ABSTRACT Cover crops (CC) and crop rotation are key components of a sustainable crop production system. The objectives of this study were to (i) evaluate the effect of winter CC on nitrogen (N) supply to the subsequent maize crop, and to (ii) evaluate the effect of CC on soil cover and weed population. Three winter CC were evaluated: black oat (BO) (Avena strigosa Schieb), white lupin (WL) (Lupinus albus), and oilseed radish (OR) (Raphanus sativus L.), as single species and in a mix. The three CC mixes included: BO+WL; BO+OR; and OR+WL. In addition to CC treatments a set of five N application rates (0, 60, 120, 180, and 240 kg N ha-1) were included on plots under winter fallow (WF). The winter CC supplied plant-available N to the subsequent maize crop varying from 25 to 53 kg N ha-1 with BO and WL, respectively. The mix of CC varied less in N supply (38-42 kg N ha-1). Soil cover and weed suppression varied between CC. The results suggest that BO can be used to attain rapid soil cover. Black oats also provided better soil cover after CC flattening, likely due to the higher C:N ratio and slower residue decomposition. The higher C:N ratio may result in some N immobilization and reduced plant available N to the maize crop. However, BO also showed great weed suppression. Mixing CC is an alternative to merge the benefits of the individual species, enhancing the overall ecosystem services provided by them.

RESUMEN Plantas de cobertura (PC) y rotación de cultivos son componentes esenciales de un sistema de producción agrícola sostenible. Los objetivos de este estudio fueron (i) evaluar el efecto de PC en la provisión de nitrógeno (N) al maíz cultivado en sucesión, y (ii) evaluar el efecto de PC en la cobertura de suelo (CS) y supresión de malezas (SM). Tres PC de invierno fueron evaluadas: avena negra (AN) (Avena strigosa Schieb), lupino blanco (LB) (Lupinus albus), y nabo forrajero (NF) (Raphanus sativus L.), en forma asociada y no asociada. Las asociaciones fueron: AN+LB, AN+NF, y NF+LB. Además, fueron incluidas cinco dosis de N (0, 60, 120, 180, y 240 kg ha-1 N) en parcelas en situación de barbecho. Las PC proporcionaron N mineral al maíz en sucesión, variando de 25 a 53 kg ha-1 N en el caso de AN y LB, respectivamente. Las asociaciones de PC proporcionaron el equivalente a 38-42 kg ha-1 N fertilizante. La CS y la SM variaron con cada PC. Los resultados sugieren que AN puede proporcionar rápida CS, y una CS más prolongada después del acamado, probablemente debido a la alta relación C:N y lenta descomposición de sus residuos, lo que podría resultar en inmovilización de N y disminución de su disponibilidad para el maíz. La AN también demostró buena capacidad de supresión de malezas. La asociación de PC es una alternativa que permite combinar los beneficios de cada especie de PC, mejorando los servicios al ecosistema promovidos por las mismas.

The objective of this study was to evaluate the effect of phosphorus sources in the absence and presence of earthworm humus on tillering, forage production and P accumulation of Panicum maximum cv. grass Mombasa. The experiment was conducted in 5 dm³ pots in a greenhouse located at the University of Mato Grosso, Alta Floresta - MT, Brazil. The treatments were arranged in a 4x2 + 1 with four replications, four P sources: simple superphosphate (SS) (18% soluble P2O5), Bayovar rock phosphate (BRP) (14% soluble P2O5), Top- Phos 280 HP (TP) (28% soluble P2O5) and bone meal (BM) (9.6% soluble P2O5), in the absence and presence of earthworm humus, and the control treatment (no P). At 46 days after emergence (DAE) the number of tillers were counted and at 46, 65 and 80 DAE cuts were made to evaluate the accumulation of dry matter and P accumulation. Application of the phosphorus sources, simple superphosphate and bone meal associated with earthworm humus resulted in higher dry matter accumulation of Mombasa grass and higher total phosphorus accumulation in the three cuts, in relation to isolated application of these phosphorus sources. The presence of humus did not influence tillering of the grass however more soluble sources promoted greater tillering.

El objetivo de este trabajo fue evaluar el efecto de fuentes de P en la ausencia y presencia de lombricompuesto sobre el macollaje, la producción de forraje y la acumulación de P del pasto Panicum maximum cv. Mombasa. El experimento fue realizado en vasos de 5 dm³ en invernadero localizada en la Universidad del Estado de Mato Grosso, Alta Floresta-MT, Brasil. Los tratamientos fueron ordenados en esquema factorial 4x2 + 1 con cuatro repeticiones, siendo cuatro fuentes de P: superfosfato simple (SS) (18% de P2O5 soluble), fosfato natural de Bayóvar (FNB) (14% de P2O5 soluble), Top- Phos 280 HP (TP) (28% de P2O5 soluble) y harina de huesos (FO) (9,6% de P2O5 soluble); en ausencia y en presencia de lombricompuesto, y un tratamiento control (sin P). A los 46 días después de la emergencia (DAE) se contó el número de macollos y a los 46, 65 y 80 DAE se realizaron tres cortes para la evaluación de la acumulación de materia seca y acumulación de P. La aplicación de las fuentes de fósforo el solapamiento simple y la harina de huesos asociados al humus de gusano proporcionaron una mayor acumulación de materia seca del pasto Mombasa y una mayor acumulación de fósforo en un total de tres cortes en relación con la aplicación aislada de estas fuentes de fósforo. La presencia de lombricompuesto no influenció el macollaje del pasto, sin embargo, las fuentes más solubles promovieron mayor cantidad de macollos.

No presente trabalho, foram comparados dois métodos de extração de cobre (Cu) e zinco (Zn) em solos com teor de matéria orgânica (MO) maior que 50g kg-1. Os métodos de extração comparados foram: Extração com HCl 0,1mol L-1 (método padrão para os estados do Rio Grande do Sul e Santa Catarina) e Mehlich 3. Este trabalho foi realizado no Laboratório de Química e Fertilidade do Solo da Universidade do Estado de Santa Catarina (UDESC), no ano de 2009. As duas metodologias de extração foram aplicadas em 286 amostras de solo provenientes do Laboratório de Análise do Solo da UDESC, todas com mais de 50g kg-1 de MO. Os teores de cobre e zinco nos extratos foram determinados por espectrometria de absorção atômica com chama. Os resultados mostraram que houve correlação significativa entre os métodos, Cu (r=0,80) e Zn (r=0,93). A solução de Mehlich 3 extraiu mais cobre e menos zinco, quando comparada à solução de HCl 0,1mol L-1. O Mehlich 3 demonstrou ser eficiente na extração de cobre e zinco em solos com alto teor de MO, podendo substituir o método atual.

In this study were compared two methods of extraction of copper (Cu) and zinc (Zn) in soils with organic matter (OM) higher than 50g kg-1. The extraction methods compared were: Extraction with HCl 0.1mol L-1 (standard method for the states of Rio Grande do Sul and Santa Catarina) and Mehlich 3. This work was performed at the Laboratory of Soil Chemistry and Fertility, Santa Catarina State University (UDESC), in 2009. The two extraction methods were applied to 286 soil samples from the Soil Analysis Public Laboratory of UDESC, all with more than 50g kg-1 OM. The copper and zinc in extracts were determined by flame atomic absorption spectrometry. The results showed significant correlation between the methods, Cu (r=0.80) and Zn (r=0.93). The solution Mehlich 3 extracted more copper and less zinc when compared to the solution of HCl 0.1mol L-1. The Mehlich 3 proved to be efficient in the extraction of copper and zinc in soils with high OM content, which may replace the current method.

Plants have shown different responses to fertilization with rock phosphate, including responses through alteration of the attributes of rhizospheric soil. The objective of this study was to evaluate soil pH alterations and alterations in the contents of forms of phosphorus in the rhizosphere of soil fertilized with rock phosphate as a result of cultivation of species of plants. An experiment was developed under greenhouse conditions to evaluate alterations in the pH and in the forms of phosphorus in the rhizosphere of an Oxisol fertilized with rock phosphate and cultivated with four species. Treatments consisted of the cultivation of four species of soybean - Glycine max (L.) Merrill, brachiaria grass - Brachiaria brizantha Hochst Stapf, millet - Pennisetum glaucum (L.) R. Brown, and sorghum - Sorghum bicolor (L.) Moench grown in PVC columns filled with soil and divided with a nylon screen (25 µm mesh) to impede root growth in part of the column. After 45 days of cultivation, the soil was divided into the layers of 0-1, 1-2, 2-3, 3-4, 4-5, 5-7, 7-9, and 9-14 mm from the rhizoplane and air dried to determine pH and P contents through Hedley fractionation. In the 1-2 and 2-3 mm layers, soybean cultivation caused an increase in pH when compared to the control treatment (without plants). In the other layers, there were no alterations in pH due to cultivation of plants. The cultivation of millet, brachiaria grass, and sorghum reduced the inorganic P content in the most labile forms only in the 0-1 mm layer from the rhizoplane.