Set Up A Nutritional Program

Introduction In the following sections, two nutrient programs are provided as examples. The examples provided are for citrus, representing tree crops and sunflower representing field crops. The programmes provided may be relevant to other, similar crops as the basic principles are the same. However, the values provided in the examples are not definite as these may vary between crops as well as between different farms growing the same crop. This is because soil, climate, crop, cultivars etc. vary. It is for this reason that all good fertilizer programmes are based on recommendations from soil and/or leaf samples for the crop and site.

Nutritional program for Tree Crops

Citrus production, as is the case of all other crops, has a specific schedule for the application of nutrients. Certain nutrients require application at critical times, while others may be applied over a longer and less specific period.

When the fertilizer applications schedule is planned all production practices must be considered. This is especially true for foliar sprays, where the application of crop protection products must be considered. Fertilizer application must be coordinated with other production practices to ensure that the right fertilizer is applied at the right time.

Various institutions will develop fertilization programs for a crop. These may vary from basic, general programs to highly specific programs. General programs may be of little value in a commercial citrus production unit. The ideal programs are formulated for a specific orchard, based on specific data from that orchard. Such specific programs are developed based on leaf and soil analyses data for the current year, as well as historic data. The leaf and soil analytical data is usually supported by information on the previous fertilizer applications (what, how much and when) and information on the previous as well as current crop information such as yields and fruit quality.

All these factors are evaluated in conjunction in order to formulate the best fertilization program. The best fertilization program is one that will result in the best possible fruit volumes and quality, and therefore give the highest economic benefit, without sacrificing sustainability.

A good fertilization program will contain the following information for each orchard:

• Orchard number or reference.
• Cultivar and variety.
• Details for soil applications:
  • Quantity in grams (g) to be applied per tree
  • Name of fertiliser
  • Time of application
• Details for foliar applications:
  • Quantity in grams (g) or millilitre (ml) to be mixed per 100l water
  • Name of fertilizer
  • Time of application
• Additional information or special instructions.

Once a programme has been provided, the orchard manager needs to develop a schedule for the Implementation of the programme provided. The schedule is developed for soil applications as well as foliar sprays so as to slot into the rest of the production programme. The programme may require adaptation to suit younger trees.

Scheduling a Soil Application Program

The best practice for citrus is to schedule soil applications on a monthly basis. Most fertiliser programmes provide the fertiliser mass or volume per month. The fertilisation programs will recommend rates per tree or per ha.

In order to develop a soil program for the farm as a whole, the applications of all the orchards are summed and presented in one working document or schedule per month. Additional information is added, such as the size of each orchard and the number of trees per hectare. Using the fertilization program in the example above as a starting point, the following Soil

Application Schedule can be Developed

It is important to note those N-containing fertilizers are not applied as a single dose, but rather spread the application as 2 to 4 applications during the month. Nitrogen is highly soluble in water and if 500g LAN per tree is applied as a single dosage, the ammonium nitrate, may scorch the roots and reduce absorption.

The high concentration of ammonium nitrate can also not be absorbed within a short period of time and subsequent irrigation may leach the nitrogen beyond the reach of the roots.

The solubility and salt index of the fertilizers, the clay content of the soil, and the rooting depth of the plants are the major factors that affect the efficiency of a fertilizer application. Leaching is less of a problem in clay than in sandy soils. The buffer capacity of clay soils is better than that of sandy soils and the temporary increase in salinity due to ammonium nitrate is lower. The salt index of fertilizers indicates the necessity of splitting an application. Fertilizers with a high salt index, such as potassium chloride, should be split into multiple applications. This may not be necessary in the case of calcium nitrate, which has a low salt index.

After the Soil Application Program has been compiled, an application schedule is developed for each month. During such as exercise, it is planned which orchard will receive its application during what time of the month, taking into consideration available manpower and equipment. Please note that if a number of applications are done in the same orchard in consecutive months, care should be taken to ensure that the applications are done on more or less the same day of each consecutive month.

In practice, it is difficult to apply exactly the recommended quantity per tree to all of the trees in the orchard. It is therefore necessary to calculate the actual average rate of the application once the application has been completed. This is done by dividing the total quantity applied to the orchard by the number of trees per orchard and thus calculating the average volume per tree. The actual average quantity per tree may vary somewhat from the recommended quantity per tree, but it is important to ensure that this variation is not larger than 10%, i.e. 618-683g per tree in the case of orchard A.

Soil application programs are developed for August, September and October, with two separate programs for the application of LAN and potassium chloride in August and September.

Developing a Foliar Application Program

A foliar application program is developed in a similar manner, although the calculations are somewhat different. The recommended foliar applications are supplied in g or ml per 100l water. The size of the trees will determine the total amount of spray mixture required. Foliar feeds are applied as medium cover sprays. The larger the tree the higher the volume applied per tree and thus the volume per hectare. On average, between 1250 and 2,500 litres of spray mixture is applied per hectare on mature citrus trees using a medium-cover spray.

The average actual application per hectare is calculated once the application has been done to ensure that the variance between the recommended quantity and the actually applied quantity does not vary by more than 10%. A foliar application program is developed for October as well. Note that it was stated in the fertilization program that the Manganese Sulphate and Solubor® sprays are compatible, and can therefore be sprayed at the same time.

Maintaining Stock Levels and Placing Orders

Ordering of fertilization must be coordinated with the production manager and the administrative staff. Ensure that documentation is provided to the responsible person in good time, and ensure that the manager is aware of all orders that are to be placed.

The fertilization program for the next season (remember that a season is from the beginning of August of one year to July of the next year) is usually prepared from March to June. During this period, leaf and soil samples are analysed and the results are used inter alia to formulate the fertilisation program. March to June is also the harvesting period for the early cultivars and a good time to evaluate the yield and quality of the late cultivars. Ordering should start during May or June to ensure that stocks are on hand when the very important application of nitrogen starts in July or August.

Click here to view a video that explains how to take soil samples on your farm.

The time required between ordering and delivery depends on the agreement between the manager and supplier. Ensure however that the fertilizers will be delivered in time if orders are placed for instance thirty days prior to the application date.

Economic considerations could limit the time between ordering and delivery. If payment is made on delivery, one would not submit an order in March for fertilizer required in July.

Requirement reports, such as the one above, are developed for each fertilizer and each month and are done for the low biuret urea required in July (foliar spray), LAN and potassium chloride required in September, lime in October and manganese sulphate and Solubor® in October.

Substitution of Recommended Fertilizer

Recommended fertilizers and chemicals for foliar sprays can be substituted with an equivalent elemental base provided that:

• The chemistry of the replacement chemical and its reaction in the soil and on the leaf will not create unwanted side effects; and
• The recommended mass or volume is adjusted to compensate for variations in the concentration of the active ingredient/s.

The person responsible for the formulation of the fertilization program should be consulted before substitutions are made. Fertilizer manufacturers may also be able to assist in this regard.

The rate of application for the replacement fertilizer is calculated as follows:

• The rate of application for recommended product multiplied by % active ingredient in recommended product divided by % active ingredient in a replacement product.
• Rate of application for the replacement product.

The application of fertilizers for sunflower and field-grown vegetables and other field crops differ in that from citrus, due to the fact that we replant each year. Therefore, most of the fertilizers will be incorporated into the soil during soil preparation, some can be applied with plants and a third part can be applied after the crop is established. In some cases, especially with high-value crops or crops with specific needs, a farmer can also apply some elements as a foliar application. Learners are referred to the previous section on citrus for information on timing fertilizer orders and replacement fertilizers.

In this section we investigate:

• Broadcast application of fertilizers to the soil.
• Applying fertilizer during ploughing.
• Band application of fertilizers with planter.
• Fertiliser top dressing after planting.
• Foliar feeds.

As for citrus, it is important to keep a record of what and when fertilizers have been applied. Some of the information to be recorded includes:

• Field number – the same number as the one indicated on the soil analysis
• Crop and cultivar
• Details for soil applications:
  • Quantity (kg) to be applied per ha
  • Name of fertilizer
  • Time of application
• Details for band placing:
  • Quantity (kg) to be applied per ha
  • Name of fertilizer
  • Time of application
• Details for top dressing:
  • Quantity (kg) to be applied per ha
  • Name of fertilizer
  • Time of application
• Details for foliar applications:
  • Quantity in grams (g) or millilitre (ml) to be mixed per 100l water
  • Name of fertilizer
  • Time of application
• Additional information or special instructions.

Determining the Amounts of N, P, K and B to Apply

During the course of this section, the information in tables 1.1 to 1.6 will be used. Table 1.1. is the information we received back after the Laboratory did the soil and plant analysis. This information will be used in conjunction with tables 1.4 and 1.5 to determine the amount of phosphorus and potassium to apply per ha of a crop field.

Table 1.2. provides an indication of the yield potential for sunflowers under a certain set of conditions. The higher the yield potential the more nutrients will be required and vice versa.

Table 1.2. will be used in conjunction with tables 1.3 to 1.5, to determine the amount of nitrogen as well as phosphorous and potassium to apply per ha of cropland under a sunflower. The information is in table 1.6. provided information on the volume of boron required.

Table 1.1. Test results were received from the Soil Laboratory for the soil sample we took.

Table 1.2. Production potential for sunflowers under dryland conditions at specific soil clay contents and soil depths. (Du Toit et al., 1994)

Table 1.3. Nitrogen recommendations for sunflower according to yield potential (FSSA, 2000).

Table 1.4. Phosphorus recommendations for sunflower according to soil analysis and yield potential (FSSA, 2000).

Table 1.5. Potassium recommendation for sunflower according to soil analysis and yield potential (FSSA, 2000).

Table 1.6. Boron recommendation (kg ha-1) for sunflower

Determining Yield Potential (Table 1.2.)

To determine the yield potential for sunflower we use the information provided in Table 1.2. The first step is to identify the field. Once the field is known, gather information on the soil depth and long-term average rainfall.

Let us assume the field of interest has a soil depth of 0.9 m, the average rainfall is 550 mm for the growing season and the clay content between 0 and 10%. Using this information and applying it to the data provided in table 1.2., the sunflower yield potential for the field number is 1.501 ton ha-1.

Determining the amount of nitrogen (N) needed per ha (Table 1.3.)

To determine the N required, the yield potential must be known. If we use the data in example 1.3.1., we assume a yield potential of 1.501-ton ha-1, table 1.3 indicates a nitrogen requirement of 22 kg ha-1.

Determining the amount of phosphorus (P) required (Table 1.4.)

To determine the P requirement, we need to know the yield potential for the crop as well as the amount of available P in the soil.

If we again use the data in example 1.3.1., we require a yield of 1.501-ton ha-1. If we assume an available P status of 8 mg kg-1, the P requirement can be determined. Table 1.4 indicates that for a yield of 1.5 tons per hectare with a P status of 8 mg/kg, we will require 11 kg P ha-1. We thus need to apply 11 kg P per ha of sunflower.

Determining the amount of potassium (K) needed per ha for field number one (Table 1.5.)

To determine the K requirement, we need to know the yield potential and the available K in the soil. If we assume the K status of the soil is 53 mh/kg and a yield of 1.501-ton ha-1, the corresponding value in table 1.5. is 10 kg K ha-1. We thus need to apply 10 kg K for every ha of sunflower we are going to plant in field number one.

Determining the amount of boron (B) needed per ha for field number one (Table 1.6.)

To determine the B requirement, we need to know the clay percentage. If we assume clay content of 0 to 10%, the B requirement is given as (Table 1.6) 9 kg Borax or 6 kg Boric acid or 5 kg Sodium oktaborate per ha.

Compiling a Fertilization Program

The information in the previous section can now be incorporated into a fertilization program. Below is an example of such a program for sunflower.

Compiling a fertilizer plan for all crop fields allows that the correct type of fertilizer is stocked and available at the relevant time. Keep in mind that you are not the only farmer who is going to need the fertilizers. Place your fertilizer order well in advance time to ensure that the fertilizer will be delivered at least a month before you will need it.

Fertilizers Application Strategies and Timing of Application

In this section, the reasons for applying certain fertilizers at a specific time will be explained.

Broadcast application of fertilizers to the soil. Broadcasting refers to the even distribution of lime and fertilizer before it is incorporated into the soil. Broadcasting is efficient and often the method of choice in areas with perennial plants. Lime has to be incorporated in the soil, at least two months before planting. This will allow the lime to rectify a pH problem, as the lime has a long reaction period.

Click here to view a video that explains managing soil acidity by targeting lime to zones of low pH.

Phosphorus-containing products have to be applied to the soil before or with plants, as phosphorus does not easily move in the soil. It can therefore not be applied as topdressing later on, as it will not wash into the soil easily as in the case of nitrogen.

Broadcasting can be done with a tractor pulling the fertilizer spreader or by hand (Fig 1.1.). Most of the spreaders can also be used to spread other dry formula chemicals (insecticides, fungicides etc.) or even broadcasting seeds. After the fertilizer has been broadcasted, it is ploughed into the soil. The two actions can also be combined into one, whereby the tractor’s spreader and plough are attached at the same time.

Figure 1.1. Tractor drawn fertilizer spreader on the left and a hand-operated version on the right.

Placing fertilizer in the soil while ploughing: With this application, the fertilizer is placed in a continuous band into the furrow during the process of ploughing. Each band is covered as the next band is turned over. No attempt is usually made to sow the crop in any particular location with regard to the plough sole bands, as is the case with band placing of fertilizers.

This method has been recommended in areas where the soil becomes quite dry up to a few centimetres below the soil surface during the growing season, and especially with soils having a heavy clay pan a little below the plough sole. By this method, fertilizer is placed in moist soil where it can become more available to growing plants during dry seasons.

This is an alternative to broadcasting. The application of lime is always done by broadcasting, while the application of fertilizers containing N, P, K and other elements are mostly done in this way.

An exception on the broadcasting of lime is when the subsoil is quite acidic. Then lime will be placed deep into the soil while the soil is being ripped with a heavy tooth implement, which penetrates the soil (Fig 1.2.) to a depth of 20 to 50 cm.

Figure 1.2. A hand-held ripper on the left and a mechanically drawn ripper on the right.

Band placement of fertilizers at the plant: This method refers to the application of fertilizers into the soil close to the seed or plant. Localized placement is usually employed when relatively small quantities of fertilizers are to be applied, otherwise, it can burn the seed leading to low germination and poor stands. Localized placement reduces the fixation of phosphorus and potassium in the soil. Localized placement is done with specialized planters and the fertilizer is placed to the side and often below the seed during the seeding operation.

This practice is done to give the young seedling a boost. The fertilizer is placed close to where its roots will grow. The seedling’s roots need not search for the fertilizer which has been mixed with the soil during tillage.

Topdressing of fertilizers after planting: Nitrogenous fertilizers containing nitrates, like sodium nitrate, calcium ammonium nitrate etc. is applied as a top dressing to closely spaced crops. In addition, urea is also top dressed. This helps in supplying nitrogen in the readily available form to growing plants. Topdressing can be done with fertilizer broadcasters.

Foliar feeding:

Click here to view a video that explains Foliar feeding - how does it work?

Click here to view a video that explains your guide to Foliar Nutrient applications.

This refers to the spraying of suitable fertilizing solutions on the leaves of growing plants. These solutions may be prepared in a low concentration to supply a plant with a single nutrient or a combination of nutrients.

It has been well established that all plant nutrients are absorbed through the leaves of plants and this absorption is remarkably rapid for some nutrients.

The foliar application does not result in a great saving of fertilizer, but it may be preferred under the following conditions.

• When visual symptoms of nutrient deficiencies are observed during the early stages of deficiency.
• When unfavourable conditions (physical and chemical) reduce the efficiency (FUE) of fertilizers occurs.
• During a drought period where soil application could not be conducted. (soil moisture insufficient)

There are certain difficulties associated with the foliar application of nutrients:

• Marginal leaf scorching may occur if concentrations of solutions are too high.
• As solutions of low concentrations (usually three to six per cent) are to be used, only small quantities of nutrients can be applied during a single spray.
• Several applications are needed for moderate to high fertilizer rates, and hence
• Foliar spraying of fertilizers is costly compared to soil application unless combined with other spraying operations taken up for insect or disease control.