Respiration and soil chemistry data from a 59-day factorial incubation testing how four consumer plastics and mineral nitrogen affect carbon and nutrient dynamics in an acidic tropical cropland soil.

Respiration and soil chemistry data from a 59-day factorial incubation testing how four consumer plastics and mineral nitrogen affect carbon and nutrient dynamics in an acidic tropical cropland soil. The experiment. A soil of the Hang Dong series (Typic Endoaqualf, pH 5.45, organic matter 1.91 per cent), sampled at 0 to 10 cm from Sop Poeng, Mae Taeng, Chiang Mai, Thailand, was incubated for 59 days in a design crossing five microplastic treatments with two nitrogen levels, eight replicate vessels each, 80 units in total. The polymers were milled from consumer products: polyethylene from clear food-grade bags, polypropylene from opaque white carrier bags, polystyrene from disposable spoons, and polylactic acid from bags sold as biodegradable. They were sieved to 53 to 250 micrometres and applied at 1 per cent by weight. Fertilised vessels received ammonium nitrate at 35 mg N per kg of soil, applied once on day 8 of the incubation; unfertilised vessels received an equal volume of deionised water at the same time. The addition falls inside the days 7 to 10 interval during which no alkali trap was in place, so the samplings on days 4 and 7 precede the nitrogen treatment and day 11 is the first measurement after it. Moisture was held at 60 per cent of water-holding capacity. Carbon dioxide was trapped in standardised sodium hydroxide and determined by titration at nine samplings: days 4, 7, 11, 17, 24, 31, 38, 52 and 59. Ammonium, nitrate, available phosphorus, organic carbon, pH and electrical conductivity were determined on every vessel at the end. Files. ● respiration_9point.csv - 720 rows, one per vessel per trapping interval: eighty vessels at nine samplings. The day-4 trap of the first unfertilised control vessel reads zero rather than being absent, its sample titre having equalled the blank exactly. The file includes the raw titration volumes and the acid normality alongside the derived values, so the carbon dioxide calculation can be reproduced rather than taken on trust. One processing rule is needed to reproduce it exactly: in 93 of the 720 intervals the sample titre exceeded the blank, which the expression returns as a negative quantity, and each of those was recorded as zero. The rule is applied identically to every vessel and changes no conclusion; the README gives the detail. ● soil_chemistry_day59.csv - 80 rows, one per vessel, all determined at the end of the incubation. ● Identifiers. Both files carry the same two. vessel_id runs from 1 to 80 and names a single incubation vessel throughout the deposit; it is the key on which the two files join. replicate is the vessel number within its nitrogen level, 1 to 8 for the unfertilised vessels and 9 to 16 for the fertilised ones, repeating for each polymer, and is unique only in combination with plastic and n_group. Either identifier reproduces the treatment means. Only vessel_id pairs the respiration of a vessel with its own final chemistry, which the correlations between cumulative respiration and the final soil variables require. ● README.md - the design, the analytical method for each variable, and what was not measured. ● Both data files are also provided in Excel format. Analytical methods. pH in a 1:1 soil-to-water suspension; electrical conductivity at 1:5; organic carbon by wet oxidation with back-titration against ferrous ammonium sulphate, with organic matter as organic carbon multiplied by 1.724; available phosphorus by Bray II with ascorbic acid molybdenum blue at 820 nm; ammonium extracted with potassium chloride at 1:10 and read as indophenol blue at 650 nm; nitrate extracted with potassium sulphate at 1:2 and read by nitration of salicylic acid at 410 nm. The two mineral nitrogen determinations used different extractants because they were run as separate procedures, and are reported on their respective bases. Three features of the conduct of the experiment are recorded because they affect interpretation. The incubation was not isothermal: temperature was controlled at 25 degrees Celsius for the first 28 days and the vessels were then held at ambient laboratory temperature, 27 to 32 degrees Celsius. No alkali trap covers days 7 to 10, so cumulative totals understate the true evolution by about 7 per cent; every vessel shares the gap, so comparisons are unaffected. Soil was removed for chemical analysis part-way through, so the final two intervals rest on 200 g of soil rather than 300 g, which is accounted for in the per-kilogram conversion. What these data cannot settle. No isotopic label was used. The respiration recorded is total soil respiration in the presence of polymer, and the excess over the unamended control cannot be separated into polymer carbon, additive carbon, and primed soil organic matter. The fillers of the consumer articles were not identified and their amounts are not reported here, so the polymer treatments carry unquantified additive loads; the ash of the polystyrene was shown not to be alkaline. Particle-size distribution and total nitrogen were not determined on the batch of soil used. Related publication. These data support the manuscript Microplastic type, not nitrogen fertilisation, governs nitrogen transformation in an acidic tropical cropland soil, prepared for submission to SOIL. Every numerical result reported in that manuscript can be reproduced from the two files deposited here. Companion manuscript. The respiration record deposited here is also the dataset analysed in a companion manuscript, A diagnostic for unidentifiable decomposition constants, and what nine-model comparison reveals about microplastic mineralisation, submitted to Scientific Reports on 30 July 2026. That paper uses the carbon dioxide data alone; the soil chemistry and the treatment comparisons appear only in the SOIL manuscript. Both papers cite each other.