Nutrient Application: beyond the golden ratio

The common mantra in farming is that it is not the quantity of fertilizer that ensures higher productivity levels, but the optimal application of different fertilizer types. The mantra is so strongly etched in public understanding of agriculture that it is rarely challenged, let alone criticized.

Why? Because inefficient practices are an easy cop-out explanation for sub-par performance of the farming sector. Of course, it is hard not to believe that fertilizer application in the country would be below optimal level; after all, ‘the average farmer is poorly educated, thus must lack appreciation for best practices’, we are told.

A superficial look at fertilizer offtake and nutrient application numbers validates such perceptions as well. The golden N, P, K ratio – 4: 2: 1 – is as frequently followed as the golden rule of Confucius in politics. The conditions on the ground are so bad that actual application for FY19 comes close to 64: 20: 1!

But ratios can be deceiving; so best to look at these numbers in percentage terms. For the full year FY18, N:P:K application stood at about 72%-27%-1% against the golden ratio of 57%-29%-14%. The situation during the past decade has been averaging in this direction, indicating that the sector faces excessive nitrogen (N) application, phosphate levels inching ever close to optimal, and potash (K) virtually missing from the picture.

Yet the long-term trend is also one of increasing fertilizer application in terms of absolute volume as net sown area has remained unchanged (in fact declining marginally) at 15.4 million hectares over the last decade. Between FY09-FY19, N, P and K application has in fact grown at a CAGR of 0.96, 4.85 and 7.52 percent, respectively.

The question then is whether relative nutrient application is moving toward the golden ratio? And second, whether increased application of phosphate (P) and potash (K) – however little – has contributed toward higher productivity.

The answer to the first question is straight forward as it reflects farm economics. Potash is missing from the picture simply because its per bag prices are twice as expensive as urea (primary source of nitrogen-based fertilizer); and thus, higher application of urea fills in as it yields better returns on investment.

It is in fact the second question that drags the golden ratio itself to stand. Fertilizer application over past five decades has improved dramatically. Both, in terms of absolute volume and relative to the golden ratio. Back in FY70, N, P & K offtake stood at 0.3million tons total which has since improved to 4.4million tons for FY19. On disaggregate basis, the ratio has changed from 88-12-0 to 75-24-1. Net sown area in FY70 stood at 14.54million hec in FY70, with an addition of only one million hec since.

Yet, it is hard to assert that increased nutrient application during the following half century has conclusively helped improve farm level productivity. While yields have increased across all major crops during this period, causal relationship appears to be missing in all cases except for wheat (see illustration).

In fact, other more informed factors better explain the yield improvements achieved. Cotton, for example, witnesses two jumps circa ’84 and early ‘00s, both periods when absolute and relative fertilizer application saw little change. Both jumps are in fact commonly attributed to introduction of higher yielding varieties, first of desi variety followed by bt. cotton introduction in 2000s.

Similar is the story of rice and sugarcane, where a combination of improved water availability post mid-seventies, mechanization, and introduction of IRRI varieties explain the tortuous yet upward mobility of yields during the fifty-year long period.

The missing returns from improved fertilizer application are most glaringly obvious in the case of maize, where yields remained flat until mid-nineties. This is when the crop picked up sudden pace upon introduction of hybrid seeds and has stayed on upward trajectory since.

Is the golden ratio faulty? Not necessarily, but the returns from improved (as well as increased) fertilizer application are definitely not uniformly distributed.

More importantly, it is also clear that compared to incremental fertilizer application, intervention in seed technology brings quantum leaps in yields for growers, glaringly obvious from distance-to-frontier for wheat and maize. Domestic yield for maize is much closer to world average compared to abysmal performance of wheat crop, where periodic improvements have primarily been a function of other inputs, with little advancement on new higher yielding varieties. Consider that fifty percent of total fertilizer offtake is consumed by wheat, not surprising considering its aggregate cropping area is still greater than the following four major crops combined.

But lastly, an anecdote-based caveat. As Dr. Shahid Afghan of Punjab Sugarcane Research and Development Board noted in a recent conversation with BR Research, higher fertilizer application may very well result in higher yield, but not always for the better.

In the case of sugarcane, according to Dr. Afghan, higher yield constrains the glucose-to-sucrose inversion process, as the crop continues to grow both in height and weight (hence higher yield) while sucrose content remains unchanged. This means that the per kg sugar retrieved from the crop remains low, despite higher weight/yield.

Such adverse outcomes are not limited to sugarcane alone. According to a 2017 paper by Agriculture Research Service-USDA, nitrogen application can in fact result in poorer lint yield and fibre quality. Never mind that over one-quarter of domestic fertilizer application is consumed for cotton production, and the complain of poor-quality raw cotton is still repeated by textile sector ad nauseum.

Then there is the case of prolonged cycles of nitrogen (N) application resulting in elevated level concentration in groundwater, in turn reducing N use efficiency. This results in poor grain yield, with wheat crop by far the most significant victim.

The golden ratio may in fact hold, as it should for all matters of human life: balance is necessary. But whether that balance needs to be discovered separately for each crop remains a question open to research. A more urgent consideration for public policy advocates is to consider whether fertilizer subsidy (N, P or K) is the best course of intervention to increase farm-level productivity, when greater returns to investment appear seemingly obvious from other tools such as seed technology.

Source: Statistical supplements Economic Surveys (various issues); Annual Fertilizer Review (2017); Punjab Board of Investment & Trade, Report on Fertilizer Sector on Pakistan; The Cotton Foundation; USDA-ARS