FIGURE 8.

Ranking of factors (primary and surrogate) determining nitrogen use efficiency [Mg cane (kg N)^-1] predicted for 6.9 million sugarcane crops simulated under a wide range of management practices, soils and climates over 84 years. The ranking of the factors was based on their improvement in predictive accuracy across the whole regression tree (Figure 9) and were ranked relative to the most influential factor. Only the four factors shown in this figure improved the predictive accuracy in the pruned regression tree.