Table 3.

Regression model estimates of soil and climatic factors on fertilizer response and agronomic nitrogen use efficiency

Fertilizer response
R 2	Adjusted R2	Predictor	Estimate	Standard error	p value	Significant level
Kenya (n = 202)
0.29	0.26	Intercept	0.483	1.275	0.204	.
		Soil pH	0.166	2.679	0.008	**
		Log-Total C	− 0.024	− 3.353	0.001	***
		Log-P-Olsen	− 0.020	− 3.041	0.003	***
		Log-N rates	− 0.002	− 1.535	0.126
		Log-Exch K	0.060	6.103	0.001	***
		Clay	0.001	0.425	0.671
		Log-Silt	− 0.007	− 2.444	0.015	*
		Log-Rainfall	− 0.0008	− 0.771	0.004	*
Sub-Saharan Africa (n = 255)
0.13	0.092	Intercept	− 0.221	− 0.734	0.464
		Soil pH	0.154	2.714	0.007	**
		Log-Total C	− 0.006	− 1.649	0.101
		Log-P-Olsen	0.021	3.049	0.003	*
		Log-N rates	0.002	2.043	0.042	*
		Log-Exch K	− 0.022	− 2.002	0.047	*
		Clay	− 0.002	− 0.591	0.555
		Log-Silt	0.003	1.185	0.237
		Log-Rainfall	− 0.0001	− 1.439	0.102	**

Agronomic nitrogen use efficiency
R 2	Adjusted R2	Predictor	Estimate	Standard error	p value	Significant level
Kenya (n = 202)
0.32	0.29	Intercept	52.652	22.943	0.023	*
		Soil pH	7.019	3.780	0.065	.
		Log-Total C	− 1.154	0.442	0.010	*
		Log-P-Olsen	− 1.098	0.404	0.007	**
		Log-Exch.K	3.429	0.589	0.001	**
		Clay	− 0.408	0.169	0.017	*
		Log-Silt	− 0.634	0.185	0.001	***
		Log-Rainfall	− 0.010	0.006	0.106
Sub-Saharan Africa (n = 255)
0.035	0.003	Intercept	11.183	11.791	0.344
		Soil pH	1.697	2.283	0.458
		Log-Total C	0.056	0.138	0.687
		Log-P-Olsen	0.544	0.273	0.048	*
		Log-Exch.K	− 0.829	0.431	0.056	.
		Clay	− 0.013	0.113	0.912
		Log-Silt	− 0.077	0.097	0.431
		Log-Rainfall	− 0.001	0.004	0.781

Significant codes: *** = 0.001; ** = 0.01; * = 0.05; . = 0.1