From a study of the data secured it appears that the causes of variation in the scores of duplicate or replicate samples are the result of (1) lack of care in making replicate random samples, (2) differences in treatment of samples before cracking, particularly as regards moisture content, (3) differences in the skill or care of the operator making the tests, (4) presence of empty nuts or shrivelled kernels in the sample which introduces variation not compensated for in a 25 nut sample and further complicates the matter because assigning penalties for shrivelled kernels involves personal judgment.
The first three of these can be minimized or eliminated by care and skill. The fourth item is not so easy but procedure can at least be standardized. Increasing the size of the sample is not practical if much testing is to be done.
All things considered it would seem that the scores indicate fairly well but not accurately the relative merit of the samples and thus can be relied upon to determine the relative merit of a variety or clone, the suitability of the variety for growing in a given locality and the variability of a variety grown in the same region but under different conditions. To determine the merit of a variety as compared to another both must be grown under the same conditions. The over-all value of a variety can only be determined from samples of well filled nuts. In any case the more samples tested the better.
The following suggestions are made as to procedure:
1. In taking a random sample no selection as to size, uniformity, or any other quality should be made. Suggested procedure would be to scoop up about 25 nuts in a berry basket or with the hands from the main supply and reduce the sample to 25 without conscious selection. What we in the Northern Nut Growers' Association want is a measure of the merit of the crop of the tree or variety in question and not the value of a highly selected sample.
2. It is not practical to bring samples to a uniform moisture content before cracking is done. The following precautions, however, may be followed: (a) Take care to see that nuts are reasonably well cleaned and free from fragments of husk. Scrubbing or beating the nuts together in a sack will usually remove most of the loose material. Of course the best practice is to wash the nuts immediately after shucking. (b) Cure samples until they are dry enough not to lose more weight preferably in an unheated room. This takes at least a month or 6 weeks. (c) Avoid storing the samples in a heated room where they will become so dry that the shells will check or crack. If this occurs the normal cracking fracture of the shell is destroyed and a satisfactory test cannot be made. (d) Nuts that have become so dry that the kernels shatter may be moistened by soaking about 2 hours in cold or lukewarm water then holding them in a moist condition for 18-24 hours, followed by drying for 10-12 hours before cracking. Nuts that are to be soaked should be weighed before soaking and the dry weight used in figuring percentages. The kernels of soaked nuts should be dried for 24 hours before weighing, preferably under the same conditions in which the samples were stored before weighing.
3. Care and skill on the part of the operator are of the greatest importance, particularly in the thoroughness of cracking. The most important variable in the score is the per cent kernel recovered at first cracking. The score is reduced by undercracking the nut so as to leave the quarters bound or by overcracking to the point of smashing the kernels. If the nuts have a long point so that the rims of the anvils do not contact the shoulders of the nut, poor cracking will result. At the present time a cracker with interchangeable anvils is not available. Using different sized iron pipe couplings in a vise may help solve the problem. Some varieties will crack better with a hammer than with a cracker of the Hershey type with standard anvils. In cracking a sample for test the operator should try to recover the most possible out of the first crack without using a pick or recracking.
4. The empty nut problem is probably the most difficult and is not satisfactorily solved by cracking nuts in excess of 25 until 26 filled nuts are secured. This necessitates weighing the sample after the nuts are cracked which is usually impracticable because of loss of parts of shells in cracking and because additional nuts are not available. Empty or shrivelled nuts in a sample are a serious defect which should count heavily against it. On the basis of experience it seems that a better method is to crack the random sample of 25 nuts and let the empty nuts and shrivelled kernels affect the score as reduced weight per nut, reduced per cent kernel and the penalty as well. Shrivelling that is obvious and which adversely affects the appearance of the kernels should be penalized. Possibly further experience will suggest a better way of handling this problem.
The proposed score of a sample is made up as follows:
1. The weight of a single nut in grams.