international fertilizer correspondent
No 4

Feed the soil to feed the people

Most people are sensible enough to know that one rarely gets something for nothing in this life. So why, when everyone recognizes that food productivity must increase, is nourishing the soil so often neglected? Balanced soil fertility is not the whole answer to yield improvement but, without feeding the soil, the question remains, how shall we feed the people?

Potash helps the farmer to have a good crop and income and thus, to feed his family
Potash helps a farmer to have a good crop and income
IPI-PRII-GAU groundnut project, Junagadh (Gujarat), 1997

India, with its 1 billion inhabitants, provides a good example of past achievement and future need. Since 1950, food grain production has quadrupled, from about 50 Mt to currently almost 200 Mt, keeping pace with the increase in population. For the last 25 years, the area under food grain cultivation has remained largely constant at about 123 million ha. The consequence, of course, is far greater demand from the soil that supports the crop. Whereas in 1950 the yield from one hectare of food grain supported four people, now it must support more than seven.

How much of this yield increase can be attributed to the use of mineral fertilizers? The usual estimates are between 35% and 40%, the balance being from better crop varieties (that depend, of course, upon higher soil fertility to achieve their potential), and better control of pest and diseases. Indian farmers have increased their use of NPK dramatically over the last 25 years from about 0.5 Mt to currently 16.2 Mt. But it is the rate of return in increased yields from the use of these fertilizers that is important in terms of total food production as well as farmers’ livelihoods. Of concern is the fact that fertilizer use efficiency has declined sharply over the same period, from around 45kg of food grain per kg of NPK fertilizer in the early seventies to currently less than 15kg. It is reasonable to expect some decline because, when mineral fertilizers are first applied to impoverished soil, crop yields will improve dramatically. Over time, if applications of fertilizer are matched to the needs of the soil and the needs of the crop, fertilizer use efficiency should remain relatively constant. Figure 1 illustrates that this is not the case and that the trend is still downward. Why, and what lessons must be learnt if food production is to keep pace with the expected increase in population to 1.3 billion people by 2025?

Figure 1: Food grain production in India increases with fertilizer use, but the apparent fertilizer use efficiency declines - a result of unbalanced fertilizer use?
MT nutrients mt food grains   kg foodgrain per kg NPK
Figure 1a Figure 1b
food grains food grains
food grains total NPK
food grains N
P2O5 P2O5
K2O K20
data source: FAI Yearbooks provisional data for 1997/98

A clue to the problem may lie in the unbalanced application of fertilizer. Indian scientists recommend that the ratio of N:P2O5:K2O should be 4:2:1 whereas, overall, it is currently 8:3:1. If the lower input of K to cereals is taken into account, the N:K ratio widens still further. In the grain growing States of Punjab and Haryana, the ratio at which N:K is used is 55:1 and 200:1 respectively (1996-97). Taking the Punjab as an example, the harvest of nearly 20 Mt in 1995-96 would have removed from the fields about 100,000 t of K2O (5kg of K2O/t of grain). If the straw is also removed from the field, the loss of K2O is much greater. This removal contrasts with the 16,000 t of potash that are applied but, because most potash goes to crops other than cereals, heavy soil K mining can be assumed in grain growing regions. A soil that is hungry for K cannot support the production of 300 Mt of food grains, the minimum that is likely to be required to support the population in 2025.

The good news is that there is still potential for yield improvement, provided that balanced fertilization is adopted. Shukla et al.* (1998) report from on-farm trials conducted in six States within the All India Coordinated Agronomic Research Project, that the recommended use of N+P+K led to increased yields of wheat by almost 800kg/ha and of rice by more than 500 kg/ha. The net return to farmers increased per rotation by Rs 3172 per ha in spite of higher fertilizer costs. Field trials in Punjab have shown that, in contrast to the average yield of 3.1 t/ha of paddy, 7.1 t/ha can be achieved with balanced fertilization.

In response to concerns about the very wide N:K ratio in fertilizer use, and the continuing level of K mining, IPI, in cooperation with the Punjab Agricultural University and the Potash Research Institute of India, held a workshop on "Balanced fertilization in Punjab Agriculture", December 15-16, 1997, in Ludhiana. The Proceedings of this Workshop, which are now available, contain 18 papers dealing with the fertility status of soils in Punjab, soil tests, long-term trials and the effect of balanced fertilization on a wide range of crops grown in the region. In this context, Bansal and Shahid Umar record that, for instance, rice receiving 40 kg/ha K2O failed to show any positive response in 1981-82. The same amount of potash applied now increases the yield by almost 700 kg/ha. A similar trend in crop response to K was obtained with wheat. It should be no surprise to find that response to K is building up. The all India K balance currently shows a deficit of some 7 million t K2O, which is many times more than the amount applied annually.

IPI will continue to initiate and support such field trials and to organize workshops to disseminate the knowledge. While care must be taken in drawing generalized conclusions from results achieved on a particular trial site, there is nevertheless ample evidence to demonstrate that if the population is to be fed, the first essential is to feed the soil.

* Shukla, N.D., Shukla, A.K. and Mishra, P.O. (1998): Production potential, production efficiency and economic variability of rice-wheat systems under farmers' and researchers' practice of fertilization. Fertilizer News, pp. 59-67, May 1998.