Table 4.
Effect of calcium magnesium carbonate and calcium magnesium hydroxide on N metabolism in a continuous culture system
| Variable | Treatment meansg | P-value Orthogonal contrasts | ||||||
|---|---|---|---|---|---|---|---|---|
| Control | CO3 | OH | CO3/OH | SEM | Trth | [CaMg(CO3)2]i | [CaMg(OH)4]j | |
| NH3-N, mg/dL | 17.6 | 16.0 | 17.2 | 16.5 | 1.06 | 0.44 | 0.17 | 0.41 |
| N flows, g/d | ||||||||
| Total N | 3.06 | 2.87 | 3.14 | 2.99 | 0.13 | 0.49 | 0.43 | 0.95 |
| NH3-Na | 0.71 | 0.65 | 0.69 | 0.67 | 0.04 | 0.49 | 0.18 | 0.43 |
| NANb | 2.35 | 2.22 | 2.45 | 2.33 | 0.12 | 0.59 | 0.62 | 0.77 |
| Bacterial Nc | 1.31 | 1.14 | 1.34 | 1.14 | 0.06 | 0.06 | 0.04 | 0.31 |
| Dietary Nd | 1.03 | 1.08 | 1.11 | 1.19 | 0.08 | 0.53 | 0.29 | 0.23 |
| ENUe | 47.4 | 41.0 | 48.3 | 40.7 | 3.01 | 0.12 | 0.06 | 0.35 |
| Bacterial efficiencyf | 20.4 | 17.9 | 20.8 | 18.1 | 1.14 | 0.14 | 0.08 | 0.44 |
aNH3-N (g/d) = mg/dL of effluent NH3-N × (g of total effluent flow/100).
bNAN = nonammonia N flow (g/d) = g of effluent N − g of effluent NH3-N.
cBacterial-N flow (g/d) = (NAN flow × atom percentage excess of 15N of effluent)/(atom percentage excess of 15N of bacteria), according to Calsamiglia et al. (1996).
dDietary N flow (g/d) = g of effluent NAN − g of effluent bacterial N.
eENU = efficiency of N use = (g of bacterial N/g of available N) × 100 (Bach and Stern, 1999).
fBacterial efficiency = g of bacterial N flow/kg of OM truly digested, according to Calsamiglia et al. (1996).
gExperimental treatments based on supplemental source of Mg: “Control” = 100% as MgO + sodium sesquicarbonate added as a buffer; “CO3” = 100% as CaMg(CO3)2; “OH” = 100% as CaMg(OH)4; “CO3/OH” = 50% as CaMg(CO3)2/50% as CaMg(OH)4. Means with different superscript within the same row are statistically different (P ≤ 0.05).
hTrt: effect of experimental treatment.
i[CaMg(CO3)2] = (CO3 + CO3/OH) vs. Control.
j[CaMg(OH)4] = (OH + CO3/OH) vs. Control.