Agronomy Advice

Improving the performance of the all important pulse crops

It is easy to overlook the nutrients required by nitrogen-fixing crops like peas and beans if they are to perform well. As with any crop, they require a complete nutrition programme, particularly phosphorus and sulphur together with micronutrients otherwise nodulation will be reduced leading to poor performance and a yield reduction.

Farmer standing in a crop field
Farmer standing in a crop field
A deficiency of any single nutrient is enough to limit yield

Whilst crop rotations do vary between farms, the majority will have a pulse crop of some sort whether winter or spring beans or peas. The purpose of these crops in the rotation is twofold, with firstly a successful crop delivering revenue for the business through its yield and quality, and secondly this same crop improving soil conditions and fertility for the following cereal crop. This fertility improvement brings a saving of typically 30 kg N/ha.

In order for these pulse crops to deliver on both counts then it is important to build a crop nutrition strategy that is an enabler for this. If we consider that these crops rely heavily on their ‘leguminous’ nature, i.e. the root nodules, as a nitrogen source for growth and development then ensuring good nodulation and their survival is paramount. The scientific literature highlights some essential nutrients that are directly required in the metabolism of the rhizobia that are in the nodules with phosphorus, sulphur, magnesium, manganese, iron and molybdenum all mentioned.

Boron and calcium are essential nutrients for nodulation.

Boron and calcium are also cited but more by way of the vital role they play in setting up an effective legume symbiosis that is required. The ‘nitrogen-fixing nodules’ are the result of the symbiosis between the crop roots and soil bacteria (rhizobia). These bacteria are the ‘engine’ of the nodules that fix the atmospheric nitrogen to ammonia, subsequently feeding the crop enabling it to produce amino acids.

A previous study in peas (Redondo-Nieto, Wilmot, et al, 2003) concluded that "Overall results indicate that the development of the symbiosis depends of the concentration of B and Ca2+, and that both nutrients are essential for nodule structure and function."

Nodulation on field beans

The nodulation process starts from 10 days but visually they can be seen after 3-4 weeks, at which point the symbiotic relationship will be functioning with the crop supplying the bacteria with carbohydrate from its photosynthesis, in return for some ammonia (nitrogen). If the nodule is pink in colour then this is a good indication that it is functioning well. If it is still grey then it is still not supplying the crop with the nitrogen, while if it is green then it is likely to be dying.

Field beans showing nodulation

Nodules on field beans

Nodules on field beans

Looking deeper into the activity of the rhizobia reveals where key nutrients play their part. The rhizobia produce the enzyme ‘nitrogenase’ that is then responsible for catalysing the reaction to convert the atmospheric nitrogen to ammonia. The nitrogenase enzyme is a very complex structure that contains key elements i.e. magnesium, molybdenum, sulphur and iron. Manganese is also required to activate the enzyme.

As the pea or bean crop develops it eventually starts to produce flowers and then seeds. As the first seeds start to fill then at this stage the plant can no longer support both the demands of the nodule for carbohydrate and that of the seed filling process. Therefore at this point the nodules lose the competition and die. It is at this stage then attention needs to turn to nutrients that ensure the plant continues to photosynthesize effectively with a healthy green canopy. Here again, key nutrients are magnesium, manganese, molybdenum and sulphur. In addition, as flowering continues, successful pollination is critical for pod set with Boron playing a vital role in this process.

A successful crop nutrition strategy should ensure adequate early supplies of phosphorus and boron to aid the nodule development, followed by foliar applications of sulphur, magnesium, manganese, molybdenum and boron to ensure an efficient canopy and flowering process.

A foliar application of YaraVita Photrel Pro supplies readily available magnesium, sulphur, boron and molybdenum with broad tankmixability which means it is easy to co-apply with other agrochemicals.

Key actions

  • Apply YaraVita Photrel Pro at a rate of 3 kg/ha from four true leaves onwards
  • Where boron deficiency is known then ensure an early application of boron is made
  • If pulses are destined for the quality market then pay particular attention to manganese to help prevent marsh spot.

How much will it cost?

See how much extra yield is needed to justify the cost of a YaraVita application.

YaraVita cost calculator

Extra yield needed to cover cost of application

23 kg/ha

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