Abstract: Field experiment was carried out to evaluate the nitrogen efficiency and nitrogen response under no nitrogen application and nitrogen application conditions. The differences of grain yield, nitrogen absorption amount, nitrogen response and nitrogen use efficiency among 16 winter varieties of oilseed rape (Brassica napus L.) were systematically studied and the contribution of nitrogen absorption efficiency and nitrogen use efficiency to nitrogen efficiency in different oilseed rape varieties were preliminarily discussed. Results showed that, the differences of grain yield, nitrogen use efficiency and nitrogen response among the 16 oilseed rape varieties were significantly, regardless of N application level; but only under no N application conditions, the differences of nitrogen absorption amount among varieties were significantly. The 16 oilseed rape varieties were divided into four different genotypes in accordance with the nitrogen use efficiency and nitrogen response under no nitrogen application condition: (1) Nitrogen High Efficiency-Nitrogen High Response, included Xy1, Xy16, Xy17, Xh19, Xh20 and Xy21. (2) Nitrogen Low Efficiency-Nitrogen Low Response (NLE-NLR), included Xy6, Xy8 and Xy9. (3) Nitrogen High Efficiency-Nitrogen Low Response (NHE-NLR), included Xy7, Xy12, Xy14, Xy15 and Xy24. (4) Nitrogen Low Efficiency-Nitrogen High Response (NLE-NHR), included Xy11 and Xy13. The variation coefficient of nitrogen use efficiency was higher than nitrogen absorption efficiency, regardless of N application level; it was also showed that the contribution of nitrogen use efficiency to nitrogen efficiency was higher than nitrogen absorption efficiency. However, variation coefficient of nitrogen absorption efficiency under nitrogen application condition was higher than under no N application condition; variation coefficient of nitrogen use efficiency was reverse. It was indicated that, under no N application condition, the variation of nitrogen efficiency because of nitrogen use efficiency was decreased and variation of nitrogen efficiency because of nitrogen absorption efficiency was increased.
INTRODUCTION
Nitrogen fertilizer application can guarantee the high yield of crop, it was a general method to improve the yield of crop. However, not only N use efficiency was declined, but also environment contamination was seriously day by day because of N fertilizer over application. So, control and decline the N fertilizer application amount is very important; it is necessary to dredge up the potential of N absorption and N use efficiency of crop. Oilseed rape (Brassica napus L.) is an important oil production crop in China. However, the N use efficiency and N efficiency of oilseed rape are very low (Schjoerring et al., 1995). The N application amount has been reached 200-330 kg N ha-1 (Schjoerring et al., 1995; Wiesler et al., 2001a) and increasing year by year. But the studies on differences of N efficiency in different oilseed rape varieties and breeding research of the oilseed rape with high N efficiency were relatively slower than other cereal. Oilseed rape requires high amounts of N for growth, but the N efficiency (seed yield per unit of accumulated N in plant) is very low. Consequently, it is necessary to improve the N efficiency (Rathke et al., 2006). In generally, N efficiency has two components: uptake efficiency and utilization efficiency (Sattelmacher et al., 1994). The differences of N efficiency between oilseed rape genotypes were significantly (Wiesler et al., 2001b; Christian et al., 1999; Kessel and Becker, 1999), measured the N concentration of organs in different oilseed rape varieties suggested that, the oilseed rape with low N concentration in dropped leaves and with high N harvesting index has higher N efficiency also; The development of N efficient genotypes and improvement of N management will require to understand the relationship between physiological processes and biomass, yield formation of crop under no N application conditions (Dreccer et al., 2000). Kamh et al. (2005) compared the differences of root growth and nitrate N exhaust in cultivar culture between high N efficiency and low N efficiency oilseed rape; larger amount of root biomass, higher root uptake activity and higher exhausted nitrate N amount were found in the high N efficiency oilseed rape; Nitrate-N uptake from soil depends on root growth and uptake activity, the amount of N depleted from the compartments significantly correlated with root-length density (Kamh et al., 2005). Seiffert et al. (2004) suggested that the N use efficiency can be increased significantly by strengthen the activities of asparagine synthetase and glutamine synthetase through transgenic methods. Obviously, it is necessary to system study on N uptake and N use efficiency in different oilseed rape. The differences of yield, N absorption and N use efficiency in different oilseed rape varieties should be compared and preliminarily discussed the contribution different of N absorption efficiency and N use efficiency to the N efficiency under different N application levels, in order to supply scientific basic and plant materials for the future study.
MATERIALS AND METHODS
Plant Materials and Experiment Design
The experiment was conducted at Agricultural Resources and Environmental
College Experiment Field in Hunan Agricultural University during Sep. 2004 to
May. 2005. Sixteen oilseed rape varieties were used as plant materials, the
number were showed in Table 1, plant materials were supplied
by China National Oilseed Crop Improvement Center, Hunan Branch. The soil used
was an alluvial for vegetable cultivation derived from river flow alluvial material,
containing organic matter 27.79 g kg-1, total N 1.90 g kg-1
and total P 0.79 g kg-1 total K 19.76 g kg-1. The NaOH
hydrolyzed N was 108.31 mg kg-1 of soil, Olsen-P 15.85 mg kg-1
of soil, available K 19.76 g kg-1 of soil with pH 5.67. Urea was
used as N fertilizer, calcium magnesium phosphate as P fertilizer (containing
P2O5 12%) and potassium chloride (containing K2O
60%) as K fertilizer.
The experiment had two N treatments; N application and no N application, 16 oilseed rape varieties used as plant materials, 32 treatments, 3 replicates, 96 districts, 10.5 m2 per district, randomized block. N application treatment: 225 kg N, 75 kg P2O5 and 150 kg K2O h-1, 50% N fertilizer used as basal fertilizer, 20% N fertilizer used as added fertilizer during winter, 30% N fertilizer used at stem elongation stage, all P and K fertilizer were used as basal fertilizer; no N application treatment: the same with N application treatment except of non-N fertilizer applied. Seedling on Sep. 25, 2004, transplanted on Nov. 2, 2004, transplanted density was 100 thousand plants per ha, management as normal.
Sampling, Determination and Calculation
Sampled whole plant at harvesting stage, separated it according to organs after
clear, dried until constant weight, measured dry weight and total N. The measurement
methods followed by the general agricultural chemistry analysis methods; the
plant total N measured by Kjedahl method (Hardy et al.,
1968). Below formula was used to calculate N use efficiency based on total
N:
N use efficiency = Grain yield/Plant total N |
All data were carried out t-test by SPSS statistic software (Norusis, 1990), cultivars with the same letter(s) are not significantly different at the p<0.05 level using SPSS software analysis.
RESULTS
The Differences of Grain Yield Between Different Oilseed Rape Varieties
The results of grain yield showed that (Table 1) , the
differences of grain yield between different oilseed rape varieties were significant,
regardless N application level. The rang of yield variation in 16 varieties
were 1060-1913 kg h-2 under no N application condition; the yields
of Xy1, Xy7 and Xh20 were higher (≥2720 kg hm-2), the yields of
Xy8, Xy9, Xy11 were lower (≤1105 kg hm-2). N response can be expressed
by ratio of (yield with N application-yield with no N application)/N application
amount. Because the N application amount of all varieties under N application
treatment were the same in this study; so, the N response can be indirectly
expressed by the differences of yield under N application condition and no N
application condition. N responses of Xy13, Xh19 and Xh20 were higher than other
varieties significantly; N responses of Xy14, Xy15 were lower than other varieties
significantly. Excepted Xy15, grain yield can be increased by N application
significantly, average increased of yield in sixteen cultivars were 35%.
N Absorption Amount and N Use Efficiency in Different Oilseed Rape Varieties
Results of Table 2 showed the relationship between N absorption
amount and grain yield; N absorbed amount of different oilseed rape varieties
were different under different N application level conditions; the differences
of N absorption amount between varieties were significantly under no N application
condition; however, the differences were smaller under N application condition.
N absorption amount of Xy1, Xy21 and Xy24 (≥1.688 g plant-1) were
more than other varieties Xy8, Xy9 and Xy13 (≤1.293 g plant-1)
significantly. The relationship between N absorption amount and grain yield
showed that, the correlation between N absorption amount and grain yield was
significantly under no N application condition, correlation coefficient was
0.685** (R0.01=0.623); but under N application condition, there was
no significantly correlation and the correlation coefficient was 0.415 (R0.05
= 0.497).
| Table 1: | Grain yield of different oilseed rape varieties (kg hm-2) |
| Mean values with the same letter(s) are not significantly different with each other | |
It was indicated that only under the no N application condition, grain yield can be increased significantly by increased N absorption amount. The differences of N use efficiency between varieties were significantly according to the differences of N absorption amount, regardless of N application level. The changes scope of N use efficiency in sixteen varieties was 7.1-12.6, the highest was Xh20 of 7.1 and the lowest was Xy6 of 12.6.
The Differences of N Efficiency in Different Varieties and its Analysis
Results of Table 1 and 2 showed that,
the differences of N efficiency, N absorption efficiency and N use efficiency
between varieties were significantly under no N application condition and the
differences of N efficiency and N use efficiency between varieties were significantly
under N application condition; while there were no differences of N absorption
efficiency between varieties almost. Grain yield of variety is higher than average
yield of 16 varieties under no N application condition was the high N efficiency
varieties; contrary it was low N efficiency variety; D-value of grain yield
of variety between no N application and N application conditions was higher
than average D-value of 16 varieties was high N response varieties; contrary
it was low N response variety. The 16 varieties can be divided into 4 genotypes
according to the above definitions (Table 3): (1) N high efficiency-N
high response; yield was higher under no N application condition; yield was
increased significantly under N application condition; included Xy1,Xy16,Xy17,Xh19,Xh20
and Xy21; (2) N low efficiency-N low response; yield was lower under no N application
condition; yield increased was indistinct under N application condition; included
Xy6, Xy8 and Xy9; (3) N high efficiency-N low response, yield was higher under
no N application condition; but the yield increased was indistinct under N application
condition; included Xy7,Xy12,Xy14,Xy15 and Xy24; (4) N low efficiency-N high
response; yield was lower under no N application condition, but the yield was
increased significantly under N application condition; included Xy11 and Xy13.
| Table 2: | N absorption and use efficiency of different oilseed rape varieties |
| Mean values with same letter(s) are not significant different with each other | |
| Table 3: | N efficiency and response type of oilseed rape |
| Table 4: | Variation of Grain yield, N absorption and use efficiency of different oilseed rape varieties |
Results of Table 4 showed that, variation coefficient of grain yield was almost the same regardless of N application level; variation coefficient of N use efficiency was higher than variation coefficient of N absorption amount under the two N application level conditions; it was suggested that, the contribution of N use efficiency to N efficiency was higher than N absorption efficiency in oilseed rape under the field condition, regardless of N application level. The differences of variation coefficient between N absorption amount and N use efficiency were smaller under no N application condition, compared with N application condition; it was suggested that, variation coefficient of N use efficiency was declined, but variation coefficient of N absorption amount was increased under N stress condition; it was indicated that, the contribution of N absorption efficiency to N efficiency was increased with N application level was declined, but the contribution of N use efficiency to N efficiency was decreased.
DISCUSSION
Evaluate the Differences of N Efficiency in Different Oil Seed Rape Varieties
Environmental contamination was reduced by less N fertilizer application,
so, breeding and spreading new crop varieties with high N efficiency was an
interesting topic recently (Xu et al., 2006;
Pei et al., 2007; Wang et
al., 2003). Many studies and reports were involved in N agriculture
efficiency, N physiological efficiency and N absorption efficiency. N physiological
efficiency and N absorption efficiency were parts of the N agriculture efficiency;
there were relationships between the three efficiency indexes. Wheat breeders
were identified selection standards based on physiological indexes, such as
high yield and high protein content (Monaghan et al.,
2001). Results showed that, the differences of N efficiency in 16 oilseed
rape varieties were significantly, regardless of N application level, it was
the same with other results (Beauchamp et al., 1976;
Pollmer et al., 1979; Balko
and Russell, 1980a; Reed et al., 1980; Russell,
1984; Moll et al., 1987; Landbeck,
1995; Bertin and Gallais, 2000). It was necessary
to select high N efficiency varieties from variety recourses. However, few of
oilseed rape varieties were used in these studies, more varieties were needed
to be selected and estimated in the future. Sixteen oilseed rape varieties were
used as plant materials in this experiment, N high efficiency types were be
better plant materials and can tolerant low N stress, these materials have high
economic benefit under low N condition; N high response types were be better
plant materials and can tolerant high N stress, these materials have high economic
benefit under high N condition. It can be seen that, the type of N high efficiency-N
high response varieties was the ideal variety.
N Efficiency of Oilseed Rape under Different N Application Level
Breeding procedure was usually conducted under N application conditions recently;
so, the varieties have high yield under N application condition, it was only
for N application condition; however, it was necessary to select high N efficiency
varieties under the low N stress condition in generally, selected the varieties
have high yield under no N application level. The correlation of various agronomic
traits (grain protein, yield and its component) were different with the changes
of N application level (Balko and Russell, 1980b; Di
Fonzo et al., 1982; Rizzi et al., 1993;
Bertin and Gallais, 2000). Therefore, the response differences
of varieties under different N application level conditions were obscured; these
problems are needed to be further studied in the future. Mollers
et al. (2000) studies suggested that, the differences of N efficiency
between different N application levels and between varieties were big, observed
significant interactions between genotype and N level suggested that the high
yielding genotypes in high N supply were not necessarily high yielding in the
low N supply. This study has the same results, the varieties have the same yield
under N application condition, but under no N application condition, the differences
of yield between varieties were big; The 16 oilseed rape varieties can be divided
into 4 different genotypes according to yield under N application and no N application
conditions (Table 3), (1) double high efficiency genotype,
yield of these varieties were higher than average yield of varieties, regardless
of N application level; included Xy1,Xy7,Xy16,Xy17,Xh19,Xh20 and Xy21; (2) double
low efficiency genotype, yield of these varieties were lower than average yield
of varieties, regardless of N application level; included Xy6,Xy8,Xy9 and Xy11;
(3) high N-high efficiency genotype, yield of these varieties were lower than
average yield of varieties under no N application condition and the result was
reverse under N application condition; included Xy12,Xy14,Xy15 and Xy24; (4)
low N-high efficiency genotype, yield of these varieties were higher than average
yield of varieties under no N application condition and the result was reverse
under N application condition; included Xy13. However, the results of Grami
et al. (1977) studied with spring rapeseed reported direct relationship
between N uptake and seed N content and concluded that, high seed N content
was good for N uptake and translocation efficiency improved, it was contrary
with this study. The above results suggested that, both of N application condition
and no N application conditions should be considered during the breeding and
selecting procedure of crop (Liu et al., 1999;
Lafitte and Edmeades, 1994).
The Contribution of N Absorption Efficiency and N Use Efficiency to N Efficiency
Many studies were involved in contribution of N absorption efficiency and
N use efficiency to N efficiency, but the results were different. High seed
protein content will cost of grain yield, this agrees with former results which
observed negative relationship between protein content of seed and grain yield
(Dudley et al., 1977; Simmsonds,
1995). Wheat breeders have reported selection standards combined with high
yield and high protein content (Monaghan et al.,
2001). Some results showed the N use efficiency was the main reason for
changes of N efficiency under low N condition and the main reason was N absorption
efficiency under high N condition (Moll et al., 1982);
the effect of N absorption efficiency on N efficiency was higher than N use
efficiency significantly under low N condition and the effect of N absorption
efficiency and N use efficiency on N efficiency were almost the same under high
N condition (Mi et al., 1998); the absorption
efficiency was the main reason for changes of N efficiency regardless of N application
level (Liu et al., 2002); N absorption efficiency
and N use efficiency of oilseed rape were studied by Yan
and Thurling (1987a), there were differences of N use efficiency between
varieties under high N condition and there were differences of N absorption
efficiency between varieties under low N condition. The results of this study
showed that, the changes of N use efficiency was the main reason of the changes
of N efficiency under low and high N conditions, but Yan
and Thurling (1987b) has the different results. In this study (Table
4) also showed that, variation coefficient of N absorption efficiency was
increased under low N condition, while the variation coefficient of N use efficiency
was declined, it was suggested that, the contribution of N absorption efficiency
to N efficiency was increased under low N condition. However, the results were
only for the varieties which used in this experiment and more varieties are
necessary to be used in the future, to reveal more exactly and generally conclusions.
ACKNOWLEDGMENTS
This study was supported by the National Natural Science Foundation of China (Grant No. 30671206), The Industry Technology System of Rapeseed, Agriculture Ministry of China (nycytx-5), Key Project of National Natural Science Foundation in Hunan (07JJ3074), Special Foundation of Hunan province for post-doctoral work (2006FJ4265).