Abstract
Accurate estimates of the quantity and rate of soil nitrogen supply (SNS) are essential to increase soil and farm N use efficiencies, in particular for soils high in organic matter. The objective of this work was to enhance the empirical understanding of the SNS of dairy grasslands on peat soils, using soil properties and weather variables. Data were collected from studies on herbage N uptake carried out between 1992 and 2017 in the western peat district of the Netherlands. For the period between March to mid October, SNS was estimated from the sum of mean growing season daily temperatures, soil organic matter (SOM) and applied calcium ammonium nitrate (CAN) N with a residual standard error of 25–27 kg ha−1. Each °C growing season temperature sum affected SNS by 78–90 g ha−1 and each g SOM per 100 g dry soil affected SNS by 3.6–3.9 kg ha−1, respectively. SNS was equally estimated for conditions with and without CAN fertilisation. Validation with data from independent field trials showed similar impacts of SOM and growing season temperature sum on SNS. The error of prediction of the presented models, however, was still too large for direct on-farm application and led to underestimations for a specific site. Nevertheless, the obtained models allow for an increased understanding of soil and farm N balances. The models can therefore be used for improved temporal and spatial SNS-adapted farming practice advice, which can potentially lead to reduced soil and farm N surpluses.
Highlights
In temperate climates, drained peatlands are often in use as grassland for dairy farming (Joosten et al 2017; Van Kekem 2004)
The following data selection criteria were applied: (1) Data had to have been collected from sites which were in use as production grasslands within a dairy farming system for multiple years before the year of measurements; (2) Herbage dry matter yields and total N content had to have been determined per harvest in the first year after cessation of the use of organic inputs; (3) Yields from at least two harvests had to have been determined using a ‘Haldrup’ small plot harvester
For soil N supply (SNS) estimations of all treatment means, soil pH and winter temperature sum correlated significantly with soil organic matter (SOM) and precipitation deficit (p \ 0.001, Table 4), and, soil pH and winter temperature sum were excluded as candidate predictors
Summary
In temperate climates, drained peatlands are often in use as grassland for dairy farming (Joosten et al 2017; Van Kekem 2004). Dairy farming on peat soils often results in farm N use efficiencies—defined as the amount of N output relative to the N input of the farm—that are relatively lower than that on mineral soils because of the high levels of soil N mineralisation (De Visser et al 2001; Van Beek et al 2009). Herbage N uptake and content are generally higher in dairy grasslands on peat soils than on mineral soils, largely due to higher levels of N mineralisation (De Visser et al 2001; Deru et al 2019; Van Beek et al 2009; Van Kekem 2004). Dutch farm management advice for peat soils is currently not adapted to spatial and temporal variations of SNS (Bemestingsadvies 2014)
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