Nitrogen budget in a soil-plant system after brachiaria grass desiccation

Figures & data

Figure 1 Root dry matter of palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf) (□), signalgrass (Brachiaria decumbens Stapf) (▲), humidicola (Brachiaria humidicola (Rendle) Schweick) (○) and Congo grass (Brachiaria ruziziensis Germain et Evrard) (●) as affected by time after desiccation with glyphosate. ns = non significant, * = significant (F test, P > 0.05) and ** = significant (F test, P > 0.01). Vertical bar indicates least significant difference (LSD) comparing species (P > 0.05).

Figure 2 Total nitrogen (Total-N) concentration in (a) shoot and (b) roots of brachiaria grasses as affected by time after desiccation with glyphosate (mean of four species: palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard)). ** = significant (F test, P > 0.01).

Figure 3 Nitrogen (N) accumulated in (a) shoot and (b) roots in palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf) (□), signalgrass (Brachiaria decumbens Stapf) (▲), humidicola (Brachiaria humidicola (Rendle) Schweick) (○) and Congo grass (Brachiaria ruziziensis Germain et Evrard) (●) as affected by time after desiccation with glyphosate. ns = non significant, * = significant (F test, P > 0.05) and ** = significant (F test, P > 0.01). Vertical bar indicates least significant difference (LSD) comparing species (P > 0.05).

Figure 4 Total nitrogen (Total-N) concentration in soil as affected by time after brachiaria grasses desiccation with glyphosate (mean of four species: palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard)). ** = significant (F test, P > 0.01).

Figure 5 Ammonium (NH₄⁺) concentration in brachiaria grasses shoot as affected by time after desiccation with glyphosate (mean of four species: palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard)). ** = significant (F test, P > 0.01).

Figure 6 Temporal variation of ammonia (NH₃-N) emission by shoot of palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf) (□), signalgrass (Brachiaria decumbens Stapf) (▲), humidicola (Brachiaria humidicola (Rendle) Schweick) (○) and Congo grass(Brachiaria ruziziensis Germain et Evrard) (●) as affected by time after desiccation with glyphosate. ns = non significant, ** = significant (F test, P > 0.01). Vertical bar indicates least signficant difference (LSD) comparing species (P > 0.05).

Figure 7 Accumulated emission of ammonia (NH₃-N) by shoot of palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf) (□), signalgrass (Brachiaria decumbens Stapf) (▲), humidicola (Brachiaria humidicola (Rendle) Schweick) (○) and Congo grass (Brachiaria ruziziensis Germain et Evrard) (●) as affected by time after desiccation with glyphosate. * = significant (F test, P > 0.05) and ** = significant (F test, P > 0.01). Vertical bar indicates least signficant difference (LSD) comparing species (P > 0.05).

Table 1 Nitrogen (N) budget in roots, shoot and entire plant after palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard) desiccation with glyphosate

Species	N amount
	0 DAD	28 DAD	Budget
	- - - - - - g per pot - - - - - -
Palisade grass	0.24	0.12	−0.12
Signalgrass	0.15	0.12	−0.04
Humidicola	0.08	0.04	−0.04
Congo grass	0.24	0.15	−0.10
LSD (P < 0.05)	0.05	0.05	0.07
	in shoots
Palisade grass	0.90	0.60	−0.30
Signalgrass	1.02	0.74	−0.28
Humidicola	0.64	0.40	−0.24
Congo grass	1.32	0.80	−0.52
LSD (P <0.05)	0.14	0.14	0.24
	in entire plants (shoot + roots)
palisade grass	1.14	0.73	−0.41
signalgrass	1.17	0.86	−0.31
humidicola	0.72	0.44	−0.28
Congo grass	1.56	0.95	−0.61
LSD (P < 0.05)	0.17	0.15	0.28

DAD, days after dessication; LSD, least significant difference.

Table 2 Nitrogen (N) budget in soil after palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard) desiccation with glyphosate

Species	N accumulated in soil†
	0 DAD	28 DAD	Budget
	- - - - - -g per pot - - - - - -
Palisade grass	14.25	14.48	0.23
Signalgrass	14.29	14.52	0.23
Humidicola	14.22	14.43	0.21
Congo grass	14.29	14.68	0.39
LSD (P <0.05)	0.36	0.36	0.16

^†12.6 kg of soil. DAD, days after dessication; LSD, least significant difference.

Table 3 Nitrogen (N) budget in soil-plant system after palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard) desiccation with glyphosate

	N in soil‒plant system			N losses from soil‒plant system
Species	0 DAD	28 DAD	Budget	NH3-N	Unaccounted
	- - - - - - - - - - - -g per pot- - - - - - - - - - - -
Palisade grass	15.39	15.21	−0.18	0.054	−0.129
Signalgrass	15.45	15.38	−0.08	0.033	−0.044
Humidicola	14.93	14.87	−0.06	0.048	−0.016
Congo grass	15.85	15.62	−0.22	0.078	−0.142
LSD (P < 0.05)	0.31	0.33	0.06	0.006	0.067

DAD, days after dessication; LSD, least significant difference.

Table 4 Estimated nitrogen (N) losses from the soil-plant system 28 days after palisade grass (Brachiaria brizantha (Hochst. ex A. Rich) Stapf), signalgrass (Brachiaria decumbens Stapf), humidicola (Brachiaria humidicola (Rendle) Schweick) and Congo grass (Brachiaria ruziziensis Germain et Evrard) desiccation with glyphosate, under greenhouse conditions, with average maximum temperature of 34.3°C and average minimum temperature of 20.8°C. Averaged over four replicates. Applied N rate equivalent to 60 g m⁻²

			N loss^†
Species	Shoot dry matter	N accumulated in shoots	Shoot	System	NH3
- - - - - -g m^−2- - - - - -			- - - - - -g m^−2 kg^−1- - - - - -
Palisade grass	1213	28.6	7.9	4.7	1.4
Signalgrass	1394	32.5	6.4	1.8	0.8
Humidicola	748	20.3	10.2	2.6	2.0
Congo grass	1757	42.0	9.4	4.0	1.4

^†N losses were estimated as g N lost per square meter per kg of shoot dry matter. NH₃, ammonia.