Interview with Dr. Brown (University of California in Davis) on the latest findings of SOP use in Nut Crops
Dr. Patrick Brown is the winner of the 2009 SOPIB award. Our congratulations and we are glad he could spare us some time. This gives us the opportunity to interview him to get first hand information on his work on plant nutrition in the nut crops almonds and pistachio.
Q: Dr. Brown, were you as undergraduate already drawn in the direction of research on plant nutrition or did this interest develop later?
My interest in this discipline started during my undergraduate degree in Agriculture and Biochemistry at the Univ. of Adelaide, where I was encouraged by Professors Andrew Smith, DJD Nicholas and Robin Graham, all prominent in the field of Plant Nutrition.
Q: What was also the research topic of your dissertation?
My Ph D dissertation focussed on the role of Nickel in Plant Nutrition and, building upon the earlier work by Ross Welch and colleagues, we established Nickel as the 14th essential mineral element in 1987. (Source: Brown, Patrick H., Ross M. Welch, and Earle E. Cary. 1987. Plant Physiol. 85:801-803.)
Q: When did the research on potassium fertilization of almonds and pistachios start in earnest? What was the initial trigger for this research?
There has been an interest in K in Californian tree crops since the mid 1950's. However, detailed research did not commence until the mid - 1980's coinciding with the great expansion in acreage of irrigated tree crops. The tremendous increase in productivity of tree crops from the mid 1990's until today and recognition that nut crops extract from 150 to 300 lbs K per acre per year has resulted in an increasing interest in management of K.
Q: If we talk about applying potassium sulphate in almonds and pistachios, can we treat these two crops in the same way, or are there major differences? If so, which are these?
Both crops share a high K-demand (averaging 200 lbs K per acre per year ~ 225 kg K per hectare per year) and have similar patterns of uptake during the season. Almond is grown on a larger percentage of K - fixing soils and this influences obviously management practices.
Q: Concentrating on almonds, what is in your opinion the optimal way in which to apply K - sulphate or is this dependant on the irrigation regime?
In soils with significant K - fixation, there is a need to minimize the potential for fixation. Historically, this has been addressed (at least partially) through use of applications that concentrate K in bands to minimize soil interactions.
While effective, this approach was developed and optimized for non-irrigated or flood irrigated orchards. With the advent of drip and micro-sprinkler irrigation the opportunity exists to utilize a more divers range of application techniques. Research in our laboratory demonstrated that the amount of K-fixation can be minimized through maintenance of a moist soil profile and avoidance of the wetting drying cycles that are more extreme in flood or solid set sprinkler irrigation. Direct injection of 'soluble / suspended' K - sulphate or shallow banding has been used effectively.
Q: If the answer to the second half of this question is "yes", do you have tailor made recommendations for each irrigation regime, i.e. different application rates and application timing?
Currently, our research base is inadequate to provide irrigation system and /or soil specific recommendations. At this moment in time, research is underway contrasting two application techniques (drip/micro) at a single site, this research will be used to develop models of K-movement through soil columns and general principles regarding timing and demand driven uptake. There remains a need to adapt this research to different soil types.
Q: What is in your opinion the greatest benefit from additional K-fertilization of almonds?
Which one do you consider as having the biggest impact for the farmer?
- Increased yield?
- Improved nutritional value?
- Improved shipping and storage properties?
- Or all three of the properties?
Currently yield is the only parameter of interest to the grower. Almonds are not known to vary in quality or storage capability in response to K-fertilization. Responses of this kind are known to occur in fleshy fruits and vegetables, but are not well described for grains or nuts.
Q: To get around the issue of K-fixation in the soil due to fluctuating soil moisture, is there a possibility to apply K-sulphate as a foliar spray?
Foliar K has a role to play during periods of peak K-requirement (May- through July in Almond) when uptake can exceed the soil capacity to provide the demand. Demand can exceed uptake as a result of fixation or as a consequence of yield induced depression of root exploration and K-extraction.
Q: By the way, for our non-Californian audience, what is the most popular irrigation system used in almonds in the Central Valley?
A recent survey indicated that 80% of acreage was drip or micro - sprinkler fertilized with the remainder of acreage either flood irrigated or solid set sprinkler irrigated. Some details of these results are presented at http://informatics.plantsciences.ucdavis.edu/apnutrition/almond1.php
Q: : If we look at the other major producers of almonds: Spain, Syria, Iran, Italy, we notice that the crop yields are considerably lower than in California. What are in your opinion the reasons for this?
- Different climatic conditions
- Lack of irrigation systems?
- Use of lower yielding varieties?
- Disease and/or insect pests, which do not occur in California?
- Lack of modern fertilization regimes?
California does have a unique combination of conditions ideal to intensive Almond production, while essentially all acreage is irrigated and planted to superior cultivars at higher density than the named countries. Undoubtedly, optimal irrigation and fertilization is a major reason for the high yields in California.
Q: Returning to California, do you expect to see any [major] changes in the recommendations of K-sulphate fertilization in almonds and pistachios in the foreseeable future, or do you feel that we can comfortably say that we reached the stage of optimal recommendations?
I believe there is considerable potential for optimization of K usage in Californian tree crops. Many growers are under-fertilizing and are inadvertently depleting soil K reserves on the basis of a historic belief that Californian soils are K rich. While this is true in a portion of Californian soils, it is not universally true and further, depletion of these reserves by perennial crops with K demands as high as almond and pistachio however, is inevitable if replacement fertilization is not practiced. Almond and pistachio exhibit moderate and strong alternate bearing, respectively. It is likely that K status of the tree plays a role in this alternate bearing.
Q: Dr. Brown, I am sure we have by no means exhausted this interesting topic, but do you have a message you would like to give to almond and pistachio growers with regards to K-sulphate fertilization?
It is undoubtedly true that it is difficult to do research in nut crops, that yield responses are slow when management is changed and that our approaches to detection of tree K status are inadequate. As a consequence it is difficult to manage K by leaf sampling or short term on farm research. A superior approach to the management of K in tree crops is to base fertilization on the principle of replacement of K removed by the crop. Fortunately, this is relatively easy to determine by multiplying yield by K concentration in the crop. The goal of a good manager is to replace K removed with a fertilization program with optimal formulation, timing and placement of fertilizers. Research to define the specifics of K fertilization program are underway but at the very least growers should start with a fertilization program that provides at least the amount of K removed in the crop. Our most current research in the paper-shell cultivar Nonpareil, indicates that a typical Californian crop yield of 16,000 kg/Ha of fruit (equivalent to 4,000 kg/Ha kernels) will remove 230 kg of K. Eighty to 85% of all K removed from the orchard is present in the hulls.
Q: Could you already tell us something about your current research program as well about the plans you have for future research?
We are currently researching the use of site specific management of N and K in Almond and Pistachio, the development of superior leaf and crop diagnosis techniques, the development of nutrient demand curves, the interaction between irrigation source and fertilizer response and the long term influence of K status on yield.
Q: What do you see as major future trends in plant nutrition which will help us to feed the growing world population?
As water becomes more limiting we must develop integrated approaches to fertilizer and irrigation. In tree crops we will see a development of precision management and remote sensing technologies that allow for a more precise application of fertilizer resources. While the application of precision agriculture in field crops has not fulfilled the early promise, these technologies have hardly been applied to tree crops, given the high value of these crops and their long life, investment in more sophisticated techniques (both engineering and human) is inevitable and obvious. Perennial crops represent the most logical application of precision technologies.
Q: My last question: Is there a topic we have not covered, but on which you definitely would like to make a comment?
The nutrition of trees (both agricultural and those that provide ecological services) is a poorly studied topic that has significant potential to contribute to both generation of income and environmental sustainability.
In both the developing and the developed world trees frequently represent the most 'efficient' return on investment in fertilizer resources as well as in capital. While many tree species (particularly Almonds and Pistachios) can tolerate poor soil conditions, the Californian experience clearly demonstrates that optimal productivity is only attained with intensive management.
Trees are also inevitably less sensitive to short term environmental fluctuations than annual crops due to the buffering offered by the large perennial biomass and generally deeper root system. If extreme meteorological events occur (e.g. a late frost during flowering or a succession of years with below average precipitation/ drought), tree crops are more resilient to these short term deficits and will regain full productivity again after "normal" conditions have returned.
Dr. Brown, we greatly appreciate answering our questions.