The effect of soil conditioners on the content of soluble carbohydrates, digestible protein and the carbohydrate–protein ratio in Lolium perenne and Dactylis glomerata

At present, there are a growing number of conscious consumers who pay attention to the way the food is produced and to its ingredients. The consumer of animal products wants to know what animals have been fed with and in what conditions they have been kept. The efforts to meet the growing demand for food, without sacrificing its quality, are based on looking for new solutions supporting various types of production. Healthy food is one of the objectives of intensely developing organic farming. In such farming, high-quality forage is needed to feed animals. On the market, there are many products now aimed at improving the quality of the feed authorised for use in this type of production. The composition of additives such as soil conditioners is based on microorganisms, seaweed extracts or humus [Higa and Parr 1994, Rathore et al. 2009, Szczepanek and Wilczewski 2011, Sosnowski 2012a, Truba et al. 2012].

There have been a number of studies on the effect of soil conditioners on the concentration of carbohydrates, digestible protein and carbohydrate–protein ratio, but they dealt mainly with UGmax, a soil conditioner, applied to Lolium multiflorum and Festulolium brauni [Sosnowski 2012b, Sosnowski and Jankowski 2013]. However, there has not been enough research on other soil conditioners and their effect on grass species. Owing to their different ability to produce considerable amounts of total protein and soluble carbohydrates, Dactylis glomerata and Lolium perenne were chosen for the present experiment [Downing and Gamroth 2007, Ghesquiere et al. 2016].

The aim of the research was to study the effect of soil conditioners, UGmax, Eko-Użyźniacz and Humus Active, used on their own and together with mineral fertilisers, on the content of soluble carbohydrates, digestible protein and the carbohydrate–protein ratio in the forage of L. perenne and D. glomerata.

A three-year field experiment (52.169°N, 22.280°E), in which each treatment was replicated three times, was set up in a randomised split-plot design in the autumn of 2011. A plot of 3 m² constituted an experimental unit. The main experimental factors were the soil conditioners with the trade names such as UGmax, Eko-Użyźniacz and Humus Active Papka; these were used alone or in combination with mineral fertiliser such as nitrogen-phosphorus-potassium (NPK).

The experimental design included

Control plot (no treatment),

The composition of the soil conditioners is presented in Table 1. The conditioners were applied every year at the beginning of the growing season in the following doses: UGmax, 0.6 l·ha⁻¹; Eko-Użyźniacz, 15 l·ha⁻¹; Humus Active Papka, 50 l·ha⁻¹. Mineral fertiliser such as NPK was used in the following doses: N, 150 kg·ha⁻¹; P, 80 kg P₂O₅·ha⁻¹; K, 120 kg K₂O·ha⁻¹.

Table 1

Ingredients of the soil conditioners.

According to the Polish classification system [2011], the soil on which the experiment was carried out was of the order of anthrosole, the type of culture soils, the subtype of hortisole, formed from light loamy sand (Table 1). Its chemical analysis showed that the concentration of organic carbon (C_org) was 13.50 g·kg⁻¹ DM, total nitrogen was 1.30 g·kg⁻¹ DM and soil pH was 6.8. The total concentration of macroelements was high: P, 0.75 g·kg⁻¹ DM; K, 1.12 g·kg⁻¹ DM; Ca, 1.80 g·kg⁻¹ DM; Mg, 1.20 g·kg⁻¹ DM; Na, 0.15 g·kg⁻¹ DM, with the following concentration of microelements: Fe, 4,562.80 mg·kg⁻¹ DM; Mn, 156.20 mg·kg⁻¹ DM; Cu, 5.60 mg·kg⁻¹ DM; Zn, 14.50 mg·kg⁻¹ DM. The soil had very high amounts of available phosphorus (P = 170.00 mg·kg⁻¹ DM) and available magnesium (Mg = 84.00 mg·kg⁻¹ DM) but moderate concentration of potassium (K = 114.00 mg·kg⁻¹ DM). Before the experiment was established, the soil was collected from a depth of about 20 cm. Soil analysis was performed at the National Chemical-Agricultural Station in Warsaw.

Sielianinov’s hydrothermal coefficient [Skowera and Puła 2004] (Table 2) showed changing weather conditions during the growing seasons of the experiment. In the first year of the experiment (2012), the optimal weather conditions and optimal soil moisture were observed only in June and October, with drought to extreme drought throughout the rest of the season. In the next experimental years, dry periods were followed by wet ones, with the best conditions only in April 2013, July 2013, and April 2014. Generally, every year, the conditions were better during the first few months of the experiment. Throughout the experiment, during 33.3% of the growing seasons, there were extreme weather conditions, mainly from July to September, ranging from severe or strong drought to wet and very wet periods.

Table 2

Sielianinov’s hydrothermal coefficient (K) values during the growing season.

Total protein and soluble carbohydrate content in DM were measured with near-infrared spectroscopy (NIRS), using the NIRFlex N-500 spectrometer, with the INGOT calibration package for dry feed. Digestible protein content was determined using the total protein content and the following formula [Kolczarek et al. 2008]:

Digestibleprotein=−<!-- - -->29.78+9.56⋅totalprotein(%DM)$$\begin{array}{} \displaystyle \rm{Digestible\,\, protein = -29.78 + 9.56 \cdot\, total\,\, protein (\text {%} DM)} \end{array}$$

The results were processed statistically with the multifactor analysis of variance with a significance level of P≤0.05, whereas the differences between means were verified with Tukey’s test. The Statistica 12 program was used to perform all the calculations.

The application of soil conditioners did not considerably lower the soluble carbohydrate content in the grass, which is why they can be applied to grass, especially on organic farms, where too high doses of mineral fertilisers are unacceptable. Interesting is the fact that the application of UGmax in combination with mineral fertilisers did not result in a significant decrease in carbohydrate content. In literature, there are reports that increasing nitrogen doses reduce non-structural carbohydrate content [Grygierzec 2008, Lattanzi et al. 2012, Conaghan et al. 2012]. It can, therefore, be assumed that this soil conditioner can minimise the negative effect of mineral fertiliser on carbohydrate level in plants. The results indicated that soluble carbohydrate content in the grass decreased with successive years of the research, which is supported by literature [Muller and Janicke 2015]. The exception was D. glomerata, which maintained similar amounts of carbohydrates through all the years of the experiment (43.3–48.7 g·kg⁻¹). As mentioned by Turner et al. [2012], L. perenne is a species sensitive to water stress and in the case of drought quickly loses its soluble carbohydrates.

According to Miller et al. [2001], Downing and Gamroth [2007], Farrar et al. [2012], Baert and Van Waes [2014], L. perenne is considered to be a species with a high content of soluble carbohydrates. This was confirmed by the results of the present experiment, showing that the species contains about one-third of carbohydrates more than D. glomerata. The difference in non-structural carbohydrate content between separate harvests was approximately 28% and decreased with the next grass harvest. Lessire et al. [2014] also observed declining amounts of carbohydrates in consecutive harvests. According to Watts [2008], this phenomenon could be caused by more intensive plant breathing, with rising temperature in the second half of the growing period.

The average digestible protein content in each year of research was different. The cause of this diversity can be attributed to different weather conditions in different growing seasons. Throughout the three growth cycles, in the first year of the experiment, the value of the hydrothermal coefficient indicated periods varying from moderate drought to severe drought, which negatively affected digestible protein content. In the second year of the research, the conditions were either wet or optimal, which in turn affected the increase in protein content in the forage. In the last year, droughts were followed by wet periods and protein content was lower than that in the previous year (2013).

As shown by the results of the research, the best carbohydrate-to-protein ratio was in the forage from plots where UGmax (0.49) or NPK fertiliser (0.40) or a combination of both (0.40) was applied. Sosnowski [2012b] observed similar results in an experiment with another species of grass, F. brauni, in which the ratio was higher when a soil conditioner was used alone or together with mineral fertiliser. According to Baert and Van Waes [2014], soluble carbohydrates have a positive impact on protein digestibility, reducing the amount of lost nitrogen.

Compared to the control, soil conditioners (UGmax, Humus Active Papka and Eko-Użyźniacz) did not reduce carbohydrate content in grass significantly. This proves that they can be applied to grass.