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Abstract
Brachiaria species are widely cultivated and the low nitrogen (N) fertility of soils is one of the limiting factors for grass production in the Brazilian savannas (Cerrados). In the present study, we compared the characteristics of N utilization in Brachiaria brizantha (BB), B. decumbens (BD), and B. humidicola (BH), which are common species in these areas. In a soil culture experiment, BB, BD, and BH were grown under 3 levels of N, equivalent to 0 application (ON), 0.1 (1N), and 0.3 (2N) g N pot−1, with N as ammonium sulfate. The plant dry weight of BB and BD increased with the increase of N levels, whereas BH showed a weaker growth response to N application and the plant dry weight of BH was lower than that of BB and BD. The amount of N accumulated in plant increased with the increase of N levels in BB and BD. The amount of N accumulated in plant in BH was slightly lower than or almost comparable to that in BB and BD. The plant N concentration was higher in BH than in BB and BD. The stronger growth response of BB and BD resulted in a higher fertilizer use efficiency (FUE) and a N use efficiency in fertilizer application (NUEF). The N absorption efficiency (NAE) of BH was higher than that of the other two grasses for 1N and 2N. In the absence of N treatment (hereafter refferred to as “ON treatment”), the specific N absorption rate in the roots (SAR) was higher in BH than in BB and BD throughout the growth period. These data suggested that the N absorption ability in roots would be higher in BH than in the other 2 tested grasses, as confirmed by the Michaelis-Menten kinetic analysis. In a nitrate absorption experiment, the K m value of BH was lower than that of BB and BD. As BH showed a higher affinity for nitrate absorption, it could maintain a higher N absorption rate. Therefore, it was considered that the performance of N accumulation of BH would be slightly lower than or almost comparable to that of BB and BD because of the high ability of BH to absorb N, although dry matter production of BH was lower than that of BB and BD.
Notes
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