Crop tolerance to soil salinity, yield and salt data under farming conditions analysed statistically.

Berseem (Egyptian clover) data were collected from 4 cuts in the winter season 1979-1980 in the villages Minyet Beni Mansur, Darawa, Mit Loza and Nizaret Fisha Balkha. The yield represents fresh green matter. ECe represents the average soil salinity over the season. As the salinity in the region is not very high, no data are available on the yield decrease at higher ECe values. The salt tolerance of Berseem is at least 4 dS/m because the trendline through the data here is (almost) horizontal and all yields are above 10 t/ha. A sharply declining trend for ECe values > 4 cannot be seen.

The cotton yield (lint+seed) was determined in the summer of 1981 in the villages Minyet Tujh, Darawa, Mit Loza and Kafr Shubra Qallug. There are not many data with salinity ECe > 8 dS/m. The salt tolerance of cotton is possibly greater than 8 dS/m. Cotton is definitely a more than moderately tolerant crop, if not a salt resistant crop.

Maize is planted in the first half of June and harvested from mid September to mid October. The grain yield of Maize was determined in 1981 in the villages Kafr Shubra, Darawa and Minyet Tukh. There are few data with salnity ECe > 6 dS/m, but from the figure it can be deduced that the tolerable salt stress of maize is 6 dS/m or higher. Maize is a moderately tolerant crop and maybe more than that.

The rice is of the short grain (Japonica) type. Rice nurseries are prepared in May and transplantation occurs in June. Harvest is in October. The grain yields were collected in 1981 and 1982 in the village Mit Loza. As the number of data with salinity ECe > 7 dS/m is small, the salt tolerance of rice cannot be exactly found, but it is at least 6 dS/m. Up to that point the trendline is slightly, but insignicantly, sloping upward. Rice is certainly a moderately tolerant crop, if not more than that.

The grain yield of wheat was collected in the winter season 1981-1982 in the villages Mit Loza, Kafr Shubra Qallug and Nizaret Fisha Balkha. Like for Berseem, the number of data with high soil salinity (> 12 dS/m) is scarce so that the salt resistance of wheat cannot be precisely determined. The figure suggests that the tolerable salt stress of wheat is at least 7 or 8 dS/m because up to that point there is no significantly descending trend. Wheat appears to be a more than moderately tolerant crop.

In contrast to the previous examples, here there were enough data with ECe beyond the tolerance threshold to be able to detect precisely where the initially horizontal trend in the relation between yield and salinity changes into a downward trend. The maximum salt tolerance of wheat in Sampla is 4.9 (say 5) dS/m before it starts to be affected negatively when the ECe increases more. This wheat crop is moderately sensitive to salt.

The wheat data of Gohana show a higher salt tolerance (threshold salinity ECe=7dS/m) than the Sampla data. The reason is unknown. The average yield below the breakpoint is somewhat less, and the variation of the yield is higher. The slope of the regression line through the data below the breakpoint is very small and insignificant, so it might be concluded that there is no effect of salinity on the yield up to the threshold. However, owing to the high variation, it might be argued that the tolerance threshold could be 6 instead of 7 dS/m. Anyway, the wheat in Gohana can be called salt tolerant.

It is a characteristic of most field data collected in small plots on the yield - salinity relation that they show considerable scatter. Mustard is no exception. Yet, the salt tolerance of mustard in the above graph shows consistently and systematically lower yields at ECe level greater than 8 compared to the yields at lower ECe levels. In this example there is a pronounced discontinuity, a sudden jump, in yields to the left and to the right of the threshold. So it can be safely concluded that mustard is "quite tolerant".

Barley, like cotton, is generally known as a salt tolerant crop. The following figure confirms this property with a threshold value of 8.9 (say 9), which proves that this crop is "quite tolerant". This barley is apparently grown in saline lands as there are many observations in the range of ECe = 10 to 25 dS/m. The random selection of plots proves that the average salinity is greater than that at the breakpoint. It seems that farmers accept a somewhat lower yield, probably because there is no alternative land use and the barley still provides them with some income.

The yield of sorghum is not negatively affected by soil salinity up to a salinity level of ECe=8.5 dS/m. Beyond that point a sharp yield decline occurs with increasing ECe values. According to the generally accepted classification, this sorghum is a salt tolerant and may even be called "quite tolerant" or "salt resistant".

In cotton, up to ECe=17 no significant yield decline can be detected. Thereafter a sharply declining trend manifests itself. Doubt may arise as to the robustness of the breakpoint on grounds of the limited number of data with an ECe value greater than 14. However, the statement that the tolerable salt stress is higher than 12 will probably not meet with much resistance. This cotton crop, according to the widely accepted classification, is very tolerant to soil salinity.