Nutrient challenges with solid-phase anaerobic digestate as a peat substitute - Storage decreased ammonium toxicity but increased phosphorus availability.

The solid fraction (SD) obtained after liquid - solid separation of anaerobic digestate is interesting as a potential fertilizer as well as a peat substitute in horticultural growing substrates. We investigated the effect of incubation of the SD obtained by screw-press separation of digestate produced from food waste and plant residues on potentially plant available mineral nutrients and plant growth. The NH4-N concentration was initially > 1000 mg L-1 but rapidly decreased, probably due to NH3 emission promoted by a high initial pH. No nitrate was detected during the first four weeks of incubation. The concentrations of potentially available P and Mg were closely related and strongly increased during incubation. The effect of adding 20 or 30 vol% of SD to a peat-based growing substrate on the growth of basil and lettuce was investigated before and after the incubation period. With the unincubated SD, the initial substrate NH4-N of 200-300 mg L-1 was potentially phytotoxic. Plant growth response ranged from inhibition to stimulation, probably reflecting variation in substrate ammonium status. After 96 days of incubation, ammonium concentrations had decreased with > 50% and basil growth was generally positively affected by addition of incubated SD. However, available P concentrations of 140-210 mg L-1 in the incubated substrates posed a high risk of P leakage. In conclusion, storage greatly reduced NH4-N concentrations and phytotoxicity when the SD was used as a partial substituent for peat in a horticultural growing substrate. Measures are needed, however, to limit available P concentrations in high-P solid digestate fractions.

Growing together gives more rice and aquatic food.

Allowing aquatic organisms to grow in rice fields - a practice called co-culture - increases rice yields while maintaining soil fertility and reducing weeds.

Closing the loop on human urine: Plant availability of zeolite-recovered nutrients in a peat-based substrate.

Recycling mineral nutrients from household wastewater is a central step in the development of a circular economy based society. The objective of this study was to evaluate plant availability of mineral elements and plant performance in a peat substrate containing nutrient-enriched zeolite (NEZ) obtained by nutrient recovery from human urine in a source separated wastewater system. Substrate content of potentially available mineral nutrients was determined by CaCl2/DTPA-extraction during a 12 weeks incubation experiment for 20:80 (R20) and 30:70 (R30) volume % of NEZ:sphagnum peat, limed R20 (R20L), and 20:80 vol% of unloaded zeolite:sphagnum peat (Z20). Plant availability of mineral elements from R20, R20L, R30 and Z20 was compared with conventionally fertilised sphagnum peat (P100) for sunflower (Helianthus annuus L.) cv. 'Topolino' in a pot experiment. Recovery of nutrients in a potentially available form in the R20 substrate after 12 weeks was 3% (K), 23% (N, P), 34% (Mg) and 90% (S). Liming increased the recovery of mineral N to 39%, suggesting that nitrification was an important driver for the release of NH4+. For R20, estimated recovery of urine-derived N in sunflower shoots was 30-36%. Shoot biomass was similar in R20 and in conventionally fertilised peat (P100). However, P100 plants had more leaves and flowers+buds. Initial addition of ammonium phosphate or supplemental fertilisation with a complete nutrient solution increased flower+bud number in R20. For the NEZ-treatments, Cu and B shoot concentrations were in the low or marginal range while Zn and Mn were high or in excess. Shoot growth and nutrient uptake of sunflower were highly restricted in the unloaded zeolite control (Z20). We conclude that 20% NEZ in a peat substrate was effective as a macronutrient source for sunflower, producing similar biomass as in conventionally fertilised peat. However, micronutrient balance and early P supply may need to be adjusted for optimal plant performance.

Organically fertilized onions (Allium cepa L.): effects of the fertilizer placement method on quercetin content and soil nitrogen dynamics.

Field-cured onions cv. Hyskin ( Allium cepa L.) supplied with organic nitrogen fertilizer were studied. The fertilizer was applied by broadcasting and harrowing, broadcasting and rotary cultivation, or placement between rows. Nitrogen dynamics were monitored throughout the growing season by soil sampling. Variation in quercetin content in the onion scales was analyzed by HPLC. The organically fertilized onions were compared with inorganically fertilized onions grown in the same field. Inoculation with arbuscular mycorrhizal fungi (AMF) in the row at sowing or during commercial transplant production was tested but did not significantly affect mycorrhizal root colonization levels in the field. Onions that received no fertilizer at all or that had fertilizer placed between rows had better establishment, probably due to more favorable soil nitrogen concentrations for seedling emergence. Broadcast application led to higher nitrogen concentration in the root zone, resulting in fewer but larger individual onions. Quercetin levels were not significantly altered as a result of nitrogen fertilizer source (inorganic or organic), application method, or mycorrhizal inoculation. However, variation between years was significant, with quercetin levels in 2004 almost twice as high as those in 2005.