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close this bookRice Production (Peace Corps)
View the document(introduction...)
View the documentAcknowledgement
View the documentIntroduction
View the documentChapter 1 - Rice morphology
View the documentChapter 2 - The growth stages of rice
View the documentChapter 3 - Varietal characteristics
View the documentChapter 4 - Seed selection and preparation
View the documentChapter 5 - Methods of raising seedlings
View the documentChapter 6 - Methods of stand establishment
View the documentChapter 7- Land preparation
View the documentChapter 8 - Plant nutrients and effect on growth
View the documentChapter 9 - Fertilizer sources and management
View the documentChapter 10 - Insect pests of rice
View the documentChapter 11 - Pest prevention
View the documentChapter 12 - Pesticide safety and agro-chemical use
View the documentChapter 13 - Pesticide calibration
View the documentChapter 14 - Diseases of rice
View the documentChapter 15 - Weeds and weed control
View the documentChapter 16 - Management of flooded soils
View the documentChapter 17 - Harvesting, threshing, drying, storage
View the documentChapter 18 - Yield calculation
View the documentGlossary of Terms

Chapter 18 - Yield calculation


Through analysis of comparative yields, the farmer and/or extension agent can determine which of the available rice varieties is best suited to local swamp systems and farming practices. Farmers are generally very shrewd at estimating yields, but they rarely quantify their estimations into standardized units of measurement. This chapter describes a straightforward, quick, and reasonably accurate method of yield calculation which will enable the extension agent to keep track of local yields for purposes of comparison and planning.

I. Farmers' Estimations

Just because a farmer may be unable to perform mathematical computations, do not assume that s/he has no accurate sense of crop yields. Never make the mistake of underestimating the knowledge of farmers, who after years and years of growing rice tend to become shrewd economists in their own right. Farmers pay very careful attention to yields (their livelihood and in fact their very survival depend on them), and although often they develop their own particular system of accounting, generally they know exactly how each crop yielded relative to other crops grown in other years. Some farmers count the number of bundles harvested, others keep track of numbers of bags filled, still others measure in terms of bushels of grain. Whatever the methodology, the farmer ends up with a pretty good idea of how well the crop yielded, and this information helps in planning for the future.

The extension agent requires a more quantitative and standardized method. It is important that yield calculations be quantitative (expressible in precise numbers) so that actual values may be compared from swamp to swamp, year to year, variety to variety. It is important that the method be standardized so that in every case measurement is made in exactly the same way.

II. Yield Calculation

Note: Since the method of yield calculation described below requires a certain amount of mathematics, it will not always be possible to teach it to farmers. Nor will this be necessary, since for their own accounting purposes farmers can perfectly well continue to rely on their time-tried methods. However, it may be a good idea to teach the method to other extension agents. As agriculturalists, they will be working in more than just one farming system, and it will be useful for them to know how to calculate yields for comparative purposes.

Calculating yields is a two-step process involving sampling the crop and calculating the yield.

1. Sampling the Crop

Sampling a crop of rice means measuring the yield of a small fraction of the total crop area. The sample should be representative of the crop as a whole (i.e., taken from an "average" section, not from a noticably lush section, nor from a section in which there has been unusual crop damage). The sample should also be large enough to be accurate -generally 10m2 is considered satisfactory. For ease of measurement, harvest ten "minisamples of 1m2 each to add up to the total sample of 10m2 Within the crop area to be sampled, peg out ten "mini-samples" of 1m2 each. Cut all the panicles within the "minisamples" and collect them in one place. Thresh the grains, being careful not to lose any (a small error in sampling may lead to a large error in calculating the yield). Sun-dry the grains for 2-3 days, or until the moisture content is close to the 14% considered suitable for storage. (It is important that the grains be well-dried, since undried grains are considerably heavier and will produce inaccurate yield figures). Winnow out all unfilled grains and carefully weigh the remaining rice.

2. Calculating the Yield

If taken exactly as described above, the sample will contain the yield of 10m2 of the total crop area. Since yields are generally expressed in terms of kg/ha (kilograms of grain per hectare), the problem now is to convert the yield figures derived from the sample (kg/10m2) into the standard units of measurement (kg/ha). Since

1 ha = 10000m2, the sample area constitutes 10/1000 ha, or 1/1000 ha.

Therefore, to determine the average crop yield in kg /ha simply multiply the weight of the sample by 1000.

Example: Careful sampling of ten 1m2 "mini-samples" results in 550g (.55 kg) of dry grain. What is the yield of the crop in terms of kg/ha?

Weight of sample =.55 kg
Area of sample = 10m2

Yield in kg/ha =.55 kg/10m2 x 1000 = 550 kg/ha.

Notes Yields measured in kg/ha can be converted into lbs/acre or bushels/acre using the following conversion rates:

1 kg = 2.2 lbs

1 ha = 10000 m2

1 lb =.453 kg

1 ha = 2.47 acres

1 bushel = 60 lbs

1 acre = 43560 f2

1 bushel = 27.18 kg

1 acre =.405 ha


Rice Production Manual (Revised Edition, 1970) Compiled by the University of the Philippines College of Agriculture in cooperation with the International Rice Research Institute (IRRI)

The definitive handbook for the extension agent working with upland or irrigated rice; includes comprehensive information about all aspects of rice cultivation, including plant growth and development, soil chemistry, response to fertilization, water management practices, etc. Available by direct mail order from: Salesroom, Department of Agricultural Communications (DAC), University of the Philippines, College of Agriculture, College, Laguna, Republic of the Philippines. One copy available through ICE to Peace Corps in-country resource centers/libraries.

Soils, Crops, and Fertilizer Use - A Guide For Peace Corps Volunteers, by Dave Leonard (ICE Reprint #8, Peace Corps). A condensed, readable, information-packed booklet dealing with technical aspects of soil chemistry, plant nutrient uptake, and fertilization; a valuable complement to this manual, especially for those lacking formal training in agriculture. Available to PCVs through ICE, Peace Corps, 806 Connecticut Avenue, N.W., Washington, D.C. 20525.

Apply Pesticides Correctly (U.S. Department of Agriculture, U.S. Environmental Progection Agency)

Although self-described as "A guide for commercial applicators," this pamphlet provides excellent background information useful to the extension agent; includes coverage of types of pests, pest control methods, pesticides, labels and labeling, pesticide use, laws and regulations; recommended particularly for those with little experience with pesticide use. Available to PCVs from ICE (see above).

Pest Control in Rice (PANS Manual No. 3 - Centre for Overseas Pest Research, London) The definitive guide to pest control in rice; very comprehensive, including discussion of weeds, diseases, molluscs, nematodes, crustacea, insects and mites, birds, and rodents. Address requests for single copies to: Centre for Overseas Pest Research, PANS Office, College House, Wrights Lane, London W8 5SJ, UK.