Effects of Compost–Chemical Fertiliser Mix and N-Timing on Tomato: Detailed Study Notes

Study Context and Objectives

• Article investigates combined use of cow-manure compost and chemical fertiliser for tomato (Solanum lycopersicum L.) grown in silty-loam soil of Changchun, China.

• Two factors evaluated simultaneously (seldom done in prior work):

  • Mixed ratio of compost to chemical fertiliser (four levels)

  • Timing of chemical-N application (two schedules)

• Comprehensive evaluation spanning:

  • Soil chemistry (available $N, P$, organic matter)

  • Plant morphology & biomass

  • Leaf photosynthetic pigments

  • Yield components & fruit quality

• Goal: identify optimal compost–chemical blend & suitable N-timing for sustainable tomato production.

Experimental Design

• Growth period: 14 May – 29 July 2019 (76 days) in controlled growth room.

• Photoperiod & climate: 14 h light/10 h dark; $550{-}600\,\mu\text{mol m}^{-2}\text{s}^{-1}$ PPFD; $32/28\,^{\circ}!\text{C}$ (light/dark).

• Plant material: ‘Little Bing’ tomato seedlings at 3-leaf stage; planted in plastic pots (⌀30 cm × 16 cm) containing 4 kg field soil.

• Soil type: silty loam; baseline properties (mean ± SE):

  • Organic matter $2.64\pm0.08\%$

  • Available $N$ $127.7\pm1.5\,\text{mg kg}^{-1}$

  • Available $P$ $20.2\pm1.6\,\text{mg kg}^{-1}$

  • Heavy metals below WHO/FAO limits.

• Cow-manure compost fully matured; organic matter $35.1\%$, available $N$ $1389\,\text{mg kg}^{-1}$, available $P$ $1710\,\text{mg kg}^{-1}$.

Treatments and Fertiliser Regimes

• Nine treatments = 4 fertiliser ratios × 2 N-timings + control (CK, no inputs):

  • Ratios (compost : chemical) based on N source:

  • CF30 70 % compost + 30 % chemical

  • CF50 50 % compost + 50 % chemical

  • CF70 30 % compost + 70 % chemical

  • CF100 0 % compost + 100 % chemical

  • N-application schedules:

  • N25 25 % urea at transplanting + 75 % at flowering

  • N50 50 % urea at transplanting + 50 % at flowering

• Five replicates per treatment (randomised; pots re-randomised weekly).

• Equal total nutrient supply for all fertilised pots:
  $0.12\,\text{g N kg}^{-1},\;0.11\,\text{g P}<em>2\text{O}</em>5\,\text{kg}^{-1},\;0.38\,\text{g K}_2\text{O kg}^{-1}$

Measurements & Protocols

• Plant height: 30, 45, 60, 75 days after transplanting (DAT).

• Final biomass: fresh shoot, dry shoot, dry root; branch number.

• Photosynthetic pigments (50 & 70 DAT) via 95 % ethanol extraction; equations:
  $C<em>a=13.36A</em>{664.2}-5.19A<em>{648.6}$ $C</em>b=27.43A<em>{648.6}-8.12A</em>{664.2}$
  $C<em>{a+b}=5.24A</em>{664.2}+22.24A<em>{648.6}$ $C</em>{x+c}=\frac{1000A<em>{470}-2.13C</em>a-97.64C_b}{209}$

• Yield at harvest: total fruit weight plant⁻¹, fruit number plant⁻¹, mean fruit mass, fruit length & diameter.

• Fruit quality: total soluble sugar, vitamin C (2,6-dichloro-indophenol titration), pH, moisture.

• Soil post-harvest: available $N$, available $P$, organic matter.

• Stats: Two-way ANOVA (factors: ratio, N-timing). Significant main effects → one-way ANOVA + Duncan at $p\le0.05$.

Key Findings: Soil Properties

• Mixed fertiliser treatments significantly ↑ soil fertility vs. CF100 and CK.

• Under both N25 & N50:

  • Available $N$ ↑ $21{-}46\%$ vs. CF100.

  • Available $P$ ↑ $55{-}312\%$.

  • Organic matter ↑ $21{-}46\%$.

• Trend: Higher compost ratio → higher nutrient retention.

• CF30 maintained available $N$ near initial level (~$125\,\text{mg kg}^{-1}$); CF100 declined to ~$86\,\text{mg kg}^{-1}$ (≈ CK).

• No significant influence of N-timing or interaction.

Key Findings: Plant Growth Traits

• Plant height:

  • Early growth vigorous; differences fade by 60 DAT.

  • Final height similar among fertilised treatments; all > CK in most cases.

• Biomass (fresh & dry) and root weight:

  • All fertilised > CK.

  • CF50 showed maximum shoot & root dry matter: $+22{-}38\%$ vs. CF100.

• Branch number: fertilised > CK; no difference among fertilised ratios.

• No main/interaction effect of N-timing on any growth trait.

Photosynthetic Pigments

• Chlorophyll $a+b$ and carotenoids significantly ↑ in all fertilised pots vs. CK.

• No difference between mixed vs. pure chemical; N-timing insignificant.

• Elevated pigments attributed to adequate $N$ supply supporting biosynthesis.

Yield Components

• Total yield and fruit number driven solely by fertiliser ratio (not timing):

  • Yield ranking: CF30 > CF50 > CF70 > CF100 ≫ CK.

  • CF30 improved yield by $17{-}85\%$ and fruit count by $21{-}108\%$ vs. CF100.

• Single-fruit metrics (length, diameter, weight) unchanged across treatments.

Fruit Quality Attributes

• Total sugar, vitamin C, pH, moisture showed no significant variation with fertiliser regime or N-timing.

• Slight (non-significant) decline in sugar & vitamin C with higher compost proportions.

• Supports idea of comparable nutritional profile between organic & conventional fruits.

Statistical Highlights

• Factor “Fertiliser ratio” significant for almost all soil & plant variables except fruit chemistry.

• Factor “N-timing” and Ratio × Timing interaction generally non-significant.

Mechanistic & Theoretical Insights

• Compost supplies slow-release nutrients, enhances microbial mineralisation and soil structure → sustained fertility.

• Medium compost proportion (50–70 %) may balance macro- vs. micronutrient supply and avoid phytotoxic/metabolic imbalance.

• High chemical-N alone can trigger rapid early growth but depletes soil N reservoir and may induce chlorosis at late stage.

Practical Implications

• Recommended blend for silty-loam tomato: 70 % compost + 30 % chemical (CF30) delivering highest soil quality and yield.

• Flexibility in N-split (25/75 vs. 50/50) has minimal impact → simplifies management.

• Organic amendments more critical for soil health than fine-tuning fertiliser application time.

• Adoption aids Integrated Soil Fertility Management (ISFM) & reduces reliance on synthetic fertilisers.

Limitations & Future Directions

• Pot study; field-scale verification needed across soil types & climatic zones.

• Single compost source (cow manure); other organic wastes should be tested.

• Long-term crop rotations & cumulative heavy-metal monitoring necessary.

• Investigate microbiome dynamics, greenhouse gas fluxes & economic cost–benefit.

Connections to Literature & Sustainability

• Aligns with ISFM principles (Vanlauwe et al.) and reports of compost boosting microbial activity.

• Addresses SDG 2 (Zero Hunger) & SDG 15 (Life on Land) by promoting sustainable nutrient cycles.

Echoes findings that nutritional superiority of organic produce is equivocal (Reganold 2010; Vinha 2014).