Table 2.
Descriptive statistics of agronomic nitrogen use efficiency for categorical variables of soil and climatic factors
| Factor | Level | Kenya | Sub-Saharan Africa | ||||
|---|---|---|---|---|---|---|---|
| Mean | SE | n | Mean | SE | n | ||
| Environmental | |||||||
| Soil order | Acrisols | 17.3 | 4.9 | 22 | 20.0 | 2.5 | 37 |
| Alfisols | 87.4 | 19.2 | 4 | 23.5 | 1.6 | 12 | |
| Alisols | 12.3 | 4.8 | 8 | – | – | – | |
| Andosols | 22.8 | 1.6 | 6 | 28.9 | 10.7 | 8 | |
| Arenosols | – | – | – | 15.3 | 2.2 | 3 | |
| Cambisols | 71.8 | 10.2 | 22 | ||||
| Ferralsols | 42.0 | 8.0 | 24 | 16.7 | 2.1 | 81 | |
| Lixisols | – | – | – | 22.5 | 5.4 | 41 | |
| Luvisols | 10.5 | 3.0 | 4 | – | – | – | |
| Nitisols | 51.2 | 5.2 | 68 | – | – | – | |
| Phaeozems | 65.8 | 4.8 | 8 | – | – | – | |
| Vertisols | 22.1 | 4.6 | 6 | – | – | – | |
| Soil textural classes | Clay | 26.7 | 6.1 | 28 | 19.5 | 14 | |
| Clay loam | 33.7 | 2.0 | 21 | ||||
| Loamy sand | 20.8 | – | 2 | 22.5 | 4.7 | 8 | |
| Sandy | – | – | – | 10.8 | 0.7 | 64 | |
| Sandy clay | 20.4 | 2.2 | 4 | 3.5 | 9.6 | 6 | |
| Sandy clay loam | 54.6 | 21.6 | 6 | 17.2 | 5.9 | 10 | |
| Sandy loam | 49.8 | 7.0 | 31 | 16.8 | 3.1 | 55 | |
| Agro-ecological zone | Lower highlands 1 | 22.8 | 1.6 | 6 | – | – | – |
| Lower highlands 2 | 75.8 | 9.6 | 6 | – | – | – | |
| Lower midlands | 28.3 | 7.7 | 4 | – | – | – | |
| Lowlands | 20.4 | 3.5 | 4 | – | – | – | |
| Upper midland | 94.3 | 15.1 | 8 | ||||
| Humid | – | – | – | 21.8 | 2.7 | 6 | |
| Sub-humid | – | – | – | 26.7 | 1.9 | 18 | |
| Management | |||||||
| Manager | Farmer | 44.6 | 3.2 | 159 | 18.3 | 1.4 | 234 |
| Researcher | 32.9 | 4.7 | 81 | 22.4 | 1.6 | 63 | |
| Nutrient type | N, P, K | 80.0 | 5.7 | 49 | 23.3 | 14 | |
| N | 30.4 | 2.5 | 149 | 18.1 | 1.4 | 235 | |
–, missing statistic of the group; n, number of observations; SE, standard error