Genotypic differences in nitrogen efficiency of white cabbage (Brassica oleracea L.)

Plant Soil (2010) 328:313–325 DOI 10.1007/s11104-009-0111-1

REGULAR ARTICLE

Genotypic differences in nitrogen efficiency of white cabbage (Brassica oleracea L.) Gunda Schulte auf’m Erley & Elsa Rakhmi Dewi & Olani Nikus & Walter J. Horst

Received: 10 March 2009 / Accepted: 14 July 2009 / Published online: 8 August 2009 # Springer Science + Business Media B.V. 2009

Abstract In vegetable production, N balance surpluses are especially high which increases the risk of environmental pollution. The cultivation of Nefficient cultivars may contribute to alleviate the problem. A 2-year field experiment was conducted with eight white cabbage cultivars of three different maturity groups at two N fertilization levels. Genotypes differed both in N efficiency (head fresh weight at low N supply) and in yield at high N supply. These differences were not related to N uptake but to N utilization efficiency. At low N supply, harvest index was the main determining factor for genotypic yield differences. For earlier maturing cultivars a slower leaf emergence was responsible for the low harvest index. The response of the cultivars to low N supply was dependent on the weather conditions, particularly temperature, (highly significant year × cultivar × N supply interaction) at early growing stages. This suggests that breeding of cultivars with generally low-temperature tolerance could contribute to enhancing N utilization. Especially at high N supply, a high N harvest index was important for yield formation

Responsible Editor: Hans Lambers. G. Schulte auf’m Erley (*) : E. R. Dewi : O. Nikus : W. J. Horst Institute for Plant Nutrition, Leibniz University of Hannover, Herrenhäuser Str. 2, 30419 Hannover, Germany e-mail: [email protected]

due to its effect on head water accumulation. For late cultivars, a high N retranslocation from leaves to the heads was related to yield both at low and high N supply. The study suggests that breeding of Nefficient cultivars may reduce N release to the environment by reducing the necessary N input and reducing the N content remaining in the crop residues. Keywords N limitation . N uptake . N utilization efficiency . Head fresh weight . Head water accumulation . Brassica

Introduction In vegetable production environmental pollution by nitrogen (N) losses into the atmosphere and hydrosphere is especially high (Greenwood 1990). This is caused by the high N fertilization levels which are common in commercial production and often exceed official recommendations (Booij et al. 1996). Especially for Brassica cabbage species, high fertilizer rates are recommended; for white cabbage in a range of 250 kg N ha−1 to 350 kg N ha−1, depending on maturity group (Scharpf and Weier 1994). During the past years, efforts have been made to decrease fertilization levels without affecting yield (head fresh weight per unit surface area). Experiments with varying N fertilization techniques, e.g. by split application or band placement, revealed only a limited reduction potential of fertilizer N for different

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Brassica vegetables (Everaarts et al. 1996; Everaarts and De Moel 1998). Another possibility to save N fertilizer is a more precise prediction of the N demand. For this purpose, models predicting the time course of cauliflower growth (Alt et al. 2000), soil N availability for cauliflower N uptake (Kage et al. 2003) or the time course of N uptake of white cabbage and Brussel sprouts (Fink and Feller 1998, 2001) have been developed. A further approach which was hardly investigated yet is the breeding of N-efficient genotypes, which are characterized by a low susceptibility in yield to reduced N fertilization levels (Schenk 2006). A high N efficiency can be achieved either by a high N uptake or by an efficient N utilization for yield formation (Sattelmacher et al. 1994). Nitrogen recovery from the soil is generally high for Brassica vegetables (Everaarts 1993). At harvest, soil Nmin contents below white cabbage are normally less than 40 kg N ha−1 at 0 cm and 90 cm soil depth with almost no N leaching during the vegetation period (Everaarts and Booij 2000 and references therein). The efficient N uptake of white cabbage is caused by the large and evenly distributed root system, reaching down to a soil depth of 2–2.5 m, and by a high ability of the roots to absorb N in all soil layers (Kristensen and Thorup-Kristensen 2004). Total dry matter production and head yields as well as plant N contents are strongly influenced by the level of N supply (Peck 1981). Ontogenesis, in contrast, does not seem to be influenced by N rate (Peck 1981), which was also found for cauliflower (Everaarts and De Moel 1995). The number of leaves developed until heading and the harvest index (Hara et al. 1982; von Brandis and Scharpf 1987) were not found to be affected by the N rate. However, sucrose accumulated in outer leaves under N-limiting conditions together with enhanced sucrose concentrations in the heads (Hara 1989) indicating a limitation for the utilization of C for growth. Head quality is impaired under excess N supply because of burst heads, tipburn (Peck 1981), lower sucrose concentration in the heads and inferior taste (Nilsson 1988; Hara 1989). Although uniformity of the heads was slightly improved and head shape was not affected by increasing N fertilization, relative core length was increased leading to a decline in head quality (Everaarts and De Moel 1998). Dry matter content of the heads usually declines with increasing N

Plant Soil (2010) 328:313–325

fertilization (Peck 1981; Everaarts and De Moel 1998). However, the ratio of marketable heads and storage losses are only slightly affected by N fertilization and do not counterbalance the yield increase (von Brandis and Scharpf 1987; Freyman et al. 1991). Summarizing, the potential for an improvement of N efficiency by increasing N uptake seems to be rather limited, but there might be potential to improve N utilization efficiency. Due to the small effects of N rate on harvest index it is difficult to predict if a higher total biomass production or an enhanced head growth might be more effective. Severe yield limitations by impaired head quality are not to be expected. The objective of this study was, therefore, to explore genotypic differences in N efficiency for cabbage cultivars of differing maturity groups and to investigate the main factors contributing to yield at limiting and optimum N supply. This is expected to help finding selection criteria for the breeding of Nefficient cultivars.

Materials and methods Field experiments were conducted in 2004 and 2005 on a loamy silt soil (FAO 2006) at the experimental station of the Faculty of Natural Sciences, Leibniz University of Hannover, Germany in Ruthe located 20 km south of Hannover. The experiments were designed as split plots with N fertilization rates as main plots and cultivars as sub-plots with four replicates. N rates comprised no N fertilization and an N supply of 300 kg N ha−1 (fertilizer plus soil mineral N content at transplanting). Eight white cabbage cultivars from different maturity groups were used in the study: Parel (Bejo, Warmenhuizen, The Netherlands) as an early cultivar, Toughma (Rijk Zwaan, Welver, Germany), Castello (NickersonZwaan, Edemissen, Germany) and Perfecta (Bejo, Warmenhuizen, The Netherlands) as mid-early cultivars and Lennox, Bartolo (Bejo, Warmenhuizen, The Netherlands), Bloktor and Novator (Syngenta, Enkuizen, The Netherlands) as late cultivars. Castello and Bartolo are used as reference cultivars in variety testing for the registration of new varieties by the Bundessortenamt, Hannover, Germany, for mid-early and late white cabbage cultivars, respectively. The other cultivars were chosen because of recommendations of plant breeders and were all considered as N-efficient.

Plant Soil (2010) 328:313–325

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mid-October). Head formation was defined to start when the newly developing leaves had a curved shape so that they covered the shoot apex. The harvest at maturity was performed when the heads reached their final size and maximum density. Replicate plots were harvested at the same day. Six plants per plot were randomly chosen for each harvest. Plants were separated into outer leaves and head including the stem. In 2005 the stem and head were separately harvested at maturity. Leaves were counted for each plant individually and then bulked for fresh weight determination. Sub-samples were taken for dry weight determination. The samples were dried at 70°C until they attained a constant weight. Nitrogen concentrations of the dried and ground plant fractions were determined using a CNS analyzer (Vario EL, Elementar Analysensysteme, Hanau, Germany). At heading, stems and heads were pooled for six plants, weighed, dried and ground for N analysis. At maturity, heads were weighed individually for each plant. Three heads per plot were sub-divided for leaf counting, then pooled together before sub-samples were taken for dry weight determination and N analysis. Water-soluble carbohydrate concentrations of outer leaves and heads were analysed using dried plant material. One hundred mg dry matter was extracted for 1 h in 20 ml distilled water and analysed by the anthrone method following the description of Yemm and Willis (1954). For nitrate analysis 100 mg dry matter was extracted for 1 h in 20 ml distilled water and nitrate concentration was determined according to Cataldo et al. (1975).

Seeds were sown in peat cubes and raised in a greenhouse for the first 3 weeks. Thereafter, the seedlings were placed in an open greenhouse to adapt the plants to the natural climatic conditions. After 5 weeks, plants were transplanted into the field on May 13 and May 19 in 2004 and 2005, respectively. Irrigation was supplied to ensure growth of the young plants. Plant spacing was 0.60 m by 0.48 m in 2004 and 0.55 m by 0.48 m in 2005 giving a plant density of 3.3 and 3.8 plants m−2 in 2004 and 2005, respectively. Individual plots were 2 m wide and 8 m long. Soil mineral N contents (0–0.9 m) at transplanting were 83 kg N ha−1 and 73 kg N ha−1 in 2004 and 2005, respectively. The high-N plots were fertilized with 150 kg N ha−1 as calcium ammonium nitrate prior to planting, and with 70 kg N ha−1 and 80 kg N ha−1 on 10 June 2004 and 22 June 2005, respectively. Weeds were controlled by hand. Oxydemeton-methyl (Metasystox) and Bacillus thuringiensis (Dipal/Turex) were sprayed for pest control in both years. Weather conditions varied between the two growing seasons studied (Fig. 1). In comparison to the long-term average, 2004 was cool and wet between May and July and warm and dry in September and October. 2005 was warmer than usual except in August, while precipitation was high in May and July, very low in June and close to normal from August to October. Harvests were performed at the beginning of heading (from mid-June to end of July, according to maturity group) and at maturity (from end of July to

20

150 2004 2005 long-term

100

10

50 5

0

0

May

June

July

Aug

Sept

Oct

Temperature [˚C]

15

Precipitation [mm]

Fig. 1 Total monthly precipitation (bars) and monthly temperature (symbols) at the experimental station Ruthe during the 2004 and 2005 growing seasons and as long-term average

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Plant Soil (2010) 328:313–325

In addition to the leaf counting during harvests, leaf numbers were determined non-destructively in 2005. Six plants per plot were chosen at heading and all outer leaves were numbered using a water proofed marker. In weekly intervals from heading to maturity, the number of the oldest leaf still attached to the plant and of the youngest unfolded leaf was recorded. From these values the ratio of lost leaves was calculated by dividing the number of leaves shed from the plant by the total number of outer leaves formed until maturity. Nitrogen efficiency was defined in this study as yield (head fresh weight) at limiting N supply (Craswell and Godwin 1984). Factors contributing to N efficiency are N uptake efficiency (shoot-N uptake at limiting N supply) and N utilization efficiency (yield per unit shoot-N taken up). N utilization efficiency was subdivided into biomass production efficiency (Ortiz-Monasterio et al. 1997), harvest index and head fresh weight/dry weight ratio. Biomass production efficiency was defined as the ratio of shoot dry weight and shoot-N uptake at maturity. Harvest index was calculated as head dry weight divided by total shoot dry weight at maturity. Since yield of white cabbage is given by head fresh weight, the ratio between head fresh and dry weight was introduced as a third factor of N utilization efficiency. Nitrogen harvest index was calculated as head nitrogen at maturity divided by total shoot-N uptake. Data were analysed using SAS version 9. Analysis of variance was performed by PROC MIXED. Years, N rate and cultivars were considered as fixed factors with years as main-plot factor, N rates as sub-plot

factor and cultivars as sub-sub-plot factor. Multiple comparisons of means were made by the LSMEANS/ PDIFF statement for N rate by cultivar interactions. Regression lines were calculated using PROC REG in SAS.

Results Maturity times differed between cultivars and N rates (Table 1). Cultivar differences were according to their maturity group. Within mid-early cultivars, cv Toughma matured earlier than cv Castello, while cv Perfecta matured later. Low N supply delayed maturity, especially for the early cultivars. This effect was stronger in 2004 than in 2005. Heading dates did not differ between N rates. Cultivars differed in yield (head fresh weight) at both N rates (Table 2). At low N supply, cv Perfecta had the highest yield of all cultivars. Within the late maturing cultivars, cv Lennox and cv Novator had a significantly higher yield than cv Bartolo. The early cultivar Parel could not be compared to another cultivar of the same maturity group. However, yield was not decreased by low N supply. The cultivars Parel, Perfecta, Lennox and Novator were classified as N-efficient, while cvs Toughma, Castello and Bartolo as N-inefficient. Cultivar Bloktor had an intermediate N efficiency. At high N supply, yield differences were more pronounced between cultivars with different maturity times. Again, cv Perfecta had the highest yield of all cultivars. Mid-early cultivar

Table 1 Heading and maturity dates (days after planting) of eight cabbage cultivars grown in Ruthe at two N supplies (N1: no fertilization and N2: 300 kg N ha−1) in 2004 + 2005 Cultivar

2004 Heading N1 + N2

Parel

31

2005 Maturity N1 75

Maturity N2 62

Heading N1 + N2 34

Maturity N1 67

Maturity N2 62

Toughma

31

105

99

39

91

85

Castello

40

113

105

46

98

91

Perfecta

56

126

117

54

111

104

Lennox

76

159

152

67

140

139

Bartolo

76

159

152

67

140

139

Bloktor

77

159

154

69

140

139

Novator

77

159

154

69

140

139

9151 10172 13128

11294 10119 10632 10533

Toughma Castello Perfecta

Lennox Bartolo Bloktor Novator ns *** *** *** ns * *

10843 9275 10140 9452

8865 9153 12551

6359

8761 7287 7961 7880

7822 7612 10145

5908

B D C CD

E D A

F

b de cd bc

e e a

f

39.2 39.5 36.8 38.2

19.9 20.3 23.6

14.9

21.3 21.6 21.4 23.2

13.3 13.1 17.8

7.7

ns *** *** *** ns *** ***

33.2 32.7 31.1 29.3

24.7 29.5 32.6

16.8

21.9 20.5 20.7 20.4

18.6 18.4 19.7

11.5

A A AB B

E D C

F

ab ab ab a

c c b

d

45.0 45.0 46.0 42.8

33.9 31.2 37.7

23.3

64.6 61.4 64.2 59.2

39.0 46.7 52.9

40.4

2004

ns *** *** ns ns * ns

50.2 52.6 47.5 45.2

36.2 38.4 44.0

30.4

65.9 70.7 56.4 59.2

49.8 50.8 52.0

40.2

2005

Biomass production efficiency (g g−1)

AB A AB BC

D D C

E

a a b b

d c c

d

0.58 0.52 0.57 0.58

0.57 0.52 0.43

0.43

0.62 0.51 0.60 0.60

0.39 0.40 0.52

0.43

2004

*** ns *** *** ns *** ***

0.55 0.49 0.54 0.50

0.58 0.56 0.63

0.65

0.55 0.48 0.53 0.51

0.62 0.57 0.59

0.61

2005

Harvest index (g g−1)

AB D ABC BCD

A BCD CD

ABC

a de ab bc

de e bc

cd

11.0 10.9 11.0 11.3

23.9 31.1 34.5

38.5

10.5 11.3 9.7 11.0

32.1 29.7 21.2

46.1

2004

*** ns *** *** ns *** ***

11.9 11.0 12.9 14.5

17.2 14.5 13.9

19.1

11.2 10.6 13.0 13.0

13.7 14.2 17.0

20.9

2005

Head fresh weight/dry weight (g g−1)

D D D D

C BC B

A

d d d d

b b c

a

0.59 0.53 0.62 0.63

0.54 0.58 0.53

0.37

0.64 0.57 0.66 0.63

0.41 0.46 0.63

0.48

2004

** ns *** ** ns *** ***

0.57 0.53 0.61 0.56

0.55 0.56 0.68

0.66

0.57 0.51 0.61 0.62

0.60 0.60 0.69

0.61

2005

Nitrogen harvest index (g g−1)

BCD E A ABC

DE CD AB

E

b cd ab ab

d cd a

c

*, ** and *** = significant at P