HOME PRODUCT FEATURES & BENEFITS Potassium nitrate and saline conditions Proper fertiliser selection to reduce salinity problems
Proper fertiliser selection to reduce salinity problems PDF Print

In greenhouses, soil salinity is caused by the use of low nutrient fertilisers, by rising water tables, and by the use of saline irrigation water. Salinization of greenhouse soils by fertilisation can be avoided by using the proper fertilisers (Sonneveld, 1988).


Table 1 shows the effect on the EC of various fertiliser combinations, compared to KNO3, when the N and K input are kept at constant levels. Replacement of KNO3 by combinations 2 and 4 will result in almost 50 % increase in the EC, while combination 3 almost doubles the EC, compared to KNO3. Therefore, proper fertiliser selection will help to reduce the risk of soil salinity and associated yield reduction, in particular when salts cannot be washed down by irrigation.


Table 1. The effect on the EC of various fertiliser combinations, compared to KNO3, when the N and K input are kept constant.

Combination

Dose rate

N

K2O

Source EC

EC per dose rate

EC

gram

gram

gram

1 g/l, mS/cm, 25 °C

mS/cm

%

1

KNO3

1,00

0,135

0,455

1,35

1,35

100

2

KCl

0,76


0,455

1,79

1,36

148

AN

0,40

0,135


1,60

0,64

Total

1,16

0,135

0,455


1,99

3

KCl

0,76


0,455

1,79

1,36

192

AS

0,64

0,135


1,91

1,23

Total

1,40

0,135

0,455


2,59

4

SOP

0,91


0,455

1,47

1,34

146

AN

0,40

0,135


1,60

0,64

Total

1,31

0,135

0,455


1,97


Crops are more salt-sensitive when grown under dry climatic conditions than under humid conditions. This was shown in a comparison of studies done on salinity yield decrease, carried out under glass in a rather humid sea climate (Sonneveld, 1988), compared to those in open air in a dry climate (Maas and Hoffman, 1977).  Salt accumulation at the soil surface will occur when conditions are dry and irrigation is not sufficient to wash down the salts.


Negative effects of salinity on the quality of glasshouse produce are often related to calcium deficiency. In such cases the supply as well as the distribution of calcium may be affected by salinity. For example in lettuce, after the addition of sodium chloride to the irrigation water equivalent to 1 dS/m (8,5 mmol NaCl/l), the yield reduction caused by tip burn (25 %) was much larger than the one caused by the growth reduction (5 %) (Sonneveld, 1988).


When potassium nitrate is not chosen as the preferred N and K source, then ammonium- and/or chloride-containing fertilisers have to be used as alternative N and K sources. This may lead to various anion and cation antagonisms in plant uptake, which consequently negatively affects plant growth and development.


References:

Maas, E.V. and G.J. Hoffman. 1977. Crop salt tolerance. Current assessment. Journal of the Irrigation and Drainage Division, Proceedings of the American Society of Civil Engineers 103 (IR2): 115-134.

Sonneveld, C. 1988. The salt tolerance of greenhouse crops. Netherlands Journal of Agricultural Science 36: 63-73.


 

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