How to measure cereal plant populations, nitrogen uptake and dry matter

An estimate of cereal plant populations and growth (in a quadrat) will indicate if targets have been met. Use this information to guide in-season crop management decisions and future strategy (e.g. seed rates).

• In late autumn (November), in fully established crops, to estimate emergence
• After winter, before significant warming and growth occurs, to estimate overwinter survival*

*At this stage, it can be hard to differentiate between plants and tillers. Plants may need to be dug up to determine actual numbers.

Option 1

1. Place a 0.5 m x 0.5 m (0.25 m²) quadrat* diagonally so that one row goes vertically from one corner to the opposite corner.
2. Count the number of plants in the quadrat.
3. Repeat in 10 representative areas of a field.
4. Take the average of all counts and then multiply by four to get the number of plants/m².

Top tip:  To make a quadrat, simply use four 0.5 m long rods placed as a square.

Option 2

1. Place a 30 cm stick/ruler/clipboard along a row.
2. Count the number of plants along the length.
3. Repeat in 10 representative areas of the field and calculate the average plant number.
4. Work out the area counted (e.g. 30 cm x drill coulter width).
5. Divide this figure into 10,000 cm² (100 cm x 100 cm) to give you a multiplication factor.
6. Take the average of all counts and multiply by the multiplication factor to give you the plants/m².

Option 2 example

Step 4: Area counted: count length (30 cm) x drill coulter width (20 cm) = 600 cm²

Step 5: Multiplication factor 10,000 cm² ÷ 600 cm² = 16.67

Step 6: Average plant population (18 plants) x multiplication factor (16.67) = 300 plants/m²

Notes

If using variable rate seed, conduct a minimum of two counts per zone.

You can also use these methods to estimate tiller numbers/m².

You can measure nitrogen uptake at any time. Throw a quadrat and cut plants within it at ground level, dry them and weigh them. Then send a subsample to a laboratory for grinding and percentage nitrogen determination.

To determine the total amount of nitrogen on an area basis, multiply the percentage nitrogen in the crop by the total dry weight of the crop.

To determine the nitrogen redistribution to the grain, conduct assessments near to harvest, with the grain separated from the straw or chaff and percentage nitrogen measured for both samples.

Measure crop dry matter at any time. Sample, dry and weigh the crop from a thrown quadrat and multiply the weight by four to determine the weight in 1m².

Alternatively, crop vegetation indices – calculated from spectral reflectance measurements taken by crop sensors – can be used as a proxy for crop dry matter.