Soil fertility and fertilizer management under saline conditions

Soil fertility and fertilizer management under saline conditions

3. Soil fertility and fertilizer management under saline conditions
The problematic soils especially the salt affected soils are associated with either excessive soluble salts or high exchangeable sodium or both. The productive potential of a particular crop can be better achieved if the nutrient essential for physiological and metabolic activities of plant are made available to them, through application of fertilizers in proper form and required amount emphasizing the modification of nutrient management to optimize the production and nutrient efficiency in salt affected soils. High level of exchangeable sodium and high pH significantly alter the nutrient management needs of alkali soils due to enhanced solubility of phosphorus compounds, high losses of applied nitrogenous fertilizers and reduced availability of certain micro nutrients.
Salt affected soils are generally poor in fertility. Agrawal and Gupta (1968) reported that saline alkali soils are low in the available nitrogen, phosphorus, potassium, manganese, calcium etc. The availability of iron, zinc, manganese and copper may be drastically reduced at high pH values. In paddy soils there is low efficiency of nitrogen fertilizers due to leaching, run off and volatilization losses under water logged conditions. Further, the calcareous soils are also deficient in micro nutrients particularly zinc.
To mitigate the adverse effect of excessive salts or exchangeable sodium there is need to increase the fertility status of the salt affected soils through judicious use of fertilizers. The quantities of fertilizers to be applied could correctly be assessed based on nutrient supply power of soil and nutrient requirement of crop to be grown.
The basic problems of fertilizer use in salt affected soils arise due to interactive effects of salts and exchangeable sodium with fertilizer nutrients which are mainly governed by nature and degree of salinity and sodicity, chemical reactivity and solubility of added fertilizers, nutrient requirements of the crop, nutrient availability in soils and salt tolerance behavior of the crops.
Fertilizer and Nutrient Management:
Fertilizer and nutrient management is important for sustainable crop production in salt affected soils. Most of the soils are deficient in nitrogen and zinc as well as iron play important role in crop production in salt affected soils. Application of organic manures along with proper amendment is vital in these soils for increasing nutrient use efficiency. For high nutrient use efficiency not only the kind of nutrient is important but type of fertilizer, its time and method of application are also very important. As far as possible acid forming fertilizers with low salt index should be used in salt affected soils. Bad effects of high salt content in soil and irrigation water can be minimized by the application of organic matter either in undecomposed (leaves of Tephrosia and Subabool, green manuring) or decomposed forms.
There are significant positive responses to fertilizer application in salt affected soils. Lal and Singh (1972) pointed out that grain and straw yields of wheat decreased with increase in EC and SAR , but at every level of EC and SAR of irrigation water better yields were obtained with higher dose of fertilizers as compared to lower dose. The fertilization tended to offset the adverse effect of higher level of EC and SAR of water to some extent. Lal and Singh (1973, 1974) also reported that uptake of N, P,K, Ca and Mg decreased with rise in EC and SAR of irrigation water but the effect was counteracted with the level of fertilizers , only where EC and SAR of water were 3.45 dSm-1 and 16.73, respectively.
Nutrients are applied to soil in the easily available form to stimulate the essential physiological function of the plant at moderate level of salinity and sodicity. Among major nutrients there was better response to nitrogen than phosphorus followed by potash.
A field study conducted by Lal and Lal (1990) revealed that NPK fertilization increased the yield of wheat at every level of EC (0.9 to 8.0 dSm-1) and SAR ( 3.7 to 26.0). Additional application of Nitrogen, Phosphorus and Potassium mitigated the adverse effect of poor quality water on grain and straw yield of wheat (Table 3.1).
Table 3.1: Average effect of Nitrogen, phosphorus and potassium on grain yield of wheat
Treatments Grain yield
1980-81 1981-82
N120 32.76 33.57
N150 36.30 36.66
N180 37.36 37.76
CD at 5% 1.22 1.18
P30 34.65 35.58
P45 36.31 36.49
CD at 5% 0.25 0.24
K20 35.12 35.51
K40 35.82 36.56
CD at 5% 0.25 0.24
Source : Lal and Lal (1990)
Puntamkar et. al. (1971a) obtained high response to both phosphorus and potash 75 Kg ha-1 in pearlmillet crop grown on two soils, viz. sandy clay loam (pH 8.4 , ECe 16.5 dSm-1 ) and sandy (pH 8.4 , ECe 6.7 dSm-1 ) under saline water (EC 10.5 and 6 dSm-1, SAR 19 and 22) at Bilara Agricultural farm (Table 3.2)

Table3.2 : Effect of Phosphorus and Potash on the yield of pearlmillet
Phosphate (Kgha-1) Potassium ( Kg ha-1)
25 50 75 Mean
25 8.00 8.75 12.26 9.68
50 8.46 10.00 13.00 10.49
75 9.26 10.08 15.06 11.64
Mean 8.57 9.78 13.44
Source : Puntamkar et. al. (1971)
Vyas and Marwaha (1970) observed an increase in yield and yield attributes of wheat with an increasing level of phosphorus from 0 to 100 kg P2O5 ha–1in salt affected soil of Jobner having pH2 8.2 and EC2 1.57 dSm-1 and ESP 15.0 (Table 3.3)
Table 3.3: Effect of phosphorus on yield and yield attributes of wheat
Phosphate

(Kg ha-1) Grain Yield

(q ha-1) Straw Yield

(q ha-1) Plant height

(cm) Ear lengh

(cm) 1000 Grain weight (g)
0 21.35 41.90 65.2 10.09 22.68
50 28.82 45.67 66.1 10.28 23.41
100 30.85 49.37 65.0 10.89 22.93
CD at 5% 0.23 1.14 NS 0.36 NS
Source: Vyas and Marwaha (1970)

Paliwal (1972) based on a large number of green house and field experiments on the use of fertilizers in soils irrigated with saline water under shallow water table conditions concluded that:
1. Application of normal dose of N and P are beneficial to wheat, barley, maize and pearl millet up to an EC value of 2.8 dSm-1 and SAR of 25 in irrigation water with a corresponding value of ECiw 6.0 to 7.0 dSm-1 and SAR up to 25 in soil solution and ESP up to 35.
2. In the presence of FYM crop responded more to fertilizer .
3. Application of nitrogen and phosphorous fertilizers upto moderate levels of salinity
and alkalinity is useful
4. Responses to fertilizers were better on salt tolerant than on salt sensitive crops.
Though there is no absolute deficiency of K in saline soils, but plant grown under high salinity may show K deficiency due to antagonistic effect of Na and Ca. Maliwal and Paliwal (1971) observed that at higher salinity in the growth medium K uptake is reduced. Under such conditions the reduction of salinity should be pre-condition for optimum plant growth.
Dungarwal et al. (1973) reported that ammonium sulphate and ammonium sulphate nitrate were found equally effective in alkaline calcareous soils .
In a green house study , application of 88 kg N ha-1 and 44 kg P2O5 ha-1 was found to yield more dry matter of maize grown on an alkali soils of Vallab Nagar and saline alkali soil of Sareri . Dry matter increased with addition of FYM also (Laddha, 1980).
Gandhi and Paliwal (1976) reported that application of nitrogen and phosphorus was more beneficial upto ECe value of 6.0 – 6.5 dSm-1 beyond a salinity of 13.5 dSm-1, it was of little agronomical value. Crop response to nitrogen was better than phosphorus. Wheat responded better than barley.
Mehta et al. (1980) observed decrease in rate of nitrification with increasing concentration of salts.
Totawat and Singh (1981) reported that application of urea or ammonium sulphate in conjunction with sulphur up to 60 kg ha-1 cause significant increase in total dry matter, nitrogen content and green pod yield of pea as well as crude protein of pod at Jobner.
A field study conducted at Jobner on loamy soil with four saline water (EC-2, 6, 10 & 14 dSm-1), the three levels of nitrogen (50,100 & 150 kg ha-1) and three level of phosphorous (20, 40 &60 kg P2O5 ha-1) revealed that there was reduction in wheat (kalyan sona) yield beyond ECiw 6.0dSm-1. The economic dose of nitrogen and phosphorous were found to be 100 kg and 60 kg ha-1 (Singh, 1981).
Khurana et al. (1982) observed that grain and straw yields, uptake of N,K and protein content of wheat increased significantly with potash application. Optimum economical dose of potash was 50 kg K2O ha-1for alkaline sandy loam soils.
Response of applied P fertilizers in saline soils , even containing high amount of available P was because of the fact that in saline soils the availability of P is more a function of plant root length area, decreased the negative effect of excess chloride on P absorption by roots (Somani, 1983, 1990).
The economic dose of N,P and K for wheat grain with poor quality waters was found to be 100 kg N, 45 kg P2O5 and 30 kg K2O ha-1 (Jat, 1986).
Garg et al. (1990) observed that improved fertility ( 80 kg ha-1 N and P2O5 ) significantly increased the growth and yield of salt tolerant ( Kharchia-65) and salt sensitive (HD-2009 and HD -4502) wheat varieties under saline water irrigation.
Mathur and Goswami (1982) observed that application of gypsum did not alter the exchangeable K content of soil, but increased PBC K values from 25 to 32 me/ 100 (m/l)1/2. Potassium application enhanced the exchangeable K content and AReK values from 0.37 to 0.40 me/ 100g and from 0.0098 to 0.0220 me/ 100 (m/l)1/2, respectively.

Application of zinc also reduced the adverse effect of higher salinity and sodicity with low salinity waters (Lal and Lal, 1980; Lal and Singh, 1980). Application of zinc at the rate of 20 Kg ZnSO4 ha-1 mitigated the adverse effect of higher salinity and sodicity of water on wheat grown on loamy sand soils (Table 3.4).
Table 3.4: Combined effect of zinc levels and qualities of irrigation water on grain yield of wheat
ZnSO4
(Kg ha-1) Qualities of irrigation water
W1 W2 W3
10 23.17 27.23 20.60
20 26.13 24.23 22.83
30 25.30 25.00 23.40
40 24.83 24.67 24.13
CD at 5% 1.07
Source: Lal & Lal (1980) W1- EC 2.1dSm-1 & SAR 23.9, W2- EC 4.2 dSm-1 & SAR 30.2, W3- EC 6.3 dSm-1 & SAR 36.0
Singh (1989) observed that hazardous effect of sodic water on wheat can be mitigated to some extent by applying 30 kg ZnSO4 ha-1 to the soil whereas, Yadav (2001) recommended application of 50 kg ZnSO4 ha-1 in soil for barley.
Kumhar (1992) reported that application of phosphorous @ 75 kg ha-1 along with 30 kg ZnSO4 was found to be most economical. Zinc sulphate showed an ameliorative effect on soil (pH 9.2& ESP 30.2) by decreasing ESP and pH of soil.
Some of the nutrients like phosphorus and zinc are rendered unavailable due to alkaline soil reaction. Joshi (1988,1990 a) reported wide variations in micro-nutrient content in the degraded soils due to high RSC water irrigation (Fe 3.5 to 13.3 mg Kg-1 , Mn 3.9 to 24.4 mg Kg-1, Zn 0.3 to 3.44 mg Kg-1 and Cu 0.22 to 24.4 mg Kg-1). In general, 50 per cent samples were deficient in Zn. The available Cu was marginal in 15 percent samples. Among the major nutrients phosphorus was low to marginal (4.1 to 18.6 kg ha-1) and potassium in medium availability ranges (75 to 443 kg ha-1)
Joshi et al. (1988) observed that the salt affected soils and associated non-saline soils contained HCl soluble, exchangeable and DTPA extractable Zn as 31.9, 1.10,1.10 and 33.4,1.37, 0.90 ppm, respectively, the corresponding contents of Cu were 5.3, 0.54 and 1.18 ppm, respectively. Soil texture, CaCO3 and organic carbon accounted for major part of variability.
Loss of urea N is more under saline conditions, which is further accelerated by water logging. The loss of nitrogen is reduced when slow release fertilizers are used, as these are less soluble in water leading to less leaching, runoff and volatilization losses and are more efficient.
Coating of urea with neem and mahua cake at 20 to 30 % level inhibits the nitrification rate in the soil and reduces losses and consequently increase the efficiency of fertilizer nitrogen (Rathore, 1974; Mago and Totawat, 1985)
Grain yield of wheat was maximum under SCU (Sulphur coated urea), which was at par with NCU (Neem coated urea) (Table3.5). Uptake of nitrogen by wheat was higher in coated fertilizers (Vyas and Singh, 1989).


Table 3.5 :Effect of slow release nitrogenous fertilizers and levels of saline water on yield and N uptake of wheat

Treatments Yield (kg ha-1)
N uptake(kg ha-1)*
Grain Straw
1981-82 1982-83 1981-82 1982-83 Grain Straw
Urea 25.90 25.71 36.99 36.71 50.3 15.9
Urea split 27.01 27.34 38.40 39.64 53.6 16.9
NCU 29.77 28.70 42.76 41.91 59.9 19.2
SCU 30.11 29.24 42.45 41.75 62.0 19.5
CD at 5% 0.72 0.54 1.70 1.04 1.58 0.98
ECiw (dSm-1)
2 31.38 30.77 43.18 46.15 66.3 21.5
6 30.28 30.04 41.00 40.59 63.4 19.8
10 27.73 27.22 39.49 39.50 53.3 16.5
14 33.73 22.99 36.84 36.85 43.0 14.0
CD at 5% 1.58 1.76 1.88 1.79 4.80 1.75
Source: Vyas and Singh (1989)
Pot culture studies on suitability of nitrogenous or phosphatic fertilizers for wheat crop grown on nine salt affected soils showed that on soils of low salinity (ECe up to 4.6 dSm-1) , all the nitrogenous fertilizers viz. ammonium sulphate, calcium ammonium nitrate , urea and potassium nitrate were found to be equally suitable but, at higher level of salinity ( ECe up to 9.5 dSm-1) , nitrate form of nitrogen was better than others. In general, in sodic soils ammonical and nitrate form of nitrogen resulted in better yields than others. Nitrate and ammonical nitrate form of nitrogen proved more effective than others in saline-sodic soils. Out of different phosphate fertilizers , TSP, super phosphate were found to be more suitable for saline soils. DAP for all types of sodic soils and DAP as well as TSP for saline –sodic soils (Carpenter et al., 1979).Mehta et al. (1980) reported that rate of nitrification was more in case of ammonium sulphate as compared to urea.
Efficacy of indigenous coating materials for urea under saline water irrigation incubated for 21 days revealed that the formation of urea-N and NH4-N decreased and the formation of NO3-N increased as the period of incubation advanced beyond three days. However, higher value of urea-N and NH4-N and the lower values of NO3-N were recorded in soil receiving urea coated with neem (Azadirachta indica) and mahua (Bassia latifolia) cakes (300g cake kg-1 urea ) in conjunction with coaltar. Efficiency of inhibition of nitrification was in the order neem cake> mahua cake> sulphur> gypsum coaltar (Mago and Totawat, 1989a). Further,urea coated with gypsum, sulphur, powdered cakes of neem and mahua used in conjunction with coaltar were found superior in improving yield and yield attributes of maize (Mago and Totawat, 1989b)
Method and time of fertilizer application :
Efficiency of fertilizers is mainly governed by time and method of application. In general, salt affected soils are common in arid and semiarid region where there is always a paucity of moisture in the soil. Adequate supply of moisture in the soil is pre-requisite for the availability of nutrients to the crop. Therefore, foliar fertilization should be done on salt affected soils.
In salt affected area high salinity is found at the surface , fertilizers can safely be applied at lower depth by drilling them where salinity is likely to be less and root will be able to utilize them better. Placing the fertilizer at 20 cm depth enhanced the water and fertilizer use efficiency and also the net monetary return per hectare.
Ammoniacal and amide nitrogenous fertilizers should be applied through foliar application because of their losses from the soil due to volatilization and slow rate of nitrification at higher pH values. If soil application of ammoniacal fertilizers is to be done, it should be applied in several splits depending upon the life cycle of the crop.
In alkali soils, the phosphatic fertilizers should be applied in bands. The best time of application for water soluble phosphorus carriers is at or immediate before planting. Broadcasting or band placement of potassic fertilizers may immediately be done prior to or at planting, however, the concentration of soluble salt is likely to be greater with use of potassic fertilizers.
Foliar feeding should be done for all cationic micro-nutrients because there is always a problem of their low availability at higher pH.
Mathur et al.(1974) found that in saline alkali soils of IGNP best resuls were obtained when half of nitrogen was applied at transplanting and rest half at maximum tillering stage of paddy crop in Anupgarh area. Inadequate fertilizer application at any one of the above two stages gave reduced yield and delayed application was found to be wasteful.
Incorporation of gypsum or sulphur significantly decreased the bulk density and increased the total air space, hydraulic conductivity and water holding capacity of soil. There was distinct decrease in pH and increase in EC. Urea 60 kg N ha-1 or ammonium sulphate (90 kg N ha-1) when applied in conjunction with sulphur or gypsum have improved the water holding capacity of soil (Totawat and Singh, 1981b).
Mathur and Talati (1984) indicated that high calcium carbonate contents (6.2-11.6%), bicarbonate in soil solution (3.3 –5.0 mel-1) and alkaline soil reaction were responsible for iron chlorosis in sugarcane crop in IGNP command. This can be corrected by foliar application of 0.5 to 3.0 per cent FeSO4 with citric acid.

Babel et al.(2001) observed that application of full N+P with Tepherosia purpuria green mauring followed by full N+P with gypsum @ 50% GR of soil reclaimed soil sodicity to appropriate level and consequently resulted in maximum productivity in pearl millet –mustard cropping system.
Babel et al.(2002) recorded highest yield of mustard (2147 kg ha-1) under Tepherosia purpuria followed by recommended dose of N and P. Maximum soil organic carbon (0.31%) was found with Tepherosia purpuria followed by D. nutan and (0.23%) under control.
Studies on nutrient management of gypsiferous soils indicated that yield of clusterbean and wheat were significantly higher in soil containing 5 to 10 per cent gypsum than control (no gypsum). Urea and Ammonium sulphate were found superior to CAN. Yields of both the crops were significantly higher when 100 per cent of recommended dose of fertilizer was applied as compared to 75 per cent of recommended dose. Studies on effect of nitrogen carriers and ECiw on yield of wheat and mustard grown on gypsiferous soil revealed that yields increased significantly when gypsum content of soil increased up to 10 per cent. The maximum and significantly higher yields were recorded when recommended dose of nitrogen was applied through 50% Urea+50% FYM in comparison to urea or FYM alone. The yields decreased significantly when ECiw increased beyond 4.0 dSm-1.
For higher nutrient use efficiency in salt affected soils type and kind of fertilizer that should be recommended for use in salt affected soil is very important. The important points that should be kept in mind while choosing particular fertilizer type are the following:

1. The fertilizer to be used on saline soil must have low salt index. On the basis of per unit of plant nutrient, mixed and high analysis fertilizers generally have low salt index values. Nitrogen and potassium fertilizers have high salt indices than phosphate fertilizers. Nitrate nitrogenous fertilizers having low salt index should preferably be used for raising the crops in saline soils.
2. Fertilizers capable of supplying nutrients slowly to the plants would be most suitable and will still be better if they are associated with calcium.
3. The sulphur bearing fertilizers are also considered superior in calcareous soils.
4. Among various nitrogenous fertilizers CAN or ammonium sulphate should be preferred over urea. Though urea was found to be inferior to other fertilizers when applied to the soil, its foliar application to paddy and wheat gave good yields of the crop.
5. For supply of nitrogen to paddy crop, ammonium fertilizers are preferred.
6. In gypsiferous soil urea and ammonium sulphate were found superior to CAN.
7. Among various phosphatic fertilizers, orthophosphates are most important. In alkaline and calcareous soils the rock phosphates as such is of little value owing to its low solubility . In general super phosphate and ammonium phosphate are quite satisfactory.
8 Acid forming fertilizers should be used on sodic soils except degraded one where the base forming fertilizers can be used.
9. If alkali soils are not calcareous, the calcium bearing fertilizer would give better results because they supply the calcium which replaces exchangeable sodium from the soil complex.
10. For calcareous alkali soils, acid-forming fertilizers like ammonium sulphate, ammonium sulphate nitrate and ammonium nitrate will be quite effective.
11. Ammonical and amide nitrogenous fertilizers could be applied through foliar application because of their losses from the soil due to volatilization and slow rate of nitrification at higher pH.

Posted in: Agriculture