•Bulk SOC increased under long-term organic fertilization.•No SOC accumulated in the MAOM fraction (<6.3 µm) over a 36-year period.•Bulk SOC increase under organic fertilization was solely attributed ...to the labile POM fractions.•oPOM-C contents are highly dynamic and depend on farming system.
Agricultural management of soils has led to severe losses of soil organic matter (SOM), accompanied by an increased release of CO2 into the atmosphere and a reduction of soil fertility. Especially under the aspect of global warming and the increasing demand for food, there is a need for sustainable management options increasing soil organic carbon (SOC) storage in agricultural soils, but knowledge gaps exist regarding C persistence in, and its transfer between functional SOC pools, within different farming systems. Here we report on impacts of different farming systems on the temporal dynamics of SOM fractions within the DOK long-term trial (Switzerland), from 1982 to 2017. A purely minerally (CONMIN), a minerally and organically (CONFYM), and a purely organically fertilized farming system (BIODYN) were compared with an unfertilized control (NOFERT). We separated archived soils from the Haplic Luvisol (0–20 cm depth) into particulate (POM) and mineral-associated OM (MAOM) fractions, via physical fractionation, and analyzed the chemical composition of selected fractions via solid-state 13C CPMAS-NMR spectroscopy. We demonstrate that under none of the analyzed farming systems, additional SOC was sequestered in the clay-sized MAOM fraction (<6.3 µm) over a period of 36 years. In all fertilized systems, the amount of SOC in this pool did not change, but strongly decreased in NOFERT (-27%). Bulk SOC increased in BIODYN (+13%) and CONFYM (+5%), but decreased in CONMIN (-8%) and NOFERT (-20%). As no additional SOC accumulated in the clay-sized MAOM fraction, this implies that bulk SOC increases were solely stored within labile POM fractions. NMR spectra showed comparable POM chemical compositions between different systems. Differences in fertilizer quality (BIODYN = composted farmyard manure vs CONFYM = stacked farmyard manure + mineral fertilizer) and the omission of pesticides resulted in better conditions for POM stabilization and consequently significantly higher C contents of occluded POM (oPOM) within aggregates, in BIODYN. However, this labile fraction is at high risk of being lost within a few days, as illustrated by the strong annual oPOM-C content fluctuations depending on the timing of soil sampling after harvest. The highest post-harvest oPOM-C losses in BIODYN indicate the higher dynamics compared to CONFYM. It is anticipated that only sustainable fertilization methods with continuous application of solely organic fertilizers in the long-run can maintain SOC in the labile POM fractions at elevated levels, thereby ensuring soil fertility. It also illustrates the need for prevention of major losses by careful management of the labile POM fractions, as this OM could associate with fine mineral particles at a later stage and thus contribute to OC sequestration in the stable SOC pool. Overall, the potential of arable soils to accumulate stable OC for long-term sequestration is questioned.
Soil organic matter (SOM) plays a vital role for soil quality, sustainable food production and climate change mitigation. It is common knowledge that SOM consists of different pools with varying ...qualities, quantities, and turnover times. However, it is still poorly understood how mineral and organic fertilization affects the formation and stabilization of mineral-associated organic matter (MAOM) and how long it can remain there. Here, we report on the long-term effects of different farming systems on the stability and turnover of the fine silt and clay-sized MAOM fraction (<6.3 μm) of a Haplic Luvisol (0–20 cm) in the DOK long-term trial (Switzerland). We compared three farming systems with contrasting fertilization (CONMIN = pure mineral, CONFYM = mineral + organic, BIODYN = pure organic) with an unfertilized control (NOFERT) between 1982 and 2017. We performed specific surface area (SSA) measurements on fractionated MAOM samples (<6.3 μm) from 1982 to 2017, before and after removal of OM, measured the 14C activity of all samples during the entire period and estimated the mean residence time (MRT) with a model taking into account ‘bomb 14C’ and radioactive decay. We found constant MAOM-C contents under organic fertilization. Results of SSA analysis indicate best conditions for MAOM-C stabilization under organic fertilization and different sorption mechanisms in MAOM between farming systems with and without organic fertilization. The modelled MRTs were significantly higher in NOFERT (238 ± 40 yrs) and CONMIN (195 ± 27 yrs), compared to CONFYM (138 ± 18 yrs) and BIODYN (140 ± 19 yrs), implying a high C turnover (i.e. more active MAOM) at high C contents under organic fertilization. Our findings show that MAOM is not the dead OM but corroborates the concept of ‘dynamic stability’. Continuous OM inputs from organic fertilizers and their rapid and constant turnover are needed to stabilize the “stable” MAOM-C fraction.
•SSA analysis reveals improved aggregate stability under organic fertilization.•Significantly shorter MRT of MAOM-C under organic fertilization.•Highest MAOM-C turnover (i.e. more active MAOM) under organic fertilization.•Constant OM input and turnover is vital for maintenance of MAOM-C contents.
•We studied two field experiments on organic vs conventional agriculture in Kenya.•Chemical, biological and physical soil quality indicators were assessed over 9 years.•At the low input level, soil ...quality decreased slightly in either farming system.•At the high input level, soil quality was mostly superior in the organic system.•P accumulation in all treatments raises concerns on input composition and amounts.
Under temperate climate conditions, organic farming systems show improved soil quality compared to non-organic systems, whereas little long-term research on the impact of organic farming on soil quality has been conducted in sub-Saharan Africa. Within the system comparison (SysCom) project, two long-term field experiments were set up in 2007 in the sub-humid Central Highlands of Kenya to compare organic and conventional farming at two input levels (high input systems with recommended rates of nitrogen (N), phosphorus (P) and pesticides and with irrigation vs. rain-fed low input systems with low N, P and pesticides), with a similar design at both sites. The two sites differ mainly in their inherent soil properties and in the amount and distribution of rainfall. At the end of each three-year crop rotation period, we analyzed a set of chemical, biological and physical soil quality parameters in 0–20 cm soil depth. After nine years, microbial parameters seemed to have reached a steady state, whereas chemical parameters were still changing. Most soil quality parameters were highest under the high input organic farming system. The high input conventional system performed well in preserving several soil quality indicators, but a trend for acidification and the lack of soil carbon build-up raise concerns about the long-term sustainability of the system. Low input organic and conventional farming systems did not improve soil quality and even showed decreasing trends in several chemical parameters. Total and available P accumulated over time, especially in both high input systems, suggesting increasing risks of losses to the environment. Pronounced site effects revealed strong interactions with pedo-climatic conditions, with soil quality under high input organic farming improving to a greater extent at the site with more favorable conditions. Besides effects on soil quality, important criteria for sustainable input levels are thus the general availability of inputs, resulting nutrient input–output budgets as well as interactions of inputs with inherent soil properties.
The aim of this paper is to discuss the demand of fresh organic matter (FOM) supply to maintain soil organic matter (SOM) levels and productivity of arable soils under organic management. The basic ...question is whether the different frame conditions in organic vs. conventional farming result in a different and system‐specific FOM demand. If this is the case, it would follow that the farming system has to be considered in the calculation of SOM balances. SOM balances are the most common decision support tools in organic matter management. A conversion to organic farming in practice usually leads to an increase of SOM levels as well as soil microbial activity over time. The system‐specific driver of this effect is the indispensable extension of the share of (perennial) legumes in crop rotations at the expense of non‐legumes such as cereals, row crops, and maize. Extended legume cropping is essential for N supply in crop rotations as the import of N fertilizer in total is limited by organic farming regulations and mineral N fertilizer may not be used at all. Based on this characteristic of organic management, we argue that the demand of FOM supply to soils must be higher than in conventional crop production. The most relevant factors are (1) the non‐existence of mineral N fertilizer as an external N source that supports the maintenance of SOM by decreasing the demand for SOM‐N, (2) benefits of increasing SOM stocks and turnover for soil productivity under organic management, and, (3) increased mass‐losses of FOM and easily degradable SOM compartments due to higher microbial activity in soils. These effects have to be quantified and must be considered in SOM balances in order to avoid misleading assessments and erroneous decisions.
The contents of sugars, organic acids, total phenolic content, and the antioxidant activity were quantified in the flesh of red beet from conventional (CON), integrated (INT), organic (ORG), ...biodynamic (BD), and control farming systems using established methods. Significant differences were measured for malic acid, total phenolic content (TPC), and total antioxidant activity, where malic acid content ranged from 2.39 g kg−1 FW (control) to 1.63 g kg−1 FW (CON, ORG, and INT). The highest TPC was measured in BD and control samples (0.677 and 0.672 mg GAE g−1, respectively), and the lowest in CON samples (0.511 mg GAE g−1). Antioxidant activity was positively correlated with TPC (r 2 = 0.6187) and ranged from 0.823 μM TE g−1 FW to 1.270 μM TE g−1 FW in CON and BD samples, respectively, whereas total sugar content ranged from 21.03 g kg−1 FW (CON) to 31.58 g kg−1 FW (BD). The importance of sugars, organic acids, phenols, and antioxidants for human health, as well as for plant resilience and health, gained from this explorative study, is discussed and put into perspective.
Improving nitrogen (N) efficiency is a priority for increasing food production while reducing its environmental impacts. N efficiency indicators are needed to achieve this goal, but current ...indicators have some limitations. In particular, current N efficiency indicators are not appropriate tools to compare farming systems with different types of production because animal N efficiency is, by nature, lower than crop N efficiency. A novel N efficiency indicator called “relative N efficiency” was developed to address this issue. It was calculated as the ratio of the actual N efficiency of the farming system to the weighted mean of the potential efficiency of each type of product output provided in literature reviews. Relative N efficiency was calculated for 557 farms of various types from France and Italy. The relative N efficiency indicator was validated by comparison with a statistical approach based on multiple linear regression. Statistical analysis showed that relative N efficiency was independent of production type and could therefore be used for unbiased comparison of different farming systems. Relative N efficiency was particularly interesting when comparing mixed farming systems with different proportions of animal and crop production.
Improving nitrogen (N) efficiency is a priority for increasing food production while reducing its environmental impacts. N efficiency indicators are needed to achieve this goal, but current ...indicators have some limitations. In particular, current N efficiency indicators are not appropriate tools to compare farming systems with different types of production because animal N efficiency is, by nature, lower than crop N efficiency. A novel N efficiency indicator called "relative N efficiency" was developed to address this issue. It was calculated as the ratio of the actual N efficiency of the farming system to the weighted mean of the potential efficiency of each type of product output provided in literature reviews. Relative N efficiency was calculated for 557 farms of various types from France and Italy. The relative N efficiency indicator was validated by comparison with a statistical approach based on multiple linear regression. Statistical analysis showed that relative N efficiency was independent of production type and could therefore be used for unbiased comparison of different farming systems. Relative N efficiency was particularly interesting when comparing mixed farming systems with different proportions of animal and crop production.
Improving nitrogen (N) efficiency is a priority for increasing food production while reducing its environmental impacts. N efficiency indicators are needed to achieve this goal, but current ...indicators have some limitations. In particular, current N efficiency indicators are not appropriate tools to compare farming systems with different types of production because animal N efficiency is, by nature, lower than crop N efficiency. A novel N efficiency indicator called "relative N efficiency" was developed to address this issue. It was calculated as the ratio of the actual N efficiency of the farming system to the weighted mean of the potential efficiency of each type of product output provided in literature reviews. Relative N efficiency was calculated for 557 farms of various types from France and Italy. The relative N efficiency indicator was validated by comparison with a statistical approach based on multiple linear regression. Statistical analysis showed that relative N efficiency was independent of production type and could therefore be used for unbiased comparison of different farming systems. Relative N efficiency was particularly interesting when comparing mixed farming systems with different proportions of animal and crop production.
Display omitted
Display omitted
•Management goals were similar for organic and conventional apple orchards.•Organic orchards employed more selective pesticide programs.•Conventional and organic ...orchards did not differ in soil quality and insect counts.•Integrated practices may be more important than being conventional or organic.
Organic farming can improve soil quality and provide effective pest control with reduced inputs compared to conventional farming. Although organic and conventional farming are often viewed as dichotomous, they may overlap in pest management and soil quality goals and outcomes. Here, we assessed similarities and differences between conventional and organic apple orchards in Washington State by quantifying pesticide program risk to natural enemies, soil quality, leaf nitrogen, and abundance of woolly apple aphid (Eriosoma lanigerum) and its natural enemies. We also interviewed orchard owners, managers, and consultants to learn about their practices and opinions of conventional and organic management for aphids and soil quality. Organic orchards used more insecticide applications than conventional orchards, but the insecticides used were rated as less harmful to natural enemies. Conventional and organic orchards had similar soil quality, pest abundance, and natural enemy abundance. Woolly apple aphid abundance was not correlated to soil, plant, or natural enemy measurements. Interviews revealed that management goals were similar in both systems. Overall, our results suggest that both conventional and organic styles of farming are heterogenous. For example, conventional farmers may simply follow recommendations for inputs of synthetic fertilizers and pesticides or go further by using some organic or integrated practices; at the same time, organic farmers can vary in their use of organically certified pesticide sprays and ecologically based management tactics. Our study suggests that integrated management strategies that use a mix of appropriate tactics may be more important than being strictly conventional or organic to achieve superior soil and pest management outcomes.
PDF
