**4.2.5 Effect of MAA on chemical properties of soil**

The chemical properties of soil at the end of experiment are showed in Table 12. The planting of radish affected these chemical properties of soil clearly. However, there were no differences in pH of soil among treatments planted with radish. On the other hand, either planting treatment or MAA treatment showed effect on nitrate in soil. Compared with the non planting treatment, the treatments of planting showed a decrease of 65~81% and 35~47% of nitrate and available P at 30 days after sowing, respectively. The different rates of decrease were due to the different growth rates led by MAA treatment.


\* The soil used in these experiments was commercialized artificial soil with lower soil density (about 0.4 g cm–3) and higher water–holding capacity. Since determination of soil chemical properties is based on dry weight, the determined values of EC and NO3––N are quite high relative to ordinary soil. However, these are not very higher in soil solution.

Table 12. Chemical properties of soil at the end of pot experiment for radish with high NO3– soil

In conclusion, the results of the present experiment suggest that application of MAA can affect activities of three enzymes of N assimilation (NR, NiR and GS). However, the exact reason for this observation is unknown and further investigation is necessary. Furthermore, the application of MAA can enhance growth, N utilization, and concentrations of proteins and amino acids, and reduce the NO3– content in plant shoots. Considerable increase of N uptake from soil was indicated by the increased 15N recovery by applying MAA compared with the control. These results suggest that the main role of MAA on nitrate uptake and assimilation might be relation with the regulation of NO3 – uptake and assimilation, but not as sources of reduced nitrogen.

#### **5. Pot experiment of radish with low NO3 – soil**
