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Relationships between yield, protein and mineral concentrations in brown rice

G.D. Batten1,2 ,Y. Hamada1,3 and L.C. Campbell1,4

1CRC for Sustainable Rice Production, Yanco, NSW 2703, Australia.
2
Faculty of Agricultural and Veterinary Sciences, Charles Sturt University, NSW 2650, Australia.
3
Aichi-ken Agricultural Research Centre, Nagakute, Aichi 480-1193, Japan.
4
Faculty of Agriculture, Food and Natural Resources, The University of Sydney, NSW 2006, Australia.

Introduction

Rice grain when harvested is primarily composed of starch with much smaller amounts of protein and minerals. The factors which influence the minerals in the grain are poorly understood. In wheat, Marr and Batten (1993) suggested that P deficiency is associated with high grain %N but lower concentrations of P, K and Mg. Here we report changes in rice grain mineral composition.

This study examined yields, grain protein and mineral nutrients in rice grown in plots which had received various combinations of no N, no P, no K, no lime or no compost for 75 years.

Methods and materials

For the past 75 years, rice (Oryza sativa cv Nippon-bare) has been grown in the same plots (Figure 1). The soil was a fine textured yellow clay at the Anio Research and Extension Station, Aichi-ken Agricultural Research Centre, Japan (latitude 3458’N). Prior to cultivation for sowing, one of nine treatments was applied annually: no fertilizer, lime only, no nitrogen, no phosphorus, no potassium, no lime, N+P+K+lime, compost at 7.5 t/ha and compost at 22.5 t/ha. Rates of application were: ammonium sulphate applied twice at 285kg/ha, superphosphate (490 kg/ha), potassium chloride (90 kg/ha), lime (1.1 t/ha). Compost treatments also had applications of N+P+K+lime. (Figure 1.)

Figure 1. Rice plots at the Aichi-ken Agricultural Research Centre which had received annual applications of fertilizer, compost or neither for 75 years.

At maturity, grain was harvested. Samples of grain were analysed for nitrogen by Dumas combustion and mineral nutrients were determined using ICPAES after nitric acid digestion.

Results

Yield

The average yield of paddy rice, averaged over two years (years 74 and 75) varied from 1.55 to 7.27 t/ha for the lime only and the all nutrients plus 7.5 t/ha compost respectively. Nil phosphate treatments averaged 1.86 t/ha. The concentrations of nitrogen and minerals are shown in Table 1.

Table 1. Grain nitrogen (N%) and mineral concentrations (mg/kg) in brown rice –averaged over 2 seasons.

Treatment

N

S

P

K

Ca

Mg

Mn

Na

Fe

Zn

No fertilizer

1.15

915

3400

2700

102

1335

22.0

17.4

13.2

30.0

Lime only

1.08

915

3600

2800

102

1425

19.6

18.1

12.7

30.5

No nitrogen

1.13

955

3450

2850

124

1315

19.6

17.6

12.6

29.0

No phosphorus

1.67

1350

1630

1755

100

715

18.2

16.2

14.4

30.5

No potassium

1.30

1100

3300

2650

156

1265

22.0

38.0

12.4

27.5

No lime

1.33

1140

3200

2700

135

1140

18.7

14.2

12.3

25.0

N+P+K+lime

1.17

990

3200

2750

134

1120

20.5

15.0

11.7

25.0

Compost (7.5 t/ha)

1.32

990

3250

2800

116

1105

20.1

14.2

11.8

23.0

Compost (22.5 t/ha)

1.65

1200

3200

2900

117

1055

24.0

13.7

12.8

21.5

Grain N%

Low grain N% values were associated with the nil fertilizer, no N and lime only plots. Compost improved grain nitrogen. Thus grain protein of these rices were between 6 and 9%. On the other hand, phosphate deficiency markedly increased grain N%.

Minerals

Grain from the no P plots had P, K and Mg concentrations which were reduced to 50, 63 and 65% respectively of the concentrations in grain from the plots which received all nutrients except compost.

Correlation matrix

Grain yield correlated strongly and negatively with Zn (Table 2), perhaps due to the continuous liming. Phosphorus was highly correlated positively with K and Mg whereas a negative relationship occurred with P and N.

Table 2. Correlation coefficients between nitrogen, minerals and yield. Values in bold are for p<0.05

 

Yield

N

S

P

K

Ca

Mg

Mn

Na

Fe

Zn

Yield

1.00

                   

N

0.26

1.00

                 

S

0.13

0.93

1.00

               

P

0.19

-0.65

-0.75

1.00

             

K

0.39

-0.57

-0.71

0.91

1.00

           

Ca

0.52

0.00

0.13

0.27

0.20

1.00

         

Mg

-0.19

-0.71

-0.75

0.91

0.70

0.18

1.00

       

Mn

0.29

0.31

0.11

0.31

0.26

0.26

0.27

1.00

     

Na

-0.09

-0.22

-0.09

0.11

0.12

0.41

0.21

0.03

1.00

   

Fe

-0.56

0.30

0.32

-0.57

-0.48

-0.57

-0.37

-0.09

0.07

1.00

 

Zn

-0.91

-0.42

-0.25

-0.17

-0.30

-0.42

0.19

-0.39

0.28

0.60

1.00

This study provides evidence that P deficiency in rice has a similar effect on grain mineral ratios as was reported for wheat by Batten and Marr (1993); namely lower concentrations of P, K and Mg but higher concentrations of grain N%.

Conclusions

This unique opportunity has provided data which supports the strong influence of P on grain N, K and Mg as well as yield. Much of the P in the grain is associated with phytate (data not presented). Avoiding P deficiency is significant for the management of crops which provide food and minerals for human or animal consumption.

Acknowledgements

The authors wish to the CRC for Sustainable Rice Production for financial assistance and Teresa Fowles, Waite Analytical Services for ICP analysis.

References

Batten, G.D. and Marr, K.M. (1993). Does phosphorus determine the concentration of nitrogen, sulphur, calcium, potassium or magnesium in wheat grain? Proceedings of the 43rd Australian Cereal Chemistry Conference, Coogee Beach, Australia.

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