Plant growth and nutrition study guide

1. Nutrients needed by plants. Major nutrients, minor nutrients and trace elements.

Resources:
NSW Department of Primary Industries Plant nutrients in the soil. This article is a concise summary of the main plant nutrients, their role in the plant and effect when deficient, typical soils where deficiencies can occur and examples of fertilisers that can help to overcome deficiencies.

NC State Extension Soils and plant nutrients. Soils and plant nutrients. The sections on plant nutrition and fertilisation are the main reading for this module. For this topic refer to Table 1-4 under Soil nutrients, Essential nutrients for plant growth.

Main points:
Below is a table showing the main nutrients needed by plants. Each nutrient is shown with its chemical symbol. The figures are approximate percentage in plants.

Plants require different relative amounts of nutrients. Nitrogen and potassium are needed in the highest amounts. This is followed by calcium, magnesium, sulphur and phosphorus. The last 6 nutrients in the table are sometimes called trace elements as they are needed in much smaller amounts. Iron is a little in-between in the amount needed. Nutrients need to be supplied in approximately these proportions. If one nutrient is in short supply then a plant may not grow so well because that nutrient may hold back the plant. An excess of any one nutrient can also cause poor or undesirable growth.

Each nutrient has a different function in the plant. For example nitrogen is mainly used to create leaves and foliage. Potassium is used to make stems strong. Phosphorus helps the plant use energy to make tissues and fruits. The trace elements are mainly used other critical molecules in the plant like chlorophyll and enzymes.

To complicate things, some plants need different amounts of nutrients. Grasses need more nitrogen to grow leaves and legumes need more molybdenum because it helps in providing nitrogen to the plant.

Jump ahead and download one or more of the resources that show a table of deficiency symptoms. The first column will usually show the function of each nutrient in the plant. Make a list to help remember the main functions of each nutrient. You will use this later when you come to diagnose and fix plant growth problems caused by shortage or excess of nutrients.

2. Where do plant get nutrients?

Resources:
NC State Extension Soils and plant nutrients. Soils and plant nutrients. The section on plant and nutrition, Soil Nutrients and Fertilizers are the main reading for this module. This section also includes information soil nutrients and fertilizers.

Kansas State University Department of Agronomy Soil nutrients sources and uptake. This reference outlines not only the main plant nutrients but also the chemical forms that are taken up by plants. There is a section on how manures supply nutrients. The emphasis in the article is how plants take up nutrients from the soil. Therefore some of the main soil factors like nutrient holding capacity, and physical factors related to soil management are discussed. The example for Grain Sorghum is used to show how nutrient uptake changes with the growth of the plant.

Simple and concise summary of nitrogen fixation Nitrogen fixation.

Main points:
Plants get nutrients from the soil, manures, fertilisers, green manures and nitrogen fixation. Plants mostly take up the nutrients they need from the soil. However soils may not provide the best balance of nutrients required by the plant. Also soils may not provide enough nutrients for the level of production required for crops. As plants grow they may need more nutrients than the soil can make available. This shortfall can be met with artificial or commercial fertilisers, from manure, compost or even from crops that are grown in the same place and allowed to break down and return to the soil. These are sometimes called green manure crops.

An important source of nitrogen is nitrogen fixation, a process where nitrogen from the air is converted to nitrogen containing compounds. Nitrogen fixation is carried out by microorganisms in water or soil that include specialised bacteria. Some are associated with plant roots most commonly in plants called legumes. The amount of nitrogen fixed this way can be very significant to improving soil fertility and plant nutrition.

3. Plant growth. Normal growth, Life cycle and seasonal growth. Difference between species.

Resources:
Kansas State University Department of Agronomy Soil nutrients sources and uptake. discusses the nutrient needs of corn plants as the crop grows.

Pasture growth rate case study. (.doc format) In this case study the growth rate of pasture on a dairy farm was measured over a period of 1 year. The actual pasture production for the year was then calculated. The graphs included clearly show the seasonal growth pattern of pasture on a rain-fed (natural rainfall) dairy farm.

Main points:
Nutrient use depends on factors like:
Types of plants herbaceous, trees, annuals, perennials
Seasonal growth pattern eg pastures, crops
Plant growth cycle eg corn plant (Kansas State reference).

4. Amount of nutrients in plants. How much do plants need? Differences between species. Above and below ground growth.

Resources:
Nutrients in plants. (pdf format) This resource shows the typical levels of nutrients in some plants and farm products. This can sometimes be shown as the nutrients taken up as a plant grows and also as the nutrients removed as a crop is harvested.

NC State Extension Soils and plant nutrients. Soils and plant nutrients. The section on plant and nutrition, Soil Nutrients and Fertilizers are the main reading for this module. This section also includes information soil nutrients and fertilizers.

What will happen to the nutrient supply if a crop is harvested and taken away from where it was grown? The short answer is that more nutrients will be needed to replace those removed. To find out just what quantities of nutrients are required the nutrient content of typical foliage can be multiplied by the weight of crop removed.

In the resources for this topic you will see several tables that show nutrient contents for selected crops and products like milk and meat, typical yields and calculated nutrients removed by that yield.

A complication you will see happening is when part of a crop, maybe all is allowed to return to the soil. How can this amount be taken into account?

Refer to the tables in the resource Nutrients in plants. (pdf format)
The first table shows typical amounts of N, P and K removed from various commercial crops. Leafy vegetables and legumes tend to remove the most N although there are some exceptions. Whole corn plants and alfalfa (lucerne) tend to remove most P (and N). In general harvested fruits tend to remove the least N and P.

For the same harvested weight, oil-seed varieties like Canola and Sunflower remove the most phosphorus. Other varieties harvested for seed like grain legumes remove slightly less phosphorus whilst cereals like wheat, barley and oats remove the least phosphorus. The implication for this is the amount of P needed for every anticipated tonne of each crop harvested. In summary: oilseeds 8 kg P, grain legumes 6 kg, cereals 4 kg.

5. How plants take up nutrients. How roots and foliage can take up nutrients.

Resources:
Kansas State University Department of Agronomy Soil nutrients sources and uptake.
Read the section on forms of nutrients used by crops and the section Nutrient uptake by plants. Also read the section Soil nutrients.

Main points:
When plant roots spread out in soil they are looking for nutrients and water. Most plant nutrients can dissolve in water and roots can take up those nutrients directly from water. Water in the soil can bring nutrients to the plant roots but it can also take those same nutrients away (sometimes called leaching).

Most plants can also take up nutrients through their leaves. The nutrients have to be already dissolved in water. The amount taken up is relatively small compared to the amount of nutrients taken up by roots. But this method can be very important commercially for example for supplying extra nutrients at critical times eg calcium for apples or for supplying nutrients like trace elements that are only needed in small qualities.

Sometimes microbes play a role in helping plant roots capture nutrients. For example a special case is nitrogen fixation. This is where nitrogen from the air is converted into nitrogen compound building blocks by specialised bacteria closely associated with the roots of certain plants often legumes. For a simple and concise summary of nitrogen fixation see Nitrogen fixation.

Another example is fungal associations called mycorrhizae. For a detailed discussion of mycorrhizal fungi from Wikipedia see Mycorrhizal fungi. Mycorrhizae are specialized fungi that grow close to a plants roots. They usually take some nutrition from the plant so they can grow but in return help supply the pant with water and nutrients.

Plants only take up nutrients slowly so there needs to be a bigger supply in the soil so that a plant doesn’t run out while it is growing. Nutrients like calcium, magnesium and potassium can be reasonably firmly held on soil particles and particularly on organic matter. This is called cation exchange. If a lot of nutrients are held the soil could be called fertile. Some nutrients like phosphorus and sulphur are usually held more loosely. Sulphur in particular can dissolve readily in the soil water and if not taken up by roots, can be lost. Phosphorus has a different problem because it can especially in acidic soils get bound up tightly in some types of soil minerals, in effect becoming unavailable to plants. Manure and organic matter has a special role here. As organic matter breaks down nutrients are released. Then the remaining organic matter can hold on to nutrients, acting as a nutrient exchange, Organic matter can also shield nutrients from reactions with soil minerals that limit availability. Because this topic is so important to plant growth it will be explored in more detail in later modules.

6. Function of different nutrients in plants.

Resources:
NSW Department of Primary Industries Plant nutrients in the soil. This article is a concise summary of the main plant nutrients, their role in the plant and effect when deficient, typical soils where deficiencies can occur and examples of fertilisers that can help to overcome deficiencies.

NC State Extension Soils and plant nutrients. Soils and plant nutrients. The sections on plant nutrition and fertilisation are the main reading for this module. For this topic refer to Table 1-4 under Soil nutrients, Essential nutrients for plant growth.

Nutrient deficiency symptoms. (pdf format) For each of the main plant nutrients this document provides a more in depth description of how a deficiency will affect a plant’s growth, health and appearance. It also discusses types of soils where some deficiencies are more likely to occur. With sources.

University of Idaho, College of Agriculture and Life Sciences. Nutrients plants require for growth. Concise and detailed summary that includes amounts of each nutrient typically required by plants, the function of each nutrient, guidance on how to identify deficiencies and types of soils where deficiencies can occur. Written for Idaho soils but there are many general principles that are useful for Aus.

Main points:
The plant essential nutrients all have different functions in a plant, therefor deficiencies show up in different ways. Some symptoms are more obvious than others eg N deficiency but others may be more subtle eg trace elements. With the help of your tutor and the Resources for this topic, make a summary of nutrients, their function and the way a deficiency is most likely to affect plant growth.

7. Using deficiency symptoms to help solve plant growth problems.

Resources:
Many of the resources mentioned so far discuss signs and symptoms of deficiencies and give suggestions about what to look for in soil conditions.

Main points:
Some nutrients are allocated preferentially to different parts of the plant or to different functions eg N, if deficient then older leaves affected first.

Phosphorus is involved in many plant processes. Therefore deficiency affects aspects like growth rate, fruiting, time to maturity.

Some nutrients are part of plant structures eg Ca and K therefore a symptom of deficiency may be stem weakness.

Nitrogen is a component of amino acids and ultimately proteins. Therefore N deficiency can affect protein quality and amount.

Iron is a component of chlorophyll molecules therefor iron deficiency results in paler green foliage.

Trace elements are often the components of enzymes so therefore plant processes are affected eg molybdenum affects nitrogen use in plants like grasses and N fixation in legumes.

Diagnosing deficiencies may not be straight forward and may be confusing. Factors to take into account are:

Nutrient requirements may be different at different times of the life cycle or growth stage of a plant for example in seasonal cycles in pasture, vegetables, deciduous vines etc.

Sometimes there is difficulty in making a direct connection between a possible deficiency and what is observed in the plant or the plant’s symptoms

Interactions between nutrients – there may be more than 1 deficiency present.

Nutrient toxicity symptoms can be confused with deficiency symptoms. This is most likely with trace elements. Nutrient toxicities are often seen as dying or burnt areas around the edges of leaves.

Some strategies:
Check if younger or older leaves more affected. For example N deficiency affects older leaves but sulphur deficiency affects younger leaves.

When looking at a total crop or pasture, nutrient deficiencies can often show as:

Poor growth rate and low yield
Dull colours eg pale green foliage
Early maturity including early setting of fruit and seed without full maturity
Sparse foliage and stunted growth
Lack of branching
Weak stems eg crops fall over
Sparse growth over a paddock
Susceptibility to diseases

Some varieties are more susceptible to deficiencies in particular nutrients eg zinc in beans. Nitrogen in grasses and corn.

Symptoms can be often classified based on where they appear: Stems, roots, leaves, fruit set, within fruit eg quality, colours to to bottom, colours and pattern on leaves.

8. Types of fertilisers, how they work and what nutrients they contain.

Resources:
NC State Extension Soils and plant nutrients. Soils and plant nutrients. The sections on plant nutrition and fertilisation are the main reading for this module. For this topic refer to the section on Fertilizers.

Inorganic: Usually the highest nutrient content per weight. Some dissolved in water quickly eg potassium chloride but others dissolve more slowly eg some phosphate fertilisers. Some can be applied as granules to the soil. This method is convenient and can supply a larger amount of nutrients. Some inorganic fertilizers are supplied as liquids that need to be diluted and then sprayed on plants or watered in around plants.
Liquid fertilisers where the components are soluble are used in hydroponics and some soilless potting mixes. Overall, inorganic fertilisers can produce good results but can be inefficient due to losses to the air (esp N fertilisers), loss to water for very soluble fertilisers eg nitrate, or losses due to binding tightly to soil minerals. High dependence on these fertilisers has in some cases lead to build-up in the soil especially on dairy farms and intensive coastal horticulture and cropping. Here it can lead to environmental problems.

Organic: slower acting but supply nutrients as needed and can hold nutrients against being leached away or bound to the soil. Usually lower nutrient content. However organic fertilisers tend to fit with natural soil processes eg manure and compost breakdown to supply nutrients. They also help to provide a more resilient soil with good plant growth characteristics.

Most trace elements tend to be inorganic but are often treated to make them more stable in the soil.

There are many natural amendments such as rock dusts and minerals that are also used as fertilisers. The rationale is that they mimic the availability and supply of nutrients from natural soil minerals.

Other amendments such as lime can be considered fertilisers as they may contain calcium and magnesium.

Most commercial fertilisers are labelled with the percentage of each major and minor nutrient that are in the fertiliser. Most often you will see N-P-K-S with numbers like 20-3-10-10 meaning the fertiliser has 20% N, 3%P, and 10% each of K and S. Minor nutrients may have their percentages included if present.

9. Making a fertiliser or nutrition plan to achieve healthy plant growth for a selected crop or species.

Resources:
Fertilising plan for a dairy farm.(pdf format) This is the preliminary fertilising plan for a dairy farm at Ranceby in SW Gippsland. This case study uses soil test results and a detailed analysis of nutrients supplied in manures and nutrients required to meet production goals. For this module you won’t have this information available but you can still map out a nutrient plan based on principles of plant nutrition for a particuar species or situation.

The case study is for a dairy farm in SW Gippsland. A complete soil test was completed before purchase and a fertiliser plan was constructed just after the farm was purchased.

The plan used information from the complete soil test. The test showed low P and K and low copper.

Guiding principles:
Contribution of manure. Base level production.
Higher production needed.
Clovers N fixing to be encouraged

An assumption was made that nitrogen needed to be supplied.

The soil was a silt-loam originally under the sea. It has very poor structure.

Organic matter was measured as high but a question remained: was that old or fresh organic matter. Fresh organic matter is likely to contain more potentially available nutrients.

The farm had a history of low fertiliser use with bias towards phosphorus.

The soil had a high test value for tendency to bind phosphorus.

The soil was acidic and although main nutrient levels were reasonable (except for P, K and Cu) and the soil had a high capacity to hold nutrients (cation exchange), a larger than desirable proportion of this exchange capacity was taken up by acidity and aluminium.

Outcomes: Keep your collection of resource material on fertilisers, deficiency symptoms, nutrient requirements of plants and soil factors that influence nutrient supply handy so that you can use it to tackle future plant growth problems. Select a type of crop or plant species of interest. Find out about its cultural needs paying attention to normal growth and life cycle, type of soil preferred, particular nutrient needs and possible or common deficiency symptoms. Make a plan to provide the nutrients needed for healthy growth.