 46 47 41 33 76 41 29 34. 46

because of the applied N. The increases in inorganic soil N plus crop N were much lower than the amounts of N applied as fertilizer. Some of the fertilizer N may have been lost as gaseous N compounds. Leaching of N was unlikely because the deeper soil layer (3090 cm) showed no major increase in NO) (tab. IV). Most of the fertilizer N which was not accounte for was presumably immobilized by microorganisms, though no significant chang'es of the extractable Norg fractions were observed due to fertilization. An increase in N org would reflect the incorporation of fertilizer N into organic N compounds. Eur. 1. Agron.

Soil nitrogen fractions

5

Table III. - Influence of sampling time on the EUF and CaCl2 extractable N fractions in soils and on the N content in plants (bulk samples of each site in March/April, NO-plots in May/June and July/August). CaCl 2 extraction (20 ' C, 120 min) according to Houba et al. (1986)

EUF according to Nemeth (1985) NOrN (kg ha- ')

TS March/April May/June July/August

NH4-N (kg ha- I )

TS

SS

NOrN (kg ha-')

No,g (kg ha-')

SS

TS

SS

TS

N o.g (kg ha- I )

NH4-N (kg ha-')

TS

SS

88

T8

N in aerial plant parts (kg ha- ')

S8

9

18

10

14

38

50

9

18

8

8

21

19

10

(0.82)

(1.76)

(0.62)

(0.91)

(1.21)

(2.61 )

(1.03)

(1.76)

(0.59)

(0.80)

(0.71)

(1.57)

(3.65)

3

7

(0.71)

(1 . 14)

7

7

6 (0.66)

7

10

42

48

4

(0.83)

(2.08)

(2.87)

(0.79)

8

7

42

45

6

(1.22)

5

2

5

23

19

43

(0.30)

(0.65)

(0.94)

(1.60)

(2 .32)

22

15

63

5

5

TS = topsoil layer 0-30 cm, 88 = subsoil layer 30-90 cm ; means of n = 36 field sites of the years 1987/88 and 1988/89 ; standard errors of the mean pair differences (n = 36) between sampling dates in brackets.

Table IV. plants.

Influence of N fertilizer rates (NO-N120) on the EUF and CaCI2 extractable N fractions in soils and on the N content in

CaCI 2 extraction (20 'C, 120 min) according to Houba et al. (1986)

EUF technique according to Nemeth (1985)

NOrN (kg ha- I )

T8

NH4-N (kg ha- I )

88

TS

N o.g (kg ha- I )

S8

T8

88

N0 3-N (kg ha- I )

T8

NH4-N (kg ha- I )

88

T8

N O' 8 (kg ha- I )

88

T8

N in aerial plant parts

apparent recovery rates of fertilizer N

(kg ha- I )

(%)

88

May/June No N 40

(0.96)

4 (0.56)

Ngo

7

3 (0.32)

6 (0.87)

4 (0.82)

7

N 40 N go N l20

48

4

(2.84)

(0.41)

7

11

40

(0.76)

(0.82)

(2.16)

10

12

44

(1.43)

(1.46)

10

11

13

44

7 (0.33)

7 (0.77)

42 (1.44)

(0.71)

7 (0.73)

10 (0.57)

(1.01)

N l20 6 July/August No

6 (0.55)

7 (0.47)

9

7

(1.25)

(0.72)

15

10

7 (0.33)

7 (0.57)

7 (0.24)

7 (0.65)

45 (3.26)

46 (2.31)

50

42

45

(1.57)

(2. 19)

43

45

(1.09)

(2.70)

5 (0.35)

4

6

3

5

(0.71)

(0.41)

(0.75)

23

19

43

(0.78)

(1.57)

(1.45)

22

19

61

(1.06)

(1.50)

(1.99)

4

7

4

7

22

18

(0.88)

(0.95)

(0.39)

(1.11)

(0.72)

(1.11)

(2.26)

6

10

5

22

21

100

6 (0.58)

7 (0.65)

7

7

43

42

(0.84)

(l.l5)

(2.83)

(1.32)

45

44

15

8

2 (0.38)

(0.53)

(0.52)

8

8 (1.19)

8

5 (0.36)

5 (0.43)

6 (0.73)

8

5 (0.27)

8 5 (0.53)

5 (0.23)

5

5 (0.35)

5

(0.36)

(0.44)

6

5

82

22

15

63

(0.85)

(0.63)

(1.96)

22

14

(0.55)

(0.82)

23

15

80

49 48

43

(2.24)

100

(0.76) (1.16)

(2.35)

24

115

15

45

46 43

TS = topsoil layer 0-30 cm, S8 = subsoil layer 30-90 cm ; N fertilizer rates No, N 40 , N go, N 120, correspond to 0, 40, 80, ·120 kg N ha- I ; means of n = 36 field sites of the years 1987/88 und 1988/89; standard errors of the mean pair differences (n = 36) between N rate plots of each site in brackets.

The relationship between the amount of applied N and the N uptake of the crop is shown in figure 1. It shows that only 36 % of the variation of the N uptake could be explained by N fertilization (r2 = 0.36). Vol. 1, n° 1 1- 992

Other factors presumably caused the large unexplained variation in N uptake. Equation 1 shows the result of the multiple regression of N uptake versus applied N and inorganic N

T. Appel and K. Mengel

6

already present in the soil layer of 0-90 cm in March/April before N fertilizer application (standard error for constant and regression coefficients in brackets). Y = 31(± 3.4) + 0.44(± 0.33) Xl + 0.75(± 0.05) X 2 r2 = 0.73

(1)

Y = N uptake (kg N ha- l ; straw + grain at maturity). Xl = fertilizer N (kg N ha- l ; applied in March/ April).

X 2 = N0 3 -N + NH4-N (kg N ha- l ; CaCl 2 extraction 20 DC, 120 min; sampling 0-90 cm March/April before fertilization). n = 144 plots.

With the intention of devising a soil N test with easy soil sampling for farmers, multiple regressions were computed for the December soil sampling of the top soil layer (0-30 cm) and are shown in equations (2.1) to (2.4), with standard errors in brackets. Y + 61(± 3.8) + 0.44(± 0.05) Xl

(2.1)

r2 = 0.37 Y = 44(± 4.0) + 0.44(± 0.04) Xl

+ 1.05(± 0.14) X 2

(2.2)

r2 = 0.56

r2

=

(2.3)

0.59

Y = 14(± 5.5) + 0.44(± 0.04) Xl

+ 0.98(± 0.13) X 2 + 15.6(± 3.4) X3 + 1.10(±0.19)X4

Y = 12(± 6.3) + 0.44(± 0.04) Xl + 1.03(± 0.14) X 2 + 16.5(± 3.5) X3 + 0.44(± 0.10) X 4 r2

Y = 37(± 4.4) + 0.44(± 0.04) Xl

+ 1.13(± 0.14) X 2 + 12.4(+ 3.7) X3

mined in the December sampling (0-30 cm) was included was much improved if, in addition to the fertilizer N and the inorganic soil N, the crop residues and particularly the extractable organic soil N were included in the regression. This finding shows that a fraction of the mineralizable soil organic N should be taken into account for predicting available soil N, if the time interval between soil sampling and the main growing period is long. The regression coefficients indicated that 44 % of the fertilizer N, 98 % of the extractable inorganic N, 110 % of the extractable organic N, and 15.6 kg N ha- l for crop residues had to be taken into account for the prediction of available N. lncluding the second CaCl 2 fraction, extracted at 80 DC, did not improve the coefficient of determination and therefore it was not included in the analysis. Also, the extractable N of soil samples taken in February was generally less useful in explaining the variation in N uptake, as compared with the samples taken in December. EUF data from soil samples taken from the upper soil layer in December basically yielded the same relationship as the data from the CaCl2 extraction as shown in the following regression (equation 3 ; standard errors in brackets). The coefficient of determination (r2 = 0.65) was somewhat lower than that for the CaCl 2 data.

(2.4)

r2 = 0.68 Y = N uptake (kg N ha- I ; straw + grain at maturity). Xl = fertilizer N (kg N ha- l ; applied in March/ April). X 2 = NOrN + NH4-N (kg N ha- I ; CaCl 2 extraction 20 DC, 120 min; December sampling 0-30 cm). X3 = dummy variable CR (crop residues: category 1 -+ X3 = 1, ~ategory 0 -+ X3 = 0). X 4 = N org (kg N ha- l ; CaCl2 extraction 20 DC, 120 min; December sampling 0-30 cm). n = 132 plots (no December sampling on 3 sites). The coefficient of determination when the N deter-

=

(3)

0.65

Y, Xl and X3 were the same variables as in equation 2. X 2 =NOrN + NH4-N (kg N ha- I ; EUF extraction 20 DC + 80 DC; December sampling 0-30 cm). X 4 = N org (kg N ha- I ; EUF extraction 20 T + 80 T ; December sampling 0-30 cm). n = 132 plots (the same as included in regression 2). The variation of the N uptake could be explained to a slightly higher degree (73 %) by taking into account the total N content of the soil (Nt) instead of the N org of the EUF or CaCl 2 fraction, respectively (equation 4; standard errors in brackets) : Y

=

22(± 4.0) + 0.44(± 0.03) Xl + 0.79(± 0.12) X 2 + 16.5(± 3.1) X3 + 5.3(± 0.66) X 4 (4) r2

=

0.73

Y, Xj, X 2 and X3 were the same variables as in equation 2. X 4 = total soil N analysed by Kjeldahl procedure (tN ha- I ). n = 132 plots (the same as included in regression 2). Eur. 1. Agroll.

Soil nitrogen fractions

7

180

DISCUSSION

0 0

The results presented above are means of various years, crops and sites which differed in soil data (tab . I), previous crops and climatic conditions. Significant relationships obtained under these conditions may therefore have a broader meaning. In general it was found that during vegetative growth N03" and NHt in the soil profil significantly decreased in plots not fertilized with N (tab. III). The order of magnitude and decrease in NHt were as high as those for N03", presumably caused by nitrification or NHt uptake. From table III it is clear that the amounts of N org were greater than N03" or NHt, respectively, and this is in good agreement with earlier findings (Appel & Steffens, 1988; Appels & Mengel, 1990). Although the crops took up appreciable amounts of nitrogen, the N org in the soil profile did not decrease; in the upper soil layer there was a slight, but significant increase (tab. III). The decrease in N03" + NHt in the profile was much smaller than the N uptake by the crop, a finding which indicates that the N03" and the NHt soil fractions are transitional fractions which lose and gain N. The same may be true for the N org fraction. Therefore the observation that the N org fraction did not decrease during the growth period per se is not an indication that this fraction plays no major part in the N supply of plants. The production of N03" and an increase of EUF N org may occur simultaneously (Hiitsch & Mengel, 1991). A decrease of Nor may occur if the soil is heavily cropped and N is deftcient as was found by Feng et al. (1990) with ryegrass grown in Mitscherlich pots. The significant increase of N org in the top soil (tab. III) in spring may reflect biologicai activity. The observation that the biomass is significantly correlated with N org (Kohl & Werner, 1987; von Rheinbaben, 1988) is in line with this statement. From the data in table IV and from the regression equations cited above it can be seen that the apparent recovery of fertilizer N was on average 44 %. This figure agrees well with results of other authors (Nieschlag, 1965; Peschke et al., 1984, Craswell & Godwin, 1984). Trials with 15N labelled fertilizer provided evidence that about 30 % of the fertilizer N may be immobilized by microbes (Becker et al., 1977, Thies et al., 1977 ; Nielsen & Jenson, 1986; Mary et al., 1988). Since these experiments were carried out under similar climatic conditions to ours we assume that substantial amounts of fertilizer N were assimilated by soil bacteria and fungi during spring in our field trials. A linear relationship was found between the N fertilizer rates applied and the N uptake of the cereals (jig . 1). The absolute quantities of N, however, taken up by the crop differed considerably even at the same fertilizer rate as can be seen from the scatter of points. Vol. I. nO 1 - 1992

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N applied (kg N . ha- 1 ) Figure 1. - Relationship between nitrogen fertilizer rates and the nitrogen uptake of cereals grown on 36 sites. Nitrogen uptake = total N in straw + grain at maturatity.

The condition of N fertilizer to the N uptake of the cereals was relatively small and from the regression equation for figure 1 it can be ct.educed that, on average, even with the highest N nite, soil N contributed to N uptake more than did fertilizer N. The relationship was much improved if besides the amount of fertilizer N the inorganic N (NO 3" + NHt) present in the soil profile in spring was included (equation 1). The resulting coefficient of determination, ,2 = 0.73, is considered as satisfactory. The relationship was less close if the inorganic N in soil samples taken in early winter from the upper soil layer was related to the N uptake. Even when incorporating into the regression equation the N fertilizer rate and the crop residues the coefficient of determination was only 0.59. This correlation was improved, however, by taking into consideration the organic soil N, determined either as EUF-N org or CaCl 2-N org or when total soil N was used, the coefficient of determination was enhanced, which provided evidence that some part of the organic N present in the upper soil layer in early winter was of significant importance for the N uptake of the cereals in the following year. The partial regression coefficients for extractable organic and inorganig soil N were close to I, the biological meaning of which may suggest that all of the CaCl 2 extractable N was

T. Appel and K. Mengel

8

available for the crop. It should be emphasized, however, that regression coefficients are just empirical values and tracer studies are needed to determine precisely to what extent the extractable N fractions are identical with N actually taken up by the crop. It is surprising that total soil N had a significant impact on the N uptake of the crop, because only a very small portion of total soil N is mineralized. Since total soil N is closely related to the organic matter of soils, total N may also reflect the water holding capacity of soils. Particularly on sandy soils water supply can be a limiting factor and hence affect growth and N uptake of the crop (Gales, 1983). T~ furt?er underst~? the role of the various N org fractIOns III crop nutntlon, more knowledge is badly needed of the chemical nature of the N org in the EUF and CaCl 2 extracts. According to investigations of Nemeth et al. (1988), Danneberg et al. (1989), Hiitsch and Mengel (1990), Recke et al. (1990), UischnerPeetz and Neumann (1990) EUF- and CaCl2 -extracts contain a substantial quantity of hydrolysable N compounds which are considered as easily mineralizable. Experiments of Mengel & Schmeer (1985) with lsN-labelled organic material have shown that the non-hydrolysable organic N is partially mineralized, too. Taking into consideration the organic N of soil samples taken from the top soil layer in early winter a coefficient of determination in the range of 0.70 was attained which was almost as high as the coefficient of determination found with samples taken from the profile in spring. This spring sampling was not identical with the Nmin method of Whermann & Scharpf (1979). However, according to investigations by Houba et al. (1990) the inorganic N concentrations of dried soil samples were very close to the inorganic N concentrations extracted from fresh samples according to the N min method. Hence our investigation also shows indirectly that the N min method is a reliable soil N test. Its drawback is the requirement to take samples from three soil layers during a short period in spring which probably explains its poor acceptance by farmers. For this reason we have tried to develop a soil test method with soil sampling from the top layer in late autumn. For establishing a N fertilizer recommendation the factors contributing significantly to the N uptake of the crop as shown above should be taken into account. In our case the coefficient of determination in the range of 0.70 obtained for the regression with soil samples taken in early winter is considered as satisfactory when regarded under the aspect that N uptake depends still on factors other than fertilizer N and soil N. Length of growth period, density of the stand, water supply and weather conditions also play a decisive part in the crop development and therefore in its N uptake. It should be emphasized that in the present investigation sites with differing climatic conditions were included, such as the North of Hessia

with relatively cold and wet climatic conditions and from the Hessische Ried with warm and dry conditions where on the sandy soils growth frequently is limited by insufficient water supply. ACKNOWLEDGEMENT The

authors

are

much

indebted

to

« Bodengesundheitsdienst» for financial support.

the

REFERENCES Appel Th. (1991). - Der Stickstoff-Umsatz in Sandboden und seine Bedeutung flir die Prognose des pflanzenverftigbaren Stickstoffs sowie des N-Dtingerbedarfs von Getreide, untersucht mitte1s Elektro-Ultrafiltration (EUF) und CaCITExtraktion. Giej3ener Bodenkundliche Abhandlungen, 9, GieBen; Wissenschaftlicher Fachverlag. Appel Th. and Mengel K. (1990). - Importance of organic nitrogen fractions in sandy soils, obtained by electro-ultrafiltration or CaCl2 extraction, for nitrogen mineralization and nitrogen uptake of rape. Bioi. Fertil. Soils, 10, 97-101. Appel Th. and Steffens D. (1988). - Vergleich von Electro-Ultrafiltration (EUF) und Extraktion mit 0,01 molarer CaCITLosung zur Bestimmung des pflanzenverftigbaren Stickstoffs im Boden. Z. Pflanzenern. Bodenk., 151, 127-130. Becker K.-W., Thies W. and Meyer B. (1977). Infiltration und Umwandlung (Metabolik) von markiertem Dtinger-N (lsNH 4 und lSN0 3) in einem Sandboden unter Bewuchs und Brache sowie EinfluB der N-Dtingerformen auf Geschwindigkeit und Hohe der Dtinger-N-Aufnahme von Sommergerste. Landwirtsch. Forschung Sonderheft, 34111, 63-73. Craswell E. T. and Godwin D. C. (1984). - The efficiency of nitrogen fertilizers applied to cereals in different climates. In : Tinker P. B., Lauchli A., Eds., Advances in Plant Nutrition, Vol. 1, New York, Praeger, pp. 1-55. Danneberg 0. H., Wenzl W. and Ellinghaus R. (1989). - Vergleich verschiedener Bodenextrakte zur Beurteilung des nachlieferbaren Stickstoffs mit Hilfe der Saulenchromatographie. VDLUFA-Schriftenreihe, 28111, KrongreBband 1988, 551-573. Feng K., Dou H. and Mengel K. (1990). - Turnover of plant matter in soils as assessed by electro-ultrafiltration (EUF) and CaCl 2 extracts. Agribiol. Res., 43, 337-347. Gales K. (1983). - Yield variation of wheat and barley in Britain in relation to crop growth and soil conditions - a review. J. Sci. Food Agric., 34, 1085-1104. Houba V. J. G., Novozamsky 1., Huybregts A. W. M. and Van der Lee J. J. (1986). - Comparison of soil extractions by 0,01 M CaCI 2 , by EUF and by some conventional extraction procedures. Plant Soil, 96, 433-437. Eur. J. Agron.

Soil nitrogen fractions

Houba V. J. G., Novozamsky 1. and Van der Lee J. J. (1990). - Some aspects of determinations of nitrogen fractions in soil extracts. VDLUFA-Schriftenreihe, 30, KongreBband 1989, 305-312. Hiitsch B. and Mengel K. (1990). - EinfluB von Bodenbearbeitung und Bodentyp auf EUF extrahierbare NFormen. VDLUFA-Kongrej3, Berlin, 17-22 Sept. 1990, Kurzfassung der Vortriige, p.40. Hiitsch B. and Mengel K. (1991). - Messung von Denitrifikationsverlusten bei Pflugbearbeitung und Direktsaat. Z. f. Kulturtechnik und Landentwicklung, 32, 70-79. Kohler W., Schachtel G. and Voleske P. (1984).Biometrie - Einfuhrung in die Statistik fur Biologen und Agrarwissenschaftler. Berlin, Heidelberg, New York, Tokyo, Springer-Verlag. Kohl A. and Werner W. (1987). - Untersuchungen zur . saisonalen Veriinderung der EUF-N-Fraktionen und zur Charakterisierung des leicht mobilisierbaren Bodenstickstoffs durch Elektro-Ultrafiltration (EUF). VDLUFA-Schriftenreihe , 20, KongreBband 1986, 33334I. Kohl A. and Werner W. (1989). - Moglichkeiten und Grenzen unterschiedlicher methodischer Ansiitze zur Prognose des mobilisierbaren Stickstoffs. VDLUFASchriftenreihe, 281II, KongreBband 1988, 1-14. Mary B., Recous S. and Machet J.-M. (1988). - A comprehensive approach to the fertilizer part of plant nitrogen uptake. In: Jenkinson D., Smith K., Eds, Nitrogen efficiency in agricultural soils. London, New York, Elsevier Applied Science, pp. 85-94. Mengel K. (1985). - Dynamics and availability of major nutrients in soils. Adv. Soil Sci., 2, 65-13I. Mengel K. and Schmeer H. (1985). - Effect of straw, cellulose and lignin on the turnover and availability of labelled ammonium nitrate. Bioi. Fertil. Soils, 1, 17518I. Montgomery D. C. and Peck E. A. (1982). -Introduction to linear regression analysis. New York, John Wiley & Sons. Nemeth K. (1985): - Recentadvances in EUF rese'arch (1980-1983). Plant Soil, 83, 1-19. Nemeth K., Bartels H., Vogel M. and Mengel K. (1988) . - Organic nitrogen compounds extracted from arable and forest soils by electro-ultrafiltration and recovery rates of amino acids. Bioi. Fertil. Soils, 5, 271-275.

Vol. I, n' I - 1992

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Nielsen N. E. and Jensen H. E. (1986). - The course of nitrogen uptake by spring barley from soil and fertilizer nitrogen. Plant Soil, 91, 391-395. Nieschlag F. (1965). - Kennzeichnende Faktoren der Bodenfruchtbarkeit (Ertragsfiihigkeit). Z. PJlanzenern. Dung. Bodenk., 109, 177-183. Peschke H., Markgraf G., Oberdoerster U., Schmitt O. and Garlitz H. (1984). Zur Wirkung von Stickstoffdijngung und Beregnung bei Hafer (A vena sativa L.). Arch. Acker-PJlanzenbau Bodenk., 28, 403-409. Recke H., Nemeth K. and Vogel M. (1990). - Zusammensetzung der EUF-Norg-Fraktionen bei 20 ·C und 80·C in Abhiingigkeit von Bodeneigenschaften. VDLUFA-Schriftenreihe, 32, KongreBbandl990, 234248. Rheinbaben W. von (1988). - Beziehungen zwischen der EUF-Norg-Fraktion und chemischen und mikrobiologischen Parametern in BOden. Third Inti. Symp. EUF, Mannheirn, May 1988, Kostensenkung und Umweltschutz Vol. II. Mannheim, Stiddeutsche Zucker~AG, pp. 425-440. Sachs L. (1978). - Angewandte Statistik. 5th edition. Berlin, Heidelberg, New York, Springer-Verlag. Schlichting E. and Blume H.-P. (1966). - Bodenkundliches Praktikum. Hamburg, Berlin, Verlag Paul Parey. Strebel 0., Bottcher J. and Duynisveld W. H. M. (1985). EinfluB von Standortbedingungen und Bodennutzung auf Nitratauswaschung und Nitratkonzentration des Grundwassers. Landwirtsch. Forschung 37, KongreBband 1984, 34-44. Thies W., B~cker K.-~. and Me(.er B. (1977). - Bil~z von marklertem Dunger-N (5NHt und 15N0:J) III natiirlich gelagerten Sandlysimetern sowie zeitlicher Verlauf des dtinger- und bodenbtirtigen N -Austrags Landwirtsch. im Vergleich Bewuchs-Brache. Forschung Sonderheft, 341II, 55-63. Uischner-Peetz C. and Neumann K.-H. (1990). - Untersuchungen zur molekularen Charakterisierung der Norg-Fraktion in verschiedenen Boden. VDLUFASchriftenreihe, 32, KongreBband 1990, 853-859. Wehrmann J. and Scharpf H. C. (1979). Der Mineralstickstoffgehalt des Bodens als MaBstab ftir den Stickstoffdtingerbedarf (Nmin-Methode). Plant Soil, 52, 109-126. Wiklicky L. and Nemeth K. (1981). - Dtingungsoptimierung mittels EUF-Bodenuntersuchung bei der Zuckerriibe. Zuckerind., 106, 982-988.