The objective of this work was to evaluate the yield and must composition of 'Cabernet Sauvignon' and 'Chardonnay' grapevines subjected to phosphorus applications to a soil from a high-altitude region of Southern Brazil, during three crop seasons. Experiments 1 and 2 were carried out in 'Cabernet Sauvignon' and 'Chardonnay' commercial vineyards, respectively, in the municipality of Água Doce, located in the Midwestern region of the state of Santa Catarina. The soil from the two vineyards was classified as a Typic Humicryept. The used source of P was triple superphosphate (45% P2O5). From 2011 to 2013, at flowering, a total of 0, 10, 20, 40, and 80 kg ha-1 P2O5 were applied in the crown projection area, to the soil surface, without incorporation, in both vineyards. Soil and leaf P concentration, yield parameters, and must quality were evaluated. The increase in P availability decreased total titratable acidity and tartaric acid in the must of the 'Cabernet Sauvignon' grapevine in the 2013/2014 crop season and increased pH and total soluble solids in the must of the 'Chardonnay' grapevine in the 2011/2012 crop season. Phosphorus application to the soil increases the levels of available phosphorus, but does not result in higher yields for 'Cabernet Sauvignon' and 'Chardonnay' grapevines.

The presence of weeds in apple orchards affects the dynamics of nutrients in the soil, including phosphorus (P). The objective of this study was to evaluate changes in distribution of P fractions in the soil of an apple orchard under different weed managements. The experiment was conducted in an apple orchard in the municipality of Urubici, Santa Catarina, Brazil. The following treatments were implemented in 2011: no weed management (NWM), desiccation of weeds in the apple-tree row (DR), and hoeing of weeds in the apple-tree row (HR). Soil samples of the 0-2.5, 2.5-5, 5-10, 10-15 and 15-20 cm layers were collected in the apple-tree rows at 24 months after the implementation of the experiment. The samples were subjected to chemical fractionation of P, obtaining the following fractions: PiAER, PiNaHCO3, PoNaHCO3, PiNaOH, PoNaOH, PiHCl, PiNaOH05, PoNaOH05, and Presidual. The presence of weeds increased the contents of the following soil P fractions in the surface layers: PiAER, PiNaHCO3, and PoNaHCO3, which are bioavailable to plants. A higher proportion of organic forms of P in the soil was found when the weeds were hoed; these fractions can be mineralized and used for nutrition of apple trees when labile P forms are exhausted.

Nitrogen (N) derived from the decomposition of litter from cover crops can contribute to the mineral nutrition of citrus trees. This study aimed to assess the prior contribution of N derived from the decomposition of forage radish (Raphanus sativus) and black oats (Avena strigosa) to Satsuma mandarin tree N demand. Forage radish and black oats were grown and enriched with ¹⁵N stable isotope. Two studies were conducted on (1) non-bearing, potted satsuma mandarin seedlings for 120 days in the greenhouse (Experiment 1) and (2) bearing field-growing Satsuma mandarin trees for 270 days (Experiment 2). Tree growth and total N and ¹⁵N concentrations were determined in annual and perennial organs of citrus and soil. The highest value of N derived from the decomposition of cover crop root residues was observed in the leaves and roots of non-bearing trees, while the highest amount of N derived from shoot residue decomposition was observed in the leaves of bearing trees. The results showed little contribution of the decomposition of residues of forage radish and black oats on the total N budget of annual and perennial organs of both bearing and non-bearing Satsuma mandarin trees, probably because the climatic conditions promoted a fast N mineralization and possible losses through volatilization and leaching.