Maize to Salinty stress and its mitigation approach of Silicon Nutrition: Maize grain is a very rich source of starch, vitamins, proteins and minerals, and gives the highest conversion of dry substance to meat, milk and eggs compared to other cereal grains.
Being glycophytic plant, maize is severely affected by salinity. A survey was done to know the extent of the problem/salinity as a pre-requisite for a proper management plan as variation in salinity exists in soils. Salinity stress is a serious threat to crop production around the globe and about 6.3 m ha land in Pakistan is salt affected. Maize is an important cereal crop having significant impact on Pakistan’s economy and food security.
Being a glycophyte, maize yield is seriously affected if grown on salt affected soils. Nutrition management can improve salinity tolerance in the crop. Silicon (Si) is a beneficial element having many beneficial effects, such as improving water use efficiency and enhancement of salt tolerance. Si application can enhance maize growth at every growth stage by manipulating the deleterious effects of salinity.
Food security is a serious threat in developing countries because of ever-increasing population. According to recent estimates, more than 2 billion people face food shortage occasionally due to poverty and natural calamities. The problem can be tackled by:
- Efficient utilization of the natural resources
- Proper application of physical inputs
- Increasing production of major food crops through either increasing area under crop production or improving crop yields per hectare.
To increase the area under crop production is not feasible due to limited farmer resources and poor management. The area available for agriculture is decreasing day by day due to:
- Urbanization of arable land
- Poor soil management practices with intensive use of cultivation, degradation of the existing arable land due to various abiotic factors including salinity and drought.
Hence, there is a direct need to improve crop yields per hectare and to take more and more poor or marginal soils under cultivation. One of the main reasons of soil desertification is soil salinity. Out of 13 billion hectares of total land, one billion is salt affected, including 30% of all irrigated land.
Most of this salt affected land is not under cultivation and has a very low productivity, if cultivated. Hence, for sustaining food security, a high priority should be given to safe use of salt affected soils.
During 2017-18, maize crop was cultivated in an area of 1,229 thousand hectares and witnessed a decline of 8.8 percent over last year’s cultivated area of 1,348 thousand hectares. Maize crop production recorded a decline of 7.0 percent as its production stood at 5.702 million tonnes compared to the last year’s production of 6.134 million tonnes.
It has a significant potential for securing food availability. In Pakistan, 6.3 mha land is salt affected. If this salt affected area is brought under maize cultivation, additional maize production would be expected, considering 50% yield reduction in these poor soils.
Soil salinity has a number of deleterious effects on crop growth, such as ion toxicity and physiological drought, decrease in water use efficiency and photosynthesis due to interveinal chlorosis which ultimately decreases crop yields. Salt stress is also the major reason to cause imbalance of the inner cellular ions.
The major reason of reduced growth of cereal crops in salt stressed conditions is specific ion toxicity (certain ions like Na and Cl uptake at an elevated level) and more than 50% yield reduction in maize has been reported in soils with EC more than six.
Taking salt affected soils under cultivation and improving crop yields on salt affected soils would be beneficial for ensuring food security. It is highly recommended to adopt strategies aiming at utilization of these marginal lands and increased crop production on salt affected lands (Irrigation water, raising beds, organic matter and salt tolerant crops like kallar grass). All of these strategies have some advantages and disadvantages.
Judicious use of mineral nutrition is a recommended shotgun strategy as it strengthens the plants to cope against salt stress. Silicon (Si) as a beneficial nutrient is known to improve plant growth particularly under abiotic stresses. It is helpful for plants in many ways as it improves plant water status in context of relative water content and transpiration rate, ameliorates the harmful effects of salinity on chlorophyll contents and plant biomass in both leaves and roots, it lowers significantly the Na+ concentrations.
Salinity-silicon interactions have been investigated in a number of plant species. Increasing the availability of Si in the growth medium can reduce salinity stress in plants by altering soil and plant factors but specific mechanisms are still debatable. Silicon uptake in a salt stressed plant increases root activity for nutrient uptake, inhibits transpiration which reduces osmotic stress.
Similarly, Si was found to increase the total dry matter, relative water content, and chlorophyll contents in maize. Additionally, it decreases electrolyte leakage and proline accumulation in maize plants. It also increases the activity of ATP Pase and P Pase in plasma membrane which ultimately increases K and decrease Na uptake. The beneficial effects may vary among plant species.
Cereals that accumulate maximum Si in their shoots usually performed better than the others but Si salt is not a cheap source to apply in field conditions alone as a soil amendment, so different methods like soil and foliar Si applications are used to make it economically viable strategy.
Salinity stress generally imposes severe impacts both on human and plants by degradation of land and poor crop growth. Cereals are mostly glycophytes and higher amounts of salts in the soil solution retard their growth and development irrespective of the growth stages. Early growth stages of cereal crops are more salt sensitive as compared to later growth stages.
Cereal crops often cannot withstand high salinity rates until some exogenous amendment. Silicon proves to be essential in such cases under salt stress conditions. It is present in higher amounts inside the plant body and prevents the crop to be transpired and lowers the activity of reactive oxygen species. It helps cereal crops to overcome a stress condition in their critical growth stage and improves many physiological and biochemical mechanisms of plants.
It also increases the crop biomass and yield so prove to be necessary for the cereal crop to accomplish healthy reproductive stage under salt stress. Thus, salt stress can be minimized and salt affected area must be utilized by growing cereal crops with foliar or soil Si application as an amendment. The beneficial effects of Si are usually expressed more clearly when plants are subjected to various abiotic and biotic stresses. Silicon is probably the only element which is able to enhance the resistance to multiple stresses.
VIA: Muhammad Nazim1 and Qurat-Ul-Ain Sadiq2
2*Department of Agronomy, Muhammad Nawaz Shareef, University of Agriculture Multan, Pakistan
4Department of Soil and Environmental Sciences, Muhammad Nawaz Shareef, University of Agriculture Multan, Pakistan.