Hub Insight: Step 1
Review the Harvested Crop

What Harvest Can Tell You About Phosphorus Capture

Before deciding next season’s phosphorus strategy, first understand what the previous crop captured.

Harvest provides an opportunity to do more than review yield.

It offers valuable insight into how effectively crops captured phosphorus during the growing season and whether phosphorus availability, accessibility or utilisation may have limited performance.

Understanding crop phosphorus capture helps growers move beyond application rates and begin assessing phosphorus efficiency.

“Harvest is the report card for the season.”
Dr Christina Baxter, Senior Research Scientist, ADAS

Why Harvest Matters

Every harvested crop removes phosphorus from the field.

Knowing how much phosphorus has been removed helps answer one of the most important stewardship questions:

Did the crop capture the phosphorus it needed to achieve its potential?

Harvest therefore provides an opportunity to review not only crop performance, but also nutrient use efficiency before making phosphorus decisions for the following season.

Combined with grain analysis, soil analysis and field observations harvest becomes one of the most valuable tools for improving phosphate stewardship.

the phosphate guide on some grain

What Did The Crop Actually Capture?

Most phosphorus decisions begin with:

  • Soil analysis
  • Soil phosphorus indices
  • Fertiliser planning

All of these are important.

However, one question is often overlooked.

Graph showing wheat phosphate offtake occurrence in the YEN+ dataset.
Similar soil P levels do not always result in similar P capture

How much phosphorus did the crop actually capture?

Understanding crop phosphorus capture shifts the focus from how much phosphate was applied to how efficiently was it utilised.

It also helps ensure sufficient phosphorus is replaced to maintain soil fertility while avoiding unnecessary applications.

Analysis of several hundred winter wheat crops through the ADAS Yield Enhancement Network (YEN) has shown that P offtake can vary by as much as 50% above or below the RB209 standard figure of 6.5 kg/ha P2O5 per tonne of grain.

This demonstrates why measuring crop phosphorus capture is an important part of phosphate stewardship.

soil analysis graphic explaining analysis vs harvest

Key Insight

Soil tests tell us what might be available.

Harvest helps us understand what the crop actually captured.

Research from YEN has shown significant variation in grain phosphorus concentration between crops grown on similar soil phosphorus indices.

This suggests that phosphorus capture is influenced by more than soil phosphorus supply alone. Understanding why those differences occur is the next step towards improving phosphate efficiency.

Grain Analysis

Turning Harvest into Evidence

Grain analysis provides one of the clearest measures of crop phosphorus capture.

Used alongside harvested yield, soil analysis and field observations it helps growers:

  • Assess crop phosphorus capture
  • Calculate phosphorus offtake
  • Compare nutrient removal between fields
  • Identify whether phosphorus may have limited performance
  • Support future nutrient planning
  • Improve phosphate stewardship decisions

Good phosphorus decisions are based on evidence not assumptions.

Grain analysis for collecting a representative grain sample

Stewardship In Practice

Measuring Crop Phosphorus Offtake

Understanding phosphorus offtake helps quantify how much phosphorus has been removed from the field and provides valuable information for future nutrient planning.

combine emptying to record harvested yield

Step 1

Record harvested yield

Accurate yield data provides the foundation for estimating phosphorus removal.

Step 2

Take a representative grain sample

Collect grain from several points during unloading or from different areas of the trailer to produce one representative sample for the field. Label each sample clearly before submitting it for laboratory analysis.

Sample steps involved in gathering a grain sample
Combine emptying to record harvested yield

The calculation:

[(Yield × P concentration in the grain)
Multiply by 19.5 (to convert to P2O5)]

Plus

[Yield × straw offtake value (RB209 average)]

Equals P2O5 offtake in kg/ha

Step 3

Calculate crop phosphorus offtake

Use the laboratory phosphorus concentration you get back from the grain analysis, together with harvested yield to calculate crop phosphorus removal. Use the average phosphorus content in straw from RB209.

P Offtake (kg P2O5/ha)
= Yield (at 15% moisture) X P content in grain & straw

Working example

Winter wheat at 0.32% gain P

Steps Calculation P2O5
Calculate grain phosphate offtake (kg P2O5/ha) t/ha fresh yield (15% moisture) × Grain P% × 19.5 9.0 × 0.32 × 19.5 = 56
Calculate straw phosphate offtake (kg P2O5/ha) t/ha fresh yield (15% moisture) × 0.5 (average offtake from RB209) 9.0 × 0.5 = 4.5
Calculate total phosphate offtake (kg P2O5) Grain + Straw offtake 56 + 4.5 = 60.5
combine emptying to record harvested yield

Step 4

Compare the results

Review phosphorus removal alongside:

  • Soil phosphorus status
  • Crop establishment
  • Root development
  • Fertiliser applications
  • Overall crop performance

This helps identify whether phosphorus capture met crop demand and informs future nutrient planning.

Graph showing the critical grain phosphorus concentration in wheat

What Does Good Phosphorus Capture Look Like?

ADAS analysis has identified a critical grain phosphorus concentration of approximately 0.32% P in winter wheat

This provides a useful benchmark when reviewing crop phosphorus capture.

However, grain analysis should never be interpreted in isolation.

Consider the result alongside:

  • Harvested yield
  • Soil phosphorus indices
  • Root development
  • Crop establishment
  • Seasonal conditions
  • Field observations

Together these provide a much clearer understanding of phosphorus performance.

Factors to consider when interpreting phosphorus uptake results

Interpreting The Results

A low result doesn't automatically mean more phosphorus is needed.

One of the biggest mistakes in phosphorus management is assuming that low crop phosphorus capture automatically means more phosphate fertiliser should be applied.

Instead, ask:

  • Did the crop have access to phosphorus?
  • Was phosphorus available when demand was highest?
  • Could root development have limited uptake?
  • Did establishment restrict phosphorus capture?
  • Are existing soil reserves being fully utilised?

These questions often provide greater insight than increasing application rates alone.

Stewardship Principle

Measure before you manage.

Harvest tells us what happened.

It doesn’t tell us why.

Understanding why phosphorus capture was lower than expected is the next step towards improving phosphate efficiency.

Phosphate Clinic
Episode 1 | What Harvest Can Tell You About Phosphorus Capture

Prefer to Watch?

Phosphate Clinic

Episode 1 | What Harvest Can Tell You About Phosphorus Capture

Join Dr Christina Baxter (ADAS) and Rob Suckling as they discuss how harvest can be used to assess phosphorus capture, calculate crop offtake and support better phosphorus decisions for the following season:

In this episode you’ll learn:

  • Why harvest is the report card for the season
  • Why grain analysis matters
  • How to calculate crop phosphorus offtake
  • How to interpret results
  • Why diagnosis should come before intervention
Factors to consider when interpreting phosphorus uptake results

Continue Your Stewardship Journey

Why Isn't The Crop Accessing Phosphorus?

Harvest provides the evidence.

The next step is understanding why crops can struggle to access phosphorus, even where soil phosphorus supply appears adequate.

Discover how phosphorus availability, root access and soil phosphorus reserves influence crop performance.

Continue to Step 2: Why Isn't The Crop Accessing Phosphorus?