Quantifying annual variations in field scale element flows and balances is essential for sustainable nutrient management in farming systems

<div><p></p><p>Element (nutrient) balances have proven useful in evaluating the sustainability of farming systems. However, most studies have been carried out over 1 year for single nutrients; thus data on annual variations are scarce, and so is the information on the behaviour of different elements. In addition, most studies have been carried out as farm-gate balances that do not include internal flows such as home-produced fodder and manure, which is crucial to assess the sustainability of management practices, in particular in organic systems. In this study, field level flows were monitored during 3 years and input–output mass balances were calculated for macronutrients (K, P) and trace elements (Cd, Zn) in adjacent organic and conventional dairy systems in Sweden. In addition, nitrogen balances were established for the first year of the study. Variations in element concentrations and mass flows between systems and years were analysed statistically for selected inputs and outputs. The K balances were negative (−39 to −22 kg ha⁻¹ yr⁻¹) all years in both systems, except one year in the conventional system, with less K harvested in organic crops. The organic P balance fluctuated around zero all years, whereas it was slightly positive in the conventional. Cadmium and Zn balances were positive in all years for both systems with lower surplus in the organic (Cd 0.24–0.70; Zn 225–463 g ha⁻¹ yr⁻¹). The inter-annual variation in flows was 10–40% for most elements. Incorporating variations, in addition to mean values, in field (soil surface) balances is recommended in order to assess and combat risks for long-term soil depletion or accumulation of essential and potential toxic elements.</p></div

Assessing biogas digestate, pot ale, wood ash and rockdust as soil amendments: effects on soil chemistry and microbial community composition

<div><p>Applying by-products as soil amendments to agricultural systems is growing in popularity. We aimed to assess the efficacy of some contemporary by-products to provide nutrients to crops as well as the potential harm of adding toxic elements to the environment. Four different by-products widely available in Northern Europe were tested for their effects on two nutrient-poor agricultural soils in terms of increasing available macro- and micro-nutrients as well as toxic elements. Assessing soil microbial community as a sensitive tool for evaluating soil quality was conducted with the focus on microbial activity, carbon metabolism and on <i>Rhizobium/Agrobacterium</i>. Wood ash increased pH and Ca_EDTA, K_EDTA and Mg_EDTA in the soils. The only increase in EDTA-extractable micronutrients in the soils was observed by applying pot ale, increasing Cu. None of the amendments increased the availability of Pb and Cd in the soils. Soils amended with the by-products thus remained similar to the unamended control but were quite different from fully mineral fertilised soils. There were no detectable adverse effects on the physiological and genetic profiles of microbial communities. The by-products were moderately beneficial and did not change the soil microbial community as much as the fully fertilised treatment with mineral fertilisers. Changes in the microbial community profiles were probably due to direct effects on microbes limited by K, Ca and N as opposed to indirect effects on plant growth. This is potentially significant in understanding how to improve impoverished and marginal soils as microbial activity affects many other ecosystem functions.</p></div