The effect of different cover crop management practices on the soil and performance of apple trees

The study aimed to supply guidelines for soil management practices that will improve soil health and promote sustainable apple production.

The nematode and soil nutrient status, cover crop performance and weed control efficacy, as well as tree performance and nutrient status were monitored.

Soil preparation disturbed the soil biology. After three to four years, the nematode community structure stabilised. Dwarf Fescue (T1) and a Saia oats monoculture (T2) facilitated recovery. The nematode communities serve as an effective bio-indicator.

Cover crops increased the organic C in the soil. Pink Seradella combined with full surface chemical control early October and early December (CC) (T3) and the pink Seradella/ Saia oats mixture combined with CC (T4) increased the available N. Fertiliser P does not correct the P concentration in the 150-300 mm soil level, but creates an over-supply in the 0-150 mm soil level.

The non-bearing trees did not need from April to November, when receiving rainfall of between 482 mm and 1219 mm. T1 (applied by industry) increased the irrigation amount by between 7 mm and 35 mm compared to the other treatments.

The canola/Caliente 199 mixture (T5) is not suitable for the relatively wet apple producing areas. The best weed control up to the end of November was achieved with T2 and T4. T1 gave the best weed control from December to March. However, T1 could eradicate only two of the thirteen dominant weeds, namely tiny club-rush and bur clover. In contrast, T3 eradicated an additional three species, namely sheep sorrel, hairy wild lettuce and narrow- leaved ribwort. T4 eradicated the same species as T3, with the exception of narrow-leaved ribwort. T2 eradicated narrow-leaved ribwort, bur clover, tiny club-rush, hairy wild lettuce, catchflies, sowthistle and the Lolium species.

The treatments did not affect tree performance significantly. However, the 2017 harvest of T3, T4 and T5 was lower than that of 2016. In contrast, the second harvest of T1 and T2 increased compared to the first harvest, with that of T2 exceeding that of T1 by 5 t/ha.

The fine roots of the apple trees were distributed throughout the soil profile under full surface irrrigation. However, the fine root distribution tended to be denser up to 1.3 m from the trunk (constrained by tractor traffic) and in the 0.2 to 0.8 m soil layer. Pink Seradella maintained the same fine root density throughout the work row.

A Saia oats monoculture should be established in apple orchards during the first two years after establishment on loamy sand and sandy soils. Thereafter, an annual rotation with pink Seradella should be maintained. Full surface post-emergence chemical control should be applied early October and early December or early January.

Cover crop management in the dryer apple producing areas, as well as on the heavier soils in the apple producing areas needs clarification. This will supply the industry with scientifically based guidelines for sustainable ‘soil and tree friendly’ soil management practices in apple orchards.