Jean-Pierre Destain

Influence of source and concentrations of dietary fiber on in vivo nitrogen excretion pathways in pigs as reflected by in vitro fermentation and nitrogen incorporation by fecal bacteria.

The inclusion of dietary fiber (DF) in diets has been suggested as a way to reduce NH(3) emission in pig barns because it contributes to a shift in N excretion from urine to feces owing to enhanced bacterial growth in the intestines. This study compared an in vitro method to measure bacterial protein synthesis during fermentation with an in vivo N excretion shift induced by diets differing in DF concentrations and solubility. The first experiment measured the effect of graded concentrations of sugar beet pulp (SBP; 0, 10, 20, and 30%) in corn- and soybean meal-based diets on in vivo N excretion partitioning between the urine and feces. A second experiment investigated the replacement of SBP, rich in soluble DF, with oat hulls (OH), rich in insoluble DF (20:0, 10.5:10.5, and 0:22%, respectively). In parallel, the fermentation characteristics of the dietary carbohydrates not digested in the small intestine were evaluated in an in vitro gas test, based on their incubation with colonic microbiota, using a mineral buffer solution enriched with (15)N. The N originating from the buffer solution incorporated into the bacterial proteins (BNI) was measured when half the final gas volume was produced (8.5 to 14.5 h of fermentation) and after 72 h of fermentation. Short-chain fatty acids were determined in the liquid phase. In the first experiment, the inclusion of SBP linearly decreased urinary N excretion from 0.285 to 0.215 g of N excreted in the urine per gram of N ingested and decreased the urinary-N:fecal-N excretion ratio from 2.171 to 1.177 (P < 0.01). In the second experiment, substituting SBP with OH linearly increased the urinary-N:fecal-N excretion ratio (P = 0.009). Unlike short-chain fatty acid production, BNI was greater at half-time to asymptotic gas production than at 72 h of fermentation. Sugar beet pulp enhanced BNI linearly (P < 0.001), 2.01, 2.06, and 2.35 mg g(-1) of diet with 10, 20, and 30% SBP, respectively, as compared with 1.51 mg for the control diet. The substitution of SBP with OH decreased BNI (P < 0.01). With the exception of final gas production, all in vitro kinetic characteristics and BNI were correlated with in vivo N excretion parameters, and regression equations for the prediction of N excretion pathways from in vitro data were identified. Even if the presence of resistant starch in the diet might alter the composition of the fibrous residue that is fermented, the in vitro method is a possible useful tool for the formulation of diets, reducing the effects of pig production on the environment.

The source of fermentable carbohydrates influences the in vitro protein synthesis by colonic bacteria isolated from pigs

Two in vitro experiments were carried out to quantify the incorporation of nitrogen (N) by pig colonic bacteria during the fermentation of dietary fibre, including non-starch polysaccharides and resistant starch. In the first experiment, five purified carbohydrates were used: starch (S), cellulose (C), inulin (I), pectin (P) and xylan (X). In the second experiment, three pepsin-pancreatin hydrolysed ingredients were investigated: potato, sugar-beet pulp and wheat bran. The substrates were incubated in an inoculum, prepared from fresh faeces of sows and a buffer solution providing 15N-labelled NH4Cl. Gas production was monitored. Bacterial N incorporation (BNI) was estimated by measuring the incorporation of 15N in the solid residue at half-time to asymptotic gas production (T/2). The remaining substrate was analysed for sugar content. Short-chain fatty acids (SCFA) were determined in the liquid phase. In the first experiment, the fermentation kinetics differed between the substrates. P, S and I showed higher rates of degradation (P < 0.001), while X and C showed a longer lag time and T/2. The sugar disappearance reached 0.91, 0.90, 0.81, 0.56 and 0.46, respectively, for P, I, S, C and X. Among them, S and I fixed more N per gram substrate (P < 0.05) than C, X and P (22.9 and 23.2 mg fixed N per gram fermented substrate v. 11.3, 12.3 and 9.8, respectively). Production of SCFA was the highest for the substrates with low N fixation: 562 and 565 mg/g fermented substrate for X and C v. 290 to 451 for P, I and S (P < 0.01). In the second experiment, potato and sugar-beet pulp fermented more rapidly than wheat bran (P < 0.001). Substrate disappearance at T/2 varied from 0.17 to 0.50. BNI were 18.3, 17.0 and 10.2 fixed N per gram fermented substrate, for sugar-beet pulp, potato and wheat bran, respectively, but were not statistically different. SCFA productions were the highest with wheat bran (913 mg/g fermented substrate) followed by sugar-beet pulp (641) and potato (556) (P < 0.05). The differences in N uptake by intestinal bacteria are linked to the partitioning of the substrate energy content between bacterial growth and SCFA production. This partitioning varies according to the rate of fermentation and the chemical composition of the substrate, as shown by the regression equation linking BNI to T/2 and SCFA (r2 = 0.91, P < 0.01) and the correlation between BNI and insoluble dietary fibre (r = -0.77, P < 0.05) when pectin was discarded from the database.

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

Labelled fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 at a total N dressing of 100kg ha−1 was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering.Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO3 and 32.3%, 48.4% and 52.5% for the NH4 carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO3 and 51.7%, 63.5% and 66.1% for the NH4 carrier.A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages.The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO3−N and to 22.5%, 12.7% and 15.2% of the applied NH4−N for the respective split applications.No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.

Fertilizer nitrogen budgets of two doses of Na15NO3 dressings split-applied to winter wheat in microplots on a loam soil

In a field experiment performed in microplots, winter wheat was fertilized at two different total N dressings (135 and 180 kg ha−1) split-applied as Na15NO3 in three equal applications at tillering, stem elongation, and flag leaf.No significant differences were found in the percentage recovery values for the entire plant at the three split applications between the two N dressings. The total percentage recovery of fertilizer N by the plant was high and practically equal at both fertilization levels (76.65% and 75.84% for 135 and 180 kg N ha−1, respectively); crop yields were also similar. In contrast, gaseous losses calculated after drawing up the balance sheet were, in absolute values, higher for the tillering and stem elongation split applications when using the 180 kg N ha−1 dressing (7.67 and 4.84 kg N ha−1, respectively) than for the 135 kg N ha−1 dressing (3.45 and 1.26 kg N ha−1, respectively). They were found to be zero at flag leaf at both fertilization levels. The amount of applied fertilizer N did not influence the amount of N taken up from the soil which was about 143 kg ha−1.

Fate of nitrogen fertilizer applied on two main arables crops, winter wheat ( Triticum aestivum ) and sugar beet ( Beta vulgaris ) in the loam region of Belgium

Since 1986, the fate of fertilizer N (NH4NO3 or NaNO3) applied in field conditions on two main arable crops, winter wheat (Triticum aestivum) and sugar beet (Beta vulgaris), has been studied using 15N. Up to a rate of 200 kg ha-1 of N, mean recovery of fertilizer by winter wheat was 70%, provided it had been split applied. Single application (with or without dicyandiamid) was less effective. For sugar beet, in 1990, 1991 and 1992, 40% of fertilizer N was found in the crop at harvest when NH4NO3 had been broadcast at 100 to 160 kg N ha-1 at sowing time. For the same N rate, recovery was 50% when row applied near the seeds and 60% for 80 kg N ha-1. For the two experimental crops, residual fertilizer N in soil was exclusively organic. It ranged from 15 to 30% of applied N and was located in the 30 cm upper layer. Losses were generally lower with winter wheat (12%) than with sugar beet (20–40%) and could be ascribed to volatilization and denitrification. Soil derived N taken up by the plant was site and year dependent.

Fertilizer nitrogen budgets of 15N-labelled sugarbeet (Beta vulgaris) tops and Na15NO3 dressings split-applied to winter wheat (Triticum aestivum) in microplots on a loam soil

The fate of N from sugarbeet (Beta vulgaris L.) tops returned to the soil (50 T ha-1) in autumn 1986 before sowing winter wheat (Triticum aestivum L.), and from NaNO3 split-applied in 3 equal dressings (at tillering, stem elongation and flag leaf stages) was studied using isotopically labelled 15N in open stainless-steel cylinders pressed into the soil.At harvest, the percentage utilization (PU) of N from sugarbeet was very low (6.66%) and negatively influenced by fertilizer N (5.59%), while that of fertilizer N was rather high (69.64%) and unchanged by addition of tops. Residual N in soil represented 25.9% of the amount applied in tops and ranged from 33% for the tillering application to 21% for the flag leaf application. N losses (mainly denitrification) from sugar beet tops amounted to 67% and were very low for mineral fertilizer (less than 5%).

Assessing and modeling economic and environmental impact of wheat nitrogen management in Belgium

Future progress in wheat yield will rely on identifying genotypes and management practices better adapted to the fluctuating environment. Nitrogen (N) fertilization is probably the most important practice impacting crop growth. However, the adverse environmental impacts of inappropriate N management (e.g., lixiviation) must be considered in the decision-making process. A formal decisional algorithm was developed to tactically optimize the economic and environmental N fertilization in wheat. Climatic uncertainty analysis was performed using stochastic weather time-series (LARS-WG). Crop growth was simulated using STICS model. Experiments were conducted to support the algorithm recommendations: winter wheat was sown between 2008 and 2014 in a classic loamy soil of the Hesbaye Region, Belgium (temperate climate). Results indicated that, most of the time, the third N fertilization applied at flag-leaf stage by farmers could be reduced. Environmental decision criterion is most of the time the limiting factor in comparison to the revenues expected by farmers. The economic and environmental impact of Nitrogen fertilization was evaluated.A complete and generic methodology for tactical N optimization is proposed.Climatic conditions occurring between sowing and flag leaf stage greatly impacts N optimization.Environment?× management interactions have to be considered when optimizing N.Environmental consideration is a more limiting factor than expected revenues for N optimization.

Yield variability linked to climate uncertainty and nitrogen fertilisation

At the parcel scale, crop models such as STICS are powerful tools to study the effects of variable inputs such as management practices (e.g. nitrogen (N) fertilisation). In combination with a weather generator, we built up a general methodology that allows studying the yield variability linked to climate uncertainty, in order to assess the best N practice. Our study highlighted that, applying the Belgian farmer current N practice (60-60-60 kg N/ha), the yield distribution was found to be very asymmetric with a skewness of -1.02 and a difference of 5% between the mean (10.5 t/ha) and the median (11.05 t/ha) of the distribution. This implies that, under such practice, the probability for farmers to achieve decent yields, in comparison to the mean of the distribution, was the highest.

Uptake and efficiency of split applications of nitrogen fertilizer in winter wheat

In Belgium, nitrogen fertilizer (140–220 kg N ha-1) is applied to winter wheat in split applications at growth stages GS25, 30 and 37. The aim of this work was to compare the efficiency of the last application (GS37) with that of the preceding ones (GS25 and 30) and to measure the uptake of applied N using 15N. Increasing the rate of the GS37 application from 20 to 100 kg ha-1 N raised grain yield by 1000 kg ha-1; efficiency remained almost unaffected (31 kg and 26 kg grain per kg N, respectively), while N recovery in whole plant was highest (77.5%) at 100 kg ha-1, as was grain quality. Conversely, increasing the rate of application at GS25 did not affect yield, and N efficiency plummeted (from 21 kg to 12 kg).

A screening technique to isolate bacterial strains producing high molecular weight bacteriocins

Bacterial strains producing high molecular weight bacteriocins can be easily and rapidly screened in two-steps procedure. The first one uses the lyspgenic property of bacteriocin production and the identification of the lysogenic cells by simple colorimetric detection of alkaline phosphatase in the culture medium after mitomycin C treatment The presence of high molecular weight bacteriocins is determined in the second step by examination in transmission electron microscopy. This procedure is tested with 302 different strains, 3 of them are identified as high molecular weight bacteriocins producers.