Microsul 40S, sulphur “by and for” microorganisms

Sulphur is one of the natural substances with the most comprehensive properties for use in crop care and maintenance. In addition to its natural potential as a fungicide and acaricide and its recognised fertilising capacity, it also offers remarkable biostimulant effects. A clear example is AFEPASA’s products featuring SULTECH® technology, such as Microsul 40S, a concentrated suspension specifically indicated for the natural correction of soils with high salinity and pH.

It is well known that sulphur is an essential nutrient for proper crop development and is absorbed by plants in the form of sulphate. However, the problem with applying sulphates directly to the soil is that they are highly soluble and are rapidly lost through leaching caused by irrigation or rainfall. By contrast, elemental sulphur is completely insoluble in water and is slowly transformed into sulphate by the microbiology naturally present in the soil.

In recent years, the use of sulphur and its fertilising value have gained increasing prominence, as sulphur deficiency in soils is becoming more frequent. Its application is therefore essential. To address this need, AFEPASA’s Microsul 40S is one of the most innovative solutions available on the market. Developed by its R&D&I team, AFEPASA is Europe’s largest sulphur producer and the second largest worldwide. Microsul 40S is based on a high concentration of SULTECH® sulphur which, due to its microbiological origin, is more readily transformed into forms that can be assimilated by plants. It also stands out for its biostimulant effects, improving and revitalising the soil. (Photo 1)

In this regard, SULTECH® sulphur is assimilated much more rapidly than any other sulphur of mineral origin by soil thiobacteria, which transform it into sulphate, with a very high capacity to reduce the concentration of sodium in the soil. They also release hydrogen protons, which help leach chlorides and can lower soil pH. At the same time, thiobacteria produce organic exudates that serve as food for other microorganisms naturally present in the soil and beneficial to the roots, resulting in the progressive enrichment of the soil. Therefore, Microsul 40S is essential for crops located in areas with high salinity, sodic soils or high alkalinity.

Furthermore, it is a clear example of AFEPASA’s commitment to the circular economy, as it is obtained from industrial waste materials that are given a “new lease of life”.

Proven efficacy in trials

The first trial worth mentioning was conducted in northeastern Almería on a four-year-old lemon crop. The main objective was to reduce soil pH and salinity in a field affected by calcareous soil and salt inputs from irrigation water. The aim was to enable the plants to make better use of organic fertilisation and thus correct potential nutrient deficiencies. One irrigation sector with an organic fertilisation programme was compared with an adjacent sector following the same programme, to which two applications of Microsul 40S at 10 L/ha were added over a 10-day period in mid-June.

The results in the soil, evaluated 35 days after the second application, showed a 0.20-point decrease in pH—from 8.02 to 7.83—due to a drastic 35.9% reduction in active limestone and a 17% decrease in available sodium. A notable increase in the availability of macro- and micronutrients was observed (Table 1), with particularly interesting increases in manganese and zinc, which are highly immobilised in alkaline soils. It was also observed that salts were leached, not only sodium salts but also potassium and magnesium salts, which had been present in excess. When evaluated in the plant, this improvement in nutritional conditions resulted in a clear increase in vigour during the August growth flush, leading to improved flowering for the following year’s harvest.

Table 1
Soil analysis

Parameter

Control

Microsul

% vs. Control

pH (1:2.5 extract)

8.02

7.83

-2.4%

Active limestone

7.94

5.09

-35.9%

Available calcium

17.80

11.30

-36.5%

Available sodium

0.53

0.44

-17.0%

Total nitrogen

1410.00

1686.00

+19.6%

Olsen phosphorus

77.00

108.00

+40.3%

Available magnesium

3.98

3.08

-22.6%

Available potassium

0.43

0.30

-30.2%

Iron (DTPA)

6.93

9.87

+42.4%

Manganese (DTPA)

13.80

36.30

+163.0%

Copper (DTPA)

2.22

1.75

-21.2%

Zinc (DTPA)

9.62

33.80

+251.4%

In the next trial, conducted on greenhouse-grown Dutch cucumber in Roquetas de Mar, Almería, the objective was to assess the effectiveness of Microsul 40S as a corrective treatment for highly saline soil receiving additional salts through irrigation water. Two strategies were compared: a conventional fertilisation strategy and the same strategy supplemented with four weekly applications of Microsul 40S at 5 L/ha through irrigation during November.

The results were highly positive, correcting the high rate of fruit abortion that occurs in cucumber when nutritional imbalances arise, with 17% fewer lost fruits (Photo 2). In terms of yield, this represented a 4.3% increase in the harvest during the two months following application. This was achieved through an average 30% reduction in soil electrical conductivity (EC), together with a significant reduction in sodium and chloride levels in both the soil and the foliar analysis.

 

The results of a third trial, this time conducted in the Campo de Cartagena, Murcia, were also very promising. The trial was carried out on greenhouse-grown zucchini with the aim of correcting soil with salinity levels above 800 µS/cm, using two applications of Microsul 40S at 10 L/ha during January.

Following soil conductivity measurements taken at different points (Graph 1), an average variation compared with the untreated control area of 20% was achieved one month after treatment and 10% after 40 days. This demonstrates the long-lasting efficacy of Microsul 40S throughout the crop cycle.

This reduction in salinity resulted in an improvement in the physiological condition of the plants, with more uniform fruit size and yield observed in the plot treated with Microsul 40S.