Soil organic matter as a function of nitrogen fertilization in crop successions

Abstract

The interdependence between the C and N cycles is reflected by the levels of soil organic matter (SOM). SOM and organic C levels in water soluble (C-WS) humic acids (C-HA), fulvic acids (C-FA), and humin fractions (C-H) were evaluated through the classic chemical fractionation method in samples of a Rhodic Eutrudox from a randomized blocks experimental design, with split-split-plots using five nitrogen sidedressing levels for corn (0; 60; 120; 180; and 240 kg ha -1 N) as the main treatment, two crop sequences (corn-corn and soybean-corn) as the secondary treatment, and two sampling depths (0 to 0.2 and 0.2 to 0.4 m) as a sub-subtreatment. Nitrogen fertilization did not affect SOM levels, but favored the synthesis of substances in the C-HA fraction. There was a quadratic effect of N rates on the C-WS and C-FA levels in the corn-corn succession. The soybean-corn succession resulted in larger SOM and organic C levels in the C-H fraction. Key words: humic acids, humin, urea, corn, soybean MATÉRIA ORGÂNICA DO SOLO EM FUNÇÃO DE ADUBAÇÃO NITROGENADA EM SUCESSÕES DE CULTURAS RESUMO: A interdependência dos ciclos de C e N reflete-se nos teores de matéria orgânica do solo (MOS).Em um delineamento experimental em blocos casualizados, com parcelas sub-subdivididas, tendo como tratamento principal cinco doses de nitrogênio de cobertura na cultura do milho (0; 60; 120; 180 e 240 kg ha -1 de N), como tratamento secundário, as sucessões milho-milho e soja-milho, e como sub-subtratamento, duas profundidades de amostragem (0 a 0.2 e 0.2 a 0.4 cm), avaliaram-se os teores de MOS e de C orgânico nas frações solúvel em água (C-SA), ácidos húmicos (C-AH), ácidos fúlvicos (C-AF) e humina (C-H), por meio do método clássico de fracionamento químico, em um Latossolo Vermelho eutrófico, de textura argilosa. A adubação nitrogenada não afetou os teores de MOS, mas favoreceu a síntese de compostos da fração C-AH. Houve efeito quadrático das doses de N nos teores de C-SA e de C-AF na sucessão milho-milho. A sucessão soja-milho resultou em maiores teores de MOS e de C orgânico na fração humina.

Soil organic carbon fractions after 16-years of applications of fertilizers and organic manure in a Typic Rhodalfs in semi-arid tropics

“…WSC appears to be an immediate substrate for the soil organisms. Our results are in agreement with Yagi et al (2005), who attributed the increase of WSC to the priming effect of the application of fertilizers or fresh organic material to the soil, which stimulated the mineralization of organic matter through increased microbial activity.…”

Soil organic matter dynamics as affected by long-term use of organic and inorganic fertilizers under maize–wheat cropping system

“…The WSC content increased with increasing level of fertilizers. The results are in agreement with Yagi et al (2005), who attributed the same to the priming effect of application of inorganic N or fresh organic material to the soil, which stimulates the microbial activity and mineralization of N present in SOM helping decomposition of SOM with rapid release of the WSC fraction. Soil carbohydrates were in proportion to organic matter content.…”

Tillage Crop Establishment and Organic Inputs with Kappaphycus - Sap Effect on Soil Organic Carbon Fractions and Water Footprints under a Six Year Rice-Wheat Rotation

“…This increase is attributed to the accretion of sulphur through FYM/ K sap application. Our results are in agreement with Yagi et al (2005), who attributed the increase of WSOC to the priming effect of the application of fertilizers or fresh organic material to the soil, which stimulated the mineralization of organic matter through increased microbial activity.…”