Phosphorus Losses to Surface Runoff Waters After Application of Digestate to a Soil Over Fertilised with Phosphorus

Anaerobic digestates from biogas plants can be used as agricultural fertilisers providing recycling nitrogen (N) and other nutrients for crop needs. It is still unclear the impact on phosphorus (P) losses to runoff waters of digestates as sources of N instead of inorganic N fertilisers in over fertilised soils with P. A field experiment was done in a sandy and acidic soil high in P. The experimental design was completely randomised with five treatments. The inorganic N fertilisation (90 kg ha−1) was done in four treatments, those with past P inputs of the following: (i) inorganic N and P fertilisers (Ni/MF), (ii) organic amendments (pig or duck dry slurry-Ni/PS and Ni/DS or cattle manure compost-Ni/CM). Digestate was applied in plots with past P input of cattle slurry (DG/CS) providing also 90 kg N ha−1. Ryegrass was sowed as cover crop. The concentration of total dissolved P in runoff waters was high in all treatments and ranged between 0.5 (Ni/PS) and 2.6 mg L−1 (DG/CS). These runoff waters pose a risk of non-source P pollution for fresh waters. In soils with low P sorption capacity and over fertilised with P, the fertilisation with anaerobic digestate as the only source of N to crops increased the risk of P losses to runoff waters compared with inorganic N fertilisation. Therefore, the amount of digestate applied to soil must be calculated considering its N:P ratio in order to not exceed the crop P requirement.

Phosphorus Leaching effects of organic and mineral fertilizers on a clay loam soil through in-situ soil columns

<p>The leaching pattern of phosphorus (P) from continuous fertilization is generally neglected in heavy-textured soils. Generally speaking, P is hard to migrate vertically compared with nitrogen (N) and potassium (K) especially in clay loam soils. However, our study has proved that P could be leached to the depth of 1 m below the groundwater under circumstances of heavy rainfalls and large temperature differences. Our research is based on in-situ soil column experiments to estimate the effects of soil P leaching in typical fertilization regimes of Northeastern China. Fertilization treatments include CK (No fertilizer), NPK (900 kg ha<sup>-1</sup> of compound fertilizer), NPKS (NPK + straw return), NPKSM (NPK + straw return + 7.5 ton ha<sup>-1</sup> of dried cattle manure compost), 80% NPKS (720 kg ha<sup>-1</sup> of compound fertilizer + straw return), 80%NPKSM2 (720 kg ha<sup>-1</sup> of compound fertilizer + straw return + 15 ton ha<sup>-1</sup> of dried cattle manure compost). In 2019 and 2020, we collected 10 leachates of each treatment and determined the concentrations of TP (Total P), TDP (Total dissolved P), PP (Particle P), SRP (soluble reactive P), and DOP (dissolved organic P). The results showed that P leaching has obviously occurred after 5-year continuous fertilization, with the leaching ratio accounted for 0.61%-2.2% of total P input, and the ratio of PP to TDP was about 1:1. Furthermore, the leaching loss caused by chemical fertilizer was equivalent to that of straw application and low-dose manure fertilizer, while high-dose manure application significantly caused more P leaching losses than the other treatments. What’s more, manure addition mainly promoted the vertical movement of PP, while straw application chiefly increased the leaching ratio of TDP. 20% reduction of chemical fertilizer significantly reduced the leaching loss of TDP, with a ratio of 16%-17% compared to full-scale chemical fertilizer. Overall, in terms of slightest environment risks from P loss via leaching in this study, the excessive manure application appears to pose a long-term risk of vertical P migration than the inorganic fertilizer and straw amendment.</p>

Microscale Heterogeneous Distribution and Speciation of Phosphorus in Soils Amended with Mineral Fertilizer and Cattle Manure Compost

Global concerns for the sustainability of agriculture have emphasized the need to reduce the use of mineral fertilizer. Although phosphorus (P) is accumulated in farmland soils due to the long-term application of fertilizer, most soil P is not readily available to plants. The chemical speciation of P in soils, which comprise heterogeneous microenvironments, cannot be evaluated with a high degree of specificity using only macroscopic analyses. In this study, we investigated the distribution and speciation of P accumulated in soils by using both macro- and microscopic techniques including chemical extraction, solution and solid-state 31P NMR, bulk- and micro- P K-edge X-ray absorption near edge structure (XANES), and electron probe microanalysis (EPMA). Soil samples were collected from a field in which cabbage was cultivated under three amendment treatments: i) mineral fertilizer (NPK), ii) mineral fertilizer and compost (NPK + compost), and iii) mineral fertilizer plus compost but without nitrogen fertilizer (PK + compost). Macro-scale analyses suggested that accumulated P was predominantly inorganic P and associated with Al-bearing minerals. The repeated application of compost to the soils increased the proportion of P associated with Ca which accounted for 17% in the NPK + compost plot and 40% in the PK + compost plot. At the microscale, hot spots of P were heterogeneously distributed, and P was associated with Fe and Ca in hot spots of the NPK + compost (pH 6) and PK + compost (pH 7) treated samples, respectively. Our results indicate that application of compost contributed to creating diverse microenvironments hosting P in these soils.

The Use of Biochar and Compost Mixtures as Potential Organic Fertilizers

Organic wastes have been used in agriculture many years ago, due to its capacity to improve soil quality. The manure was used before the occurrence of chemical fertilizers and treated / untreated sewage sludge, started to be used as a fertilizer a few years ago. The aim of the study is to evaluate the organic matter, organic carbon, organic content and soil composition, after application in greenhouse conditions, of mixtures made from sewage sludge biochar and cattle manure compost. The biochar and compost used in different concentrations, at 5 t/ha and 30 t/ha, application rates, in greenhouse conditions, for a period of 90 days, improved organic matter, organic carbon and organic content from the soil used in experiment. The sewage sludge biochar and the cattle manure compost had similar effects on the parameters determined in the study. Organic and inorganic soil components, identified by the ATR-FTIR method, have not been modified by application of sewage sludge biochar and cattle manure compost.