Abstract
There is an urgent need for better management practices regarding livestock farm nutrient imbalances and for finding alternatives to the actual use of mineral fertilizers. Acidification of animal manure is a mitigation practice used to reduce ammonia emissions to the atmospheric environment during manure storage and land application. Acidification modifies manure physicochemical characteristics, among which soluble N and P significantly increase. The main objective of this study was to investigate if acidification and the addition of a nitrification inhibitor to manure and placement of the treated manure close to the seed can stimulate maize growth by enhancing nutrient availability, specially P and consequently plant P uptake, at early development stages without the use of mineral N and P as a starter fertilizer. Raw dairy slurry and solid fractions from dairy slurry and digestate from a biogas plant were acidified to pH 5.5 and applied with or without a nitrification inhibitor (DMPP, 3,4-dimethyl pyrazole phosphate) to maize in a pot experiment, where biomass productivity, nutrient uptake and soil P availability were examined. Acidification increased the water-extractable P fraction of all slurry and digestate organic residues (by 20–61% of total P) and consequently plant P uptake from solid fractions of both slurry and digestate compared to the untreated products (by 47–49%). However, higher plant biomass from acidification alone was only achieved for the slurry solid fraction, while the combination of acidification and DMPP also increased plant biomass in the digestate solids treatment (by 49%). We therefore conclude that the combination of acidification and a nitrification inhibitor can increase the starter fertilizer value of slurry and digestate products sufficiently to make them suitable as a maize starter fertilizer.
Highlights
During the early growth stages of maize, the plant typically has a high nitrogen (N) and phosphorus (P) demand due to a fast plant development rate.Low soil temperatures have negative effects limiting root development, decreasing the soil volume that can be explored for sources of available P, which results in a reduced root surface area for P uptake.P uptake efficiency per unit root length is decreased at low temperatures [1]
Raw dairy slurry was included as a standard reference manure available for crop fertilization on all dairy farms, while the solid fraction obtained by mechanical separation of raw dairy slurry or digestate from an anaerobic digestion plant was included because the solids produced by mechanical separation are more concentrated in N and in particular P than their unseparated sources [22], and more suitable as a starter fertilizer
The highest buffering capacity for digestate solid fraction (DSF) was observed between pH 6.7 and pH 5.5, while for Raw dairy slurry (RS) and raw dairy slurry solid fraction (RSSF), buffer capacity was highest between pH 2.5 and pH 1.5 (Figure 1)
Summary
During the early growth stages of maize, the plant typically has a high nitrogen (N) and phosphorus (P) demand due to a fast plant development rate.Low soil temperatures have negative effects limiting root development, decreasing the soil volume that can be explored for sources of available P, which results in a reduced root surface area for P uptake.P uptake efficiency per unit root length is decreased at low temperatures [1]. During the early growth stages of maize, the plant typically has a high nitrogen (N) and phosphorus (P) demand due to a fast plant development rate. Low soil temperatures have negative effects limiting root development, decreasing the soil volume that can be explored for sources of available P, which results in a reduced root surface area for P uptake. P uptake efficiency per unit root length is decreased at low temperatures [1]. P has a low mobility in soil and the speed of diffusion towards the plant root is decreased under cool conditions [2]. This, together with the high demand for exogenous P during early growth stages, can result in plant P deficiency, limiting growth and potential yields in maize crops [3]. An optimal soil or fertilizer P supply during planting and the six-leaf stageis essential to ensure maximum maize
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