Soil properties and not inputs control carbon : nitrogen : phosphorus ratios in cropped soils in the long term

Abstract

Abstract. Stoichiometric approaches have been applied to understand the relationship between soil organic matter dynamics and biological nutrient transformations. However, very few studies have explicitly considered the effects of agricultural management practices on the soil C : N : P ratio. The aim of this study was to assess how different input types and rates would affect the C : N : P molar ratios of bulk soil, organic matter and microbial biomass in cropped soils in the long term. Thus, we analysed the C, N, and P inputs and budgets as well as soil properties in three long-term experiments established on different soil types: the Saria soil fertility trial (Burkina Faso), the Wagga Wagga rotation/stubble management/soil preparation trial (Australia), and the DOK (bio-Dynamic, bio-Organic, and “Konventionell”) cropping system trial (Switzerland). In each of these trials, there was a large range of C, N, and P inputs which had a strong impact on element concentrations in soils. However, although C : N : P ratios of the inputs were highly variable, they had only weak effects on soil C : N : P ratios. At Saria, a positive correlation was found between the N : P ratio of inputs and microbial biomass, while no relation was observed between the nutrient ratios of inputs and soil organic matter. At Wagga Wagga, the C : P ratio of inputs was significantly correlated to total soil C : P, N : P, and C : N ratios, but had no impact on the elemental composition of microbial biomass. In the DOK trial, a positive correlation was found between the C budget and the C to organic P ratio in soils, while the nutrient ratios of inputs were not related to those in the microbial biomass. We argue that these responses are due to differences in soil properties among sites. At Saria, the soil is dominated by quartz and some kaolinite, has a coarse texture, a fragile structure, and a low nutrient content. Thus, microorganisms feed on inputs (plant residues, manure). In contrast, the soil at Wagga Wagga contains illite and haematite, is richer in clay and nutrients, and has a stable structure. Thus, organic matter is protected from mineralization and can therefore accumulate, allowing microorganisms to feed on soil nutrients and to keep a constant C : N : P ratio. The DOK soil represents an intermediate situation, with high nutrient concentrations, but a rather fragile soil structure, where organic matter does not accumulate. We conclude that the study of C, N, and P ratios is important to understand the functioning of cropped soils in the long term, but that it must be coupled with a precise assessment of element inputs and budgets in the system and a good understanding of the ability of soils to stabilize C, N, and P compounds.

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

“…Other studies have observed that adding additional phosphorus and sulfur at the time of residue C incorporation increased SOC throughout a 1.6 m soil profile (Frossard et al, ; Kirkby, Richardson, Wade, Conyers, & Kirkegaard, ). The SOC increases we observed throughout the 2 m profile may have been similarly facilitated by the relatively large amounts of P, S (>25 kg/t) and other nutrients applied in the poultry manure compost alongside compost‐C inputs.…”

“…Increased soil available N provided by the leguminous WCC may have increased the microbial use efficiency of WCC-C inputs, leading to greater incorporation of WCC-C into microbial bodies and ultimately greater soil organic C pools (Lange et al, 2015). Other studies have observed that adding additional phosphorus and sulfur at the time of residue C incorporation increased SOC throughout a 1.6 m soil profile (Frossard et al, 2016;Kirkby, Richardson, Wade, Conyers, & Kirkegaard, 2016). The SOC increases we observed throughout the 2 m profile may have been similarly facilitated by the relatively large amounts of P, S (>25 kg/t) and other nutrients applied in the poultry manure compost alongside compost-C inputs.…”

Spatial and Temporal Trends of Recent Dissolved Phosphorus Concentrations in Lake Tana and its Four Main Tributaries

“…The breakup of aggregates made the soils finer (Costa et al ., ; Tebebu et al ., ). This then resulted in both more leaching of nutrients (Frossard et al ., ) and greater sediment concentrations in surface runoff (Fernández‐Sanjurjo, ; Tebebu et al ., ; Zhang et al ., ). To maintain crop yield, fertilizer and pesticide use increased, leading to even greater nutrient losses (Tilman et al ., ).…”

“…Thus, nutrient depletion, land degradation, and water quality under continuous cultivation after deforestation are strongly related. While the effect of nutrient depletion on land degradation has been well researched (Drechsel et al ., ; Oenema et al ., ; Frossard et al ., ), less is known with respect to water quality and eutrophication.…”

Agricultural land abandonment in Mediterranean environment provides ecosystem services via soil carbon sequestration

“…Agricultural soils are a source of CO 2 emission around the world, and this is accompanied by mismanagement that results in high erosion rates, soil aggregate loss, low infiltration rates, and changes in the soil biota (Bruun et al, 2015;Choudhury et al, 2016;de Moraes Sá et al, 2015;de Oliveira et al, 2015;Frossard et al, 2016;Gelaw et al, 2015;Leifeld and Mayer, 2015). The impact of CO 2 on global warming has resulted in a growing interest in reducing emissions and increasing sequestration, and soil can be a good sequestration option under appropriate management (Carr et al, 2015;Ferreira et al, 2016;Hu et al, 2015;Hombegowda et al, 2016;Poeplau et al, 2016).…”