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Crofting Agriculture
Chapter XII. Agricultural Arithmetic


58. Calculating Manuring for Root Crops

It struck me, when pacing out a garden the other day to determine the amount of lime to be applied, that a few figures and constants might be useful to keep for reference. Crofters deal with small acreages and often enough with fractions of an acre, so that when it comes to applying dressings of a concentrated manure it is most necessary to have calculations accurate. And this not only for the sake of economy of use, but for the welfare of the plant to be dressed ; a too heavy dressing may kill the crop.

The first number to keep in mind is the number of square yards in an acre. Nowadays, only the Imperial acre has any significance—4840 square yards. The Scottish acre of 6104 square yards might as well be forgotten except for historical purposes.

Unfortunately, the figure 4840 does not give an easily measured or remembered square root to enable us to plot an acre on the square. Probably 70 yds. square is the best figure we can use for rough purposes—giving 4900, or 80 x 60—giving 4800 sq. yds. An acre is also 10 sq. chains, a chain being 22 yds. long, containing 100 links of 7.92 in. With a chain, therefore, acreage can be rapidly computed, or an acre laid out by measuring 2 chains x 5. One chain is a common width for the lands in ploughing, and in such pieces of ground as allow the use of this width of a land it gives an easy guide to measurement of acreage. When you have to rely on pacing for computing areas, it is well to remember that

it needs a pretty good pace to make a yard, a good 6 in. more than a pace in ordinary walking. I have taken the trouble myself to check and practise making paces of a yard so that I can be fairly sure of not being more than a foot or two out of true in a 100 yds. All the same, I keep a 2-yd. and a 3-yd. stick in the barn, which are notched at intervals of a foot, the first foot being marked in inches also and the second and third foot in 3-in. intervals. These are most useful for marking out rows during the spring work when the rows do not conform to the normal 27-in. width made by a ridging plough. For example, carrots may be sown 15 to 16 in. apart, mangolds, swedes and early potatoes 24 in. and peas 36 in.

A useful point to remember is that a dressing of 1 ton (2240 lb.) to the acre means less than lb. to the square yard. How small a quantity then is needed per square yard of a concentrated fertilizer like nitro-chalk where 1 cwt. to the acre may be used—-just over oz.! Such a small quantity gives little room for mistakes on a small patch of ground.

It is best, I think, not to calculate such concentrated manures in quantities per square yard but in terms of yards of crop, where this may have been sown in rows. The large farmer, for example, dressing his potatoes with 3 cwt. of superphosphate to the acre, will be sowing the fertilizer in standard drills of 27 in. This width equals yd. and gives for all practical purposes 6450 lineal yards of crop to the acre: 3364 / 6450 = 0.052, or that is, 4/5 oz. per yard of crop. Our 1 cwt. of nitro-chalk which gave between and 3/5 oz. per square yard when broadcast would give 2/5 oz. per lineal yard of crop if applied to the drills. In row-crop work it is obviously an economy to apply fertilizer to the drills where it is required and not to the weeds between the drills.

Early potatoes would be planted only 2 ft. apart, which would mean 7260 lineal yards of crop per acre instead of 6450 yds. of standard drills. Therefore, the standard dressing of 3 cwt. of superphosphates would have to be increased to the relation of 7260 / 6450 = 1.13, which is a useful factor if you are dealing with a biggish acreage, but for small patches it would be better to stick to the quantity per yard of crop. Here is a field example : say we have ten rows of early potatoes, 2 ft. apart and 57 yds. long ; that gives 570 yds. of crop at 4/5 oz. per yard of superphosphate at the rate of 3 cwt. to the acre = 570 x 4/5 x 1/16 = 31 lb.

59. Calculating Yields and Quantities

From the figures given in the preceding section, it should be easy to work out the number of lineal yards of crop per acre with varying widths of row and calculate dressings of fertilizers for small areas. There remains the estimate of yield by weighing the crop from average stretches of the rows. When the rows are the standard 27 in. apart, a yield of 1 lb. per lineal yard gives a yield per acre of 2 tons, 17 cwt., 2 qrs., 13 lb. Thus, supposing a good average crop of potatoes gave 3 lb. per lineal yard, the yield per acre would be three times the figure given above, namely, 8 tons, 12 cwt., 3 qrs., 11 lb. to the acre.

Obviously, the narrower the distances between the rows the higher would the acre yield be, calculated from the yield of representative lineal yard stretches, and vice versa. Thus, if the rows were 2 ft. apart the yield per acre from 1 lb. per lineal yard would be 5 cwt., 3 qrs., 1 lb. more than for the standard drill of 27 in., making a total per acre of 3 tons, 3 cwt., 2 qrs.; and if the rows were 30 in. apart the yield per acre would be 2 tons, 11 cwt., 3 qrs., 12 lb.

In giving these figures per lineal yard, do not let it be thought that I suggest that crop yields should be calculated from separate measured yards, because a very slight error in the yield of 1 yd. would be enormously exaggerated when reckoned per acre. Representative stretches of 10 yds. should give moderate accuracy, and they should be measured, not paced.

The estimation of yields and quantities required for the normal working of the croft certainly adds to the interest of the work. I always like to work on the basis of a winter period of 200 days, that is from 20th October to 8th May, and allow a cow 14 lb. of hay a day for that period. There are 160 stones in a ton, so the cow's ration should be 25 cwt. for the winter. If sheaves are fed for part of the time, adjustment must be made on this figure. I should like my cows to have 42 lb. of roots a day for the period, roots being widely interpreted to include such green fodder as kale. A cow, therefore, would consume 600 stones or 3 tons, 15 cwt. of roots in the season. Unfortunately, my poor cows never do get this quantity ! But it is not excessive by dairy cow standards—indeed, it is hardly adequate—but our cows are smaller than down-country cattle and do not give the quantity of milk.

Measurement of the quantity of hay one has won is quite difficult because our stacks are small, and often round, and its texture may not be representative of hay in other districts where measurement for buying and selling is common. The standard East Lothian measure is that a cubic yard weighs 14 stones = 1 cwt. West Highland hay in small circular stacks would probably weigh 1 cwt.

The contents of a circular stack may be measured by squaring the average girth in feet and multiplying by 0.07958; multiply the resulting figure by the height of





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