When plant breeders showcase yield increases achieved by their recent releases over older materials, they often fail to mention the respective levels of fertilizer applied. Conversely., when fertilizer experts show the correlation between cereal yields and fertilizer input over time, they often fail to indicate which cereal varieties their time series relates to. When environmental activists discuss the historic Green Revolution and related phenomena, they occasionally criticize the alleged fertilizer dependence of modern varieties as proof that a mere conversion of precious fossil energy to food (or feed) calories is taking place, suggesting some sort of an environmental zero sum game.

CIMMYT has recently published interesting data on the relationship of land and fertilizer input in the production function of old and modern wheat varieties (Fig. 1).

Varieties typical of the 1950s, 1960s, 1970s and 1980s were compared to show how their respective yields changed with variations in land and fertilizer inputs.

To show the changes in the efficiency of input utilization CIMMYT chose a production function which takes output as fixed; in the case of Fig. 1 five tons of wheat. The functions show which combinations of area and fertilizer are needed to produce 5 tons of wheat with the respective cultivar.

The comparison is illuminating. It indicates that the traditional tall wheat of the 1950s needed 2 hectares of land in the absence of fertilizer to produce the 5 tons of wheat whereas the 1980s semidwarf wheats needed only 1.5 hectares, also without fertilizer.

It is hence not true--as sometimes claimed--that modern wheats cannot perform well in the absence of fertilizer. Even without this input they are more productive than the old tall varieties. In addition, they are also more productive than earlier "Green Revolution" semidwarf wheats. Decade after decade, CIMMYT wheats use less land and less fertilizer to produce the same level of output.

CIMMYT's data also show, for instance, that producing 5 tons of wheat on 1 hectare of land was impossible with the 1950s varieties, no matter how much fertilizer was applied. With the 1960s cultivars 110kg of fertilizer was needed to obtain 5 tons of wheat; with the 1970s varieties the fertilizer requirement had slightly dropped to 100kg while the 1980s varieties met the output target with only 60 kg of fertilizer input, always on 1 hectare of land. Certainly no zero sum game.

The superior performance of modern varieties also shows up quite strikingly when looking at the production functions at the 1.5 hectare point. To produce 5 tons of wheat on an area of 1.5 hectares, the tall varieties needed some 70 kilograms of fertilizer per hectare; the 1960s and 1970s semidwarfs required about 35 kilograms of fertilizer whereas the 1980s varieties needed no fertilizer at all.

Fig. 2 shows how the nitrogen/grain conversion ratio of CIMMYT cultivars developed over time. With 300 kg of nitrogen fertilizer input per hectare, the 1950 variety (Yaqui 50) yielded 10 kg of wheat for 1 kg of fertilizer. At the same imput level, the 1985 variety (Opata 85) yielded more than double, i.e. 21 kg of grain for 1 kg of fertilizer. The highest fertilizer conversion efficiency was attained by the 1981 variety (Genaro 81) which yielded a stunning 70 kg of wheat for each kg of fertilizer input at the moderate application level of 75 kg of nitrogen fertilizer/hectare.

These results contradict conventional wisdom that modern semidwarf cultivars require more nitrogen fertilizer than older cultivars. CIMMYT's experience with wheat is certainly not unique. Similar progress in nutrient conversion efficiency has been achieved in other grains such as rice and maize. But higher efficiency in nutrient conversion is only one among several goals of cereal improvement work. Other important crop research objectives include conservation of genetic resources; water use efficiency; enhancing yield stability in terms of improved tolerance of biotic and abiotic stresses; improved palatability, as well as better milling, baking and cooking qualities.

When looking at modern crop research it is important to realize that the creativity of scientists is the only non-finite resource in the production equation. Raising the efficiency of crop production by improving plants and fertilizer management is arguably the best way of protecting natural resources such as land and fossil energy reserves, while contributing to the food supplies needed by a growing planetary population.