The Response of Malling Jewel And Malling Exploit Raspberries to Different Soil Moisture Conditions and Straw Mulching

The raspberry varieties Mailing Jewel and Mailing Exploit were used to study growth and crop responses to mulching and irrigation from 1957 to 1962 inclusive.

Treatment A consisted of a wheat straw mulch applied deeply enough to form a complete surface cover; treatments B and C of water applications on unmulched cultivated soil at soil moisture tensions of 20 cm. and 50 cm. of mercury respectively, measured at 1 ft. depth. Treatment B was changed after i960 to a single 2-in. water application given when the raspberry fruits began to ripen. Plots under treatment D were cultivated, unwatered and unmulched.

Irrigation greatly increased the rate of cane growth but this was found to be a disadvantage in raspberries grown as continuous rows because the new cane tended to chafe and obscure ripe berries. Restricting irrigation to the pre-picking period reduced height growth but did not appear to reduce cane numbers or crop yield. Crop yield was increased by irrigation to about 30% more than was produced on the unwatered and unmulched plots, mainly as a result of increased berry size, but the full effect of irrigation on yield was not realized because cane numbers and height were restricted. Under the conditions of this experiment, in which the canes were thinned to a given density and tipped to a given height, a single 2-in. application of water at the commencement of ripening, i.e. when the berries showed the first tinge of pink, was a very economic irrigation treatment. Irrigation slightly delayed ripening, probably because of the harder tipping required by the irrigated canes.

The mulch conserved the equivalent of 2 in. of moisture and was intermediate in effect between the irrigation treatments B and C and treatment D in height growth, crop yield and berry size, but had a depressing effect on the production of new canes by the weaker-growing variety Mailing Jewel.