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Nitrogen accumulation and recovery from Legumes and N Fertilizer in Rice-based cropping systems

M.M. Rahman, Takahisa Amano, H. Inoue and Y. Matsumoto

Laboratory of Plant Production Systems, Graduate School of Agriculture, Kyoto University, Japan.
Corresponding author, M. Motior Rahman mmotiorrahman@yahoo.com

Abstract

This study was established in the long-term experimental plots of Kyoto University Farm at Takatsuki, Japan. Double cropping systems including rice (cv. Hinohikari)-fallow, rice-broad bean (Vicia faba L.), rice-hairy vetch (Vicia villosa Roth), and rice-naked barley (Hordeum vulgare Nudum) and 15N-labeled fertilizers at rates 0, 40, 80 and 120 kg ha-1 were tested. The legumes broad bean and hairy vetch produced 3350 to 10820 kg aboveground biomass ha-1, accumulated 131 to 352 kg N ha-1 of which 41 to 78 % was derived from N2 fixation (% Ndfa). Legume residues significantly increased rice yield and recovery of 15N-labeled fertilizer (% of N applied). Recoveries of 15N-labeled fertilizer were 80, 76, 74 and 72 % in rice-broad bean, rice-hairy vetch, rice-naked barley and rice-fallow systems, respectively.. The greater performance of rice-broad bean systems was reflected in greater N fixation. The effects of combined application of unlabeled legumes and labeled fertilizer on N losses are lower than those obtained with a single application of labeled fertilizer N. Results show that legumes N can supply a substantial proportion of the N requirements of wetland rice.

Media summary

Legume incorporation into rice-based cropping systems contribute increased productivity and maintenance of soil fertility by virtue of their capacity to fix large amounts of atmospheric N.

Key Words

15N-balance, Rice productivity, Soil fertility

Introduction

Rice N requirements are closely related to yield levels, which in turn are sensitive to climate, particularly solar radiation and supply of other nutrients and crop management practices (Kropff et al. 1993). These factors also affect the pattern and quantity of N supplied from indigenous soil resources. Fertilizer-N management strategies must therefore be responsive to potentially large variations in crop N requirements and soil N supply (Cassman et al. 1993). Nitrogen is the most important nutrient in rice systems, accounting for 67% of total fertilizer applications to rice worldwide (Vlek and Byrnes, 1986). Nitrogen uptake patterns in rice over the growing season depend on the availability of soil N and fertilizer N. When fertilizer N is applied preplant, fertilizer N uptake tends to be concentrated toward the beginning of the season, with soil N being the dominant N pool after the fertilizer N supply is depleted or immobilized (Bufogle et al. 1997). The relationship between fertilizer N uptake and total N uptake over the growing season depends on timing of the fertilizer N application (Guindo et al. 1994) and the amount of fertilizer N available (Bufogle et al. 1997). Enhanced N use efficiency for greater biomass production is essential in systems where N availability is often low and limiting for plant growth (Muchow et al. 1993) and development.

Because of intensification of cereal production, double cropping systems need additional amounts of nitrogenous fertilizer to maintain soil fertility. Inorganic N fertilizers are considered expensive by resource-poor Asian farmers. Leguminous crops are sources of N, and may also enhance soil fertility through their effects on soil physico-chemical properties. Legumes have the potential to increase the soil’s N supplying capacity for succeeding crops. Thus, legume-based double cropping such as rice–legume represents a viable alternative for maintaining soil fertility while reducing production costs and protecting the environment by using less chemical fertilizer. Therefore, research was conducted to determine the effect of legume crops and 15N labeled fertilizer on N accumulation, recovery and grain yield of wetland rice.

Materials and Methods

This study was developed in the long-term experimental plots of Kyoto University Farm at Takatsuki, Japan. Treatments were arranged in a split plot design, with double cropping system viz. rice-fallow; rice-broad bean (grain legume); rice-hairy vetch (legume as cover crop) and rice-naked barley (i.e. cereal after cereal) as main plot treatments and 15N-labeled fertilizer as subplot treatments. 15N-labeled fertilizers rates were 0, 40, 80 and 120 kg ha-1. Treatments were replicated three times. No fertilizer was appliedto winter crops. The experiment was initiated on November, 2001 and continued until October 2002. Broad Bean (cv. Minpo), hairy vetch, naked barley (cv. Ichiban Boshi) and rice (cv. Hinohikari) were used. Naked barley was used as reference crop for estimation of biological nitrogen fixation (BNF). Micro-plots were established in each subplot and fertilized with 15N-labeled ammonium sulphate [(NH4)2SO4] at 3 atom % 15N per treatment schedule. To prevent lateral movement of the labeled 15N, wooden barriers surrounding the micro plots were inserted into the soil to a depth of approximately 20 cm. All data were recorded from labeled plant samples. The 15N-labeled plants were analyzed for the concentration of N and atom percent of 15N using a combustion continuous flow isotope ratio mass spectrometer. Plant tissue N concentration was also determined by Kjeldahl digestion. The proportion of N derived from 15N-labeled fertilizer in the plant and soil and percent 15N recovered by the plant and that remaining in soil were calculated with the following equation:

(atom % 15N excessplant) (Nplant)

N recovery of 15N-labeled fertilizer = -------------------------------- X ------------X 100

(atom % 15N excessfertilizer) (Nfertilizer)

Where atom % 15N excessplant = atom % 15N excess (over back ground levels) in the plant, atom % 15N excessfertilizer = atom % 15N excess in the labeled fertilizer N, Nplant = total plant N (kg ha-1), and Nfertilizer = fertilizer N applied (kg ha-1).

Estimates of the proportion of plant N derived from N2 fixation (% Ndfa) were calculated by the N difference procedure by comparing N accumulated in the legume with the nonlegume reference as follows:

100[(Legume N – Reference N)]

% Ndfa= -------------------------------------------

(Legume N)

Results and Discussion

Aboveground biomass yields of hairy vetch and broad bean were 3350 and 10820 kg ha-1, with corresponding N accumulations of 131 to 352 kg ha-1. Broad bean produced significantly higher biomass and N accumulation than hairy vetch. Legumes, however derived N from both soil and atmosphere (BNF). In this study, the plant N derived from N2 fixation (% Ndfa) in broad bean and hairy vetch were 41 to 78 %. Contributions of BNF to the total above ground N accumulation ranged from 54 to 274 kg ha-1 (Table 1). The larger amounts of N2 fixed in broad bean resulted from better growth and higher biomass accumulation. Contributions of BNF to the aboveground N accumulation ranged from 91 to 240 kg ha-1 in legumes (Ladha et al. 1996). Estimates of % Ndfa for other forage legumes and pigeonpea were with in the range of 44 to 95 % (Peoples and Herridge, 1990). In this study legumes play a positive role in the maintenance of soil N fertility, they must leave behind more N from N2 fixation than the amount of soil N they remove (Table 1).

Table 1. The contributions of legume crops grown during winter season in Japan 2002.

Legume crops

Biomass
kg ha-1

N
accumulation
kg ha-1

N fixed by
legumes
kg ha-1

Soil N removal
by legumes
kg ha-1

Plant Ndf
N2 fixation (%)
ND method

Broad bean

10820

352

274

78

78

Hairy vetch

3350

131

54

77

41

Above ground total N accumulations were influenced by cropping system, N fertilizer, and their interaction. Regardless of N fertilizer levels, rice-broad bean systems recorded the highest N accumulation. Rice-hairy vetch systems with N 120 produced identical N accumulation. Rice-hairy vetch systems using N 40, 80 and rice-naked barley with N 120 and rice-fallow systems with N 120 produced identical and moderate N accumulation. The smallest quantities of N accumulation were obtained from the rice-fallow and rice-naked barley systems all without N (Table 2). In this study, the increased plant N following broad bean and hairy vetch incorporation indicates an increase in plant N accumulation.

The plant N recovery of 15N-labeled fertilizer (% of N applied) values measured in this study were in the range of 41 to 56%. The highest plant N recovery from 15N-labeled fertilizer was achieved in the rice-fallow systems. Rice-broad bean systems with N 40 and hairy vetch systems with N 80 and N 120 achieved moderate plant N recovery from 15N-labeled fertilizer. Minimum plant N recoveries of 15N-labeled fertilizer were obtained from the rice-naked barley and rice-hairy vetch systems with N 120 (Table 2). The rice recovered 65 to 94 % from applied 15N-labeled fertilizer and legume residue incorporation. At the same labeled 15N rate 65 to 78 % was recovered by rice-fallow systems. Rice-broad bean systems recovered the highest total N recovery (68 to 94 %). Recovery was poor when rice crop received both unlabeled legume residue and labeled fertilizer (> 40 kg ha-1) regardless of legumes. In rice-fallow systems plant N recovery was higher from 15N-labeled fertilizer while soil N recovery was poor compared to rice-broad bean and rice-hairy vetch systems (Table 2). A combined application of non labeled legume with 40 kg labeled N fertilizer resulted in significantly higher recoveries of N in the soil than that of labeled N fertilizer applied alone at the same N rates. Thus, based on total 15N balances, N losses (N unaccounted for) from the soil-plant system in rice-fallow systems were appreciably higher than those in rice-broad bean and rice-hairy vetch systems. Therefore, recovery of 15N-labeled fertilizer of rice-broad bean and rice-hairy vetch systems indicate a positive contribution of biological nitrogen fixation on rice production without deteriorating soil fertility.

Table 2. N accumulation, recovery determined by 15N dilution method and grain yield of rice as affected by N fertilizer and cropping systems in Japan 2002.

Cropping systems

N fertilizer
kg ha-1

N
accumulation
kg ha-1

Recovery of 15N-labeled fertilizer
(% of N applied)

Grain yield
kg ha-1

Soil

Plant

Total

 

Rice-broad bean

0

194

-

-

-

7280

40

198

46

48

94

6920

80

200

32

45

77

6880

120

204

23

45

68

6910

Rice-hairy vetch

0

129

-

-

-

5230

40

166

35

46

81

6600

80

178

33

47

80

6880

120

187

24

42

68

6500

Rice–naked barley

0

109

-

-

-

5420

40

135

35

41

76

6180

80

149

34

43

77

6520

120

163

26

44

70

6530

Rice-fallow

0

92

-

-

-

4670

40

123

22

43

65

5940

80

144

20

54

74

6790

120

176

22

56

78

7170

CS - LSD (0.01)

 

16

     

967

N - LSD (0.01)

 

11

     

630

CS X N–LSD (0.01)

 

22

     

1260

The recovery of 15N-labeled fertilizer (% of N applied) from plant was greater in rice-fallow systems rather than incorporation of legumes over the growing season. Diekmann et al., (1993) found similar evidence when green manure was incorporated in rice. The substantial amount of N unaccounted for from labeled fertilizer is probably due to losses by ammonia volatilization, and denitrification from the flood water occurring during the first few days after fertilizer application as reported by Vlek and Byrnes (1986). The total recoveries of 15N-labeled fertilizer found in the present study support the results of John et al. 1989; Diekmann et al. 1993). Incorporation of legumes in rice-broad bean and rice-hairy vetch systems compared with rice-naked barley and rice-fallow systems increased the soil N availability through an increase in net N mineralization and corresponding addition of fertilizer 15N. The increase in fertilizer N uptake was associated with an increase in soil N uptake when broad bean or hairy vetch was incorporated (Table 2). Therefore the rate of fertilizer N application can be reduced when broad bean and hairy vetch are incorporated.

Grain yield of rice was affected significantly by cropping systems, N fertilizer and their interaction. Regardless of N fertilizer levels, rice-broad bean systems produced higher yield which was similar to rice-naked barley with N 80 and N 120, rice-hairy vetch with N 40, N 80 and N 120, and rice-fallow with N 120. Minimum yield was obtained by rice-fallow, rice-hairy vetch, and rice-naked barley systems without N. Rice-hairy vetch systems with N 40, N 80 and N 120 gave similar yields. Rice-naked barley systems with N 80 and N 120 showed similar yield. No appreciable difference was observed on rice-fallow systems with N 80 and N 120 (Table 2)

Conclusion

Legume residues incorporated into the soil supplied N to wetland rice and produced benefits comparable with that of 40 to 80 kg fertilizer N. Such winter legumes that improve annual productivity of rice might be attractive to farmers, who are generally resource-poor farmers, since the benefit of a steady increase in soil N and soil fertility is clear. Thus, legumes have the potential to substitute for or supplement chemical/inorganic fertilizer.

References

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Guindo D, Norman RJ and Wells BR (1994). Accumulation of fertilizer nitrogen-15 by rice at different stages of development. Soil Science Society of America Journal 58, 410-415.

John PS, Buresh RJ, Pandey RK, Prasad R and Chua TT (1989). Nitrogen-15 balances for urea and neem-coated urea applied to lowland rice following two cowpea cropping systems. Plant and Soil 120, 133-241.

Kropff M.J, Cassman KG, van Larr HH and Peng S (1993) Nitrogen and yield potential of irrigated rice. Plant and Soil 155/165, 391-394.

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