Starter Nitrogen for Vining Peas

Purpose

One question raised in the MicroFarm Discussion Group was whether a starter fertiliser might enhance vining pea yields.

MicroFarm soil testing showed bckground fertility was good. So it was questionable whether to apply anything. Numerous Plant & Food Research and Foundation for Arable Research trials have demonstrated no economic response of seed peas to applied fertiliser. Would vining peas be any different?

Process

Mark Redshaw, our Ballance AgriNutrients Advisor, put a simple comparison together in Paddocks 3 and 4, both planted with the same Ashton variety on the same day.

Background soil fertility (0-15 cm) was measured before any fertiliser was applied. Available N was 121 in Paddock 3 and 82 kg N/ha in Paddock 4. Other key fertility indicators (pH, Olsen P, MAF K) were within optimum ranges suggested for peas in both paddocks. The only limiting factor was Sulphur. Sulphate levels ranged from 1-3mg/kg.

Treatments

At planting:

  • Paddock 3 received 100 kg/ha of PhasedN (25.3%N, 28.5%S and 5.7%Ca)
  • Paddock 4 received 100 kg/ha of Sulphur Gain Pure (95%S)

Soil conditions were not ideal with moisture levels quite high, and compromises being made around fertiliser rates due to size of paddocks.

The fertiliser was applied with the planter to avoid an extra pass- but separation of product and seed was compromised due to soil conditions. High slug numbers were noted.

NicolleGreatPlains

With the exception of fertiliser practice both paddocks were managed identically during the season. Neither paddock was irrigated.

Results

Paul Johnstone, a Plant & Food Research member of the Discussion Group, and colleagues observed the comparison, took measurements and analysed the data collected.

At maturity they harvested plants from three sample areas (each 0.75 m2) in each paddock. For each sample they:

  • Determined the plant population
  • Calculated total plant biomass and fresh yields
  • Calculated the key components of yield (number of pods per plant, number of peas per pod, and mean mass of individual peas)
  • Measured quality using TR score.

Observations

General

Visually, Paddock 4 appeared to have a weaker canopy throughout the season. Soil investigation also indicated the paddock had poorer soil structure related to historical compaction.

Plant population

Paddock 4 had more plants per m2 than Paddock 3 but there was little evidence to suggest this was related to the starter fertiliser. In both paddocks, plant populations were considerably lower than the planting target of 110 plants per m2.

Crop roots were not inspected for nitrogen fixation activity.

Yield and yield components

Overall fresh yields varied greatly, ranging from 7.8 to 13.8 t/ha across the individual samples. On average there were between 5-6 pods per plant, with each pod containing 6 peas averaging around 0.4 g per pea.

Starter fertiliser practice did not affect total plant biomass, fresh pea yield or the components of yield (pod number, pea number and mean pea mass) even when variable plant population was considered.

Maturity

TR scores were 120 in Paddock 3 and 126 in Paddock 4. These are higher than optimal for processing (usual target is 110-115) indicating that the crop was harvested a day or two late.

There was no effect of the different starter fertilisers on TR scores.

Bottom line

At this site there was no evidence of a yield or quality response to increased N supply at planting.

This was despite a visually weaker canopy where no N fertiliser was applied. The canopy weakness may have been related to soil compaction in the paddock rather than N deficiency.

Pre-trial soil available N measurements showed fertility was moderate in both paddocks. This might have masked any crop responses to the applied fertiliser treatment.

So this comparison supports research that, at least on moderately fertile paddocks, there is no benefit from applying starter fertiliser to vining peas.

Thanks to Ballance AgriNutrients, Hill Laboratories, Plant & Food Research, Nicolle Contracting and the Centre for Land and Water for their support with this MicroFarm study.

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