Pecans, how understanding Nitrogen can improve yield and quality.

Getting Pecan growth right means balancing the needs of the crop for N to produce yield, with the propensity of the crop to too easily go vegetative. This is the reason for problems with alternate year yield bearing, water stage fruit split and also for problems managing Boron and calcium deficiency.

Here we discuss how form of N influences where the crop grows, and how Pecan growers can benefit from changing how they apply it.

Conventional nitrogen applications put growth in the wrong place creating problems.

Nitrogen on pecans is mostly taken up as nitrate (NO3), as regardless of the form it is applied as it rapidly converts in the environment to nitrate ahead of crop uptake. Nitrates are processed in the leaf, where the plant must use energy to convert them into the amine nitrogen required to build the proteins that build the crop.

As nitrates accumulate in leaves the crop starts to produce increased levels of the auxin growth hormone, leading to the crop emphasising vegetative growth. The more nitrates the crop takes up the more vegetative the growth becomes, leading to too much leaf and not enough resource allocated to nut growth.

Farmers must provide enough nitrogen to produce growth, but oftentimes the growth is mostly in the wrong place, leading to alternate year yield bearing and physiological problems.

Changing nitrogen source can help reduce vegetative growth and improve yields.

Unlike nitrate nitrogen amine N (NH2) is not processed in foliage, rather it is processed I roots. Amine N does not create vegetative growth, instead it is used predominantly to develop roots, and reproductive growth (flowers and nuts). Unfortunately simply applying N in a standard form (urea) does not give this effect, as it is mostly converted to nitrate before the crop takes it up.

Levity have developed technology that stabilises amine N, so that crops can receive the kind of N that drives reproductive growth. Use of Lono-K provides Amine N alongside K and can be used to improve nut development and yield, decrease excess vegetative growth and reduce alternate year yield bearing.

Lono-K should be applied in early spring as the crop wakes up, and then again in early summer during kernel filling.

Excess vegetative growth creates issues with Boron and Calcium

Because both calcium and boron are not phloem mobile in Pecans, they move through the plant with water (upwards and outwards). When nitrogen creates excessive vegetative growth it creates a sink for these nutrients, preventing adequate supply to developing flowers and nuts.

In the case of Boron the problem is made worse, as the plant needs boron to reduce nitrates in the leaf. The more nitrates the plant accumulates in the leaf the more boron it uses, leading to both nitrogen induced boron deficiency, and also lack of transport to flowers and developing nuts.

Applying calcium and boron to soil does little to help correct this as it just ends up being transported to the leaf, bypassing the developing crop. This in turn contributes to water stage fruit split and fruit drop.

Growth must be supported with foliar applications of Ca and B.

Water stage fruit split occurs when fruit develops rapidly. Research shows that improved levels of Calcium and Boron can reduce fruit splitting. Boron improves the strength of cells walls during cell expansion as cells become larger and the walls stretch. Calcium makes cell walls stronger also resulting in less splitting and shedding.

As Boron is not phloem mobile in Pecans, foliar application is necessary as B taken up by roots will mostly accumulate in leaves and not reach the developing crop where it is needed to set and develop nuts.

Damu is an advanced B formulation developed by Levity that is more mobile, on Pecan it can applied at flowering to encourage setting and reduce issues with fruit splitting. Because it has improved leaf to fruit mobility Damu can be used effectively at low rates to improve Pecan production.

Calcium should also be applied foliar during Kernal development, but care must be taken to use a product that can be properly absorbed by the fruit.

Because Ca absorption is linked to auxin hormone levels (used during cell division) conventional calcium fertiliser is not easily absorbed by the nut as it starts to grow. This makes calcium applications very hit and miss, as they are more easily absorbed by growing shoots than by expanding fruit.

Levity have developed Albina, which contains LoCal a technology that allows developing fruit to absorb calcium outside of the normal ‘window of opportunity’. It can help reduce fruit drop and improve quality.

Recommendations

Lono-K apply at 5-10 L/Ha in spring, and again during kernel filling, this will improve yield, nut size, nut retention and reduce alternate year yield bearing for more consistent cropping from season to season. Can be applied via drip or foliar.

Damu – Apply foliar at flowering at 1-2L/Ha to reduce splitting and increase setting.

Albina – apply at 1L/Ha during kernel fill to reduce fruit drop and improve quality.