Stepwise Precision Fertilization To Quantify Nutrient Accumulation And Partitioning In Double-season Sweet Potato Systems

Summary

This protocol details a stepwise precision fertilization method synchronized with physiological growth stages to optimize nutrient supply in double-season sweet potato systems. It includes procedures for quantifying organ-specific nutrient accumulation, fitting nonlinear dynamic models to absorption trajectories, and calculating apparent nutrient balances to mitigate environmental risks.

Abstract

Double-season fresh sweet potato production often experiences a mismatch between soil nutrient supply and crop demand, leading to suboptimal yield and inefficient resource use. Traditional fertilization often relies on basal applications that fail to meet the crop's dynamic requirements under distinct spring and autumn meteorological conditions. This article presents a comprehensive protocol for a stepwise precision fertilization strategy that synchronizes nitrogen, phosphorus, and potassium inputs with critical phenological nodes. The method partitions total nutrient inputs into five distinct application events corresponding to specific growth stages: seedling establishment, vine expansion, tuber initiation, rapid bulking, and maturation. The protocol further describes a rigorous destructive sampling regime to dissect whole-plant nutrient partitioning. By employing logistic nonlinear regression models, researchers can quantify the maximum accumulation capacity, duration of the rapid uptake phase, and inflection points of nutrient uptake. This approach enables precise identification of critical absorption windows and evaluation of apparent nutrient balances. The application of this protocol facilitates the optimization of fertilization regimes, enhancing both storage root yield and commercial quality while reducing the risks associated with nutrient deficits or surpluses in intensive double-cropping systems.

Introduction

Sweet potato (Ipomoea batatas. L.) has evolved from a subsistence crop into a high-value functional food source and industrial raw material^1,2. In intensive agricultural regions, double-cropping systems—where two crops are harvested annually from the same land—are increasingly adopted to maximize land equivalent ratios and economic returns³. However, the sustainability of these high-intensity systems is frequently compromised by inefficient nutrient management strategies that overlook the temporal variability in crop nutrient demand and seasonal climatic variations<....

Protocol

1. Experimental site preparation and design

1. Select an experimental site with flat terrain, efficient drainage, and homogeneous soil fertility to minimize spatial heterogeneity.
2. Collect composite soil samples from the top 0–20 cm layer using an Edelman auger. Take samples from five random points within each plot and combine them into a single plastic bag prior to land preparation for each growing season (spring and autumn).
3. Air-dry the soil samples at room temperature, grind them mechanically, and pass them through a 2 mm stainless steel sieve to analyze baseline physicochemical properties, including pH, organic matter, ....

Results

Baseline soil characteristics and seasonal variations

Table 1 presents the physicochemical properties of the topsoil (0–20 cm) determined prior to transplanting in both the spring and autumn growing seasons. The analysis reveals that fundamental soil characteristics, including pH (maintained within a weakly acidic range of 6.38–6.42), organic matter content, and bulk density, remained statistically stable between the two seasons. This stability confirms that t.......

Discussion

The implementation of the Stepwise Precision Fertilization (SPF) protocol demonstrates that high-yield formation in double-season sweet potato systems relies heavily on the synchronization of nutrient delivery with crop physiological demand^26,27. The results confirm that the supply rhythm is as critical as the total dosage. By utilizing the stepwise protocol, we effectively mitigated the common trade-off between vegetative growth and reproductive storage, a pheno.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Analytical sieve (0.25 mm)	Retsch	AS200	Particle size standardization
Calcium superphosphate	Sinofert Holding Co., Ltd. (China)	≥12% P2O5	Phosphorus source
Compound fertilizer (N–P2O5–K2O)	Sinofert Holding Co., Ltd. (China)	Custom formulation	Used for stepwise precision fertilization
Digestion block system	Gerhardt	Kjeldatherm	Acid digestion of plant material
Drip irrigation and fertigation system	Netafim	Standard agricultural system	Optional fertigation treatment
Drying oven (forced-air)	Memmert	UF110	Sample drying at 75–105 °C
Electronic balance	Mettler Toledo	MS204S	Used for precise fertilizer weighing
Flame photometer	Sherwood Scientific	Model 420	Potassium determination
Kjeldahl nitrogen analyzer	Foss	Kjeltec 8400	Determination of total nitrogen
Paper sample bags	Whatman	Grade 1	Drying and storage of plant samples
Potassium sulfate	Sinofert Holding Co., Ltd. (China)	≥50% K2O	Potassium source for bulking stage
Soil auger	Eijkelkamp	Edelman auger	Soil sampling (0–20 cm depth)
Spade and hand tools	Local agricultural supplier	—	Destructive sampling of whole plants
Stainless steel plant grinder	Retsch	ZM200	Grinding dried plant samples
Statistical analysis software	R Foundation	R version 4.3.0	Logistic model fitting and ANOVA
Sweet potato planting material (Ipomoea batatas L.)	Local certified seed supplier	—	Uniform cultivar used for double-season field experiment
Urea (N fertilizer)	Sinofert Holding Co., Ltd. (China)	≥46% N	Nitrogen source for split application
UV–Vis spectrophotometer	Shimadzu	UV-1800	Phosphorus colorimetric analysis