Module 6. Yield and Fruit Size. Presenter: Stephan Verreynne

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1 Presenter: Stephan Verreynne definition Yield Yield refers to the amount of fruit produced, and can be expressed in terms of: Tree yield kg per tree kg/tree Orchard yield tons per hectare t/ha Export yield 15kg carton equivalents per hectare cartons/ha (10kg carton equivalents for soft citrus) Introduction The success of a citrus grower depends on the quality, size and volume of fruit that he can produce for the market. All three these factors can be manipulated through production practices, but before he can decide which practices to employ, the grower needs to know what the current situation is. As we approach harvest time, the grower also needs to be able to estimate how much fruit is hanging on his trees, and what the size range of the fruit is. This information is used in his harvesting planning, and is sent through to the packhouse so that they can do their planning. Citrus Fruit Development Citrus fruit growth follows a sigmoidal curve, with three phases. Phase 1 is mainly cell division, phase 2 is mainly cell enlargement, and phase 3 is when ripening takes place and the fruit colour changes from green to orange, and sugars increase and acids decrease. There is little fruit growth during phase 3. Climatic conditions during phases 1 and 2 of fruit growth are very important. A single factor, or a combination of controllable and uncontrollable factors, can have an impact on fruit growth and fruit size. 1

2 definition Sigmoidal Curve The term sigmoidal is used to describe an S-shaped object. In this case, it describes the growth curve of citrus, meaning that, in terms of fruit size, growth is slow in the beginning, speeds up in the middle and slows down again at the end. Uncontrollable Growth Factors Uncontrollable factors include climate, and mainly temperature. Fruit growth takes place mostly between 20 C and 28 C. Seasonal differences also affect fruit growth and size. Rainfall and humidity also play an important role. Controllable Growth Factors The controllable factors that impact on fruit growth and size, that are selected before harvesting, are the soil type (depth and structure), and the cultivar and rootstock that we select. Vigorous rootstocks produce larger fruit. Tree age also plays a role. Older trees produce more but smaller fruit, while younger trees bear fewer fruit but they are larger. Fruit Growth Factors Uncontrollable Factors Temperature C for fruit growth Humidity Rainfall (related to irrigation) Controllable Factors Soil type (depth and structure) Cultivar fruit size characteristic of cultivar Rootstock more vigorous, larger fruit summary 2

3 Production Practices Irrigation Irrigation plays a very important role in fruit growth, particularly during phase 2. During this phase, the trees must under no circumstances experience water stress, as this will cause a decrease in the growth rate of the fruit. Plant Nutrition Plant nutrition also plays a major role. The potassium level in the leaves should not be lower than 0.9%, as lower potassium levels cause smaller fruit. The nitrogen-potassium ratio must be between 1:6 and 2:2. Tree and Root Health Tree and root health is very important, specifically nematodes and Phytophthora (root rot). If these are present in the orchard, you will have smaller fruit. Other Practices There are a few other factors that we can control to produce bigger fruit. We can delay the harvest, but during phase 3 there is little fruit growth, so not much will be gained in fruit size. We can also harvest selectively and pick the bigger fruit first. Summer girdling is labour intensive and isn t common practice. Pruning can be used to improve light distribution in the tree, resulting in bigger fruit. 3

4 Fruit Thinning Tree fruit load affects fruit size, specifically the number of fruit on a tree. The more fruit there is on a tree, the smaller the fruit will be. Fruit thinning reduces the number of fruit per tree, and therefore competition between fruit, resulting in bigger fruit. Thinning can be done by hand, but it is more common in citrus production to use synthetic auxins. definition Auxins Auxins are natural plant hormones or synthetic substances that affect the growth and development of all plant parts. Production Practices summary Production practices that impact on fruit size and yield are: Irrigation Plant nutrition Maintaining tree and root health Delaying harvesting Harvesting selectively Summer girdling Pruning Fruit thinning Production Guidelines information Please consult the CRI Production Guidelines for more information, as follows: Irrigation Volume II, section 2 Plant nutrition Volume II, section 1 Plant manipulation (summer girdling, pruning, etc.) Volume II, section 5 4

5 Harvest Planning To do harvest planning, it is important to know if the fruit is generally large or small. It is also important to identify markets for specific fruit. Smaller fruit is sent to different markets than large fruit. One also needs to determine the fruit size range per tree, to know what size the orchard will peak at. It is also important to predict the yield, in kilogram per tree, and to determine whether the fruit size comply with export standards. Should it not comply with export standards for size, the management programme must be adjusted. Fruit Size Estimates To predict fruit size, we measure fruit, using one of two methods. We can measure the of a representative sample of 50 to 150 fruit from two to five representative trees with a typical fruit load. Representative trees are trees of a typical size and with a typical fruit load. It is important to measure at least 500 fruit per unit, meaning per block or per cultivar. Use a calliper, preferably a digital one, with a logger to download the data directly onto the computer. The second method is to pick all the fruit from one or two representative trees, and to measure them one by one. We use the measured fruit sizes to determine the size range at picking, based on long term growth curves and gradients and the predicted harvest time. From historical data, we can forecasts more or less when picking in a block should begin. To compile historical data and determine growth curves, certain fruit are marked and they are measured weekly, biweekly or monthly, depending at how much time you have, from physiological fruit drop to harvest time. 5

6 information Index Trees To build accurate historical data, it is important to measure and test the fruit of the same index trees at the same time every year. Yield Estimates The number of fruit per tree is also determined after fruit drop. The one method is to put a sticker on every fruit in a tree, and then counting the number of stickers you used, to determine the number of fruit in the tree. The other method is to remove and count all the fruit from the tree, in which case the fruit can also be measured to predict the fruit size distributions. The number of fruit is used to calculate the percentage in every size. The number of fruit per size, multiplied by the average fruit weight, gives the kilograms in every fruit size. The weights for all size categories are added up to give the weight per tree. The number of trees per ha is then used to calculate the yield per hectare in tons. Please see the skills sheets on Fruit Size Estimates and Yield Estimates. Estimate skills example We have a citrus farm in Citrusdal in the Western Cape. In the middle of January we decide to do a yield and fruit size spread estimate for our Washington navels. Before we start to measure the fruit, we need to prepare a data table so that we know in which size categories the fruit will be at this time. We start our spreadsheet by putting down the count categories for navel oranges and the minimum fruit at picking for each (this information is industry standards). 6

7 Count (Fruit / 15kg carton) at picking From past experience we know that we will start harvesting our Washington navels at the end of June. We now need to work out how much we can still expect the fruit to grow before it is harvested. To do this, we use information that is available from people that do citrus research the monthly fruit growth increments table. Citrus Type Dec Jan Feb Mar Apr May Jun Jul Aug mm fruit per month Mihowase Satsuma Nules Clementine Eureka Lemon Navel (mean) Bahianinha Palmer Robyn Washington Valencia (mean) Delta Midknight Valencia Table 1. Monthly fruit growth increments in Citrusdal, based on historical data from 3 consecutive years. (Navel and Valencia in bold represent the means of all Navel or Valencia cultivars, respectively.) From the row for Washington navels, we calculate that we can expect our fruit to still grow by 26.35mm from middle January to end of June ( ). We now add another column to our spreadsheet, in which we subtract from the minimum at harvest. This gives us the minimum that the fruit will be in January for each size. 7

8 Count (Fruit / 15kg carton) at picking on 15 Jan We now go to our index tree and measure 100 fruit on the tree, and sort them into the categories that we have on our spreadsheet. We also count all the fruit on our index trees, and find that we have on average 500 fruit per tree. We can now add the following information. Count (fruit / 15kg carton) at picking on 15 Jan Fruit measured per size Fruit in size per tree Total Now we know how many fruit we have in each per tree in our orchard at the moment. But now there is another factor that we must take into account summer-fall fruit drop, during which the trees will all lose some fruit. From historical data on the farm, we know that we can expect to lose about 30% of the fruit on the trees before the end of June. We can therefore estimate that the number of fruit per size per tree at the end of June, will be as follows: 8

9 Count (fruit / 15kg carton) at picking on 15 Jan Fruit measured per size Fruit / size / tree Fruit / size / tree at end June Total Now we would like to calculate what our yield per tree will be in kilogram. To do this, we need to know what the mean fruit weight will be per size. This is easy enough to calculate remember that we know how many fruit goes into a 15kg carton, so we can simply divide that number of fruit into 15 to get the mean fruit weight in kilogram. If we now multiply the mean weight per fruit with the number of fruit that we have estimated there will be on the trees at the end of June, we get the yield per fruit size in kilogram. If we add together this column, we get the estimated yield per tree. Count (fruit / 15kg carton) at picking on 15 Jan Fruit measured per size Fruit / size / tree Fruit / size / tree at end June Mean fruit weight (kg) Yield per tree (kg) Total kg 9

10 Our Washington navels are planted at the trees spacing of 5x3m, which means that we have 667 trees per hectare. We can therefore calculate our yield per hectare as follows: Yield per hectare = yield per tree x trees per hectare = 74.8kg x 667 = 49,891.6kg = 49.9 ton/ha active learning Watch the DVD clips, read through the learning material and do workplace research to gather the knowledge and information to complete the assignment(s) below. Activity 6.1 Workplace Interview Interview a subject matter expert such as a citrus grower or farm manager, and find answers to the following questions: What was the yield per hectare for one orchard of a particular type of citrus during the last season? What was the average fruit size for this orchard? How did this compare to the estimated yield and fruit size for that orchard? When were the estimates done? Can you explain to me, step-by-step, how the estimates were done? Activity 6.2 Practical Ask your coach / supervisor to monitor you while you prepare and use equipment to measure fruit size. Make sure that you follow the correct procedures according to your organisation s SOP manual. 10

11 Learner Workbook Activity 6.1 Workplace Interview Interview a subject matter expert such as a citrus grower or farm manager, and find answers to the following questions: Details of interviewee Name and surname: Date of interview: Signature of interviewee: What was the yield per hectare for one orchard of a particular type of citrus during the last season? What was the average fruit size for this orchard? How did this compare to the estimated yield and fruit size for that orchard? When were the estimates done? Can you explain to me, step-by-step, how the estimates were done? 11

12 Learner Workbook Activity 6.2 Practical Ask your coach / supervisor to monitor you while you prepare and use equipment to measure fruit size. Make sure that you follow the correct procedures according to your organisation s SOP manual. Tools and equipment Handling before, during and after task completion SOPs: Day Details of tasks completed Time spent on tasks Signature of supervisor 12

13 Skills Sheets Fruit Size Estimates Requirements Calliper (preferably digital with logger) Method 1 1. Select 2 to 5 representative trees (trees of typical size and fruit load) per unit (block or cultivar) 2. Measure 50 to 150 fruit on representative trees 3. Measure at least 500 fruit per unit (block or cultivar) 4. Transfer information to computer system or note by hand 5. Calculate average fruit size per unit (block or cultivar) 6. Repeat measurements on regular basis, noting results to develop growth curves 7. Use predicted growth to estimate fruit size range at picking Method 2 1. Pick all the fruit from one or two representative trees 2. Measure fruit one by one 3. Follow steps 4 to 7 of method 1 13

14 Skills Sheets Yield Estimates Requirements Self-adhesive labels Method 1. Select 2 to 5 representative trees per unit (use same trees as for fruit size estimates) 2. Put on label on each fruit in tree 3. Count the number of labels used from box by looking at the backing paper that remains Alternatively, if method 2 is used for fruit size estimates, all fruit that is removed are counted. 4. Use number of fruit to calculate percentage per size 5. Weight per size = fruit per size x average fruit weight 6. Weight per tree = total of weights per size categories 7. Yield per hectare = weight per tree x trees per hectare 14