Grain mineral contents in southeastern Australia

An understanding of the nutrient concentrations of grains such as wheat is important in developing nutrient budgets, and they can also be used diagnostically to assess particular nutrient deficiencies or toxicities for the crop from which the grain was derived. There have been several studies undertaken on grain nutrient densities in Australia and much of that information has been collated and published in “Plant Analysis – An Interpretation Manual” (Reuter and Robinson 2006). The values published there are considered as benchmarks and were used in developing regional nutrient budgets as part of the National Land and Water Resources Audit (2001) (Table 1).
Table 1 Macronutrient wheat grain concentrations (kg/t) from Reuter as used in the National Land and Water Resources Audit (2001). * N values were estimated on a regional basis and values are presented as both 11% moisture content and on a dry grain basis.

Species	N	P	K	S	Ca	Mg
Wheat (11%)	*	2.6	3.6	1.4	0.38	1.2
Wheat (0%)	*	2.9	4.0	1.6	0.43	1.4

However, regional, cultivar and annual changes in grain nutrient concentrations give a degree of uncertainty to possible long term nutrient balances calculated as the product of grain yield and nutrient density. This report aims to report values for nutrient densities for wheat, particularly in south-eastern Australia so that there can be confidence in the values used in nutrient budgets. It also provides a data set which can be used to test the amount of genetic, temporal and spatial variability in grain nutrient densities.

Materials and Methods
Wheat grain samples were obtained from site managers involved in the National Variety Testing (NVT) system which operates across the Australian grain production region to compare crop cultivars and then to provide that information to growers. A single sample of each of two varieties, Yitpi and Gladius, were collected from each site in southeastern Australia where they were grown in 2009. There were eight sites from New South Wales, 21 sites from South Australia and 17 from Victoria and these were in 12 agroecological regions across southeastern Australia. Samples from 23 sites from South Australian in 2008 were also provided and these were also included. So, a total of 70 sites across two years were analysed for grain nutrient concentration.
The NVT sites are managed using commercial best practice which includes regional fertilizer products and rates, as well as normal establishment and crop protection operations. Details of these practices are available as well as soil tests for most sites. All sites had top 10 cm Colwell P, as well as pH (water and CaCl₂), exchangeable cations (Ca, Mg, Na, K), EC and organic carbon values reported, as well as exchangeable cations in the subsoil (10-60 cm). Sulphur levels in the top 10 cm were reported for 24 sites and Zinc for 12 sites.
Grain yield and grain protein (N) content were taken from the NVT reports published in 2008 and 2009 along with soil test values. Grain protein content was assessed using NIR calibrated against the Dumas method (AACC 46-30) and grain protein is expressed as %N x 5.7 on a fixed moisture basis (11% wheat). These values were then converted back to a dry grain (0% moisture) basis.
Appendix Tables 1, 2 and 3 give a list of the sites, soil test values and their locations on Figures 1, 2 or 3.
Between 18 and 30 grains of each line (approx. 0.8 g) from each site were randomly selected from the harvested grain, dried, weighed and processed for nutrient analysis by ICP-OES. Grain was digested with 11 ml of nitric acid (HNO₃)/perchloric acid (HCIO₄) mixture (10:1 v/v), boiled down to approx. 1 ml of HCIO₄ and made to 25 ml final volume using de-ionised water. This final solution was then analysed for nutrients on Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES; ARL 3580 B, Appl. Res Lab. SA, Ecublens, Switzerland) and results are reported on a dry grain basis). Analytes reported from this analysis are Al, B, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Se, Ti and Zn.
Because the data set developed was not balanced, nor were there replicated samples for each cultivar from each site in each year, the data were assessed using a one-way analysis of variance to compare nutrient densities using either state (Victoria, New South Wales, South Australia), region (70 site years), varieties (Gladius and Yitpi). In addition, the data set from South Australia was used to compare annual nutrient densities in 2008 and 2009.

Results
Table 2 provides a summary of the nutrient densities for the 13 nutrients assessed, giving the mean and standard deviation for each region and then aggregated data for states and then for the complete data set. The values are presented on a dry weight basis except for N, which is given on 11% moisture content. Levels of other analytes assessed under ICPOES were generally low, at the lower limits of detection for that instrument. These values were Ni<0.4 mg/kg, Co<0.4 mg/kg, Mo<0.4 mg/kg, Se<4.0 mg/kg, Pb<1 mg/kg and Cd<0.1 mg/kg. In addition, Ti and Cr were reported to determine in the samples may have been contaminated by soils or during grinding. Three samples were found with high Ti and Cr levels and these were not further reported.
The values reported show considerable regional differences, with N, P, K and S showing coefficients of variation (CV) of 18%, 20%, 14% and 13% (see Appendix Table 4) respectively although within each region, the CV’s for N, P, K and S were usually less than 5%. There were some important exceptions to this, with P in southern New South Wales and P, K and S CV’s for the North East and North Central regions of Victoria, although these values were derived from the smallest subsets within the data.
Figures 1 and 2 show the frequency of grain N from the data set, and Figure 2 shows P, K and S contents and this reflects the distributions and CV’s for these nutrients discussed previously. The distribution of S contents is relatively consistent when compared to the three other nutrients. Table 2 gives the P value of the F statistic from the one-way analyses of variance for each of the main factors tested. shows that nutrient concentration for the macronutrients did not differ among the three sets of state means for N, P, K, S and Ca, although there were significant regional differences for these nutrients. N, P and S contents were not different between the two cultivars compared. Grain micronutrient concentration did differ between states and regions, except for state level Zn and Al contents.
Table 2. Mean and standard deviations of macronutrients (N, P, K,S, Mg, Ca and Na) and micronutrients (Fe, Mn, B, Cu, Zn and Al) for wheat samples from the 2008 and 2009 NVT sites for Yitpi and Gladius. All values are for dry grain (0% moisture content).

Sites/Years

Number of values

Region

N %

P mg/kg

K mg/kg

S mg/kg

Ca mg/kg

Mg mg/kg

Na mg/kg

Fe mg/kg

Mn mg/kg

B mg/kg

Cu mg/kg

Zn mg/kg

Al mg/kg

NSW

4

8

South East

3.13 ±0.15

3613 ±202

5075 ±217

1963 ±70

466 ±29

1261 ±37

7.1 ±6.0

42.1 ±2.2

57.6 ±3.6

1.6 ±0.3

3.9 ±0.4

23.0 ±2.4

3.5 ±1.3

4

8

South West

2.52 ±0.15

2678 ±202

4238 ±217

1709 ±70

408 ±29

1173 ±37

7.6 ±6.0

39.5 ±2.2

54.4 ±3.6

1.7 ±0.3

4.1 ±0.4

23.5 ±2.4

5.1 ±1.3

16

Mean

2.83 ±0.12

3145 ±168

4656 ±161

1836 ±55

437 ±22

1217 ±30

7.3 ±4.6

40.8 ±1.7

56.0 ±3.3

1.7 ±0.3

4.0 ±0.3

23.3 ±1.8

4.3 ±1.0

SA

6

12

Lower EP

2.17 ±0.12

3075 ±165

4533 ±177

1492 ±57

343 ±24

1223 ±30

38.7 ±4.9

30.3 ±1.8

25.3 ±3.0

2.3 ±0.3

4.4 ±0.3

18.7 ±2.0

1.6 ±1.1

7

14

Mid North

2.67 ±0.11

3900 ±153

4686 ±164

1803 ±53

460 ±22

1359 ±28

21.0 ±4.5

39.1 ±1.6

51.1 ±2.7

1.3 ±0.3

5.6 ±0.3

25.4 ±1.8

3.1 ±1.0

9

18

Murray Mallee

2.79 ±0.10

3467 ±135

4533 ±145

1789 ±47

424 ±19

1349 ±25

23.7 ±4.0

40.1 ±1.4

38.9 ±2.4

1.9 ±0.2

5.2 ±0.2

19.2 ±1.6

7.6 ±0.9

5

10

South East

2.45 ±0.12

3620 ±181

4870 ±194

1780 ±63

488 ±26

1295 ±33

29.3 ±5.3

35.9 ±1.9

26.8 ±3.2

1.5 ±0.3

3.5 ±0.3

24.5 ±2.2

1.1 ±1.2

12

24

Upper EP

2.78 ±0.08

3117 ±117

4758 ±125

1778 ±41

419 ±17

1237 ±22

47.6 ±3.4

35.9 ±1.2

49.3 ±2.1

2.4 ±0.2

4.9 ±0.2

26.0 ±1.4

5.5 ±0.8

6

12

Yorke Penn.

2.40 ±0.12

3083 ±165

4433 ±177

1650 ±57

411 ±24

1202 ±30

35.0 ±4.9

31.3 ±1.8

41.8 ±3.0

1.8 ±0.3

5.6 ±0.3

22.2 ±2.0

3.0 ±1.1

90

Mean

2.63 ±0.04

3354 ±71

4641 ±68

1729 ±23

423 ±9

1278 ±13

33.8 ±1.9

35.9 ±0.7

40.8 ±1.4

1.9 ±0.1

4.9 ±0.1

22.9 ±0.8

4.2 ±0.4

Vic

8

16

Mallee

2.42 ±0.10

3088 ±143

4256 ±154

1662 ±50

396 ±21

1291 ±26

12.5 ±4.2

34.9 ±1.5

36.8 ±2.6

3.4 ±0.2

5.1 ±0.3

18.9 ±1.7

4.5 ±1.0

2

4

North Central

2.42 ±0.21

2900 ±286

4250 ±307

1793 ±99

348 ±41

1293 ±53

9.6 ±8.4

41.0 ±3.0

55.8 ±5.1

1.7 ±0.5

4.7 ±0.5

25.5 ±3.4

3.4 ±1.9

2

4

North East

2.75 ±0.21

2950 ±286

4275 ±307

1933 ±99

380 ±41

1230 ±53

6.3 ±8.4

44.3 ±3.0

53.3 ±5.1

1.4 ±0.5

5.1 ±0.5

28.8 ±3.4

5.1 ±1.9

5

10

Wimmera

2.60 ±0.13

4110 ±181

5040 ±194

1733 ±63

470 ±26

1424 ±33

21.7 ±5.3

36.2 ±1.9

49.2 ±3.2

4.6 ±0.3

4.8 ±0.3

27.3 ±2.2

4.6 ±1.2

34

Mean

2.51 ±0.08

3350 ±115

4488 ±111

1730 ±38

410 ±15

1323 ±20

14.2 ±3.2

37.1 ±1.2

44.6 ±2.2

3.3 ±0.2

4.9 ±0.2

23.3 ±1.3

4.5 ±0.7

Total

140

Mean

2.62 ±0.46

3329 ±671

4606 ±645

1742 ±220

421 ±89

1282 ±122

26.0 ±21.2

36.8 ±6.9

43.5 ±13.8

2.2 ±1.3

4.8 ±1.2

23.0 ±7.3

4.3 ±4.1

The data set analysed does have a strong weighting to data from South Australia so the “national” mean values presented in Table 2 are not indicative of the values across each agroecological zone. For all the nutrients tested, regional values differed significantly (Table 3), suggesting that there is no universal value that can be used for a nutrient budget at regional or sub-regional (ie farm) level, rather that values should be based on data from that region. Cultivar and annual differences were not significant for P, S, Mg or Na so that a single regional value would seem appropriate for these nutrients. If the level of interest is in a national scale measure of nutrient balance, then the values in table 2 would appear to be appropriate as there is no significant difference between the values at the state levels for the macronutrients.

Table 3. P values for the F test in one-way analyses of variance for states, regions or cultivars from the NVT data set analyzed. Highlighted cells show a significant effect of the factor on a particular wheat grain nutrient concentration.

	N	P	K	S	Ca	Mg	Na
States	0.071	0.509	0.476	0.191	0.597	0.014	0.000
Regions	0.000	0.000	0.014	0.000	0.002	0.000	0.000
Culitvars	0.998	0.017	0.001	0.236	0.000	0.090	0.872
Year (SA only)	0.000	0.864	0.001	0.116	0.000	0.000	0.382
	Fe	Mn	B	Cu	Zn	Al
States	0.027	0.000	0.000	0.011	0.950	0.941
Regions	0.000	0.000	0.000	0.000	0.003	0.001
Cultivars	0.695	0.568	0.661	0.565	0.001	0.007
Year (SA only)	0.700	0.007	0.000	0.041	0.049	0.651

Conclusions
Regional values for grain nutrient contents may be more appropriate when undertaking nutrient budgets, especially for the macro-nutrients which show large regional differences.