The Timing of School Transitions and Early Adolescent Problem Behavior

This longitudinal study investigates whether rural adolescents who transition to a new school in sixth grade have higher levels of risky behavior than adolescents who transition in seventh grade. Our findings indicate that later school transitions had little effect on problem behavior between sixth and ninth grades. Cross-sectional analyses found a small number of temporary effects of transition timing on problem behavior: Spending an additional year in elementary school was associated with higher levels of deviant behavior in the Fall of Grade 6 and higher levels of antisocial peer associations in Grade 8. However, transition effects were not consistent across waves and latent growth curve models found no effects of transition timing on the trajectory of problem behavior. We discuss policy implications and compare our findings with other research on transition timing

Sources and rates of potassium for sweet orange production

Fruit yield and quality of citrus trees (Citrus spp.) is markedly affected by potassium (K) fertilization. Potassium chloride is the major source of K, even though other sources are also available for agricultural use when crops are sensitive to chloride or where potential for accumulation of salts in soils exists. Only few studies addressed the effect of K sources on yield and quality of citrus fruits. Therefore, the present study was conducted to evaluate K2SO4 and KCl fertilizer sources at 0, 100, 200, and 300 kg ha-1 per year K2O on fruit yield and quality of 'Pêra' and 'Valencia' sweet orange trees in the field. The experiments were carried out in a 4 × 2 factorial design under randomized complete blocks, with four replicates from 2001 to 2004. Fruit yield increased with increased K fertilization. Nutrient rate for maximum economic yield of 'Pêra' was 200 kg ha-1 of K2O and for 'Valencia', 270 kg ha-1 of K2O. Differences were attributed to higher production and K exportation by fruits of 'Valencia'. Fruit mass also increased with increased K fertilization what decreased total soluble solids in juice, and which correlated with leaf K concentrations for 'Valencia' (r = 0.76; p < 0.05). Leaf Ca, Mg and B concentrations decreased with K rates. Additionally, leaf Cl increased up to 440 mg kg-1 with KCl rates, even though no negative effects occurred either on fruit yield or quality of trees