Rhyzoshere Conference

Rhyzoshere Conference

Poster paper delivered at September 2007 Rhizosphere 2 Conference – Montpellier, France.
The Effect of a New Slow Release Compost, Fulvic acid and Micro-organisms on Soil fertility, Yield and Quality of Potatoes grown in Sandy Soil.

C Malan, H Kotze* – Agrilibrium, P O Box 10908, Vorna Valley 1686, South Africa.*ARC SAND Experimental Farm.


The commercial production of potatoes in South Africa are mostly done on sandy soils that contains less than 5% clay with almost no organic matter content (% C < 0.1%). This results in low binding (low CEC) and retention of plant nutrients as well as inefficient nutrient exchange and utilization by plants. Therefore high application of chemical nutrients is standard practice in potato production to achieve acceptable yields. Furthermore, due to the low organic matter content and high free salt concentration in the soil solution, microbial activity is totally absent resulting in sub optimal root development. In practice the high nutrient and water application requirement per kg harvested are becoming prohibitively expensive.

It was hypothesized that by restoring balance and synergy in the soil through firstly a new long lasting slow release compost not containing any manure or straw using fresh wood fiber and selected micro-organisms, secondly a unique high concentration fulvic acid developed using a renewable plant resource (phytofulvate) and lastly to complete the soil applied treatment with a combination of specific rhizosphere micro-organisms, this equilibrium farming and synergy concept would restore soil balances, improved nutrient and water uptake, increase yield and quality including mineral nutritional value. An extra treatment was added where micronutrients and growth stimulants were foliarly applied.

In this statistical trial done at the SAND Experimental Farm a highly significant best treatment (soil plus foliar) increase in yield of 24.7 ton/ha (43%) was achieved. Compost alone yielded 6% (3.5 ton/ha) higher than the control while the addition of fulvic acid and microbes resulted in 19% (11 ton/ha) increase in yield. The soil treatment had a direct effect on soil chemical changes (higher CEC (15%) and %C (38%), lower resistance (-38%)). Mineral nutrient retention in the soil eight months after treatment was between 7% (Zn) and 46% (Mn) higher than in the non-treated soil. Content of certain minerals also increased in harvested potatoes resulting in improved nutritional value to the consumer. The synergism and symbiosis between micro-organisms and potatoes grown in a balanced soil environment are evident in the results.


Soil fertility depends on various chemical, physical and biological factors and the balance between them. From a chemical and physical perspective, water and nutrient holding and availability potential of sandy soil are very low which are further exacerbated by low carbon content.

Biological factors include those that affect the growth of roots like growth promoting rhizosphere organisms and their production of phytohormones and organic acid (malate,citrate) producing organisms influencing the mineralisation potential to supply plant utilizable nutrients. The population density of microorganisms is high in the rhizosphere since roots are a source of organic carbon from sloughed-off cells and exudated organic molecules like sugars and aminoacids that according to Haller and Stolp 1985 and Marschner 2002 supply between 75 and 85% of the total organic carbon supply for microbial activity. However, in sandy soil where root growth is generally suboptimal due to lower availability of water and mineral nutrients, microbial numbers and activity are also negatively affected.

The total number of rhizosphere organisms as well as the different types with their physiological characteristics like phytohormone production, N2 fixers, soil mineralizing organic acid producers and pathogen antagonists vary due to the availability of their organic carbon food, moisture, O2 and mineral nutrients such as N and Ni (Marschner 2002, Ankel-Fuchs and Thauer,1988).

The hypothesis was therefore tested where a longlasting carbon source (wood fibre compost), an immediate available liquid carbon source (phytofulvate) and a blend of rhizoshere microorganisms were used to improve and balance soil fertility and improve yields in sandy soil using potatoes as indicator crop.

Material and Methods

Potato Cultivar BP1 was grown under centre pivot irrigation. A standard 80 t/ha fertilization program applying 50:60:80 kg/ha N, P and K respectively was used.

In the split plot replicated trial layout treatments consisted of splitting the trial into 2 main treatments, minus and plus compost (30m3 /ha). Within the compost treatments further separate treatments were :

  1. Soil Treatment: A 4 liter/ha application each of the phytofulvate (ByoCarb 50) and the microorganism blend (QCM 360) was applied through the irrigation system to wash it into at least 15 cm soil profile. This treatment was repeated at 2 + 2 liter of the products on weeks 5, 6 en 7 after emergence.
  2. Foliar Treatment: BioKelp (7 L/ha), BioPhos (7 L/ha), Fulvic 5000 (2 L/ha), CalTrain (5 L/ha) en DynoMob (1,5 L/ha).
  3. A combination of treatments 1 and 2.

Measurements eight months after commencement of the trial included replicated soil analysis and chlorophyll measurements using a SPAD meter. Standard yield and tuber size were done. A standard analysis of variance was done on the separate data sets.

Results and Discussion

Figure 1 clearly demonstrates that the addition of the wood fibre compost alone, although not significant, already had a 6% increase in yield. No significant differences were found in all treatments where no compost was used. The highest and statistically highly significant yield increase of 43% (24,7 ton more per hectare) were achieved where compost soil treatments were done in conjunction with phytofulvate and microorganisms and followed up with the prescribed foliar sprays of macro and micronutrients, hormones and antioxidants. The compost soil treatment with phytofulvate and microorganisms without foliar sprays already yielded a significantly higher than the control yield improvement of 19% (11 tons/ha) demonstrating the crucial effect of organic material and seeding with slected strains of plant growth promoting micro-organisms.


Tuber size quality.

The treatments also had an effect on quality of potato tubers harvested. Figure 2 shows the effect of the highest yielding treatment namely compost plus soil and foliar treatments on the shift in tuber size where the number of large tubers decreased by 2.3%, medium tubers for which farmers earn the most income, increased by 10.4% and smaller unwanted sizes all decreased in number.


Chlorophyll content.

Chlorophyl content in potato leaves measured at tuber initiation stage showed significant differences between no compost and compost treated blocks (Fig 3). Higher chlorophyll content implies higher photosynthetic activity and this correlates to the higher yields achieved. The higher chlorphyll content will probably be the result of better uptake and utilization of nutrients and in particular the four micronutrients Fe, Cu, Zn and Mn that is associated with the superoxide dismutase enzyme (fig 4). This enzyme that occurs in both the chloroplast and mitochondria optimizes the antioxidant system and therefore protect organelle distruction from oxygen radical attack during stress situations (Malan et al 1980).


Chemical and physical changes in the soil.

Over the trial period of eight months the slow decomposing wood compost used simultaneously with phytofulvate and the microorganism blend changed the soil chemical and physical structure of this sandy soil significantly (figs 4 and 5). Figure 4 clearly shows the relative change in soil nutrient retention as compared to the non compost treated control. These results also explain in part the higher yields achieved since all biochemical production processes could function more efficiently. This argument is further supported by the change of 38% increase in CEC (fig 5) that correlates with the same increase in % carbon (fig 4) measured in the soil after the 8 month period. Furthermore, soil resistance indicating nutrient salts in the soil solution, decreased (fig 5). The simultaneous increase in binding sites for nutrients (CEC) and decrease in resistance indicates firstly that nutrients were better available for uptake by the potato roots and secondly it has an impact on the amount of nutrients being leached from this sandy soil that implies that a nutrient reserve is available for a follow-up crop. The nutrients are thus bound to the organic material and is available and more effective over a longer period that has positive financial implications for the farmer and sustainability.




The use of this new longer lasting compost made from wood fibre used in conjunction with the liquid organic acids in phytofulvate and the blend of selected strains of rhizosphere microorganisms had a marked and significant effect on the following parameters measured on sandy soil grown potatoes:

  • Yield and quality improvement of potatoes harvested;
  • Chlorophyll content and associated photosynthetic and production capacity;
  • Changes in soil fertility as a result of improved soil chemical and physical characteristics.

Finally this trial showed that farming with potatoes in the sandy soils of the Western Cape in South Africa is sustainable.


  1. Ankel-Fuchs,D and Thauer, R.K. (1988). The Bioinorganic Chemistry Of Nickel, pp93-110.Verlag Chemie. Weinheim.
  2. Haller, T and Stolp, H. (1985). Plant Soil 86, 207-216.
  3. Malan, C, Greyling, M M & Gressel, J (1990). Correlation between CuZn superoxide dismutase and glutathione reductase, and environmental and xenobiotic stress tolerance in maize inbreds. Plant Science. 69(2) : 157 -166.
  4. Marchner, H. (2002). Mineral Nutrition of Higher Plants. Academic Press.

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