By Prof Wiehann Steyn

This blog article, probably not surprisingly, is about water and climate. Research in the Crop Production programme is aimed at achieving the goals and address risks to the Orchard of the Future. At the 2016 HORTGRO Science symposium, attendees scored water availability and climate change as the greatest future risks that our industries face.

A strategy for water availability-related research was agreed upon by the Irrigation and Nutrition workgroup of the Crop Production programme. The first step of the strategy entails that we determine the water needs of our crops. Current work is being done in collaboration with the Water Research Commission (WRC) to determine the water needs of high yielding, unstressed Golden Delicious and Cripps’ Pink orchards in the Koue Bokkeveld and EGVV. The hard, factual benchmark data that the project is generating will aid us in discussions with government, water regulatory bodies, etc. This line of research tends to be very expensive and is only made possible by our partnership with the WRC. Apart from the water requirements of apple orchards, the project is yielding some interesting, unanticipated (though obvious when one thinks about it) information on orchard factors that affect water needs. The leaf area per ha seems to be the main determinant of water use – hence, we don’t want (with hindsight, very aptly named…) water wasting water shoots in our trees. Trees on dwarfing rootstocks should be more water use efficient (less water per kg fruit) and also more water use productive (more R per L of water) than more vigorous rootstocks. This will be the research focus in future projects.

After establishing the water needs of a tree and, by extrapolation, an orchard, the next step in our water research strategy is to investigate water saving technologies. We, again in collaboration with the WRC, are currently scoping a new project that will aim to establish the water savings possible under fixed and draped nets. Talking apples, we are producing fruit at the same latitude as countries like Morocco and Tunisia. The 30% of our crop that is processed, is arguably our biggest inefficiency compared to our competitors. Ways to increase our efficiency of production is to shift to more efficient rootstocks and to modify/attenuate the climate that our trees experience. We also grow fruit in a water scarce environment – and it’s certainly not going to become more abundant.  Nets might be a way to use water more efficiently and productively by decreasing the water requirement of trees while also increasing fruit quality.  Observations suggest that water use can be 20% less in covered orchards due the attenuating effect of nets on wind and evaporation – nets may also decrease transpiration, but this needs to be established.

Oak Valley

Granny Smith under nets at Oak Valley in Grabouw

We typically only consider the major potential benefits of nets when calculating their potential cost effectiveness. Hence, installing fixed nets in hail prone regions or over Granny Smith makes much sense, but not so much other scenarios. Whereas the growth under fixed nets will therefore mostly be limited by the rate at which we plant new orchards – very few growers will be installing nets at R250k per ha over old style Golden orchards – draped nets can have a much greater application in the shorter term. Anton Muller of KROMCO has been conducting some trials with draped nets and from his findings, it is clear that draped nets might change the calculations quite significantly. It can also be applied after fruit set. Factored into the sum to determine the benefit of nets, should also be: 1) potential water saving and resultant increases in water use productivity in R per L water, 2) impact on fruit quality (size, sunburn, wind rub, but also colour), 3) getting more growth out of a more efficient, dwarfing rootstock, 4) reduced heat stress and vapour pressure deficit-induced closure of stomata with resultant decreased photosynthesis, 5) nets providing similar physical benefits as a mulch.

In line with current grower interest in nets, there will be a talk at the 2017 HORTGRO Science technical symposium on the physiological effects of nets. One of the main attractions at the event, though, will be Dr Michael Zoth from the Bodensee region of Germany who will present a talk on the “Nuts and bolts of net structures and managing under nets”.  Michael will also accompany attendees on the pome fruit field day where a newly netted orchard at Loxtonia in the Warm Bokkeveld will be visited. Net structures failing during storms are a major concern while growers are being confused with the purported benefits of the myriad colours of nets. Michael will cover and shed some light on these topics.