Growth and Nitrogen Uptake by Potato and Cassava Crops Can Be Improved by Azospirillum brasilense Inoculation and Nitrogen Fertilization

Nitrogen (N) is the nutrient most taken up by potato and cassava crops and Azospirillum brasilense may contribute to the growth of these crops. Pot experiments evaluated A. brasilense and mineral N application on leaf N concentration, plant growth, and N uptake by potato and cassava grown under natural and disinfected soil. The rates of 2.8 x 10(8) colony-forming units mL(-1) of A. brasilense combined with 0, 75, 150, and 300 mg dm(-3) N or 0, 50, 100, and 200 mg dm(-3) N were used for potato or cassava grown. At low N supply in natural soil, A. brasilense inoculation increased N concentration in potato leaves by 23-38%, without benefits to plant growth or N uptake. At unfertilized N treatments of both soils, A. brasilense inoculation increased cassava leaf N concentration by 25-33%, but an 11-32% increase in shoot biomass occurred in treatments inoculated and N supplied. Potato crops responded positively to mineral N supply, but cassava responded to fertilization only in disinfected soil. In disinfected soil fertilized with N, A. brasilense inoculation increased cassava N uptake by 27-40%. In contrast, in natural soil, A. brasilense minimized the negative effect of N excess on the tuber development of cassava. These results show that the use of A. brasilense is a more interesting alternative to improve N status and growth in cassava than in potatoes.

Automated summary

Nitrogen is the most important nutrient for potato and cassava crops, and Azospirillum brasilense can enhance their growth. Field experiments were conducted to investigate the effects of A. brasilense inoculation and mineral nitrogen application on plant growth, nitrogen uptake, and leaf nitrogen concentration in both natural and disinfected soil. The results showed that inoculating A. brasilense increased leaf nitrogen concentration in potato plants, but did not significantly improve plant growth or nitrogen uptake. However, in cassava, A. brasilense inoculation increased leaf nitrogen concentration and shoot biomass, especially when nitrogen was supplied. In disinfected soil, A. brasilense inoculation also increased cassava nitrogen uptake. Conversely, in natural soil, A. brasilense minimized the negative effects of excessive nitrogen on cassava tuber development. These findings suggest that A. brasilense may be a more effective option for improving nitrogen status and growth in cassava compared to potato.