**4.2.4 Recovered fertilizer nitrogen**

It has become evident that amino acids are a principal source of nitrogen for certain plants, such as mycorrihizal, heathland species (Read, 1993), non–mycorrihizal plants from arctic and alpine ecosystems (Chapin et al., 1993; Kielland, 1994) and boreal forest plants (Näsholm et al., 1998; Persson and Näsholm, 2001). These systems are similar in that N mineralization rates are heavily constrained by climate, and plant N demands cannot be met through the uptake of inorganic ions (Raab et al., 1999). Based on these researches, the amino acids were used to partially replace NO3– in hydroponic experiment or spray to leaves in many plants. In most case, the application of amino acids led to the decrease of nitrate content and total nitrogen content in lettuce, Chinese cabbage, onion, pakchoi or other leafy crops (Chen and Gao, 2002; Gunes et al., 1994, 1996; Wang et al., 2004). It had been suggested that plants probably preferred amino acids as sources of reduced nitrogen, and nitrate uptake was inhibited by amino acids.

In this study, the high NdfF was found in MAA treatments (Table 11), indicating that applied MAA did not act as a source of nitrogen for plants. On the contrary, plants had taken up more NO3 ––N from soil due to the regulation of MAA on NO3 – uptake and assimilation. The results for the possible regulation of NO3 – uptake and assimilation by amino acids for higher plants are contradictory. Many authors agreed that amino acids can down regulate the NO3 – uptake and assimilation in higher plants (Aslam et al., 2001; Ivashikian and Sokolov, 1997; Oaks et al., 1979; Radin, 1975, 1977; Sivasankar et al., 1997). But Aslam et al. (2001) reported that inhibition did not occur when the concentration of NO3 – in the external solutions had been increased to 10 mM. This result is consistent with the other research, which indicated that radish treated with mixed amino acids containing 5.0 mM NO3 – in growth medium show significantly increased the NO3 – uptake. In this experiment, the positive effect on NO3 – uptake by applying MAA was due to very high NO3 – content in soil (1906 mg Kg–1).


NdfF; the percentage of N derived from fertilizer, QNdfF ; the quantity of N derived from fertilizer, NdfFRec ; the fertilizer-N recovery

Data are means ± SD (n=4). 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 11. Nitrogen derived from fertilizer in the radish shoots

For responses of growth, the application of MAA showed enhanced effects obviously. 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 Chinese cabbage growth. Among the treatments of MAA, the growth responses were increased by increasing the application rate of MAA. The increases of yield were due to the positive adjusting of MAA on growth of plants, thus contributing to the increases of N utilization (Table 10) even though the total N

It has become evident that amino acids are a principal source of nitrogen for certain plants, such as mycorrihizal, heathland species (Read, 1993), non–mycorrihizal plants from arctic and alpine ecosystems (Chapin et al., 1993; Kielland, 1994) and boreal forest plants (Näsholm et al., 1998; Persson and Näsholm, 2001). These systems are similar in that N mineralization rates are heavily constrained by climate, and plant N demands cannot be met through the uptake of inorganic ions (Raab et al., 1999). Based on these researches, the amino acids were used to partially replace NO3– in hydroponic experiment or spray to leaves in many plants. In most case, the application of amino acids led to the decrease of nitrate content and total nitrogen content in lettuce, Chinese cabbage, onion, pakchoi or other leafy crops (Chen and Gao, 2002; Gunes et al., 1994, 1996; Wang et al., 2004). It had been suggested that plants probably preferred amino acids as sources of reduced nitrogen,

In this study, the high NdfF was found in MAA treatments (Table 11), indicating that applied MAA did not act as a source of nitrogen for plants. On the contrary, plants had taken up more

and assimilation in higher plants (Aslam et al., 2001; Ivashikian and Sokolov, 1997; Oaks et al., 1979; Radin, 1975, 1977; Sivasankar et al., 1997). But Aslam et al. (2001) reported that inhibition

10 mM. This result is consistent with the other research, which indicated that radish treated

– content in soil (1906 mg Kg–1).

– uptake. In this experiment, the positive effect on NO3

**Treatments NdfF QNdfF NdfFRec** 

A0 65.9 ± 1.5 b 24.8 ± 0.7 d 33.0 ± 1.3 d A1 68.6 ± 2.2 ab 32.7 ± 1.1 b 43.6 ± 2.0 b A2 71.6 ± 0.9 a 36.3 ± 0.8 a 48.4 ± 1.9 a A3 67.2 ± 2.1 ab 28.5 ± 1.0 c 38.1 ± 2.1 a NdfF; the percentage of N derived from fertilizer, QNdfF ; the quantity of N derived from fertilizer,

Data are means ± SD (n=4). 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 11. Nitrogen derived from fertilizer in the radish shoots

are contradictory. Many authors agreed that amino acids can down regulate the NO3

– uptake and assimilation. The results

– uptake

– uptake by applying

– uptake and assimilation by amino acids for higher plants

**(%) (mg/plant) (%)** 

– in the external solutions had been increased to

– in growth medium show significantly

content was decreased in MAA treatments (Table 9).

and nitrate uptake was inhibited by amino acids.

did not occur when the concentration of NO3

with mixed amino acids containing 5.0 mM NO3

for the possible regulation of NO3

MAA was due to very high NO3

NdfFRec ; the fertilizer-N recovery

––N from soil due to the regulation of MAA on NO3

NO3

increased the NO3

**4.2.4 Recovered fertilizer nitrogen** 
