Discussion

According to studies conducted by other authors (Zaeem et al., Reference Zaeem, Nadeem, Pham, Ashiq, Ali, Gillani, Moise, Elavarthi, Kavanagh, Cheema, Galagedara and Thomas2021; Demydas and Veiler, Reference Demydas and Veiler2022), legumes have greater concentrations of P, K, Ca and Mg compared to cereals. This is consistent with the results obtained in our own research. In the opinion of Schoebitz et al. (Reference Schoebitz, Castillo, Jorquera and Roldan2020), the cultivation of lupins increases acid phosphatase activity in the soil compared to the cultivation of cereals. Thus, legumes can recover P from inaccessible forms by secreting organic acids that lower the pH of the rhizosphere and release P from inaccessible compounds (Sammama et al., Reference Sammama, El Kaoua, Hsissou, Latique, Selmaoui and Alfeddy2021). The difference in P concentration in legumes compared to cereals, as stated by Stagnari et al. (Reference Stagnari, Maggio, Galieni and Pisante2017), may also be due to differences in root systems that have access to different soil layers and thus different forms of P. As claimed by Rengel and Damon (Reference Rengel and Damon2008), the efficiency of K uptake by plants depends on their ability to dissolve inaccessible forms into plant-available ones and their ability to transport them through the plasma membrane of root cells to other parts of the plant. According to the authors, this is important due to the fact that, K is transported to the roots by diffusion which is a slow process. In the opinion of Wong et al. (Reference Wong, Edwards and Barrow2000), on light soils, due to leaching, it is advantageous to grow plants that put down roots and uptake more K from deep in the soil profile and transport it to aboveground plant parts. Thus, it is advantageous to grow legumes with a long root system. Witter and Johansson (Reference Witter and Johansson2001) showed that deep-rooted legumes uptake greater amounts of K from the soil compared to plants with fibrous root systems. As Xue et al. (Reference Xue, Xia, Christie, Zhang, Li and Tang2016) stated, Ca uptake from the soil environment varies significantly among plant species, but legumes concentrate greater amounts of Ca compared to cereals. As stated by these authors, uptake of Ca by plants through compensatory proton release leads to soil acidification by rhizobium N₂ fixation in legume roots. Such soil acidification, as mentioned earlier, increases P availability to plants. As reported by Xie et al. (Reference Xie, Cakmak, Wang, Zhang and Guo2021) Mg, due to its highest hydrated ionic radius and correspondingly poor adsorption to soil colloids, is very susceptible to leaching. Therefore, it is reasonable to assume that legumes concentrate a greater amount of Mg compared to cereals due to their deeper developed root system. Farhat et al. (Reference Farhat, Elkhouni, Zorrig, Smaoui, Abdelly and Rabhi2016) additionally reports that Mg is the least absorbable nutrient. The authors attribute the low ability to concentrate Mg to both root tissues and other plant organs. This statement is confirmed in our own research, as among the minerals analysed, the concentration of Mg in the mixtures was the lowest. Xie et al. (Reference Xie, Cakmak, Wang, Zhang and Guo2021) also point to a reduction in Mg uptake by plants when K availability in the soil is high. In our study, the availability of K in the soil where the field experiment was conducted was relatively high. Thus, this could have been the reason for the relatively low Mg content in our own study compared to the studies of other authors (Gill and Omokanye, Reference Gill and Omokanye2018; Jakubus and Graczyk, Reference Jakubus and Graczyk2022). In our study, different levels of concentrations of the analysed macroelements was as follows K > Ca > P > Mg. Also other authors obtained an analogous relationship of macroelements content in other grain legume mixtures and pure sowings (Gill and Omokanye, Reference Gill and Omokanye2018; Turan et al., Reference Turan, Seydoşoğlu, Sevilmiş and Oluk2020; Ibrahim and El-Sawah, Reference Ibrahim and El-Sawah2022; Panasiewicz, Reference Panasiewicz2022).

In our research, harvesting narrowleaf lupine and spring triticale mixtures at the flat green pod stage of narrowleaf lupine resulted in a significant reduction in the content of P, K, Ca and Mg compared to mixtures harvested at the flowering stage of narrowleaf lupine. Other authors have also obtained a reduction in macroelements content in other legume and cereal crop mixtures harvested at later stages of plant development (Asci et al., Reference Asci, Acar and Arici2018; Peprah et al., Reference Peprah, Darambazar, Biligetu, Iwaasa, Larson, Damiran and Lardner2021; Bo et al., Reference Bo, Dong, Zhang, Soe Htet and Hai2022). According to Molla et al. (Reference Molla, Wondimagegn and Chekol2018), the decrease in macroelements content with plant maturation is related to natural dilution and movement of nutrients from the vegetative part to the root system. Other authors (Maillard et al., Reference Maillard, Diquélou, Billard, Laîné, Garnica, Prudent, Garcia-Mina, Yvin and Ourry2015; Etienne et al., Reference Etienne, Diquelou, Prudent, Salon, Maillard and Ourry2018) point out the remobilization of macroelements from the vegetative parts to the seeds with plant maturation. Thus, it is reasonable to assume that during seed formation with the simultaneous growth of biomass and low uptake of macronutrients by the root at this stage of growth (Etienne et al., Reference Etienne, Diquelou, Prudent, Salon, Maillard and Ourry2018) there is a reduction in the macroelements content of the total of the above-ground parts of the plants. In our study, the sensitivity of macroelements to percentage reduction in concentration with delayed harvest date was as follows: K > Ca > P > Mg.

The own research revealed an increase in the concentration of the analysed macroelements in the growing season with less total precipitation and high average temperature compared to seasons with greater total precipitation and lower average temperature. The results obtained in our own research are in line with the results obtained by other authors in studies on legume-cereal mixtures (Gill and Omokanye, Reference Gill and Omokanye2018; Turan et al., Reference Turan, Seydoşoğlu, Sevilmiş and Oluk2020). In the opinion of other authors (Bhattacharya, Reference Bhattacharya2021; Ghafar et al., Reference Ghafar, Akram, Saleem, Wang, Wijaya and Alyemeni2021; Wahab et al., Reference Wahab, Abdi, Saleem, Ali, Ullah, Shah, Mumtaz, Yasin, Muresan and Marc2022), water shortages change the architecture and morphology of crop roots. As stated by these authors, as a result of abiotic stresses, plants increase root mass, mainly by increasing root length. Thus, it can be assumed that as a result of water shortages, the deeper developed root systems of plants my access to greater amounts of minerals in the soil, and increased root mass allows uptake of greater amounts of minerals thereby increasing the concentration in vegetative parts. On the other hand, other authors (Kaushal and Wani, Reference Kaushal and Wani2016; Khatun et al., Reference Khatun, Sarkar, Era, Islam, Anwar, Fahad, Datta and Islam2021; Zeroual et al., Reference Zeroual, Baidani and Idrissi2023) report that plants, as a result of water stress, take up smaller amounts of macroelements from the soil environment. In addition, reported by many authors (Kamal et al., Reference Kamal, Gorafi, Abdelrahman, Abdellatef and Tsujimoto2019; Venugopalan et al., Reference Venugopalan, Nath, Sengupta, Pal, Banerjee, Banerjee, Chandran, Roy, Sharma and Hossain2022; Wahab et al., Reference Wahab, Abdi, Saleem, Ali, Ullah, Shah, Mumtaz, Yasin, Muresan and Marc2022), the effect of water shortages is a reduction in crop yields. Analysing the statements of other authors, it can be assumed that as a result of reduced development of vegetative parts of plants due to drought, despite the lesser uptake of macroelements from the soil, the dilution of these nutrients in the biomass will be less. Alghamdi (Reference Alghamdi2009) also came to similar conclusions. In our own study, the greatest percentage reduction as a result of great water availability was recorded for Mg, followed by Ca, K and the least for P concentration.

Green forage from mixtures of narrowleaf lupine and spring triticale reached the required P level of 1.6 g/kg DM for dry gestating beef cows. In contrast, only the green fodder obtained from spring triticale failed to meet the requirements for lactating cows at 2.6 g/kg DM (NRC, 2000). The K content of the green forage obtained from the crops analysed was well above the required value of 7.0 g/kg DM (NRC, 2000). Adequate Ca values for dry gestating beef cows (1.8 g/kg DM) and lactating cows (5.8 g/kg DM) (NRC, 2000) were also achieved by all crops. The suggested Mg content of 1.2 g/kg DM for dry gestating beef cow (NRC, 2000) was also met. In contrast, the requirement for lactating cows of 2.0 g/kg DM (NRC, 2000) was achieved only in the green forage derived from narrowleaf lupine. All other mixtures were below the suggested content.

Another study by the authors (Górski and Płaza, Reference Górski and Płaza2023) on the presented field experiment also revealed a high content of total carbohydrates, water-soluble carbohydrates, crude ash and crude fat in the green forage of mixtures of narrowleaf lupine with spring triticale. Similarly to the content of macroelements, the highest concentration of nutritive value components was revealed in mixtures with the highest proportion of narrowleaf lupine at sowing. As in the case of macroelements, also harvesting mixtures at a later developmental stage of narrowleaf lupin resulted in lower content of nutritive value components. Also, growing season conditions had an analogous effect on the content of nutritive value components as well as on the content of macroelements in green forage. A higher content of nutritive value components was obtained in a year with low total precipitation and high average temperature compared to seasons with higher total precipitation and lower average temperature.

Studies conducted by other authors (Ginwal et al., Reference Ginwal, Kumar, Ram, Dutta, Arjun and Hindoriya2019; Solangi et al., Reference Solangi, Gao, Solangi and Cao2021) on legumes and cereal crops showed greater uptake of minerals by legumes compared to cereals. This is consistent with the results obtained in our own studies. Legumes generally produce less aboveground biomass compared to cereals, but the greater macroelements content allows for higher uptake overall. In our study, the greatest uptake of P, K, Mg and Ca was obtained in a mixture with an equal proportion of both components. Mixtures of legumes and cereals make it possible to obtain significantly greater yields compared to pure sowing (Pflueger et al., Reference Pflueger, Redfearn, Volesky, Bolze and Stephenson2020; Bacchi et al., Reference Bacchi, Monti, Calvi, Lo Presti, Pellicanò and Preiti2021). According to the authors (Ajal et al., Reference Ajal, Jäck, Vico and Weih2021; Li et al., Reference Li, Wang, Bao, Sun, Yang, Wang, Wang, Wu, Liu, Tian, Wang, Li, Wang, Xia, Mei, Wang, Zhao, Yu, Zhang, Che, Gui, Callaway, Tilman and Li2021), it is due to better use of available resources, and positive interaction of plants grown in a mixture with each other. Thus, greater yields of green fodder from mixed crops guarantee the achievement of higher uptake of macroelements. This is confirmed by results obtained by other authors (Ginwal et al., Reference Ginwal, Kumar, Ram, Dutta, Arjun and Hindoriya2019; Arif et al., Reference Arif, Kumar and Pourouchottamane2022). Also, analysing the calculated correlation coefficient (Table 8), it can be concluded that the greatest correlation occurred between the dry matter yield of the mixtures and the uptake of macroelements. The correlation between macroelements content and uptake was much less, while for K it was not significant. The harvesting of mixtures at the later of the analysed development phases resulted in a significant increase in the uptake of the analysed macroelements. In the period from the flowering stage to the flat green pod stage, there is a significant increase in biomass (Gecaitė et al., Reference Gecaitė, Arlauskienė and Cesevičienė2021). Thus, in spite of a decrease in macroelements content in dry matter, there was an increase in the uptake of P, K, Ca and Mg. In our study, an approximately twofold increase in the uptake of all analysed macroelements was obtained. The greatest increase was recorded for Mg followed by P, Ca and K. In our study, the greatest uptake of macroelements was revealed in a year with deficient precipitation. Other authors point out less crop yield under water deficit conditions (Venugopalan et al., Reference Venugopalan, Nath, Sengupta, Pal, Banerjee, Banerjee, Chandran, Roy, Sharma and Hossain2022; Wahab et al., Reference Wahab, Abdi, Saleem, Ali, Ullah, Shah, Mumtaz, Yasin, Muresan and Marc2022), but in our study, a much greater macroelements content in dry matter compensated for less yield.

Table 8.

Correlation coefficients among dry matter yield, content and uptake P, K, Mg and Ca in narrowleaf lupin/spring triticale mixtures

* not significant.

In the feed provided to livestock, the interrelationship among the macroelements is as important as their content. In the opinion of Kumar and Soni (Reference Kumar and Soni2014), Ca and P metabolism are interrelated. In addition, as stated by the authors, Mg is related to the functions that Ca and P play in the livestock body. As stated by Turan et al. (Reference Turan, Seydoşoğlu, Sevilmiş and Oluk2020), the Ca/P ratio in livestock feed should be between 1 and 2, while K/(Ca + Mg) should be less than 2.2. According to Başbağ et al. (Reference Başbağ, Çaçan and Sayar2018) and Özyazıcı and Açıkbaş (Reference Özyazıcı and Açıkbaş2019), feeding livestock feeds with higher than optimal Ca/P before longer periods can lead to health disorders. On the other hand, as stated by Crawford et al. (Reference Crawford, Masie, Sleper and Mayland1998), too high K/(Ca + Mg) ratio in feed can lead to hypomagnesemia in livestock. In our study, all of the green feed samples analysed showed greater than optimal Ca/P ratios. Studies conducted by Turan et al. (Reference Turan, Seydoşoğlu, Sevilmiş and Oluk2020) on other legume-cereal mixtures also revealed excessively high Ca/P ratios. In this study, the increase in Ca/P in years with less water availability was due to a much greater increase in Ca content in dry matter in relation to P. In the case of harvesting mixtures at a later developmental stage of narrowleaf lupine, the reduction in Ca/P ratio was due to a greater reduction in Ca content in dry matter in relation to the reduction in P. Also Asci et al. (Reference Asci, Acar and Arici2018) in their study noted a reduction in Ca/P ratio in mixtures harvested at later developmental stages. In the presented study, also the K/(Ca + Mg) ratio in the green forage of all analysed samples was greater than optimal. Similar results were also obtained by Turan et al. (Reference Turan, Seydoşoğlu, Sevilmiş and Oluk2020) and Asci et al. (Reference Asci, Acar and Arici2018). In our own study, the lesser K/(Ca + Mg) ratio in the year with the highest total precipitation was due to a more intense reduction in K content in relation to Ca + Mg under conditions of optimal water availability. A similar relationship was observed as a result of harvesting mixtures at the later of the analysed development phases. On the other hand, the observed increase in the K/(Ca + Mg) ratio with increasing the proportion of spring triticale in the mixture with narrowleaf lupine can be attributed to a greater reduction of Ca + Mg in dry matter (especially Ca) in relation to K. Also, Asci et al. (Reference Asci, Acar and Arici2018) observed an increase in K/(Ca + Mg) with an increase in the proportion of the cereal crop in the mixture with the legume. However, the authors observed an increase in K/(Ca + Mg) when the crop was harvested at a later stage, which is not consistent with the results of their own study.