The effect of time of winter urine deposition on mineral nitrogen leaching and implications for grazed forage crops

Figures & data

Table 1. Monthly rainfall and average monthly air temperature, compared with the 30-year (1980–2010) long-term average (LTA).

Figure 1. Soil solution ammonium-N (NH₄-N) and nitrate-N (NO₃-N) concentrations during winters 2012 and 2013, after simulation of forage crop grazing in winter 2012. The break in plotted lines denotes the spring/summer of 2012/2013. Treatments denote June or July applied urine, with or without dicyandiamide (DCD) application. Error bars represent the standard error of the mean.

Figure 2. Soil solution ammonium-N (NH₄-N) and nitrate-N (NO₃-N) concentrations during winters 2012 and 2013 after simulation of pasture grazing in winter 2012. The break in plotted lines denotes the spring/summer of 2012/2013. Treatments denote June or July applied urine, with or without dicyandiamide (DCD) application. Error bars represent the standard error of the mean.

Table 2. Measured soil mineral N content (kg N ha⁻¹) at the end of drainage, 2012.

Depth	Urine timing			DCD effect			Timing × DCD
(mm)	Early	Late	P value	−DCD	+DCD	P value	E − DCD	E + DCD	L − DCD	L + DCD	P value
Forage crop
0–150	14	56	Lg***	30	40	Lg*	9	19	51	60	Lg*
150–300	37	115	Lg***	72	79	Lg*	25	49	120	110	Lg**
300–600	120	131	Lg ns	118	133	Lg ns	98	142	138	125	Lg*
Total	170	302	21.8***	220	252	21.8 ns	131	209	308	295	30.9*
Pasture
0–150	21	26	Lg*	22	25	Lg ns	20	22	23	28	Lg ns
150–300	19	28	Lg ns	18	29	Lg ns	14	24	22	33	Lg ns
300–600	109	144	Lg*	116	138	Lg ns	93	125	138	150	Lg ns
Total	149	198	22.7*	155	192	22.7 ns	127	172	183	212	32.1 ns

Notes: Individual soil horizons required log transformation before analysis of variance (‘Lg’).Total mineral N (0–600 mm) did not require transformation, and the standard error of the difference is included as well as level of significance. For the individual horizons, arithmetic means are provided but level of significance is based on log transformation.

***<.001; **<.01; *<.05; after log transformation.

Table 3. Estimated leaching of mineral N (kg N ha⁻¹).

Year	Urine timing			Back-transformed means with bias correction
	Early	Late	P value	Early urine		Late urine		LSR
				−DCD	+DCD	−DCD	+DCD
Forage crop
2012	183	57	***	179	195	67	39	1.7
2013	84	118	ns	74	107	109	114	1.9
Total	267	175	***	248	297	191	147	1.4
Pasture
2012	185	66	***	193	185	68	58	1.8
2013	54	82	*	24	79	78	88	2.4
Total	239	148	**	212	259	144	158	1.5

Notes: Log transformation was required before analysis of variance. Arithmetic means are provided as well as back-transformed values. LSR = least significant range.

***< .001; **< .01; *< .05; after log transformation.

Table 4. A partial nitrogen (N) balance at the end of drainage 2012 based on measured N leached and soil mineral N.

Treatment	Mineral N
	Leached	Soil	Total
Forage crop
Early	183 ± 11.1	170 ± 14.6	353 ± 20.5
Late	57 ± 12.9	302 ± 15.2	359 ± 20.6
Pasture
Early	185 ± 1.8	149 ± 17.1	334 ± 22.5
Late	66 ± 20.3	195 ± 17.1	264 ± 24.2

Note: All DCD treatments are included (i.e. 16 replicates per value).