Tree crop stress management during summer
Editorial written byRoop Sandhu, Business Management – Horticulture, TEC for the Summer 2020/2021 Seasons Magazine.
Every 1 per cent reduction in plant stress can significantly improve farm profitability. Most of a horticulture consultant’s time is spent trying to minimize these plant stresses so we can help plants achieve as much of their genetic potential as possible.
Healthy soil and active biology
Soil nutrient analysis is always a good start, along with visual observations of soil structure, while microbial analyses can assist in fingerprinting the population and diversity of microbes. The role of soil microbiology in alleviating plant stress has been well researched but there are still significant knowledge gaps among growers about best practice implementation. Diverse and active soil microbes can provide an improved nitrogen use efficiency, increased phosphorus availability and uptake by plants due to solubilization of tied up P, decomposition of organic matter to humus, and significant other benefits resulting in improved root growth and systemic stress resistance.
The Trichoderma spp. produce auxins, which can enhance plant growth and reduce plant stress. Plant growth-promoting rhizobacteria (PGPR) also reduce plant stress by mobilizing soil nutrients and secretion of signal molecules. The biological dimension of soil ecosystem needs to be better understood, promoted and implemented as part of best practices to achieve a more resilient and productive farming system.
Targeted nutrition program
A common expression of stress in plants is the excessive production of Reactive Oxidative Species (ROS), which can lead to oxidative damage. It can be caused by stresses such as heatwaves, which can also affect the plant’s uptake of mineral nutrients. A year-round balanced soil nutrition (not just crop nutrition!) program is required. Several nutrients can positively impact stressed plants and reduce the resulting damage. We are not suggesting a more generous application of these nutrients to ameliorate the stress, however, A balanced nutrition program is necessary to ensure all nutrients are well supplied to make plant more resilient.
Potassium has an essential role in stomatal regulation, water balance and source-sink transport of sugars. Potassium-sufficient plants are more able to reduce their stress, particularly water stress.
Macronutrients such as nitrogen and phosphorus also play an essential role but it’s important to consider micronutrients, too. Zinc plays a role in tissue formation and reduces the water loss, particularly under stress conditions by improving the membrane stability. It improves antioxidant enzyme activity, which can counter ROS.
Chlorine is found in the soil as chloride (Cl-) and there is generally a concern about salt injury to roots from chloride-based fertilizers such as muriate of potash in horticultural crops. These concerns are valid to some extent, but some are misplaced. Our growers have achieved great success in terms of improved yields and fruit quality with controlled use of this vital nutrient. It’s needed to split water molecules during the photosynthesis and control stomata in leaves. Another nutrient well known for its role in flowering and fruit set, Boron, plays an essential role in carbohydrate metabolism and improvement of photosynthesis rate, which in turn reduces the ROS damage. Similarly, magnesium helps to improve the photosynthetic rate as it’s a part of the chlorophyll molecule. Magnesium enhances the production of sugars and their translocation through plants, reducing ROS production and lowering stress.
Other nutrients such as silicon, manganese and iron, also play a critical part.
Role of technology
Agtech can help us detect stress before it causes a significant loss of productivity. A change in leaf colour is an early sign of plant stress but, by the time it can be detected visually, plants have already been under stress for an extended period. Satellite technologies such as Elders’ AgIntel platform can pick up subtle changes in plant health and allow us to address the issues quickly. The cost of these technologies is negligible when it comes to the benefits it can deliver in terms of preventing a loss of yield or quality. The key stress mitigation strategy is to take an all-encompassing approach to plant management. The approach of optimisation of photosynthesis is critical to achieving a consistently high yield and crop quality.
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