How to increase oat leaf and shoot numbers

Nitrogen affects leaf and tiller numbers

Nitrogen is the single most important nutrient for achieving high yields. Adequate supplies will give more shoots and bigger leaves, with each leaf developing faster. Nitrogen deficiency on the other hand reduces the rate of primordia initiation, which reduces the number of potential spikelets (grain sites).

The amount of nitrogen applied essentially depends on the amount of available nitrogen in the soil. In soils with high humus (organic matter) content, oats may get all the nitrogen from these nitrogen reserves, however, in intensive cultivation on mineral soils the amount of nitrogen applied will usually be between 40 kg/ha and 150 kg/ha. Typically nitrogen will double or even treble the yield achieved.

This extra yield comes from the improved size and duration of the photosynthesizing leaf canopy, and the increased tillering that leads to correct number of spikes per unit area. For every tiller that is initiated extra roots develop so sufficient applications of nitrogen also increase the ramification of the roots, improving the water and nutrient uptake by the plant. The survival of the shoots / tillers that are produced can be influenced by interactions between nitrogen application rates and timing.

Where shoot numbers are below the optimum, the applications of higher nitrogen rates early in the season (Zadoks 25 – 30) will increase shoots and thereby final ear numbers. This crop manipulation should not be used where plant populations are on target, as it can lead to excessive leaf and shoot growth and lodging. Lower application rates early should be used where shoot numbers are on target.

Where spring oats are grown the time for leaf and total shoot production is very limited so early supplies and high rates of nitrogen are critical for achieving the required early growth rate and shoot numbers.

Nitrogen timing has an impact on the yield of spring oats with early nitrogen being fundamental in yield attainment.

Phosphorus affects leaf and tiller numbers

Phosphorus is considered to be the second most important nutrient after nitrogen in terms of its influence on plant growth and development. After the crop has developed two to three leaves it will begin to rely on soil available phosphorus for continued leaf and shoot numbers growth. Phosphate availability in the soil is influenced by many factors including pH, other nutrients such as aluminum, iron and calcium, soil moisture and temperature.

The single most important process that phosphate is involved in is in the store and transfer of energy as the chemical compound ATP – Adenosine Triphosphate. This chemical energy store is used as the fuel for many of the plant physiological processes.

It is important to ensure that freshly available phosphate is applied to avoid this limiting early root and shoot growth. In oats there are two timings that are important to consider. Firstly during early crop establishment (Zadoks GS 13-25) when it is growing rapidly with shoots and roots developing, and secondly as spring growth commences (Zadoks GS 31-49) when over a few weeks 70% of phosphate will be taken up. Applications of phosphate fertiliser should be targeted to meet this demand.

Phosphorus has been linked to the production of cytokinin with phosphate deficient plants having lower levels of cytokinin content in plants (Jose´ M. Franco-Zorrilla The Plant Journal (2002) 32, 353–360). One of the main features of cytokinins are their involvement in cell division, root growth and branching and cell differentiation.

Cereals need approximately 4 kg of phosphorus per one ton of grain. Phosphorus deficiency is often a problem if the soil is cold and the root system is not fully developed. Foliar phosphate applications can be included into the phosphate crop nutrition program to again improve the crops phosphate status when soil availability is limited to improve autumn and early spring growth and development.

Sulphur is critical for growth of developing shoots

Sulphur nutrition is another critical nutrient required by the plant to ensure continued growth of the developing shoots. The building blocks for plant growth are the sulphur based amino acids from which many of the plant proteins develop. Land based sulphur emissions from industry have decreased between 90 and 70% depending on the region. The sulphur supply for crops has therefore become more reliant on applications through fertiliser.

Sulphur is poorly translocated around the plant with new growth showing deficiency symptoms first. To overcome this a continual supply through multiple applications of sulphur should be made to satisfy the peak demand period. Foliar sulphur can also be included to overcome transient deficiencies. A plants nitrogen use efficiency is poor where sulphur is limiting so heavy yield losses are experienced.

The sulphur that can be taken up by plants needs to be in the form of sulphate. Other forms of sulphur such as elemental sulphur needs to be oxidized to sulphate in the soil that can take a number of weeks depending on soil characteristics such as moisture and temperature.

Manganese and zinc influence leaf and tiller numbers

Manganese and zinc are two important micro nutrients that will affect the developing components of yield, such as increasing the ear number and grain size, resulting in increased final harvested yield.

Manganese plays an important role in photosynthesis, protein synthesis, the growth of the root systems, and in drought resistance. Manganese also affects the formation of lignin with poor lignin development showing as flaccidity of leaves and weak root system growth. Oat is the cereal that is most susceptible to manganese deficiency.

Manganese and zinc have also been associated with improving the uptake of other nutrients, both macro and micro nutrients.

Other crop management practices increasing leaf and shoot numbers in oats

The number of shoots that develop will be affected by the following:

• Varietal choice / oat type – varieties vary in their tillering capacity and speed of development.
• Drilling date – early drilling increases tiller numbers/plant.
• Seed rate drilled – high seed rates give more main shoots and fewer tillers.
• Soil / seedbed conditions – poor seedbeds, and compaction slows early tiller development
• Pest control e.g. slugs
• Soil nutrient status – good fertility (high nitrogen status) increases tiller numbers.

In general as the number of seeds is reduced, and the earlier the drilling, the more each individual plant will tiller, with the final shoot number being dependent on the number of tillers that survive through to producing ears.

The tiller number and survival can be influenced by:

• Autumn and winter weather conditions (in winter oat) - cold conditions slows leaf and tiller initiation.
• Application of plant growth regulators – plant growth regulators can be used to reduce apical dominance, increasing tiller numbers/survival.
• Nitrogen applications – applications of nitrogen give an increase in leaf size, tiller number and tiller survival.