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The study examines the performance of different organic phosphate and nitrogen fertilisation methods in organic farming.

Sewage sludge incineration-ash (FB-I) represents a potential alternative phosphorus (P) fertiliser with a high concentration of P, although with relatively low crop availability. In this study, we investigated two P-solubilisation approaches (acidification and P mobilisation by citrate) to enhance plant P uptake from the FB-I ash in a pot study by using various biotic strategies: (1) a pre-treatment of ash with a Penicillium bilaiae inoculum, (2) an isogenic line of wheat that excretes citrate from the root tip, (3) nitrogen (N) provided as (Formula presented.) combined with nitrification inhibitor dicyandiamide (DCD). All strategies were tested combined with each other and with different methods for ash application: (1) completely mixed within the top one third of soil in a pot, or (2) applied as distinct band at 10 cm depth. Triple super phosphate (TSP) at a rate of 15 mg P kg−1 soil per pot was sufficient to support maximum shoot growth. Ash mixed into the first top third part of soil in the pot at a rate of 180 mg P kg−1 soil (equivalent to 60 mg P kg−1 soil throughout the pot) significantly increased the soil water-extractable P and the subsequent shoot P uptake and shoot biomass for both wheat lines and microbial pre-treatment to support maximum plant performance. Shoot P concentration in these treatments was further enhanced when the plants received (Formula presented.) and DCD, although not leading to a significant increase in shoot biomass. The citrate secretion by the root tips and pre-inoculation with P. bilaiae of the ash did not influence plant growth. In conclusion, root-zone soil acidification by (Formula presented.) nutrition is regarded as a promising strategy to improve the fertilising effect of such alternative P fertilisers originating from urban waste streams.

Background: Phosphorus recycling from waste and localised placement of fertilisers can be means to improve sustainable P management in agriculture. However, knowledge about root and plant P uptake responses to placement of complex waste- derived fertilisers is lacking. Methods: Sewage sludge (SS) and sewage sludge ash (ASH) were tested against triple superphosphate (TSP) in a rhizobox setup where shoot and root growth of maize was followed for 30 days. The three P sources were either mixed homogenously into the soil (labelled with 33P) or localised in a patch close to the seed. Results: While localised TSP and SS both increased root length density around the fertiliser patch, it was at the expense of the remaining root system and soil P uptake for SS. Hence, total P uptake was slightly lower and dry matter yields similar to mixed SS. Thus, only TSP enhanced dry matter yield and fertiliser P uptake compared to the mixed source. No root response was found for localised ASH, and mixed ASH more than doubled dry matter yield and P uptake in comparison. Conclusions: Localised placement of fertilisers can be expected to be beneficial for young maize plants only for fertiliser types that can supply sufficient amounts of readily available P.

Determining genotypic responses to soil fertility may assist selection of cultivars that can be adapted to varied soil fertility regimes, and such selection under field conditions is still limited. A two-year field experiment was conducted in long-term field trials to investigate wheat genotype effects on early growth, yield and nutrient accumulation as affected by varied long-term soil fertility managements and nitrogen (N) fertilization. Results show that the early growth, grain yield and nutrient accumulation of spring wheat plants were strongly affected by soil fertility managements and genotypes. Early shoot and root biomass of singly grown plants and leaf canopy growth under standard growth density was associated with subsequent grain yield of plants under standard growth density across the gradient in soil fertility levels. Taifun and Thasos had stable higher yield and N and phosphorus (P) uptake across varied soil fertility regimes compared with other genotypes. Økilde, however, increased yield by 8–34% and N and P accumulation by 1– 22% only when grown in the high organic manure treatment compared with other genotypes, indicating that it is more adapted to high organic fertility regimes. Therefore, the different responses and adaptations of genotypes to soil fertility regimes should be included during selection of cultivars.

Background: Penicillium bilaii may enhance P availability to plants, since it has been shown to increase plant growth and P uptake. There is currently increasing interest in using microorganisms to promote P mobilisation from organic P sources. An investigation was conducted to determine the e ects of P. bilaii on P uptake and growth of wheat in the presence and absence of sewage sludge. Two soils di ering in P contents and pH were used, as it was hypothesised that these a ect the e ciency of P mobilisation. Methods: A pot experiment, in which wheat was grown for 35 days in a moderately acidic soil of low P status and a calcareous soil of moderate P status, was conducted. A full factorial design was used with two non‐sterilised soils, three amendments [control, sewage sludge and triple superphosphate (TSP)] and two P. bilaii treatments (with/ without). Shoot and root length, biomass and nutrient contents were analysed in plant, whereas soil samples were analysed for water‐extractable P and soil pH. Results: The shoot length and root biomass of wheat were signi cantly higher when sewage sludge was applied in combination with P. bilaii seed inoculation, in the moderately acidic soil. In contrast, shoot length and biomass and root biomass were higher with P. bilaii compared to the control, but no synergistic e ects of P. bilaii and the organic P source were observed in the calcareous soil. A systematic, but not signi cant increase in total P uptake was found for all treatments inoculated with P. bilaii and for both soils, with the control of the low fertility moderately acidic soil being a notable exception. Conclusions: Sewage sludge was seen to be an e cient P source, on par with TSP in the moderately acidic soil. In the calcareous soil, the P. bilaii treatments without added P fertilisers had the greatest e ect, with both root and shoot biomass increasing signi cantly.

Sewage sludge (SS) can be used as an alternative fertilizer in agriculture. It is normally broad- casted and plowed into soil, but it is not clear if it has a potential as a placement fertilizer. A rhizo- box experiment was conducted to investigate the placement effect of SS and mineral nitrogen (N) fertilizer on shoot and root growth as well as nutrient uptake of spring wheat (Triticum aesti- vum L.). The treatments included localized SS, mixed SS, localized SS and ammonium, local- ized ammonium, and a control without addition of SS and ammonium to examine the effect of SS placement and, further, if ammonium co-localization would enhance the placement effect. The re- sults show that SS fertilization improved soil N and P availability, which significantly increased plant N and P uptake and enhanced shoot growth, while root length was significantly reduced compared to the control. Localized SS increased root proliferation in the placement region, re- sulting in enhanced uptake of P from the SS patch compared to homogenous application. How- ever, co-localized application of ammonium with SS significantly depressed plant shoot and root growth. Localized ammonium markedly restricted root proliferation in the placement region and reduced soil pH in both bulk soil and placement region, contributing to decreased nutrient uptake and plant growth.

The use of crops and catch crops with deep rooting can strongly improve the possibility of retaining nitrate-N that will otherwise be leached to the deeper soil layers and end up in the surrounding environment. But will it always be an advantage for the farmer to grow a catch crop? This will depend on factors such as soil mineral nitrogen level, soil water holding capacity, winter precipitation, rooting depth and N demand of the scceeding crop. These factors interact, and it can be very difficult for farmers or advisors to use this information to decide whether growing a catch crop will be beneficial. To analyse the effect of catch crops under different Danish soil and precipitation conditions, we used the soil, plant and atmosphere model Daisy.