Nitrogen balance during growth of cauli¯ower
Applied Research for Arable Farming and Field Production of Vegetables (PAV), P.O. Box 430, 8200 AK Lelystad, Netherlands
Accepted 1 July 1999
The potential for loss of nitrogen to the environment during growth of cauli¯ower was investigated. A comparison was made between cauli¯ower growth and nitrogen uptake without, and with, nitrogen application of the recommended amount (225 kg haÿ1minus mineral nitrogen in
the soil layer 0±60 cm, applied at planting) on sandy clay soils under natural rainfall conditions. In two experiments, with low mineral nitrogen availability at planting, the quality and yield were reduced when no nitrogen was applied. The rate of nitrogen uptake by the crop rapidly increased from about four weeks after planting. Concurrently the amount of mineral nitrogen in the soil started to decrease. Most of the nitrogen was taken up from the 0±30 cm soil layer. The amount of nitrogen in the crop at harvest with the recommended amount of nitrogen applied ranged from 170 to 250 kg haÿ1, while 7±100 kg haÿ1mineral nitrogen remained in the soil (0±60 cm layer). Crop
residues contained about 95±140 kg haÿ1
nitrogen. No evidence was found for leaching of fertilizer nitrogen during crop growth. With the recommended amount of nitrogen applied, during crop growth the measured amount of nitrogen in the crop and soil (0±60 cm), generally, was lower than the amount of available nitrogen (calculated as the amount of nitrogen in the crop and soil without nitrogen application plus the amount of fertilizer nitrogen applied). No period could be indicated in which there was a particularly great difference between the measured and calculated amount of nitrogen in the cropsoil system. It is concluded that the potential for loss of nitrogen to the
environment is greater after crop harvest, when nitrogen may be lost from crop residues and soil, than during growth. Perspectives to reduce nitrogen fertilizer input by split application are discussed.#2000 Elsevier Science B.V. All rights reserved.
Keywords: Cauli¯ower,Brassica oleraceavar.botrytis; Nitrogen uptake; Soil mineral nitrogen; Nitrogen fertilizer recommendation; Quality; Yield
E-mail address: firstname.lastname@example.org (A.P. Everaarts).
The nitrogen fertilizer recommendation for cauli¯ower in the Netherlands is 225 kg nitrogen at planting, minus the amount of mineral nitrogen present in the soil layer 0±60 cm (Anonymous, 1995). This recommendation is based on the results of a series of experiments in which the effect of the amount of nitrogen and the method of application on the quality and yield of cauli¯ower was evaluated (Everaarts and De Moel, 1995; Everaarts and Van Den Berg, 1996). In the same experiments, the effect of applied nitrogen on nitrogen in the crop and in the soil at harvest and on removal of phosphorus and potassium was studied (Everaarts et al., 1996; Everaarts and De Moel, 1997). No study was made, however, of the uptake pattern of nitrogen by cauli¯ower during crop growth and the potential for loss of nitrogen from the cropsoil system
during that period. Such observations for cauli¯ower are rare. Kaufmann (1967) and Welch et al. (1987) provided data on nutrient uptake of cauli¯ower during growth in the ®eld and in the greenhouse or under plastic ®lm cover, respectively. No data were found, however, quantifying both, the nitrogen uptake and concurrent soil nitrogen depletion. The present paper reports the results of ®eld experiments in which the nitrogen uptake and soil nitrogen depletion by cauli¯ower during crop growth were measured. With these data, an evaluation of the potential for loss of nitrogen from the cropsoil system during crop
growth was made.
2. Materials and methods
The experiments were carried out from 1995 to 1997 in farmers ®elds (Lutjebroek) and at the research stations at Lelystad and Zwaagdijk (Table 1). The cultivar Fremont was used. Soil properties of the experimental ®elds are
Location and cultivation period of the experiments
Experiment Location Planting date First harvest Last harvest (days after planting)
1 Zwaagdijk 19 June 1995 72 98
2 Lelystad 06 June 1995 73 94
3 Lutjebroek 13 June 1996 76 99
4 Lelystad 13 June 1996 67 81
5 Lutjebroek 15 May 1997 77 81
given in Table 2. Soil classi®cation is according to soil clay content (Steur and Heijink, 1991). Soil cultivation as preparation for planting was carried out shortly before planting. Module-raised transplants were planted by hand (experiments 1± 4) or with a planting machine (Experiment 5), at a distance of 0.75 m between rows and 0.50 m within the row. Plots contained 40 (experiments 1, 3 and 5) or 42 (experiments 2 and 4) plants. Nitrogen was applied broadcast as calcium ammonium nitrate (27% N). Shortly after planting, pigeons damaged the crop in Experiment 2.
2.2. Experimental procedures
The experiments were laid out as randomized complete block designs with three (experiments 1, 2 and 4) or four (experiments 3 and 5) replicates and six, eight, four, eight and six nitrogen fertilizer application treatments for experiments 1±5, respectively. In this paper, only the data of treatments where no fertilizer nitrogen was given or where the recommended amount of fertilizer nitrogen was applied, are presented. The recommended amount of nitrogen for cauli¯ower is 225 kg haÿ1 minus the mineral nitrogen (Nmin) in the soil layer 0±60 cm, broadcast at planting (Anonymous, 1995). With the recommended amount of nitrogen 165, 189, 28, 156 and 35 kg haÿ1
nitrogen was broadcast at planting in experiments 1±5, respectively.
Analysis of variance was carried out with the Genstat programme (Genstat 5 Committee, 1993). Standard errors for nitrogen uptake and mineral nitrogen depletion (soil layer 0±60 cm) during crop growth were estimated with a generalised linear model, assuming variance proportional to the mean and linklogarithm, with blocks and time as model terms. Standard errors for the
calculated and the measured amount of nitrogen in the cropsoil system were
2.3. Plant sampling
In each of the experiments 1, 2 and 4, the dry weight (after drying for 48 h at 708C) and the total nitrogen content of three samples of the planting material, consisting of the above-ground parts of 40, 42 and 42 plants, respectively, were determined.
In these three experiments, extra plots of the zero nitrogen and the recommended amount of nitrogen treatments were added to each replicate to allow for sampling the crop four (experiments 1 and 2) or ®ve (Experiment 4) times during crop growth. With each sampling in each plot, the fresh and dry weight and the total nitrogen content of the above-ground part of four randomly chosen plants were determined. The fresh weight of the above-ground part of the other plants in the plot was also determined and the relation between the fresh weight of the four plants and the total fresh weight of the plants in a plot was used in the calculation of the nitrogen uptake of the crop. At the ®rst sampling after planting in Experiment 2, dry weights and total nitrogen content of the above-ground part of all plants of a plot were determined.
During the harvest period, at 78, 80, 83 and 71 days after planting (DAP) for experiments 1±4 respectively, the above-ground part of four randomly chosen plants in each plot was harvested and the dry weight and the total nitrogen content of stem, leaves and in¯orescence (experiments 1 and 2) or stem, leaves, in¯orescence and the lower part of the leaves and bracts surrounding the in¯orescence (experiments 3 and 4) were determined. The weight and nitrogen content of the four plants was used to calculate the nitrogen uptake of the crop at harvest.
The total nitrogen content in plant material was determined using the indophenolblue method (Walinga et al., 1995).
2.4. Soil sampling
Before planting each replicate of the experimental ®elds was sampled diagonally to determine the amount of mineral nitrogen in the soil layers 0±30, 30±60 and 60±90 cm. In experiments 1, 2 and 4 (except at 14 DAP in Experiment 4) at the time of the plant sampling during crop growth, soil samples were taken at the position of each of the four sample plants. To obtain a representative sampling of a possible soil nitrogen depletion gradient around a plant (Everaarts et al., 1996), three soil samples of each of the soil layers 0±30 and 30±60 cm were taken along the diagonal between two plants at 4.5, 22.5 and 45 cm distance from the plant. Composite samples were made for each soil layer.
Similar observations were made around four weeks after planting in experiments 3 and 5 at the positions of four randomly chosen plants in each plot in the treatment without nitrogen application. At that time, in Experiment 3
the soil was sampled in the 0±60 cm layer and in Experiment 5 in both the 0±30 and 30±60 cm layers. At harvest in experiments 1±4, soil samples were taken as described above around each of the four sample plants for the soil layers 0±30, 30±60 and 60±90 cm.
Depending on the experiment, 3±10 successive harvests were carried out. Curds, comprising the white in¯orescence and the lower part of the leaves and bracts surrounding the in¯orescence, were evaluated for being marketable, as being of Quality I or Quality II (Anonymous, 1977), and graded as size `six', `eight' or `ten'. The aim was to harvest curds of Quality I, size `six'.
3.1. Mineral nitrogen
The amount of mineral nitrogen available at planting was particularly high in experiments 3 and 5 and this amount had increased at four weeks after planting (Table 3). Mineral nitrogen at planting was lowest in Experiment 2. Planting in Experiment 1 was delayed because of prolonged rainfall. Mineral nitrogen in Experiment 1 at four weeks after planting had increased considerably as compared to the ®rst sampling. The amount of mineral nitrogen after planting in experiments 2 and 4 showed little or no increase. Amounts of mineral nitrogen were highest in the experiments with high soil organic matter contents (Table 2).
The percentage of plants harvested, the percentage Quality I of curds harvested and the percentage Quality I size `six'of curds harvested with no nitrogen and with the recommended amount of nitrogen applied at planting (225ÿNmin0±60 cm, kg ha
Experiment Plants harvested (%) Curds Quality I (%) Curds Quality I size 'six' (%)
no nitrogen nitrogen recommended
no nitrogen nitrogen recommended
no nitrogen nitrogen recommended
1 91 94 ± 90 93 ± 89 90 ±
2 77 95 15 6 95 9 0 92 7
3 79 71 ± 97 91 ± 81 78 ±
4 94 98 ± 77 93 7 0 90 10
5 81 84 ± 94 92 ± 93 90 ±
Only in Experiment 2 did nitrogen application increase the percentage of plants harvested (Table 4). The percentage Quality 1 of the curds harvested and the percentage Quality 1 size `six' was increased by nitrogen application only in experiments 2 and 4, where mineral nitrogen at four weeks after planting was low. In the other experiments, application of nitrogen to the recommended amount had no effect on the yield of cauli¯ower.
3.3. Nitrogen in the crop
During the ®rst four weeks after planting, uptake of nitrogen by the crop was limited (Fig. 1). Around four weeks after planting, the nitrogen uptake rate increased and the amount of nitrogen in the crop generally increased up to harvest. The rate of nitrogen uptake by the crop in that period was around 4± 6 kg haÿ1 per day. In Experiment 2, the amount of nitrogen in the crop unexpectedly decreased towards harvest. Nitrogen application increased the amount of nitrogen in the crop at harvest in experiments 2 and 4 (Table 5). This observation is consistent with the comparatively low availability of mineral nitrogen in these experiments. With the recommended amount of nitrogen applied, the nitrogen harvest index, that is the percentage of the total crop nitrogen uptake removed from the ®eld with the product, was 48% and 43% for experiments 3 and 4, respectively.
3.4. Nitrogen in the soil
Fig. 1. Nitrogen (N) uptake by the crop and nitrogen availability (Nmin) in the soil layers 0±30 and
0±60 cm during crop growth with the recommended amount of nitrogen applied at planting (225ÿNmin 0±60 cm, kg ha
ÿ1 ) (Standard error bars for the N uptake and N
min 0±60 cm
generally fall within the symbols).
The amount of nitrogen in the above-ground part of the crop and in the soil at harvest with no nitrogen and with the recommended amount of nitrogen applied at planting (225ÿNmin0±60 cm, kg ha
Experiment Nitrogen in the crop (kg haÿ1
) Nitrogen in the soil (0±60 cm) (kg haÿ1
) Nitrogen in the soil (60±90 cm) (kg haÿ1
no nitrogen nitrogen recommended
no nitrogen nitrogen recommended
no nitrogen nitrogen recommended
1 205 250 ± 29 61 ± 6 11 ±
2 80 170 30 6 7 ± 1 1 ±
3 201 208 ± 75 100 ± 36 58 ±
4 91 189 23 6 16 ± 3 7 3
in¯uenced by fertilizer application, which is an indication that leaching of fertilizer nitrogen was limited or absent.
3.5. Nitrogen in the cropsoil system during growth
The amount of nitrogen available in the cropsoil system was calculated as
the amount of nitrogen in the crop and soil (0±60 cm) without nitrogen application plus the amount of fertilizer nitrogen applied. Fig. 2 shows the calculated amount of available nitrogen in the cropsoil system during crop
Fig. 2. The calculated amount of nitrogen available in the cropsoil system during crop growth and the measured amount present, with the recommended amount of nitrogen applied at planting (225ÿNmin0±60 cm, kg ha
ÿ1) (s.e.standard error).
growth and the measured amount present at the recommended amount of nitrogen applied. During the ®rst few weeks of crop growth in Experiment 1, more nitrogen was found present than was calculated as available. Possibly, mineralisation of nitrogen was higher where fertilizer nitrogen had been applied. During the second half of crop growth in this experiment, the measured amount of nitrogen in the cropsoil system was lower than the calculated amount of
available nitrogen. The latter situation was generally found in experiments 2 and 4.
The percentage of plants harvested without nitrogen application was reduced only in Experiment 2, where mineral nitrogen availability at four weeks after planting (Table 3) was the lowest. In previous research, the number of plants harvested was not at all, or not consistently in¯uenced by nitrogen availability (Everaarts and De Moel, 1995). Based on that research, it was also concluded that nitrogen availability had little or no effect on the percentage of curds Quality 1 (Everaarts and De Moel, 1995). However, the results of experiments 2 and 4, particularly those of Experiment 2, now show that low nitrogen availability may severely affect the percentage of curds Quality 1. It is dif®cult to indicate whether the especially strong effect in Experiment 2 was related to the early pigeon damage in this experiment.
No indications were obtained that the present nitrogen fertilizer recommenda-tion for cauli¯ower should be altered. However, when mineral nitrogen availability in the soil layer 0±60 cm at planting was around 200 kg haÿ1
, as was the case in experiments 3 and 5, additional nitrogen fertilizer application to the recommended amount of 225 kg haÿ1
nitrogen, was not necessary to realise maximum yield. Apparently, in soils where available mineral nitrogen is already that high at planting, additional mineralisation during crop growth can be expected and this is suf®cient to prevent yield loss. Rahn et al. (1998) found no yield response of cauli¯ower to fertilizer nitrogen when mineral nitrogen at planting was around 210 kg haÿ1
in the soil layer 0±30 cm, or 270 kg haÿ1 in the 0±90 cm soil layer.
Nitrogen uptake by the crop at harvest in the crop supplied with the recommended amount of nitrogen, ranged from 170 to 250 kg haÿ1. This is in agreement with the previously published data (Everaarts, 1993a; Everaarts et al., 1996) and also with recent observations from Denmark (Van Den Boogaard and Thorup-Kristensen, 1997). With a nitrogen harvest index of around 45%, an estimated amount of 95±140 kg haÿ1
harvested. Earlier observations on nitrogen in cauli¯ower crop residues were 100±120 kg haÿ1
(Everaarts et al., 1996).
The amount of nitrogen left in the soil layer 0±60 cm at harvest was very low in experiments 2 and 4, when the recommended amount of nitrogen was applied at planting. In these experiments, little or no nitrogen mineralisation occurred after planting. Higher amounts were found in experiments 1 and 3, where considerable mineralisation was found after planting. As the uptake of nitrogen by the crop obviously is limited, ongoing mineralisation during crop growth may result in increased amounts of soil mineral nitrogen at harvest. Only in Experiment 3, a substantial amount of mineral nitrogen was found in the 60±90 cm soil layer.
Apart from the early situation in Experiment 1, where the measured amount of nitrogen in the cropsoil system was higher than the calculated amount, the
measured amount of nitrogen generally was lower than the calculated available amount of nitrogen. No period during crop growth could be indicated where the difference was particularly great. The difference observed might partly be due to a higher, unaccounted for amount of nitrogen in shed leaves in the treatment with fertilizer as compared to the treatment without fertilizer application. Denitri®ca-tion is unlikely to have played a role in view of the magnitude of the difference. Leaching of fertilizer nitrogen beyond the rooting zone as a cause for the difference is not likely either, as evapotranspiration usually exceeds rainfall during summer. Also, the absence of major differences between the no nitrogen and nitrogen application treatments in the amount of mineral nitrogen in the soil layer 60±90 cm at harvest indicates that leaching of fertilizer nitrogen was not substantial. It is likely that most of the difference between measured and calculated amount of nitrogen in the cropsoil system was caused by
immobilization of fertilizer nitrogen by the soil, whether temporarily (Neeteson et al., 1986) or for longer periods. Excluding the situation in Experiment 2 at 80 days after planting, where the amount of nitrogen in the crop unexpectedly decreased towards harvest (Fig. 1), the maximum difference between calculated and measured amount in the experiments was88 kg haÿ1nitrogen, recorded at
78 days in Experiment 1. Generally, the difference was considerably less. When part of this amount of nitrogen is not lost, but ®xed in the soil, it implies that the potential for loss of nitrogen to the environment with cultivation of cauli¯ower, at the recommended amount of fertilizer nitrogen, is greater after crop harvest, when more nitrogen may be lost from crop residues and soil, than during crop growth. Loss of nitrogen increases when more nitrogen than recommended is applied (Everaarts et al., 1996). Strategies to limit loss of nitrogen from crop residues, or soil, have been discussed previously (Everaarts, 1993b; Everaarts et al., 1996).
Fertilizer nitrogen could possibly be saved by split application of nitrogen (Everaarts, 1993b). A lower amount of nitrogen than recommended could be applied at planting. By measuring soil available nitrogen at four weeks after planting, and then applying nitrogen up to the recommended amount, an amount
of fertilizer nitrogen equal to the amount of nitrogen mineralised in the ®rst four weeks after planting could be saved. The results of the experiments show, however, that a second nitrogen application in experiments 3 and 5, with already high amounts of mineral nitrogen at planting, would not have been necessary as nitrogen availability still increased after planting. In experiments 2 and 4, with low amounts of nitrogen at planting, mineralisation after planting was low, and the scope for saving nitrogen by sampling again at four weeks after planting was too limited to warrant the effort. Only in Experiment 1, a situation was found in which fertilizer nitrogen could have been saved by sampling at four weeks and then applying fertilizer nitrogen up to the recommended amount of 225 kg haÿ1 minus mineral nitrogen in the soil layer 0±60 cm. However, it is dif®cult to indicate what the minimum nitrogen availability for the crop shortly after planting should be. Uptake of nitrogen in that period is limited and so is rooting depth. Lorenz et al. (1989) advised a nitrogen availability of 130 kg haÿ1
in the soil layer 0±30 cm up to the fourth week after planting. In Experiment 1, 44 kg haÿ1 nitrogen available at planting, and 83 kg haÿ1
at four weeks after planting, (Table 3) were suf®cient to prevent yield reduction (Table 4). In view of the very limited uptake of nitrogen by the crop during the ®rst four weeks after planting (Fig. 1), it is suggested that a nitrogen availability of 100 kg haÿ1
at planting in the soil layer 0±30 cm could be a safe option in situations where a high mineralisation of nitrogen historically takes place after planting or where high mineralisation can be expected from freshly incorporated crop residues. Further research will have to prove the validity of this suggestion.
W. Van Den Berg (PAV, Lelystad) provided statistical assistance. C.L.M. De Visser (PAV, Lelystad) and Dr. R. Booij (AB-DLO, Wageningen) are thanked for their comments on the manuscript.
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