**6.2.3 Effect of AAF on contents of N and P**

The data in Table 20 showed that N contents of the plants were affected by using amino acid fertilizer. The NO3 – content of radish was decreased by application of AAF (*P* < 0.05) compared with the reference treatment. Among the treatments, A1 gave the best result in reducing the nitrate to 1.16 mg g–1 (FW), with a decrease of 24% in relation to the highest NO3– content found in A0. This result agrees with the interpretation that amino acid can negatively regulate nitrate content in higher plants (Gunes et al., 1994, 1996; Chen and Gao, 2002; Wang et al., 2004). But this interpretation was not supported in all cases. It was observed that the mixed amino acids increased NO3 – content slightly in radish when the plants growing in nutrient solution. The contradiction may reside in amino acids treatment method. It was demonstrated in other studies that amino acid pretreatment decreased NO3– accumulation slightly, but Gln and Asn led to NO3– concentration increase in barley roots when they were used together with nitrate (Aslam et al., 2001).

With respect to the main products of NO3– assimilation, amino acids and proteins (Table 20), the plants in treatment A1 gave the highest contents of these compounds (*P* < 0.01). In the A1 treatment, high activities of main enzymes of NO3– assimilation could explain the predominance of these nitrogenous compounds in radish. Under treatments of A2 and A3, the increases of amino acids and proteins derived from the direct uptake of amino acids from AAF.


Values are means ± SD (n=3). Analysis of variance (ANOVA) was employed followed by Duncan's new multi range test. Values with similar superscripts are not significantly different (P>0.05)

Table 20. Effect of amino acid fertilizer on contents of nitrogen and phosphorus in radish 23 day after sowing

The total N content of the plants was also affected significantly by the use of AAF (*P* < 0.01). Treatments of A1, A2 and A3 showed to increase the total N to 32%, 21% and 15% relative to the control, respectively. These increases were due to the positive adjusting of AAF on uptake and assimilation of N, and attributing to the increases of N utilization and net N uptake. The P content of radish was not affected significantly by the application of AAF (Table 20).

These results are in agreement with those observed by Chen et al. (1997), who reported that application of amino acids led to positive effects on cabbage growth. However, among the treatments of AAF, the growth responses were decreased by increasing the application rate of AAF. This may probably be related to the feed–back inhibition of high rate application of

The data in Table 20 showed that N contents of the plants were affected by using amino acid

compared with the reference treatment. Among the treatments, A1 gave the best result in reducing the nitrate to 1.16 mg g–1 (FW), with a decrease of 24% in relation to the highest NO3– content found in A0. This result agrees with the interpretation that amino acid can negatively regulate nitrate content in higher plants (Gunes et al., 1994, 1996; Chen and Gao, 2002; Wang et al., 2004). But this interpretation was not supported in all cases. It was observed that the mixed amino acids increased NO3– content slightly in radish when the plants growing in nutrient solution. The contradiction may reside in amino acids treatment method. It was demonstrated in other studies that amino acid pretreatment decreased NO3– accumulation slightly, but Gln and Asn led to NO3– concentration increase in barley roots

the plants in treatment A1 gave the highest contents of these compounds (*P* < 0.01). In the A1 treatment, high activities of main enzymes of NO3– assimilation could explain the predominance of these nitrogenous compounds in radish. Under treatments of A2 and A3, the increases of amino acids and proteins derived from the direct uptake of amino acids

A0 1.53 ± 0.11 a 1.29 ± 0.02 b 1.28 ± 0.08 c 27.2 ± 1.6 c 6.8 ± 0.3 a A1 1.16 ± 0.17 b 1.38 ± 0.02 a 1.98 ± 0.16 a 35.9 ± 1.6 a 7.1 ± 0.4 a A2 1.32 ± 0.20 ab 1.33 ± 0.02 ab 1.74 ± 0.06 b 33.0 ± 0.9 ab 6.8 ± 0.4 a A3 1.48 ± 0.08 a 1.32 ± 0.04 ab 1.70 ± 0.09 b 31.2 ± 1.2 bc 6.9 ± 0.5 a Values are means ± SD (n=3). Analysis of variance (ANOVA) was employed followed by Duncan's new

Table 20. Effect of amino acid fertilizer on contents of nitrogen and phosphorus in radish 23

The total N content of the plants was also affected significantly by the use of AAF (*P* < 0.01). Treatments of A1, A2 and A3 showed to increase the total N to 32%, 21% and 15% relative to the control, respectively. These increases were due to the positive adjusting of AAF on uptake and assimilation of N, and attributing to the increases of N utilization and net N uptake. The P

multi range test. Values with similar superscripts are not significantly different (P>0.05)

content of radish was not affected significantly by the application of AAF (Table 20).

**NO3– Amino acids Proteins Total-N Total-P** 

**(mg g–1 FW) (mg g–1 DW)** 

– content of radish was decreased by application of AAF (*P* < 0.05)

– assimilation, amino acids and proteins (Table 20),

amino acids.

from AAF.

**Treatments** 

day after sowing

fertilizer. The NO3

**6.2.3 Effect of AAF on contents of N and P** 

With respect to the main products of NO3

when they were used together with nitrate (Aslam et al., 2001).

### **6.2.4 Effect of AAF on chemical properties of soil**

The chemical properties of soil in middle growth period and at the end of experiment were showed in Table 21 and Table 22. The planting of radish affected total N of soil clearly, except at 35 days after sowing, with a fall of 10% compared with non planting treatment. However, there were no differences in total N of soil among treatments planted with radish. On the other hand, either planting treatment or AAF treatment showed effect on nitrate in soil.


Table 21. Chemical properties of soil in the middle of growth period (25 day after sowing) for radish

In the soil of non planting, nitrate was decreased by leaching and runoff by rain. Compared with the non planting treatment, the treatments of planting showed 20~30% decrease at 25 days after sowing and 23~42% decrease at 35 days after sowing in the nitrate content of soil. Although with the lowest net N uptake, the lowest concentration of nitrate in soil was found in A0 treatment both at two sampling times. This was due to the fact that the vegetation covers of AAF treatments were higher than treatment of A0, and could effectively prevent nitrate of soil from leaching or runoff. The planting treatments showed lower values of EC than non planting treatment, but all were in the range of general soil. There were no significant differences among all treatments in pH and organic matter of soil. Moreover, very small differences were observed in available P due to different growth rate of the plants.


Table 22. Chemical properties of soil at the end of field experiment (35 day after sowing) for radish

Effect of Mixed Amino Acids on Crop Growth 151

With respect to red pepper which was planted in high NO3– soil, foliar MAA sprays increased activities of the three enzymes, while reduced NO3– content, concentrations of proteins and amino acids, total N and N utilization. Partially different results were found in red pepper which was planted in low NO3– soil, including decreased activities of NiR and GS and increased of NO3– content in plant shoots by the application of MAA. The reason for

planting, and avoid N losses through leaching and runoff due to increases of N utilization and vegetation cover. In addition, the application of AAF enhanced activities of three enzymes,

plant shoots. Similarly, for red pepper, the use of AAF led to increase of N utilization. However, decrease of total N content in red pepper plants was found in AAF treatments.

These results of 15N labeled experiments and field experiments suggest that the main role of amino acids on nitrate uptake and assimilation might be relation with the regulation of NO3

uptake and assimilation, but not as sources of reduced nitrogen. In pot experiments, it was indicated that the N utilization of plants was depended on soil NO3– uptake which was regulated by application of MAA. In field experiment of radish, the increase of N utilization is about 200 times more than N supplied by applying AAF, indicating application of AAF

of plant growth. For leaf radish, response of enzymes activity and yield was not affected by the stage of growth, while N accumulation (total N content) was more sensitive to applied amino acids in vegetative stage than that of young stage. With regard to red pepper, effects of amino acids on enzymes activity and N content in different growth stage were quite similar, while

A better understanding of effect of amino acid on process of NO3– uptake and assimilation will undoubtedly help in developing an approach to improve the management of fertilizer nitrogen and to prevent N loss through leaching or runoff. In the further study, more detailed researches should be carried out to investigate the precise manner by which MAA

Andrews, M. 1986. The partitioning of nitrate assimilation between root and shoot of higher

Ashley, D. A., W. A. Jackson, and R. Volk. 1975. Nitrate uptake and assimilation by wheat seedlings during initial exposure to nitrate. Plant Physiol. 55, 1102–1106. Aslam, M, R. L. Travis, and D. W. Rains. 1996. Evidence for substrate induction of a nitrate

Aslam, M., R. L. Travis, and D. W. Rains. 2001. Differential effect of amino acids on nitrate uptake and reduction systems in barley roots. Plant Sci*.* 160, 219–228.

– uptake and assimilation. The researches will focus on the effect of MAA on

– uptake and assimilation was also influenced by stage

– removal rate by

– content in

–

In field experiment of radish, the foliar sprays of AAF increased NO3

biomass production, and concentrations of proteins and amino acids, reduced NO3

could enhance the ability of uptake and assimilation of inorganic N by plants.

growth (dry biomass) showed to be increased significantly in vegetative stage.

efflux system in barley roots. Plant Physiol. 112, 1167–1175.

NR gene expression and relation between GDH and GS.

plants. Plant Cell Environ. 9, 511–519.

these differences is the same to that of radish.

Finally, the effect of amino acids on NO3

influences NO3

**8. References** 


Table 23. Effect of amino acid fertilizer on nitrate removal from the soil

The data of NO3– removal are showed in Table 23. Even though the highest NO3– removal was found in treatment A0, the most removed NO3 – was leached (73.7%) and would lead to pollution for groundwater. The application of AAF can enhance NO3– removal rate by planting, and avoid N losses through leaching and runoff due to increases of N utilization (Table 18) and vegetation cover (Table 19).

In conclusion, the results of the present experiment suggest that application of amino acid fertilizer can affect activities of three enzymes of N assimilation (NR, NiR and GS) and increase the growth and N assimilation in radish. However, the exact reason for this observation is not known and requires further investigation. The planting of radish proves very effective for nitrate removal in soil by its fast growth and very high biomass production (345.7~404.4 g DW m–2) and N utilization (9.33~14.48 g m–2) in short time (only 35 days in our experiment). Furthermore, the application of amino acid fertilizer can enhance biomass production, N utilization, and concentrations of proteins and amino acids, and it can reduce N losses through leaching and runoff.
