This article is taken from a letter to Frank Brenmuhl by Professor David McNeil of Tasmania.
(There is a link at the bottom of this page to a full 72 page report)
(NB This article has been adapted by editor)
There are 2 main ways of looking at how yields develop in a Walnut orchard.
1) Use of resources.
2) Development of components.
There is then a 3rd aspect of conversion of yield to profit (ie costs (efficiency) and effectiveness of operations (eg harvest compare layout to harvest efficiency) and quality management for value retention (eg drying effectiveness and efficiency, marketing)
The best way for growers to improve yield is to (a) understand these as they apply to their particular orchard and (b) compare them to other gowers and to industry standards.
Generally I therefore get growers to (a) measure these (through discussion on how to do it) and then for (b) I facilitate work with other growers to compare and find potential improvements.
1) Positive resources are light, land area, water, time, temperature and nutrients. Negative ones are disease load, temperature (ie can be positive and negative), wind run, & other specific issues etc
To measure these one needs needs to look at length of time and (daily and seasonal) amount of light intercepted, (per tree and per area) temperature, water use and availability, trunk cross sectional area, & rate of increase of these over time relative to production (ie rapid increase of tree size with low yield increase early is good but needs to change as light interception increases) The critical things here are for example light intercepted at 10 am 1 pm and 4pm this gives (max energy available for yield) trunk cross sectiion diameter year by year, early and late season light interception (late retention of leaf (post physiological maturity) can store carbohydrates for next year), water use realtive to potential use and amount supplied (want this to be high generally), important measures here then are light interception, trunk cross sectional area and water use versus time.
For negative aspects primarily frost versus time, disease incidence vs time, wind speed in orchard and edges, max leaf and fruit temps (generally more an Australian issue)
2) the critical issues here are developmnet of flowering branches (ie flowering tips per sq m of canopy), flowers and loss vs time, size developmnet and fill developmnet vs falls and quality then look for causes (eg low fill if high numbers of fruit in low light situations), disease drop, of nutlets, frost drop of flowers.
It is working through all these processes comparing them and then looking for solutions, eg late N for late leaf retention to encourage carbohydrates for rapid leafing next season and high yields. If yield vs trunk cross sectional area is low there must be some point at which flowers, nutlets or nuts are lost or missing where is it and why (maybe frost , wind disease etc).
In the first season to start this off the main measures are flower development and retention, trunk area shifting to include light disease and water with time.
The big thing is then to work with the growers throughout the season.
The big problem is just to look at yield in isolation.
A 72 page detailed document from David and K.J.Evans about improving walnut orchard management can be accessed here. Improved management of walnut quality factors under grower control