Rodinei Facco Pegoraro

Manejo da água e do nitrogênio em cultivo de capim-elefante

A intensificacao do manejo do solo, visando ao aumento da produtividade de forrageiras pode contribuir para a degradacao fisica e quimica do solo se mal conduzida. Neste contexto, o presente estudo objetivou avaliar a producao de MS, os conteudos acumulados dos nutrientes na parte aerea de capim-elefante (Pennisetum purpureum Schum.) e as alteracoes nos atributos fisicos e quimicos do solo apos a adicao de doses de nitrogenio e aplicacao ou nao da irrigacao. Para tanto, amostras de planta e solo foram coletadas em area experimental de pastagem com capim-elefante no quarto ano de cultivo sob doses crescentes de nitrogenio (100; 200; 300 e 400 kg ha-1 de N, anualmente no periodo de verao) em sistema irrigado e nao irrigado. Os resultados mostraram que apos quatro anos de cultivo de capim-elefante o manejo com sistema irrigado combinado com adubacao nitrogenada propiciou maior producao de MS da parte aerea, o que determinou maiores extracoes de K, Ca e P pela planta, reducao no teor de P extraivel por Mehlich 1 no solo e incrementos nos teores de carbono orgânico total, K e Ca trocaveis. O solo com sistema nao irrigado apresentou maior densidade.

Crescimento de soja em solos em resposta a doses de Boro, calagem e textura do solo

Neste trabalho, objetivou-se quantificar a producao de materia seca e os conteudos de B, Ca e Mg na cultura da soja cultivada em solos com diferentes texturas que receberam doses crescentes de B e calagem, e correlacionar o conteudo de B absorvido pela planta com o teor de B recuperado com agua e CaCl2 ferventes sob influencia de doses de boro e a calagem aplicadas em tres solos distintos. O experimento foi conduzido em casa de vegetacao em esquema fatorial 3 x 2 x 6, consistindo de tres solos: textura arenosa (RQ), textura media (LVA1) e textura argilosa (LVA2), com e sem calagem, e seis doses de B (0; 1,5; 3; 6; 9 e 15 mg dm-3), em blocos casualizados com tres repeticoes. Determinou-se o teor de B no solo extraivel com agua e CaCl2 ferventes apos 45 dias da adicao das doses de B aos solos, massa de materia seca da parte aerea e os teores de B, Ca e Mg na soja. Os teores de B recuperado, tanto pela agua fervente, quanto pelo CaCl2 fervente foram semelhantes nos tres solos estudados e, apresentaram altas correlacoes com o conteudo de B e o peso de materia seca. As doses de B adicionadas aumentaram a sua absorcao pelas plantas, mas causaram reducao na producao de materia seca da parte aerea nos solos RQ (textura arenosa), LVA1 (textura media) e o LVA2 (textura argilosa) com calagem, neste ultimo solo, o efeito e minimizado na presenca de maior teor de argila.

BIOMARCADORES DERIVADOS DE PLANTA E DE MICRORGANISMOS EM SOLOS DE TABULEIROS COSTEIROS CULTIVADOS COM EUCALIPTO E ACÁCIA

Changes in the management systems for the cultivation of different forest stands and the use of species rotation can lead to alterations in the quality of soil organic matter (SOM) and plant residue deposition. This study evaluated the stage of decomposition and the contribution of plant and microbial origin for SOM through biomarkers, such as lignin-derived phenols, carbohydrates and amino sugars in continuous short rotation eucalypt ( Eucalyptus urophylla x Eucalyptus grandis hybrid) (seven years) compared to a rotation system including acacia ( Acacia mangium Willd.) after short-rotation eucalypt; and long-rotation eucalypt (24 years). A native vegetation (Atlantic Forest) was used as a reference for the original site condition representative for the northern coast of Espirito Santo state. To do so, we estimated the content of total organic C (TOC), total N (TN) and the contents of lignin-derived phenols (VSC), the carbohydrates and the amino sugars derived from soil microorganisms, and acids/aldehyde ratio of groups vanilil ((Ac/Al)vanilil) and syringyl ((Ac/Al)syringyl) of the lignin, hexoses/pentoses (H/P) ratio of carbohydrates, besides glucosamine/muramic acid (Gluc/Ac. Mur) and glucosamine/galactosamine (Gluc/Gal) ratios for soil and litter samples. The results indicated that litter of the continuous short-rotation eucalypt has greater dry mass, lignin (VSC) and carbohydrates contents, C/N and VSC/N ratios; a similar proportion of coarse litter to fine litter and C content, but a lower N content in comparison to the species rotation system that includes the leguminous acacia. In the soil, acacia cultivation increases C, N and carbohydrates content, widened the acid/aldehyde ratio of vanilil groups of lignin and the glucosamine/muramic acid ratio of amino sugars derived from microbial activity. The longer rotation of eucalypt (24 years) increased C content and decreased the VSC/N ratio in SOM compared to the continuous short-rotation eucalypt, but still having C and N content lower than in soil of acacia and native forest. The smallest Ac/Al ratio of lignin-derived phenols in soils cultivated with eucalypt (in long and short-rotation) indicates that the SOM is in less advanced stage of decomposition (humification) than in the soil cultivated with acacia, and that under native forest. In soils under acacia, followed by that of short-rotation eucalypt, the higher glucosamine/muramic acid ratio suggested a greater contribution of fungi in SOM cycling, whereas in the native forest and long-rotation eucalypt there is greater abundance of bacteria-derived compounds. Overall, the results indicate that there was a recovery in the quality of the soils cultivated with eucalypt for a longer rotation and also with acacia in relation to the continuous short-rotation eucalypt.

FENÓIS DERIVADOS DA LIGNINA, CARBOIDRATOS E AMINOAÇÚCARES EM SERAPILHEIRA E SOLOS CULTIVADOS COM EUCALIPTO EM SISTEMAS CONVENCIONAL E FERTIRRIGADO

The study aimed to evaluate the content of phenols derived from lignin, carbohydrates, amino sugars, the stage of decomposition of compounds and the relative contribution of plant-and microbial-derived compounds to the soil organic matter (SOM) in the conventional and fertirrigated till age of eucalyptus. Samples of litter and soil (Ultisol) were taken from two tillage systems (conventional and fertirrigated) at two collection sites (line and between-line) with three replications. It was evaluated the litter production, content of total organic C (TOC), total N (TN), lignin and phenols-derived lignin and its Ac/Alratio, carbohydrates and their hexose/pentose ratio, amino sugars and the glucosamine/muramic acid ratio in the soil. The cultivation of eucalyptus in fertirrigated system promoted higher litter fall, reduced the carbohydrate content and maintained the content of lignin in the litter in comparison to the conventional system. In soil, the greater accumulation of the litter (22%) in fertirrigated system increased the contents of carbohydrates, lignin and amino sugars, mainly in the between-lines position. The hexoses/pentoses ratio also increased, indicating a greater presence of compounds of microbial origin. Among the compounds of microbial origin, a larger abundance of glucosamine was observed, indicating a greater contribution of fungal to the SOM formation under fertirrigated cultivation.