ABSTRACT Soil fertility evaluation is important for adopting conservation management and adequate nutrient supply. The objective of this study was to identify critical levels and soil fertility classes using the boundary line method for rainfed crops (corn, cowpea and sabiá [Mimosa caesalpiniifolia]) in the Brazilian semi-arid region. A database of 226 soil fertility analyses of samples from the 0.00-0.20 m soil layer, and corn, cowpea and sabiá yields from Ceará State was used to generate interpretation classes (at 80 and 95 % of maximum yield). In a scatter plot, soil nutrient concentrations (x-axis) and relative crop yields (y-axis) were correlated, and the border points fitted to a quadratic model. Proposed interpretation classes were classified as very low, low, adequate, high and very high, except for Na+, whose adequate class was considered tolerable. Generated models showed coefficients of determination (R2) for the chemical properties ranging from 0.54 to 0.92. Based on the interpretation classes, the critical level was determined as 6.3 for pH, 10.8 g dm-3 for OM, 20.9 mg dm-3 for P, 81 mg dm-3 for K, 55 mmolc dm-3 for Ca2+, 24 mmolc dm-3 for Mg2+ and 8 mg dm-3 for S-SO42-. Interpretation classes for soils with high-activity clay in the Brazilian semi-arid region were superior to those in the reference literature. Boundary line method established fertility classes and critical levels for soil chemical properties in more than one crop, using the concept of relative yield. supply corn (corn Mimosa caesalpiniifolia caesalpiniifolia] semiarid semi arid 22 0.000.20 000020 0.00 0.20 0 00 20 0.00-0.2 layer at 9 yield . yield) plot xaxis x axis (x-axis yaxis y (y-axis correlated model low Na Na+ tolerable R2 R (R2 054 54 0.5 092 92 0.92 63 6 3 6. pH 108 10 10. dm3 dm dm- OM 209 20. P K 5 Ca2 Ca Ca2+ 2 Mg2 Mg SSO42. SSO42 SSO S SO42 SO S-SO42- highactivity activity literature 000 0.000.2 00002 0.0 020 0.2 0.00-0. (R 05 0. 09 0.9 1 SSO4 SO4 S-SO42 0.000. 0000 02 0.00-0 S-SO4 0.000 0.00- S-SO

RESUMEN El objetivo de esta investigación fue evaluar el efecto del tiempo de contacto del fertilizante superfosfato simple con semillas de pasto Massai (Megathyrsus maximus) sobre la calidad fisiológica de las semillas. El experimento se realizó con semillas de pasto Massai en dos condiciones: laboratorio y campo. El experimento se llevó a cabo en Teresina, Piauí, Brasil. El diseño experimental fue completamente al azar, con tres repeticiones para ambas condiciones. Los tratamientos consistieron en siete tiempos de contacto: 0, 3, 6, 9, 24, 48 y 72 h. Se evaluaron porcentajes de germinación (PG) y emergencia (PE), altura de plántula (AP), longitud de raíz (LR) e índice de velocidad de germinación (IVG). El tiempo de contacto del fertilizante con las semillas tuvo un efecto significativo en todas las variables, excepto en la longitud de las raíces y la emergencia a los 7 d. Para PG en la segunda toma de datos e IVG no hubo diferencias hasta las 3 h de contacto; sin embargo, para PG en la primera colecta, SH e IVG a los 21 d, el contacto de las semillas con el fertilizante durante 3 h tuvo efectos negativos sobre estas variables, reduciéndolas en 23.33%, 12.13 cm y 14.28% respectivamente. A mayor tiempo de contacto entre el superfosfato simple y las semillas de M. maximus (cv. Massai), menores valores de germinación y vigor.

ABSTRACT The aim of this research was to evaluate the effect of the contact time of simple superphosphate fertilizer with Massai grass (Megathyrsus maximus) seeds on the physiological quality of the seeds. The experiment was conducted with seeds of Massai grass in two conditions: laboratory and field. The experiment was carried out in Teresina, Piauí, Brazil. The experimental design was completely randomized, with three replicates for both conditions. The treatments consisted of seven contact times: 0, 3, 6, 9, 24, 48, and 72 h. Germination (GP) and emergence (EP) percentages, seedling height (SH), root length (RL), and germination speed index (GSI) were evaluated. The contact time of the fertilizer with the seeds had a significant effect on all variables, except root length and emergence at 7 d. For GP in the second data collection and GSI, there were no differences up to 3 h of contact; however, for GP in the first collection, SH and GSI at 21 d, the contact of seeds with fertilizer for 3 h already had negative effects on these variables, reducing them by 23.33%, 12.13 cm and 14.28% respectively. The longer the contact time between single superphosphate with M. maximus (cv. Massai) seeds, the lower the germination and vigor values.