Harvest SA 85
Identifying Constraints Under South African Growing Conditions
A local example of how Crop Nutritional Monitoring can identify a constraint, guide corrective action and track the crop's response
A local blueberry case demonstrates how CNM can identify a production constraint, guide corrective action and track the crop's response under South African conditions. Initial monitoring in December 2023 identified strongly acidic conditions in the mon-itored root zone, with soil-solution pH values of approximately 4.4 to 4.6. The crop was also displaying low root activity and poor yield, while the analytical results indicated a potential aluminium-related risk.
Assessment of the wider crop system linked the acidic conditions to intensive use of ammonium-based nitrogen fertilisers together with irrigation water with low buffering capacity. Corrective measures included reducing ammonium-form inputs and introducing a potassium hydroxide-based amendment within a revised fertigation and pH-management strategy.
Measured response
Follow-up monitoring in February 2024 showed substantial change at several points. At 30 cm, soil-solution pH increased from 4.61 to 5.81, while at 50 cm it increased from 4.48 to 6.24. The fertigation solution increased from 4.42 to 7.88. At 15 cm the measured value moved from 4.47 to 4.24.
Corrective measures included reducing ammonium-form inputs and introducing a potassium hydroxide-based amendment within a revised fertigation and pH-management strategy.
The differing response at each depth is significant: root-zone con-ditions are not uniform, and a single measurement cannot always show how water, nutrients and pH are distributed through the profile. The reported outcome was recovery of root activity and crop vigour together with improved yield.
Seeing the whole crop: GIS and NDVI mapping
GIS and NDVI mapping complement CNM by adding a spatial view of the crop. While soil, water, soil-solution and foliar results explain conditions at sampled points, mapping can show where variability exists across the wider orchard or production block. This helps growers and agronomists relate analytical results to crop vigour and field pat-terns, identify areas that may need closer investigation, and build a more complete picture of how crop performance relates to soil, water and plant information.
Used together, CNM, GIS and NDVI strengthen decision-making. They help position sampling more strategically, verify whether observed variability is linked to nutrition, irrigation or root-zone con-ditions, and support more targeted management responses across the block.
The same principle applies across macadamias, citrus, avocados, berries and other crops. Sampling and management responses vary according to crop, soil, climate and production objective, but the aim is consistent: understand the crop system at the right stage and use measured information to guide the next decision.
From Sample to Strategy
The value of CNM lies not only in what is collected in the field, but in how that information is transformed into meaningful Agro-nomic insight.Soil, Irrigation or fertigation water,soil solution col-lected through lysimeter suction probes, and foliar or other plant material are sent to the laboratory for analysis, creating the analytical foundation for informed crop-management decisions.
From there, Microchem and AGQ combine laboratory results with crop stage, root-zone conditions and production objectives to identify constraints, interpret crop response and guide practical recommend-ations. The result is more than a laboratory report-it is a clearer understanding of the crop system and a stronger basis for decisions around nutrition, irrigation and corrective management.
Monitoring point
Dec 2023
Feb 2024
Change
Fertigation solution
4.42
7.88
+3.46
Soil solution - 15 cm
4.47
4.24
-0.23
Soil solution - 30 cm
4.61
5.81
+1.20
Soil solution - 50 cm
4.48
6.24
+1.76
Fertigation solution and soil-solution pH measured at different root-zone depths.
Representative diagram of soil-solution sampling at 15, 30 and 50 cm.
Case study snapshot
CONSTRAINT
Representative diagram of soil-solution sampling at 15, 30 and 50 cm.
CNM ANALYSIS
ACTION
RESPONSE
• Low root-zone pH • Aluminium-related risk• Low root activity • Poor yieldFertigation and soil-solution results assessed at multiple root-zone depths
• Reduced ammonium-form inputs• KOH-based correction• Revised fertigation strategy• Improved pH at key depths• Recovery of root activity and vigour • Improved yield reported