Soil health: looking for suitable indicators. What should be considered to assess the effects of use and management on soil health?

Soil Health refers to the ecological equilibrium and the functionality of a soil and its capacity to maintain a well balanced ecosystem with high biodiversity above and below surface, and productivity. To understand and use soil health as a tool for sustainability, physical, chemical, and biological properties must be employed to verify which respond to the soil use and management within a desired timescale. Attributes with a rapid response to natural or anthropogenic actions are considered good indicators of soil health. Among the physical indicators, soil texture, aggregation, moisture, porosity, and bulk density have been used, while among chemical indicators total C and N, mineral nutrients, organic matter, cation exchange capacity, among others are well established. However, most of them generally have a slow response, when compared to the biological ones, such as microbial biomass C and N, biodiversity, soil enzymes, soil respiration, etc., in addition to macro and mesofauna. Thus, a systemic approach based on different kinds of indicators (physical, chemical and biological) in assessing soil health would be safer than using only one kind of attribute. Many human activities have caused desertification, loss of biodiversity, disruption of aggregates, loss of organic matter and nutrients, among others. Today, it is imperious to maintain soil health and productivity with increasing emphasis on reforestation and recuperation of degraded areas through the use of organic amendments, reintroduction of plants, soil fauna and microorganisms. This review focused on an integrative view on indicators of soil health to be used as tools for prediction of sustainability in production systems.

Soil health: looking for suitable indicators. What should be considered to assess the effects of use and management on soil health?

Soil Health refers to the ecological equilibrium and the functionality of a soil and its capacity to maintain a well balanced ecosystem with high biodiversity above and below surface, and productivity. To understand and use soil health as a tool for sustainability, physical, chemical, and biological properties must be employed to verify which respond to the soil use and management within a desired timescale. Attributes with a rapid response to natural or anthropogenic actions are considered good indicators of soil health. Among the physical indicators, soil texture, aggregation, moisture, porosity, and bulk density have been used, while among chemical indicators total C and N, mineral nutrients, organic matter, cation exchange capacity, among others are well established. However, most of them generally have a slow response, when compared to the biological ones, such as microbial biomass C and N, biodiversity, soil enzymes, soil respiration, etc., in addition to macro and mesofauna. Thus, a systemic approach based on different kinds of indicators (physical, chemical and biological) in assessing soil health would be safer than using only one kind of attribute. Many human activities have caused desertification, loss of biodiversity, disruption of aggregates, loss of organic matter and nutrients, among others. Today, it is imperious to maintain soil health and productivity with increasing emphasis on reforestation and recuperation of degraded areas through the use of organic amendments, reintroduction of plants, soil fauna and microorganisms. This review focused on an integrative view on indicators of soil health to be used as tools for prediction of sustainability in production systems.

Interactions between diazotrophic bacteria and mycorrhizal fungus in maize genotypes

Some diazotrophic bacteria can fix nitrogen biologically in gramineous host plants. Generally, gramineous plants are also associated with mycorrhizal fungi, that can improve mainly plant P uptake. Among the factors affecting plant-microbe interactions, the plant genotype plays an important role. This study evaluates the effect of diazotrophic bacteria and an arbuscular mycorrhizal fungus (AMF), on five genotypes of maize (Zea mays L.), in relation to plant biomass, shoot N and P concentrations, and fine root morphological traits. The experimental design was entirely randomized in a factorial 5 × 4 × 2 arrangement, i.e., five maize genotypes (hybrids C333B, AS3466, and PREMIUM, and the inbreed lines lg40897-1 and lg40505-1), three diazotrophic bacteria (Azospirillum lipoferum, A. amazonense, and Burkholderia sp.) in addition to a control without bacterial inoculation, co-inoculated or not with the AMF Glomus clarum. The non-mycorrhizal plants inoculated with Azospirillum exhibited the highest N concentrations. The lines lg40897-1 and lg40505-1 showed higher P concentrations as compared to the hybrids, mainly when colonized by AMF. The higher levels of mycorrhizal colonization (90%) occurred in the C333B and lg40897-1 genotypes, which also exhibited a greater root diameter. Mycorrhiza increased shoot and root biomass, besides root traits as total length, specific length, total surface, and incidence of root hairs in all genotypes. In addition, mycorrhiza also stimulated the root colonization by diazotrophic bacteria. The bacteria did not affect root morphological traits and mycorrhizal colonization.

Algumas bactérias diazotróficas podem fixar N biologicamente em gramíneas, as quais se associam a fungos micorrízicos, o que pode levar a um aumento principalmente da absorção de P. Dentre os fatores que afetam as interações planta-microrganismos, o genótipo da planta tem importante papel. Esse trabalho avalia o efeito de bactérias diazotróficas e de um fungo micorrízico arbuscular (FMA) em cinco genótipos de milho (Zea mays L.), em relação à biomassa das plantas, teores de N e P na parte aérea e parâmetros relacionados à morfologia das raízes finas. O delineamento experimental foi inteiramente casualizado, em arranjo fatorial 5 × 4 × 2, sendo cinco genótipos de milho (híbridos C333B, AS3466, PREMIUM e as linhagens lg40897-1 e lg40505-1), três bactérias diazotróficas (Azospirillum lipoferum, A. amazonense e Burkholderia sp.), mais um controle sem bactéria, co-inoculadas ou não com o FMA Glomus clarum. As plantas sem FMA e inoculadas com Azospirillum apresentaram os maiores teores de N. As linhagens lg40897-1 e lg40505-1 apresentaram maior concentração de P em relação aos híbridos, principalmente quando micorrizadas. Os maiores níveis de colonização micorrízica (90%) ocorreram nos genótipos C333B e lg40897-1 que, por sua vez, apresentaram maior diâmetro de raízes. O FMA aumentou a biomassa da parte aérea e das raízes, comprimento total e específico, superfície total e incidência de pêlos nas raízes em todos os genótipos. O fungo micorrízico também estimulou a colonização das raízes pelas bactérias diazotróficas. Já as bactérias não alteraram as características morfológicas das raízes e nem a colonização micorrízica.

Interactions between diazotrophic bacteria and mycorrhizal fungus in maize genotypes

Some diazotrophic bacteria can fix nitrogen biologically in gramineous host plants. Generally, gramineous plants are also associated with mycorrhizal fungi, that can improve mainly plant P uptake. Among the factors affecting plant-microbe interactions, the plant genotype plays an important role. This study evaluates the effect of diazotrophic bacteria and an arbuscular mycorrhizal fungus (AMF), on five genotypes of maize (Zea mays L.), in relation to plant biomass, shoot N and P concentrations, and fine root morphological traits. The experimental design was entirely randomized in a factorial 5 × 4 × 2 arrangement, i.e., five maize genotypes (hybrids C333B, AS3466, and PREMIUM, and the inbreed lines lg40897-1 and lg40505-1), three diazotrophic bacteria (Azospirillum lipoferum, A. amazonense, and Burkholderia sp.) in addition to a control without bacterial inoculation, co-inoculated or not with the AMF Glomus clarum. The non-mycorrhizal plants inoculated with Azospirillum exhibited the highest N concentrations. The lines lg40897-1 and lg40505-1 showed higher P concentrations as compared to the hybrids, mainly when colonized by AMF. The higher levels of mycorrhizal colonization (90%) occurred in the C333B and lg40897-1 genotypes, which also exhibited a greater root diameter. Mycorrhiza increased shoot and root biomass, besides root traits as total length, specific length, total surface, and incidence of root hairs in all genotypes. In addition, mycorrhiza also stimulated the root colonization by diazotrophic bacteria. The bacteria did not affect root morphological traits and mycorrhizal colonization.

Algumas bactérias diazotróficas podem fixar N biologicamente em gramíneas, as quais se associam a fungos micorrízicos, o que pode levar a um aumento principalmente da absorção de P. Dentre os fatores que afetam as interações planta-microrganismos, o genótipo da planta tem importante papel. Esse trabalho avalia o efeito de bactérias diazotróficas e de um fungo micorrízico arbuscular (FMA) em cinco genótipos de milho (Zea mays L.), em relação à biomassa das plantas, teores de N e P na parte aérea e parâmetros relacionados à morfologia das raízes finas. O delineamento experimental foi inteiramente casualizado, em arranjo fatorial 5 × 4 × 2, sendo cinco genótipos de milho (híbridos C333B, AS3466, PREMIUM e as linhagens lg40897-1 e lg40505-1), três bactérias diazotróficas (Azospirillum lipoferum, A. amazonense e Burkholderia sp.), mais um controle sem bactéria, co-inoculadas ou não com o FMA Glomus clarum. As plantas sem FMA e inoculadas com Azospirillum apresentaram os maiores teores de N. As linhagens lg40897-1 e lg40505-1 apresentaram maior concentração de P em relação aos híbridos, principalmente quando micorrizadas. Os maiores níveis de colonização micorrízica (90%) ocorreram nos genótipos C333B e lg40897-1 que, por sua vez, apresentaram maior diâmetro de raízes. O FMA aumentou a biomassa da parte aérea e das raízes, comprimento total e específico, superfície total e incidência de pêlos nas raízes em todos os genótipos. O fungo micorrízico também estimulou a colonização das raízes pelas bactérias diazotróficas. Já as bactérias não alteraram as características morfológicas das raízes e nem a colonização micorrízica.