international fertilizer correspondent
Feed the soil to feed the people,
the IPI jubilee
Session 1: Policy issues related to food supply
and the environment
Imbalance in nutrient supply as a threat to sustainable crop production
In many countries, the regrettable practice of unbalanced fertilization means that only a fraction of K that is removed by harvested crops is being replaced by potash. This holds true particularly for Asian countries. In contrast, the level of N fertilizers that are used matches closely that which is removed by crops. The consequences of continued imbalance in fertilization have been mentioned frequently in this issue of ifc, namely; yields below potential, poor and non-competitive quality, higher susceptibility to biotic and abiotic stress, decline in soil fertility, decreasing income which may ultimately trap farmers into poverty.
To get an inside view on this we asked representatives from Iran, India and China to report briefly, in a panel discussion, on the status of nutrient supply and its consequences.
Mohammad J. Malakouti from the Soil and Water Research Institute (SWRI) in Tehran, Iran, reported significant yield increases and crop quality improvements in a range of annual crops, fruit trees and ornamentals when potash was applied with N and P. K rates based on soil tests proved effective in annual crops. With ornamentals, it appears that the current recommendations have to be updated because higher rates still gave significant yield increases. Higher K rates than those currently recommended for fruit trees also increased yield but to the detriment of fruit quality because the increasing K/Ca ratio had the effect of reducing shelf-life. Current fertilizing practice in Iran contrasts sharply with that necessary to achieve a good response from crops, although the nutrient ratio has improved considerably during recent years. There is much scope for improvement.
MS Brar from the Punjab Agricultural University in Ludhiana, India, showed that fertilizer consumption in India has made impressive progress during recent decades. It increased from 0.07 Mt in 1950 to currently 16.7 Mt nutrients with a consumption ratio of 7.0:2.7:1.0 for N:P2O5:K2O. However, there is considerable variation within the country as far as the nutrient ratio is concerned. It varies from 3.8:1.7:1.0 in the southern region to 205.0:47.0:1.0 in the rice-wheat cropping system in northern India.
The very low use of potash in the cereal belt of northern India is a matter of concern for the future sustainability of the rice-wheat system. At the current level of 206 Mt of food grains, there is an annual deficit of about 10 Mt nutrients, mostly K. For feeding a population of 1.4 billion 25 years from now, India will need to produce 311 Mt food grains and will require 35 Mt of fertilizers.
It took some years to show a response in annual crops to potash application. Initially there was mostly a good response to N, a weak response to P and no response to K. The picture has changed substantially. Response to N declined or even became negative in acidic red and lateritic soils; response to P increased to a certain extent but response to potash strongly increased. It is clear that application of solely N and P as practised in northern India is not sufficient to sustain crop yield and the use of K is becoming essential.
Jianmin Zhou from the Institute of Soil Science at the Chinese Academy of Science in Nanjing, China, rightfully mentioned that China is the biggest country in the world for both production and consumption of food and fertilizers. Consumption, at 41.2 Mt, greatly exceeds fertilizer production even though the latter has increased substantially, to 29.4 Mt. Most of the potash that is needed must be imported.
Fertilizers play an important role in crop production in China, accounting for 50% of total investments in agricultural production. However fertilizer use efficiency is fairly low. One of the reasons is the unbalanced consumption ratio of 6.5:2.4:1.0, which is comparable to the situation in India. Organic manure is still a major source of K to the farmland. As a result there is a deficit of K in most of the arable land.
To realize China's goal of food security, Jianmin Zhou said that fertilizer use must be increased. What needs to be done urgently is to improve fertilizer use efficiency and restore soil fertility by applying balanced fertilization. Further measures to be taken include the increased use of potash, distribution of more fertilizers into highly productive areas, adjusting fertilizer composition, production of high analysis fertilizers, exploring new patterns of management, persisting in the application of organic manures, and establishing and improving advisory services.