High Nitrogen Fertilization of Tobacco Crop in Headwater Watershed Contaminates Subsurface and Well Waters with Nitrate

Table 1

Particle-size distribution in soil surface layer at sampling points, for five transects and different points in the watershed.

Transect	Position/use^*	Soil layer (m)	Pebbles	Gravel	Sand	Silt	Clay
			g kg^−1
1	1, tobacco	0.0–0.2	470	87	177	196	70
		0.2–0.4	292	190	152	247	119
1	2, tobacco	0.0–0.2	272	91	259	292	85
		0.2–0.4	317	58	270	261	95
1	3, tobacco	0.0–0.2	299	20	313	259	109
		0.2–0.4	336	96	247	224	97
1	4, tobacco	0.0–0.2	241	86	260	309	103
		0.2–0.4	543	0	186	203	68
2	1, tobacco	0.0–0.2	152	0	308	314	226
		0.2–0.4	141	0	279	230	350
2	2, tobacco	0.0–0.2	119	0	415	292	175
		0.2–0.4	143	0	345	316	196
2	3, forest	0.0–0.2	383	251	164	149	55
3	1, tobacco	0.0–0.2	148	100	313	360	81
		0.2–0.4	437	90	238	169	65
3	2, tobacco	0.0–0.2	204	65	314	315	102
		0.2–0.4	51	0	358	434	156
3	3, grassland	0.0–0.2	122	86	404	297	90
		0.2–0.4	75	0	453	358	114
3	4, grassland	0.0–0.2	151	273	294	223	59
4	1, tobacco	0.0–0.2	294	0	397	187	122
		0.2–0.4	151	231	352	156	109
4	2, tobacco	0.0–0.2	249	101	362	183	104
		0.2–0.4	156	130	362	212	139
4	3, tobacco	0.0–0.2	253	395	121	146	83
		0.2–0.4	176	302	220	191	110

Pebbles (>20 mm), gravel (2–20 mm), sand (2–0.05 mm), silt (0.05–0.002 mm), and clay (<0.002 mm). ^*Position: 1: upper slope, 2: mid slope, 3: lower slope, and 4: plateau.