Available Nitrogen and Responses to Nitrogen Fertilizer in Brazilian Eucalypt Plantations on Soils of Contrasting Texture

Abstract

Eucalyptus plantations have seldom responded to N fertilization in tropical and subtropical regions of Brazil. This implies that rates of N mineralization have been adequate OPEN ACCESSForests 2015, 6 974 to supply tree needs. However, subsequent crop rotations with low N fertilization may result in declining concentrations of organic and potentially mineralizable N (N0), and consequent loss of wood productivity. This study investigated (a) in situ N mineralization and N0 in soils of eucalypt plantations in São Paulo state, Brazil; (b) tree growth responses to N fertilizer applied 6-18 months after planting; and (c) the relationships between N0, other soil attributes and tree growth. We established eleven N fertilizer trials (maximum 240 kg ha −1 of N) in E. grandis and E. grandis x urophylla plantations. The soil types at most sites were Oxisols and Quartzipsamments, with a range of organic matter (18 to 55 g kg −1 ) and clay contents (8% to 67%) in the 0-20 cm layer. Concentrations of N0 were measured using anaerobic incubation on soil samples collected every three months (different seasons). The samples collected in spring and summer had N0 140-400 kg ha −1 (10%-19% total soil N), which were best correlated with soil texture and organic matter content. Rates of in situ net N mineralization (0-20 cm) ranged from 100 to 200 kg ha −1 year −1 and were not correlated with clay, total N, or N0. These high N mineralization rates resulted in a low response to N fertilizer application during the early ages of stand growth, which were highest on sandy soils. At the end of the crop rotation, the response to N fertilizer was negligible and non-significant at all sites.

Effect of Timber Harvest Intensities and Fertilizer Application on Stocks of Soil C, N, P, and S

“…Our results and others [29,41] suggest that Eucalyptus trees can access P fractions not identified by traditional soil analysis methods. Regarding N concentrations, even with high harvest outputs (more than 500 kg·ha −1 in each crop rotation) no response to N application by fertilization was found in terms of wood productivity in Brazilian conditions [28]. More research is essential to better understand the sources and the cycle of this nutrient within tropical soil-plant systems.…”

“…The largest stock of oxidizable C in the soil was observed in the ReM + F treatment (p > 0.001), and 2004), before the harvest of the first rotation (2012), and at four years into the second rotation (2016) in a Eucalyptus plantation under different harvest residue management and fertilizer application strategies. P was determined by resin extraction, S was determined by extraction with Ca(H 2 PO 4 ) 2 0.001 mol·L −1 , and available N was calculated assuming that 10% of total N is mineralizable [28]. Columns with the same letter are not significantly different from each other.…”

“…P was determined by resin extraction, S was determined by extraction with Ca(H2PO4)2 0.001 mol L −1 , and available N was calculated assuming that 10% of total N is mineralizable [28]. Columns with the same letter are not significantly different from each other.…”

Fertilization Response, Light Use, and Growth Efficiency in Eucalyptus Plantations across Soil and Climate Gradients in Brazil

“…The soils were analyzed using the methodology described by Raij et al [18] for the following chemical variables: pH (CaCl 2 ), organic matter (OM), P, Ca, K, Mg, and micronutrients. Nitrogen was not directly included in the original analysis, but we used organic matter amount as an indicator of nitrogen soil content [19][20][21]. Brazilian Eucalyptus plantations typically do not respond to nitrogen fertilization [21].…”

“…Nitrogen was not directly included in the original analysis, but we used organic matter amount as an indicator of nitrogen soil content [19][20][21]. Brazilian Eucalyptus plantations typically do not respond to nitrogen fertilization [21]. Source: Sentelhas et al [22] All stands received maintenance fertilization with N, P, K, Ca, and Mg according to the conventional prescriptions of the company (Table 2).…”