Last update: April 11, 2012 02:58:22 PM E-mail Print

 

Lucerne Yields from Varying Irrigation Treatments

HW Turpin

 

THE autumn growth of lucerne does not equal that of the summer; also, there is a great difference between the growth early and late in the season, particularly as far as irrigation practice is concerned.

At the Grootfontein School of Agriculture it has been found that with those irrigation treatments where the crop is watered regularly every cutting, the yield for the first three cuttings is about the same for each, representing approximately 20 percent of the yield for the year, or a total of 60 percent for the first three cuttings. The yields for the subsequent three cuttings approximate 17 percent, 12 percent and 10 percent of the seasonal yield for the 4th, 5th, and 6th cuttings respectively. This means that on the average the first three cuttings produce 60 percent, and the last three only 40 percent of the total yield for the season.

 

Low Autumn Yield is Seasonal

It would seem that the low yield from the autumn cuttings of lucerne is definitely seasonal and has little or no connection with possible depletion of plant food by the earlier crops in the season. It has been found that the unirrigated lucerne plots, although the effective rainfall for each cutting is about the same, still show the same trend in yield, as do the other treatments. In view of the very low yields from the unirrigated plots, fertility can hardly playa part.

Again in the three treatments where the two spring, the two summer and the two autumn crops in the season only are irrigated, we find that the percentages of the total yield obtained from the two irrigated crops are respectively, for the three treatments, 61.8 percent, 55.3 percent and 47 percent This means that the yield following the irrigation of the two spring crops is definitely higher than that from two crops irrigated later in the season-in other words, the low yield in autumn is quite definitely due to the season of the year.

It follows from the above that water may be used in an uneconomic manner If the crops in the autumn receive the same quantity per cutting as do the cuttings earlier in the season, and also that higher yields would be obtained from a given quantity of water were this to be applied to the first three cuttings in the season on an area twice the size instead of irrigating all six cuttings of an area half the size.

 

Various irrigations

Based on the yields obtained in our irrigation trials at Grootfontein, the following figures of yields are presented to show what would happen were water to be used on the first three cuttings on one morgen as compared to the yield from the same quantity of water applied to half a morgen for all six cuttings: -

If half a morgen were irrigated 3 inches after cutting and 3 inches 14 days later for all cuttings, the yield will be 16,402 lb. (average for 7 years), whereas if one morgen be irrigated 3 inches after cutting and 3 inches 14 days later for the first three cuttings only, the yield will be 19,523 lb., but in addition there will be a carry-over effect of the water applied to the first three cuttings, resulting in a yield of 2,283 lb., from the fourth cutting, 1,184 lb., from the fifth, and 962 lb., from the sixth, giving a grand total from the morgen of 23,952 lb. for the season, or an increase of 7,550 lb. over the half morgen which has been irrigated for all six cuttings.

From this it will be seen that where only the first three cuttings are irrigated, but where twice as much land is used, there is an increase in hay of approximately 3¾ tons over irrigating all six cuttings with the same quantity of water.

Using another irrigation treatment or 6 inches per cutting, the position will be: -

By irrigating 6 inches per cutting for the first three cuttings only on one morgen the yield will be 15,853 lb., and the carry-over effect of water on the three unirrigated cuttings will result in a yield of 4,429 lb. giving a total yield for the two acres of 20,282 lb., whereas by irrigating 6 inches per cutting for all six cuttings on half a morgen the yield will be 13,814 lb., so that the increased yield obtained by watering the first three cuttings only will be 6,468 lb. or approximately 3.2 tons.

Assuming that only the first three crops are irrigated and that there is no carry-over effect to the fourth, fifth and sixth crops, then the difference in yield obtained from the above methods of irrigating- would be: -

Irrigating one morgen 3 inches, and 3 inches 14 days later for the first three cuttings would give a yield of 19,523 lb. less 16,402 lb. from watering all six cuttings on half a morgen, a difference of 3,121 lb. or approximately 11 tons; or where one morgen is irrigated 6 inches per cutting for the first three cuttings, there would be a yield of 15,853 lb. less 13,814 lb. from watering all six cuttings on half a morgen, making a difference of 2,039 lb. or approximately 1 ton.

 

Economical Use of Water

The yields given above being from experimental plots are no doubt higher than would be obtained under field conditions, but the same principles will apply.

It would appear therefore, that where the lucerne grower has some control over the water so that he can regulate the quantity used, it may be of great economic importance to him to increase his area under lucerne and use all his water on the first three cuttings. Where however, the water is from fountains and is available the whole season, it is possible that the water may be used more economically on other crops later in the season. Crops like potatoes or summer crops for grazing suggest themselves.

 

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