Harvest Index vs Harvest Maturity Index: What’s the Difference and Why It Matters

• The harvest index and harvest maturity index maximize yield and quality but involve different purposes, measurement methods, stakeholders, timing, and target crops.
• The harvest index is used during the research and cultivar development stage to measure plant function efficiency and estimates the carbon allotted to make harvestable products.
• The harvest maturity index estimates the best time to gather a crop to extend postharvest shelf life and the development and maintenance of quality during each season.

The term harvest index is sometimes used instead of or as a short form of harvest maturity index. However, the two terms refer to very different concepts and are helpful for diverse stakeholders in the food chain. To understand the differences, find out what the two terms refer to and their applications in this article.

Harvest Index

Harvest index (HI) measures plant function efficiency and partitioning of photosynthates to harvestable products. The harvestable product can be seeds (cereals, pulses, and oilseeds)  tubers, flowers, or fruits in different crop species. HI is estimated as a ratio of yield to the total plant biomass.

In the case of fruits, HI refers to the amount of biomass allotted annually to the harvestable sinks. It is calculated as the “annual fruit dry mass divided by the tree’s total annual dry mass.”

The concept of defining reproductive yield to total shoot biomass was introduced in 1914 by Beaven but was called the “migration coefficient.” The term “harvest index” was used to describe the concept later and is extensively applied in plant breeding programs. The harvest index has helped scientists assess progress in increasing yield potential.

Improving the harvest index has increased the yield potential of several vital food crops. Genetic factors, environment, and crop management influence crop HI.

The basis of HI is carbon-centric. The amount of carbon fixed by photosynthesis is estimated by the shoot and root dry matter, though often only shoot dry matter is considered. The carbon is used for respiration, growth, and allocation to the sinks (seeds, fruits, or flowers), which are the harvestable parts. Hence, the source-sink dynamics of the crop plant are crucial to improving the harvest index.

Harvest Index Applications

Initially, the harvest index was used to improve the yield potential of cereals. For example, a single mutation responsible for dwarfism produced short and high-yielding rice and wheat varieties.

Nowadays, HI is also used to improve fresh produce yield and quality. The aim is to reduce investment by fruit trees and vegetable plants in standing tree structures through genetics, rootstocks, pruning, and canopy management to allow more carbon allocation to sinks or harvestable products. Therefore, dwarfism or size control of the trees has also been instrumental in improving the HI among fruits. For example, rootstocks that confer dwarfism on the scions, increase anchorage, and uptake of water and nutrients will increase the harvest index.

The HI values differ among food types and species. Check Table 1 for various HI values for everyday agricultural products. In the case of fruits, the HI of apples on dwarfing rootstocks is 60-70% & and significantly higher than the HI of 40% for kiwifruit.

Table 1: “Harvest index (dry mass of harvested component/total shoot dry mass) varies with crop species,” Atkinson et al. 2013. (Credits: https://rseco.org/content/641-harvest-index.html)

Like HI, the harvest maturity index also aims to improve yield and quality, but the timing and applications of its use differ considerably.

Harvest Maturity Index

The harvest maturity index measures if fruits and vegetables are mature enough for harvest. Optimum maturity at harvest ensures adequate storage and transport time, long shelf-life, and further development and maintenance of fruit quality to meet consumer demands postharvest.

The index helps fix harvest time and is helpful in postharvest sorting, grading, and regulation compliance.

Fresh produce can be harvested at physiological or horticultural maturity, depending on the species.

• Horticultural maturity: Harvested fresh produce is ready for its intended use. The harvestable product may or may not have reached full fruit development has not occurred. For example, immature fruits like cucumber, leafy greens, flowers, ripe apples and mangos (climacteric fruits), and berries (non-climacteric fruits) are harvested at various horticultural maturitys.
• Physiological maturity: It is the stage where fresh produce is fully developed or mature, and it is a point that balances further development of quality parameters like appearance and flavor with extended storage and shelf-life. Climacteric fruits like apples, pears, bananas, avocados, etc., are harvested at physiological maturity.

Harvest Maturity Index Estimation Methods

Harvest maturity indices can be based on intrinsics fresh produce quality parameters or crop chronology.

Quality parameters

Fresh produce quality parameters, helpful as harvest maturity index, are physical, chemical, and physiological. Many are non-destructive and helpful for repeat measurements of crops on plants before harvest, such as color, size, or sugar estimation. Some can be destructive, such as firmness or juiciness.

• Physical parameters: These are the most common harvest maturity indices, mostly external and easy to evaluate. Physical harvest maturity indices are size, shape, weight, ease of abscission, surface attributes, peel and pulp color, firmness, juiciness, and specific gravity.
• Chemical parameters: Increasingly, internal chemical quality parameters are used as they are objective, and modern technology gives precise estimations in real time. The parameters used are soluble sugar content (SSC), dry matter, titrable acidity, taste, phenols, and starch.
• Physiological parameters: Maturity and ripening are marked by ethylene production and respiration. These are not used often, as standardization is difficult due to differences among cultivars.

Crop chronology

Several aspects of crop chronology can serve as non-destructive and easy harvest maturity indices. While they are broad recommendations, they help a grower prepare for harvest and narrow the time for more specific tests. Features such as days from planting or flowering are the most used in this category. Heat units, which consider season and weather, are other examples.

No single solution

Several harvest maturity indices exist, as no single parameter can estimate maturity time for all fresh produce. The optimum harvest maturity index varies based on species, distance to the intended market, and planned end use.

• Dry matter is valid only for climacteric fruits. SSC, size, color, and weight are used for all fruits, such as grapes.
• Often, more than one index will be necessary to get a better picture of the fruit maturity stage, for example, in peaches.
• The value of a harvest index can differ based on use, even for a single species or cultivar. For example, different peel colors and SSC levels estimate the five harvest stages in tomatoes based on market and use.

The harvest maturity index’s importance can be judged because unreliable indices account for 40-50% of loss in the mango supply chain.

Comparison of Harvest Index and Harvest Maturity Index

Table 2: Differences between harvest index and harvest maturity index.

	Harvest index	Harvest Maturity Index
Definition	Measures plant function efficiency in terms of carbon partitioning for the harvestable product	Estimates the optimal harvest time that ensures the extended shelf life and postharvest quality to meet consumer demands
Purpose	Maximizes harvest potential by optimizing genotype, environment, and crop management practices	Maximizes actual harvest by optimizing only the harvest time for the intended market, end-use, and transport/storage distance
Stakeholders	Used by scientists in crop development stages	Used by growers in the field to increase ROI
Timing	Used in plant breeding and crop science to improve potential yield and quality	Used during the production of fresh produce to maximize actual yield and quality
Application targets	Used for all crops- cereals, pulses, tubers, flowers, and fresh produce	Used for fresh produce
Measurement method	It is the ratio of the dry mass of annual yield to the total annual dry mass of the plant	It involves the measurement of various quality parameters and crop chronology

 

While both the harvest index and harvest maturity index aim to improve harvest results, a comparison shows significant differences. A summary of the differences is given in Table 2.

Definition: HI indicates plant function efficiency and carbon allocation to form the harvestable product, while the harvest maturity index measures only the optimal harvest time.

Purpose: HI is used to evaluate the success of plant breeding programs and crop science to develop genotypes and research crop management practices that optimize crop growth conditions and allow more diversion of assimilated carbon to sinks or harvestable products. It improves the potential yield of a cultivar and species. The harvest maturity index optimizes fresh produce quality and yield by choosing the correct time customized for a species and cultivar that extends shelf life and enhances and maintains quality.

Stakeholders and timing: HI is used by scientists in the research phase of crop development in laboratories and institutions. In contrast, growers use the harvest maturity index during food production, at each harvest, to choose an optimal time to maximize the current season’s yield and quality for the intended market and use.

Application targets: HI can be used for all agricultural, horticultural, and floricultural products. The harvest maturity index is used mainly for horticultural crops-fruits and vegetables.

Measurement method: HI is measured as a ratio of the dry mass of the harvestable product to the total annual plant biomass. Harvest maturity indices measure several fresh produce quality parameters and crop chronology.

Measuring Quality Harvest Maturity Indices

Non-destructive and destructive techniques can estimate internal chemical attributes like sugar, titrable acidity, and dry matter. Non-destructive methods are gaining popularity as they save crops, are precise, and give real-time results. Felix Instruments Applied Food Science provides tools that are considered industry standards and helpful throughout the fresh produce supply chain. The company has one general device that can be used for several crops. While others are customized for major fruits like mango, avocado, kiwifruit, and melon, which help measure internal chemical quality parameters used as harvest maturity index.

Check our quality meters to learn how to improve the yield and quality of your fresh produce harvest on the field.

Sources

Asefa, G. (2019). The role of harvest index in improving crop productivity. Journal of Natural Science Research, 9(6), 24-28.

Atkinson, C. J., & Else, M. A. (2003, October). Enhancing harvest index in temperate fruit tree crops through the use of dwarfing rootstocks. In Proceedings of the International workshop on cocoa breeding for improved production systems (pp. 118-131).

Atkinson, R. G., David A. Brummell, D. A., Burdon, J. N., Patterson, K. J., & Schaffer, R. J. (2013). Chapter 11-Fruit growth, ripening and postharvest physiology. Plant in Action. Plant and Food Research. Retrieved from https://rseco.org/content/chapter-11-fruit-growth-ripening-and-post-harvest-physiology.html

Bajcar, M., Saletnik, B., Zardzewiały, M., Drygaś, B., Czernicka, M., Puchalski, C., & Zaguła, G. (2016). Method for determining fruit harvesting maturity. The Journal of Microbiology, Biotechnology and Food Sciences, 6(2), 773.

FAO. (n.d.). Chapter 2. Basic harvest and postharvest handling considerations for fresh fruits and vegetables. Retrieved from https://www.fao.org/4/y4358e/y4358e05.htm

Paoletti, A., Rosati, A., & Famiani, F. (2021). Effects of cultivar, fruit presence and tree age on whole-plant dry matter partitioning in young olive trees. Heliyon, 7(5), e06949. https://doi.org/10.1016/j.heliyon.2021.e06949

van Hooijdonk, B.M., Tustin, D.S., Dayatilake, G.A., Oliver, M.J. and Richardson, A. (2018). Harvest index of apple and kiwifruit – how high can we go by optimising plant architecture and canopy management? Acta Hortic. 1228, 307-314. DOI: 10.17660/ActaHortic.2018.1228.46