Assessing internal crop nitrogen use efficiency in highyielding irrigated cotton
Ian J. Rochester
5
CSIRO Plant Industry
Cotton Catchment Communities Cooperative Research Centre
Abstract Improving the efficiency of nitrogen (N) fertiliser use is one means of reducing
10
greenhouse gas emissions, particularly in irrigated crops such as cotton (Gossypium
hirsutum L.). Internal crop N use efficiency (iNUE) was measured within two N fertiliser
rate experiments that covered a wide range of N fertility over six cropping seasons.
Internal crop iNUE was determined by dividing lint yield by crop N uptake. No nutrients
other than N limited cotton growth or yield and the crops were not drought-stressed. Crop
15
NUE was measured over five cropping seasons within an N fertiliser rate experiment that
provided a wide range of soil N fertility. The optimal N fertiliser rates were determined
from fitted quadratic functions that related lint yield with N fertiliser rate for each
cropping system in each year. When the optimal N fertiliser rate was applied, crop iNUE
averaged 12.4+0.3 kg lint/kg crop N uptake. The crop iNUE was then related to the
20
economic N fertiliser rate N fertiliser rate to determine the degree to which N fertiliser
was under or over-applied. Low iNUE values were a consequence of excessive N
fertiliser application. Crop iNUE was determined in 82 commercial cotton crops in five
valleys over the final 4 years of this study. The crop iNUE value was high in 8 fields
(10%), optimal in 9 fields (11%) and low in 65 fields (79%). Crop N uptake averaged 247
25
kg N/ha, yield 2273 kg lint/ha and crop iNUE 10.1 kg lint/kg crop N uptake for these
sites. Averaged over all sites and years, about 49 kg N/ha too much N fertiliser was
applied. Apparent N fertiliser recovery ranged from <10% in fertile fields where legume
crops had been grown, to more than 60% following winter cereal crops. Information on
crop iNUE enables cotton producers to assess their N fertiliser management and adjust N
30
fertiliser rates for future crops. This study demonstrated that there is scope to
substantially reduce N fertiliser inputs to Australian cotton fields without reducing yields.
Keywords Crop nutrition · N fertiliser · N fertiliser recovery ·
1
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Introduction
A heightened focus on greenhouse gas emissions and the cost of N fertiliser has prompted
greater attention to the efficient use of N fertilisers. While most cotton crops require N
fertiliser to achieve high yields, producers must ensure that N fertiliser inputs are used
appropriately. The economic optimal fertiliser input can be estimated by using presowing
40
soil analysis and/or in-crop tissue analysis (Rochester et al. 2001b).
Because of the global consequences of green-house gas emissions, greater
attention is being given to N fertiliser management (Snyder et al. 2007). Nitrous oxide
emissions are exacerbated by excessive N fertiliser use, which can also reduce yield and
delay harvest. Growers cannot afford to under-fertilize with N (or other nutrients) and
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tend to manage risk by ensuring their cotton crop yields are not limited by N deficiency.
It is imperative to consider the amount of N in the soil at sowing when deciding on
quantities of N fertiliser to apply, as well as the crop rotation system, which dictates the
rate of mineralization of N through the season (Rochester et al. 2001a).
Given that most Australian cotton-growing soils are medium to heavy clays that
50
are prone to waterlogging following flood irrigation or heavy rain, losses of 50-100 kg
N/ha can occur (Rochester 2003). Much N can be lost through denitrification and
leaching, leading to inefficient use of N fertilisers under these conditions. Nitrous oxide
(N2O), the most potent greenhouse gas, may be a small fraction of gases emitted from
alkaline soils (Rochester 2003), but it is a dominant component of the total eCO2
55
emissions from fertilised cropping systems (Millar et al. 2009).
Internal crop N use-efficiency (iNUE = kg lint/kg crop N uptake) indicates how
efficiently cotton produces lint relative to the N accumulated by the crop. Crop iNUE
measurements have been reported for cotton (Bronson 2008, Zhang et al. 2008a), rice
(Witt et al. 1999) and sugarcane (Robinson et al. 2007), to compare cultivar performance
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and agronomic practices. However, it has not been related to the optimum N fertiliser rate
determined in N fertiliser experiments. This measure does not discriminate between soil
N or fertiliser N sources and therefore may not indicate N fertiliser use-efficiency.
This research aimed to assess crop iNUE within N fertiliser rate experiments and
relate this to the economic optimum N fertiliser rate. This would provide a relationship
2
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between crop iNUE the over- or under-use of N fertiliser. Crop iNUE could then be
measured in commercial cotton crops to gauge the efficiency of N fertiliser use.
Materials and Methods
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Measuring iNUE in N rate experiments
Crop iNUE was determined in field experiments over a six-year period at Narrabri NSW
Australia (150oE, 30oS) in two cropping systems experiments investigated the interaction
of N fertiliser and crop rotations. These experiments were initiated in 1994 and 1995, and
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compared 2-year rotation cycles. The rotation crops included faba beans (Vicia faba L.),
vetch (Vicia villosa Roth) and wheat (Triticum aestivum L.), that were grown in the first
year and cotton grown in the second year. The two experiments were out of phase by 1
year. Cotton was grown annually in one experiment (Fig. 1). Cropping treatments were;
C~C~C (annual cotton), CVCVC (annual cotton with green-manured vetch each winter),
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CW~C (cotton followed by wheat then fallow until cotton), CWVC (cotton followed by
wheat then green-manured vetch, then cotton), CV~C (cotton followed by green-manured
vetch then fallow until cotton), and CFb~C (cotton followed by faba bean then fallow
until cotton). All rotation crops were grown through winter, harvested or green manured
in late-spring. These systems provided a wide range of soil N fertility. The experiment
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was a split plot design, rotation crops were the main plots (8 x 200 m) and N rates were
the subplots (8 x 16 m). The design included four replicates.
Nitrogen fertiliser treatments were applied prior to sowing cotton in the second
year of each cropping cycle, N (anhydrous ammonia) was applied at rates between 0 and
200 kg N/ha in 25 kg N/ha increments (or 0 and 256 in 2004/05 season). This range of N
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fertiliser rates was sufficient to achieve maximum lint yield in each rotation system.
The soil at this site was self-mulching medium grey clay overlying brown clay
and is classified as a fine, thermic, montmorillonitic Typic Haplustert (Soil Survey Staff,
1996). Clay content averages 530 g/kg soil and 220 g/kg soil each of silt and sand and 30
g/kg of organic matter; it has a uniform profile of medium to heavy clay and shows
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seasonal cracking extending to more than 150 cm depth; soil total N was 0.9 g/kg soil,
3
organic carbon 11.0 g/kg soil and cation exchange capacity 45 cmolc/kg; the surface soil
pH (1:5 soil:water) was 8.3 and 8.8 at 1 m depth (Ward et al., 1999). This soil has been
cultivated for almost 40 years; previously, the area was under native grasses and
woodland. Compared with many cotton-growing soils that have higher clay content and
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lower organic matter, this soil is well aerated and less N fertilizer is lost through
denitrification (Rochester and Constable 2000).
All cotton crops were grown on 1 m spaced ridges that were maintained
throughout the experiment. Crops were irrigated according to commercial practice and
insects were controlled when they exceeded commercial threshold levels. Weeds were
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controlled with mechanical cultivation and herbicides.
Above-ground biomass of cotton crops was measured 3 weeks before chemical
defoliation when at least 25% of bolls were open; 1 m2 of crop which was cut, dried,
weighed, milled and analysed for N concentration (using Kjeldahl digestion) to determine
crop N uptake.
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Apparent N fertiliser recovery (ANFR) was calculated as the difference in crop N
uptake between fertilised and unfertilized treatments, divided by the N application rate
and expressed as a percentage of the N applied.
After chemical defoliation when at least 60% of bolls were open, two central rows of
each plot were mechanically picked and a subsample of seed cotton was ginned to
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determine lint content of the seed cotton and lint yield.
The SigmaPlot program (SPSS 2000) was used to fit quadratic curves to the lint yield
response to N application. Bauer et al. (1993) used a quadratic function to define the lint
yield response of cotton to N fertilizer application, whereas Bronson et al. (2001) used a
quadratic-plateau model that suited their data and produced lower NFopt than a quadratic
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curve.
The economic optimum N fertiliser rate (NFopt) was determined for each cropping
system by examining the fitted quadratic N fertiliser response curve where the marginal
cost of N fertiliser (AU$1.50/kg) equaled the marginal price received for lint
(AU$1.80/kg). This function was then used to determine the economically optimum N
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fertilizer application using the marginal cost to apply N fertilizer (AU$1.50/kg) and the
4
marginal return for lint (AU$2.20/kg). The difference in NFopt and the N fertiliser
applied indicates whether a crop received insufficient or excess N fertiliser.
Measuring iNUE in commercial cotton crops
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In 4 years, 2006, 2007, 2008 and 2009, iNUE was calculated for several commercial
cotton crops within six cotton growing districts in Australia (Hillston, Warren, Narrabri,
Moree, Goondiwindi and Emerald). Crop N uptake was measured as described as above.
Where the farmer could not provide an accurate estimate of the crop yield, lint yield was
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estimated by hand-picking 2 m2 of cotton plants in an adjacent area to where the crop N
uptake was measured. In 2007, seven Pima (G. barbadense) crops were also assessed in
the Moree district.
Statistical analysis
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Genstat (Payne, 1987) was used to test for differences using ANOVA. Linear regression
analyses were performed using the SigmaPlot V9.0 program (Systat Software Inc., 2004).
*, **, *** denote statistical significance i.e. P<0.05, P<0.01, P<0.001, respectively; ns
denotes not statistically significant.
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Results
Measuring iNUE in N rate experiments
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There was a greater response in lint yield to applied N in the non-legume systems (Fig.
1). The legume-based systems generally required less N fertiliser than non-legume based
systems and the legume-based systems generally yielded higher than the non-legume
systems. Much of the variation in lint yield between years was attributed to seasonal
conditions. Higher yields were afforded in those years (e.g. 2008) when water stress was
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less severe and when milder temperatures promoted photosynthesis and reduced the
evaporative demand from the crops.
5
Crop N uptake for the 6 years is presented in Fig. 2. The experiments produced a
wide range of soil N fertility resulting from N2-fixation by the legume crops as well as N
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fertiliser application; this resulted in a wide range of lint yield and crop N uptake (Fig. 2).
Crop N uptake increased with N fertiliser application in all years (P<0.001), and there
were differences (P<0.05) among the cropping systems in all years except 2005 and
2006, but there was no N fertiliser x cropping system interaction in any year.
Crop iNUE declined (P<0.05) with higher N fertiliser rates in each year of the
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experiment (Fig. 3). Differences (P<0.001) in crop iNUE between the cropping systems
were identified in 2004, 2007, 2008 and 2009. The interaction between N fertiliser rate
and cropping system was not statistically significant in any year. Crop iNUE increased
between the first (2004-2006) and second (2007-2009) 3-year periods by 45% (9.21 cf
13.4 kg/kg). This was achieved by a 12% reduction in crop N uptake (231 cf 203 kg
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N/ha) and a 20% increase in lint yield (2154 cf 2586 kg lint/ha).
Crop iNUE was related to N fertiliser addition, with respect to the economic
optimum N rate (Fig. 4). Cotton that had been supplied with excess N fertiliser, relative
to the economic optimum N rate had lower iNUE, whereas under-fertilised crops had
higher iNUE. Where N fertiliser was applied at the economic optimum rate, the crop
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iNUE value was close to 12.4 (+0.3) kg lint / kg crop N uptake. For crop iNUE to be
within one unit of the optimal 12.4 kg lint/kg crop N uptake, N fertiliser must be applied
within a 50 kg N/ha of the optimum N fertiliser rate. Similarly, for crop iNUE to be
within 0.5 units of the optimal iNUE, N fertiliser must be applied within a 25 kg N/ha of
the optimum N fertiliser rate.
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Apparent N fertiliser recovery in the experiment
The apparent recovery of fertiliser N varied (P<0.001) among the cropping systems (Fig.
5a), but there was no effect of N fertiliser application rate or N x cropping system
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interaction. The N-fertile legume-based systems recovered <20% of the N fertiliser
applied while the continuous cotton and cereal-based systems recovered about 60% of the
6
N fertiliser applied. The non-legume systems required higher rates of N fertiliser and
demonstrated higher N fertiliser recovery (Fig. 5b).
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Commercial cotton crops
The crop iNUE was determined for 82 commercial cotton crops and the N fertiliser
requirement was estimated using the relationship in Fig. 4. The fields covered a wide
range of N fertility levels and yields; the highest yielding crops were grown in fallowed
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fields and in northern regions where the growing seasons were long. Higher yields and
lower crop N uptake were measured in the N experiments, compared with the commercial
crops. Lint yield and crop N uptake at the commercial sites is shown in Fig. 6. In the
seven Pima (G. barbadense L.) crops, iNUE averaged 5.66, suggesting that a separate
calibration is needed for Pima cotton, which may take up similar quantities of N, but
200
yields considerably less than G. hirsutum.
The optimum iNUE of 12.4 occurred where N uptake was 177 kg N/ha at the
commercial sites (Fig. 7), whereas this point was at 213 kg N/ha in the N experiment.
When the data were combined, crop N uptake was 193 kg N/ha when crop iNUE was
12.4. To achieve optimal crop iNUE, cotton crops need to take up about 200 kg N/ha.
205
Only nine of the 82 (11%) commercial crops had optimal iNUE (values between
11.4 and 13.4). Most of the crops (65 of 82 crops – 79%) indicated poor crop iNUE
(values less than 11.4, the lowest was 4.2). Only eight of the 82 crops (10%) had iNUE
values more than 13.4, indicating high crop iNUE. Two of these crops had very high
iNUE values of more than 20; these crops showed symptoms of poor P nutrition that
210
limited N nutrition.
Using the relationship shown in Fig 4, the degree of under- or over-fertilisation
was established for all the commercial cotton crops sampled. On average, 49 kg N/ha was
applied in excess of the optimum N rate. The crops with the lowest crop iNUE values
took up in excess of 400 kg N/ha and were over-fertilised by more than 200 kg N/ha.
215
Discussion
7
Crop iNUE measurements
220
This study has defined the levels of internal crop N use-efficiency for high-yielding
irrigated cotton crops in Australia. While growers may strive for higher N use-efficiency,
the use of N fertiliser must be optimised to maximize economic returns (Fig. 1). Hence,
optimum N fertiliser application produces a iNUE level of 12.4 kg lint/ kg crop N uptake.
In comparison, Naklang et al. (2006) reported iNUE of 46 kg rice grain/ kg crop N
225
uptake. In China, Zhang et al. (2008b) reported iNUE of 9.7 for upland cotton that
yielded up to 1000 kg/ha.
Higher iNUE, cotton yields and profits are achieved through careful irrigation,
soil, pest and nutrient management. Producers are able to predict the crop N fertiliser
requirement through soil analysis pre-sowing and crop tissue analyses during crop growth
230
(Rochester et al 2001a).
Fig. 2 indicates that crop iNUE was optimised in cotton crops that took up 200220 kg N/ha. Crop N uptake beyond this leads to lower iNUE; iNUE was reduced to less
than 8 kg/kg where crop N uptake exceeded 300 kg N/ha (Fig. 6). This indicates a
substantial change over the past two decades where Ockerby et al. (1993) and Constable
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and Rochester (1988) indicated the optimum lint yield was obtained with crop N uptake
of 120-130 kg N/ha.
In northern Syria, flood-irrigated cotton yielded 1800 kg lint/ha, took up 300 kg
N/ha, resulting in an iNUE of 6.0 (Janat 2008). There was no increase in lint yield by
applying N fertiliser, confirming that these crops took up more N than was required to
240
produce moderate yields and were probably over-supplied with N. Further, apparent N
fertiliser recovery was also low (37 and 16% in 2 years), confirming the soil was highly
N-fertile (high mineral N was measured throughout the soil profile). This level of N
fertiliser recovery was typical of the systems that included legume crops in Fig. 3 and
were highly N-fertile. Earlier, Janat (2005) had reported low iNUE values (5.3 to 6.9 and
245
reducing with N fertiliser application) but iNUE was 10.4 for unfertilized cotton.
In China, Zhang et al. (2008b) reported iNUE between 9.6 and 7.1 (declining with
N rate) for cotton that yielded between 1200 and 1700 kg lint/ha. By using the quadratic
N response curve used in Fig. 1, the economic optimum N rates were 142 and 219 kg
8
N/ha in the two years studied; the iNUE would be 7.9 and 7.3 for the respective crops at
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the optimum N rate, indicating poorer iNUE for their experiment, compared with the
iNUE of 11.9 determined in this research. However, Zhang et al. (2008b) also reported
that iNUE was not affected by applying P and K fertilisers, as lint yield, N uptake and
ANFR were increased. Some commercial fields (Fig. 5) had high iNUE due to poor P
and/or K uptake that limited N uptake, but produced moderate lint yields.
255
Bronson (2008) reported iNUE values averaging 12.2 for irrigated cotton in Texas
USA, which were similar to the optimal iNUE reported in Fig. 4 (i.e. 11.9). Yields
averaged 1510 kg lint/ha and N uptake 124 kg/ha. Apparent NFR averaged 52% (c.f. Fig.
5) and ranged from 18 to 72%. Similarly, Bassett et al. (1970) determined iNUE of ~10 in
their cotton, while Mullins and Burmester (1990) report iNUE of only 5.
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The Pima (Gossypium barbadense L.) crops took up more N than most of the
upland cotton crops, but yielded considerably less. Hence, the iNUE values were
substantially lower for Pima and there needs to be a separate iNUE calibration for this
species. The Pima crops examined in the survey averaged iNUE of 5.7 (yields averaged
1494 kg/ha and N uptake 264 kg N/ha). Little research has been published on iNUE for
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Pima cotton.
Commercial crops – N fertiliser use
Almost 50 kg N/ha was applied in excess of the optimum amount required to the
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commercial cotton crops. Given the average N fertiliser rates for cotton are 200-250 kg
N/ha, the Australian cotton industry could safely reduce N fertiliser inputs by 20-25%
without reducing yield. Thus, NUE can be improved industry-wide by a similar amount.
Low iNUE resulted from excessive N fertiliser application. This, in turn, increases
the risk of elevated greenhouse gas emissions, especially nitrous oxide (Snyder 2007). It
275
is critical to optimise the N fertiliser rate by assessing soil N levels pre-sowing, and
monitoring N levels in the developing crop (Rochester et al 2001a), especially where high
N fertiliser rates have been used in the past. Through better N fertiliser management in
fields with poor iNUE, lint yields may improve while costs are reduced and gross
margins substantially improved.
9
280
Importantly, the economic optimum N fertiliser rate may change over time
because of changing costs of N fertiliser and prices for lint, and with cotton species and
between countries. Clearly, the specified optimum iNUE value (12.4 here) reflects
current N fertiliser prices and returns for produce. The long-term aim to identify and
adopt better N management practices can be quickly assessed using this technology.
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Cotton iNUE can be improved through careful irrigation management, by maintaining
well-aerated and well-structured soil and by matching N fertiliser applications to the
crop’s demand for N.
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Acknowledgements Financial support from the Cotton Research and Development
Corporation and the Cotton Catchment Communities CRC is gratefully acknowledged, as
well as the many cooperating farmers. Emma Brotherton, Sally Ceeney, Kellie Gordon,
Rod Gordon, James Hill, Susan Maas, Julie O’Halloran, Jo Price, Greg Roberts, Doug
Sands and Duncan Weir provided technical assistance with crop sampling and N
295
analyses.
References
Bassett, DM, Anderson WD, Werkhoven CHE (1970) Dry matter production and nutrient uptake
300
in irrigated cotton (Gossypium hirsutum). Agron J 62:299-303
Bauer PJ, Camberto JJ, Roach SH (1993) Cotton yield and fiber quality response to green
manures and nitrogen. Agron J 85:1019-1023
Bronson K (2008) Nitrogen use efficiency of cotton varies with irrigation system. Better Crops
with Plant Food 92:20-22
305
Bronson KF, Booker JD, Bordovsky JP, Keeling JW et al. (2006) Site-specific irrigation and
nitrogen management for cotton production in the Southern High Plains. Agron J 98:212-219
Bronson KF, Onken AB, Keeling JW, Booker JD, Torbet HA (2001) Nitrogen response in cotton
as affected by tillage system and irrigation level. Soil Sci Soc Am J 65:1153-1163
Constable GA, Rochester IJ (1988) Nitrogen application to cotton on clay soil: timing and soil
310
testing. Agron J 80:498-502
10
Janat M (2005) Assessment of Nitrogen Content, Uptake, Partitioning, and Recovery by Cotton
Crop Grown under Surface Irrigation and Drip Fertigation by using Isotopic Technique.
Comm Soil Sci Plant Anal 35:2515-2535 DOI: 10.1081/LCSS-200030355
Janat M (2008) Response of Cotton to Irrigation Methods and Nitrogen Fertilization: Yield
315
Components, Water-Use Efficiency, Nitrogen Uptake, and Recovery. Comm Soil Sci Plant
Anal 39:2282- 2302 DOI: 10.1080/00103620802292293
Millar N, Robertson G, Grace P, Gehl R, Hoben J (2010) Nitrogen fertilizer management for
nitrous oxide (N2O) mitigation in intensive corn (Maize) production: an emissions reduction
protocol for US Midwest agriculture. Mitig Adapt Strateg Glob Change DOI
320
10.1007/s11027-010-9212-7
Mullins and Burmester (1990) Dry matter, Nitrogen, Phosphorus and Potassium
accumulation by four cotton varieties. Agron J 82:729-736
Naklang K, Harnpichitvitaya D., Amarante S. T., Wade L. J, and Haefele S. M. (2006)
Internal efficiency, nutrient uptake, and the relation to field water resources in rainfed
325
lowland rice of northeast Thailand. Plant Soil 286:193-208.
DOI: 10.1007/s11104-
006-9037-z
Ockerby SE, Lyons DJ, Keefer GD, Blamey FPC, Yule DF (1993) Irrigation frequency and
nitrogen fertilizers modify cotton yield at Emerald, Central Queensland. Aust J Agric Res
44:1389-1402
330
Payne RW (1987) Genstat 5 reference manual. Clarendon Press. Oxford
Robinson N, FletcherA, Whan A, Critchley C, von Wiren N, Lakshmanan P, Schmidt S
(2007) Sugarcane genotypes differ in internal nitrogen use efficiency. Func Plant Biol
34(12): 1122–1129 doi:10.1071/FP07183
Rochester IJ (2003). Estimating nitrous oxide emissions from flood-irrigated alkaline grey clays.
335
Aust J Soil Res 41: 197-206
Rochester IJ, Constable GA. (2000) Denitrification and immobilization in flood-irrigated alkaline
grey clays as affected by nitrification inhibitors, wheat straw and soil texture. Aust J Soil Res
38, 633-42
Rochester IJ, Peoples MB, Constable, GA (2001a) Estimation of the N fertilizer requirement of
340
cotton grown after legume crops. Field Crops Res 70:43-53
Rochester IJ, Peoples MB, Hulugalle NR, Gault RR, Constable GA (2001b) Using legumes to
enhance nitrogen fertility and improve soil condition in cotton cropping systems. Field Crops
Res 70:27-41
11
Snyder CS, Bruulsema TW, Jensen TL (2007) Greenhouse gas emissions from cropping systems
345
and the influence of fertilizer management – a literature review. International Plant Nutrition
Institute, Norcross, Georgia, USA
Soil Survey Staff (1996) Keys to Soil taxonomy, 7th edition. Natural Resources Conservation
Service of USDA: Washington DC, 644 pp
Systat Software Systems (2004) SigmaPlot for Windows. Version 6.00.
350
Varco JJ, Spurlock SR, Sanabria-Garro OR (1999) Profitability and nitrogen rate optimization
associated with winter cover management in no-tillage cotton. J Prod Agric 12:91-95
Ward WT, McTainsh G, McGarry D, Smith KJ (1999) ‘The soils of the Agricultural Research
Station at “Myall Vale”, near Narrabri, NSW, with data analysis by fuzzy k-means’. Technical
Report 21/99. (CSIRO Land and Water: Canberra)
355
Witt C, Dobermann A, Abdulrachman S, Gines HC, Guanghuo W, Nagarajan R,
Satawatananont S, Son T, Tan P, Tiem L, Simbahan G, Olk D (1999) Internal
nutrient efficiencies of irrigated lowland rice in tropical and subtropical Asia. Field
Crops Res 63:113-138
Zhang L, Spietz JHJ, Zhang S, Li B, van der Werf W (2008) Nitrogen economy in relay
360
intercropping systems of wheat and cotton. Plant Soil 303:55–68 DOI 10.1007/s11104-0079442-y
Zhang Y, Hu W, Gao Y, Yao Y, Tang M, Hu G (2008) Fertilising irrigated cotton for high yield
and high nitrogen use efficiency. Better Crops with Plant Food 92:6-7
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Caption to figures
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Fig. 1 Lint yield response to N fertiliser applied pre-sowing. The star symbols indicate
the economic optimum N fertiliser rates, which are derived from the relative cost of N
fertiliser and the price received for lint. CC refers to continuous (annual) cotton. Bars
represent the crop x N interaction lsd5% where this was statistically significant
370
Fig. 2 The relationships between crop N uptake and N fertiliser applied in a cropping
systems experiment over four years. The crop N uptake x N application rate interaction
was not statistically significant in any year
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Fig. 3 Crop N use efficiency (iNUE– defined as lint yield / crop N uptake) as related to N
fertiliser application in six years in a cropping systems experiment
Fig. 4 Crop N use efficiency (iNUE) measured over six years in a N fertiliser rate
experiment where the economic optimum N fertiliser rate was identified. The N fertiliser
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excess or deficit was derived as the difference between the economic optimum N
fertiliser and the N fertiliser applied. The dashed lines represent the 95% confidence
limits of the regression line
Fig. 5 The relationships between apparent N fertiliser recovery (% of N applied) and N
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fertiliser applied in the N rate experiment, meaned over five growing seasons (20052009)
Fig. 6. Lint yield and crop N uptake at the N experiments and commercial sites between
2006 and 2009. The Pima crops were not included in the commercial site regression
390
Fig. 7. The relationships between crop N use efficiency (iNUE) and crop N uptake in
cotton determined in N fertiliser experiments and 82 commercial crops over four years
(2005 to 2009). The Pima crops were not included in this figure
13
3000
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Lint yield (kg/ha)
2004
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N applied (kg/ha)
Fig. 1 Lint yield response to N fertiliser applied pre-sowing. The star symbols indicate
the economic optimum N fertiliser rates, which are derived from the relative cost of N
fertiliser and the price received for lint. CC refers to continuous (annual) cotton. Bars
400
represent the crop x N interaction lsd5% where this was statistically significant
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2004
N uptake (kg/ha)
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wheat-fallow
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0
2009
400
300
300
200
200
100
100
0
50
0
0
50
100
150
200
N applied (kg/ha)
0
50
N applied (kg/ha)
Fig. 2. The relationships between crop N uptake and N fertiliser applied in a cropping
405
systems experiment over four years. The crop N uptake x N application rate interaction
was not statistically significant in any year
15
20
20
iNUE (kg/kg)
2004
18
18
16
16
14
14
12
12
10
10
8
8
6
6
4
2005
4
0
50
100
150
200
250
20
0
iNUE (kg/kg)
18
18
16
16
14
14
12
12
10
10
8
8
6
6
4
100
150
200
100
150
200
100
150
200
2007
4
0
50
100
150
200
20
0
50
20
2008
iNUE (kg/kg)
50
20
2006
2009
18
18
16
16
14
14
12
12
10
10
8
8
6
6
4
4
0
50
100
150
N applied (kg/ha)
410
CC
CC-vetch
wheat-fallow
wheat-vetch
faba bean-fallow
200
0
50
N applied (kg/ha)
Fig. 3 Crop N use efficiency (iNUE– defined as lint yield / crop N uptake) as related to N
fertiliser application in six years in a cropping systems experiment
16
20
2004
2005
2006
2007
2008
2009
18
16
iNUE (kg/kg)
14
12
10
8
6
Y = 12.4 - 0.0201X (r2=0.50) ***
4
-200
-150
-100
-50
0
50
100
150
200
N fertiliser deficit (-) or excess (+) (kg N/ha)
415
Fig. 4 Crop N use efficiency (iNUE) measured over six years in a N fertiliser rate
experiment where the economic optimum N fertiliser rate was identified. The N fertiliser
excess or deficit was derived as the difference between the economic optimum N
fertiliser and the N fertiliser applied. The dashed lines represent the 95% confidence
limits of the regression line
420
17
Apparent N fertiliser recovery (%)
80
2
Y = - 93 + 31.2(lnX) (r 0.70) *
60
40
20
CC
CC-vetch
wheat-fallow
wheat-vetch
faba bean-fallow
vetch-fallow
0
-20
0
50
100
150
N applied (kg/ha)
200
0
20
40
60
80
100
120
140
160
Optimum N fertiliser (kg/ha)
Fig. 5 The relationships between apparent N fertiliser recovery (% of N applied) and N
425
fertiliser applied in the N rate experiment, meaned over five growing seasons (20052009)
18
3500
Lint yield (kg/ha)
3000
2500
2000
1500
N experiments
commercial sites
1000
0
100
200
300
400
500
600
Crop N uptake (kg/ha)
430
Fig. 6. Lint yield and crop N uptake at the N experiments and commercial sites between
2006 and 2009. The Pima crops were not included in the commercial site regression
19
22
20
commercial sites
N experiment
18
iNUE (kg/kg)
16
14
12
10
8
6
4
2
0
100
200
300
400
500
600
Crop N uptake (kg/ha)
Fig. 7. The relationships between crop N use efficiency (iNUE) and crop N uptake in
435
cotton determined in N fertiliser experiments and 82 commercial crops over four years
(2005 to 2009). The Pima crops were not included in this figure
20