Data for 'Complementary measures of soil texture, organic nitrogen accessibility and rhizosphere dynamics improve nitrogen supply prediction for short-cycle leafy vegetables.'

Description

This is data for 'Complementary measures of soil texture, organic nitrogen accessibility and rhizosphere dynamics improve nitrogen supply prediction for short-cycle leafy vegetables.' Abstract: 'Accurate estimation of soil nitrogen (N) supply to plants is important for optimising fertiliser application, particularly for fast-growing, short-cycle crops with high N demand. Fertiliser recommendations for salad crops rely primarily on pre-sowing soil mineral N (SMN), which may not capture soil N supply via mineralisation during the cropping period. This study evaluated whether the plant N uptake by babyleaf spinach could be predicted by combining measures of soil N availability with soil properties. Six measures of soil N availability: KCl-extractable SMN, Total soil N, Anaerobically mineralizable N, Plant Root Simulator (PRS®)-N, Hydrolysable N and N contained in the free and lightly-occluded light fraction of SOM (FLOLF-N) were compared with plant N uptake across 15 soils. KCl-extractable SMN was a poor predictor of plant N uptake (R2adj = - 0.075), while no individual N availability measure explained more than 28% of its variation. We found that sandy soils with relatively low organic matter could supply substantial quantities of plant-available N. Bayesian multiple regression identified a model including soil texture, PRS® and FLOLF-N that explained 77% of the variation in plant N uptake. These results suggest that predicting N supply for short-cycle crops may benefit from integrating rhizosphere inorganic N availability and N contained within physically accessible SOM fractions with the soil physical properties that control nutrient accessibility and transport.'

Steps to reproduce

Soils (n=15) were collected from southern England to span diverse N fertility, amendment regimes and land‑use histories. At each site, four random points were sampled (0–20 cm depth) using a cleaned hand trowel; 2.5 kg soil per point was composited (10 kg). Large organic matter and fauna were removed. Fresh subsamples were stored at 4 °C for mineral N and anaerobic incubation assays; 1 kg was air‑dried (40 °C, 2–4 days), sieved (2 mm), and stored airtight for physicochemical analyses and pot experiments. For spinach N‑uptake trials, air‑dried soil was weighed into 15 cm pots so that rehydrated mass (70% WHC) equalled 3.0 kg. Soils were rewetted with ultrapure water, equilibrated 24 h, and sown with six Spinacia oleracea cv. Montego seeds (2 cm depth). Seedlings were thinned to three plants. Pots were grown in a glasshouse (Reading, UK) in August, maintained at 70% WHC by gravimetric watering every two days. To ensure N limitation, P, K and Mg were supplied at RB209 rates equivalent to 200 kg P ha⁻¹, 225 kg K ha⁻¹ and 100 kg Mg ha⁻¹. Plants were harvested individually when ≥4 true leaves reached 8–10 cm. Aboveground biomass was weighed fresh, dried (60 °C, 48 h), reweighed, ground, and analysed for total C and N via dry combustion with QC materials traceable to GBW07412. Plant N uptake (mg N kg⁻¹ dry soil) was calculated from dry biomass × N concentration, adjusted for pot soil mass; kg N ha⁻¹ values assumed bulk density 1.3 g cm⁻³ and 30 cm depth. Total soil N was measured on finely ground, air‑dried subsamples (10 mg) by dry combustion with QC soils. Mineral N was extracted from fresh soil (40 g, 5 mm sieved) using 1 M KCl (200 ml, 1 h shaking at 20 °C), filtered (GF/A), stored at 4 °C, and analysed for NH₄⁺ and NO₃⁻ using a continuous‑flow analyser. Plant uptake efficiency was calculated as plant N uptake divided by initial mineral N. Potentially mineralisable N was determined via 14‑day anaerobic incubation: three subsamples were extracted immediately (baseline), and three were flooded with ultrapure water, sealed, flushed with N₂, incubated at 30 °C in the dark, then extracted with 2 M KCl (final 1 M). Mineralisable N was the change in NH₄⁺‑N. PRS® probes(WesternAg Innovations Inc, Saskatoon, Canada) (one AEM, one CEM per pot) were inserted one week after sowing and left for 14 days. Probes from three replicates were combined per soil, cleaned, stored moist at 4 °C, and analysed by WesternAg. Free + lightly occluded light SOM fractions were isolated from air‑dried soil (15 g) using sodium polytungstate (1.8 g cm⁻³) and sonication (22 J ml⁻¹), followed by centrifugation, GF/A filtration, washing, drying (70 °C), and gravimetric quantification. Material was ground and analysed for C and N by dry combustion. Hydrolysable organic N was measured by cold then hot (95 °C, 8 h) 6 M HCl hydrolysis of air‑dried soil (1.5 g), neutralisation with NaOH, centrifugation, filtration (0.45 µm), and TOC/TN analysis.

Institutions

• University of Reading

  England, Reading

Categories

Funders

• Biotechnology and Biological Sciences Research Council

  UK Research and Innovation

  England, Swindon

  Grant ID: BB/V509759/1

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