Nemeikšienė D.¹, Arlauskienė A.¹, Šlepetienė A.²

Role of biological nitrogen in legume based cropping systems

¹Joniškėlis Experimental Station, ²Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry

Abstract. The current paper presents the effects of perennial grasses (Trifolium pratense L., Medicago sativa L., x Festulolium ) as preceding crops for winter cereal  their aboveground biomass management methods (removed from the field, mixed, mulched) on nitrogen balance under organic farming conditions. Field experiments were carried out at the Joniškėlis Experimental  Station of the Lithuanian Research Centre for Agriculture and Forestry on an Endocalcari-Endohypogleyic Cambisol (CMg-n-w-can). Application of aboveground mass of legumes or their mixtures with festulolium for the manure determined the positive nitrogen balance and higher total nitrogen accumulation in soil in crop rotation part: legumes (or legumes / festulolium) – winter wheat – winter triticale.

Key words: perennial legume; green manure; nitrogen.

Introduction. Nitrogen is an important and in many cases yield limiting nutrient. Nitrogen, within the system of ecologic farming is collected by applying aids of the crop rotation for the regeneration of the soil productivity by cultivating legumes and cover crops for the green manure, by applying farmyard manure. Many literature sources suggest that plant residues and farmyard manure helps to maintain the nutrients’ balance in the farm but the only true import of N comes from imported manures from outside of the holding and by fixation of atmospheric N₂ by legumes defines that within the crop rotation, the more valuable are such legume crops, which gather N in plants’ residues more rather than in the above-ground mass, i.e. they have the low N harvest index [2, 3]. Therefore, in order to enrich the soil with higher amount of the biological N (especially in ecological low-specialised arable farm) it would be useful to apply the aboveground mass of legumes for the green manure. A green manure is a crop used primarily as a soil amendment and a nutrient source for subsequent crops [4]. In temperate conditions, crops cultivated for the green manure usually are: clovers (Trifolium), vetchs (Vicia), lucerne (Medicago), lupins (Lupinus). Perennial legume crops offer the higher above-ground mass yield and have high N₂ fixing capacity, if compared to annual [5]. Researchers indicate that the green manure which has a high level of nitrogen > 2.0–2.5% (C: N ration is approximately 20) initiate the division during the first week after the incorporation. The nitrogen release from incorporated organic manure is determined by the granulometric soil composition, microbiological activeness, environment conditions, temperature, moisture. Within the sequence of crops from legumes to non-legumes, it is important to assess the synchronic features of nitrogen release from the incorporated crops’ residues or green manure and need for nitrogen of cultivated crops. Aim of researches is to identify the effect of biomass of perennial legumes, applied for the green manure on the accumulation of biologically fixed nitrogen and for the crop rotation nitrogen balance of: legumes (or legumes / festulolium) – winter wheat – winter triticale – in clay loam Cambisol.

Materials and methods. Experiments were set up in 2007–2010 at the Joniskelis Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry on an Endocalcari-Endohypogleyic Cambisol, the texture of which is clay loam on silty clay with deeper lying sandy loam. Agrochemical characteristics of the plough layer: pHKCl – 6.4, mobile P₂O₅ and K₂O – respectively 154 and 224 mg kg^-1 of soil, N_sum. – 0.135%, C_org. – 1.68%.  Research was performed in such part of the crop rotation: perennial grasses – winter wheat – winter triticale. Factor A – perennial grasses: 1) festulolium (x Festulolium ) (F), 2) red clover (Trifolium pratense L.) (RC), 3) mixture of red clover and festulolium (RC+F), 4) lucerne (Medicago sativa L.) (L), 5) mixture of lucerne and festulolium (L+F); factor B – management methods of aboveground mass of perennial grasses: 1) removed from the field, 2) mixed method (the first grass was removed from field, second and third – mulched), 3) mulching. Aboveground mass for green manure was cut by a self–propelled mower, equipped with a mulching device, then chopped and evenly spread on the plot. In the second half of August, the plots of all treatments were disked and 2 weeks later were ploughed at the 25 cm depth. In 2009 growing winter wheat (Triticum aestivum L.), in 2010 – winter triticale (x Triticosecale Wittm.). Ecological winter cereal cultivation technology was applied. Soil samples for the determination of N_total content were collected from the 0–25 cm layer before experiment establishment and at the end of experiment. N_total was determined by Kjeldahl method. Elementar analyzer “Vario EL” and “Carry 50” were used for the determination of nitrogen in biomass of perennial grasses and cereal grains. Soil and plants’ analysis were performed in Laboratories of Chemical Researches at Institute of Agriculture Lithuanian Research Centre for Agriculture and Forestry. Nitrogen content fixed from the atmosphere (BNF = N_2fix, kg ha^-1) in legume biomass was calculated using the method of difference. The experimental data were processed by the analysis of variance and correlation-regression analysis methods using a software package “Selekcija”.

Results and discussion. Incorporated in the soil nitrogen content was significantly dependent upon species of perennial grasses and ways of applying their aboveground mass. Major nitrogen content passed to soil after ploughing biomass of pure legumes sward (Table 1). Cultivation of legumes in mixtures with festulolium had a characteristic to reduce the nitrogen content, incorporated to soil. Significantly lower nitrogen content incorporated to soil together with biomass of pure festulolium, averagely 3.2 and 3.4 times less if compared to red clover and lucerne sward. Total nitrogen, accumulated in festulolium biomass, was taken from the soil.

According to methods of the aboveground mass management, biological nitrogen fixed (BNF) efficiency in red clover biomass was 61.6–68.0%, in lucerne – 63.7–70.9%. During the assessment of management methods of the aboveground mass of perennial grasses it was defined, that the accumulated symbiotic nitrogen content in plants’ biomass was the highest when mulching of perennial legumes was performed. Hence this method of the aboveground mass use can not be assessed unambiguously, because reoccurring perennial grasses could use mineralized nitrogen from previously spread mulch. According to Hatch et al. (2007), mulching of the aboveground mass of clover-grass led to reduction of relative part of fixed nitrogen in biomass [1].

Table 1

The effect of preceding crops and green manure on the nitrogen balance in sequence: legume-w. wheat-w. triticale

The nitrogen accumulation in the cereal yield, cultivated during two years (in wheat grains, triticale grains and straws) was significantly dependent upon types of grasses and ways of application of their aboveground mass (P<0.01). The majority of nitrogen was accumulated when winter cereal was cultivated after legumes, the lower content – after their mixture with festulolium, the lowest – after festulolium. Watson et al. (2002) states that incorporation of organic materials containing low level of nitrogen (non legume) or having the different content (legume and non legume), products of their division interact with the soil N as well as interact with each other, therefore part of N can be temporarily immobilised in the soil compositions or in the biomass of microorganisms [4]. Therefore this nitrogen becomes available later, during the next period of vegetation. Application of the part of aboveground mass of the red clover (mixed method) or the whole aboveground mass (mulching method) for the green manure did not have any significant effect on N accumulation in grains. Lucerne or their mixture with festulolium as the pre-crops, determined the highest N accumulation in gain yield when the whole aboveground mass was mulched. It can be explained by the higher gain of lucerne biomass as well as nitrogen accumulation in the second part of summer. The nitrogen balance was positive in the crop-rotation part, when legumes were cultivated or their mixture with festulolium (difference between the nitrogen, brought with biomass of perennial grasses and accumulated in the winter cereal yield, cultivated for two years). The lowest positive (+18.4 – +41.9 kg ha^-1) N balance was observed when the aboveground mass of perennial legumes and their mixture with festulolium were removed from field. German researchers indicate that crop rotation in ecologic farming should have the slightly positive N balance (+50 kg ha^-1) in order to maintain the reserves of the soil organic matters as well as nitrogen [2].

Mulching of the aboveground mass determined averagely 7.7 times higher and the combined application – averagely 5.1 higher positive nitrogen balance than in cases when the grass was removed from field. However, the majority of nitrogen from the green manure mineralised and was accumulated in grains of winter wheat during the first year of cultivation. Red clover and lucerne, as pre-crops for wheat, determined high yield of winter wheat grains, respectively 5.31 and 5.01 t ha^-1, and their mixtures with festulolium – lower, respectively 3.86 and 3.90 t ha^-1. During the second year when winter triticale were cultivated after perennial grasses, the grain yield was lower (1.96–2.66 t ha^-1). N, accumulated in grains, was lower than during the first year. This was affected by winter wheat straws, applied for manure, which have a low N (C:N = 81), but are the good source of energy for microorganisms. Therefore, the mineralisation processes in soil became weaker and N immobilisation processes became stronger. During the second year of effect, the higher N accumulation in the winter triticale yield was determined by application of legumes / festulolium or the aboveground mass for the green manure.

Negative N balance was identified after festulolium, when their aboveground mass was removed from field. Application of the part of the whole aboveground mass of festulolium for the green manure, the N balance was slightly positive. After festulolium, the winter wheat and triticale yield was not high, respectively 2.23–2.58 t ha^-1 and 2.17–2.25 t ha^-1. When aboveground mass of legume or their mixture with festulolium was removed from field, there was a lack of biological nitrogen fixation (BNF) for covering the nitrogen, accumulated in cereal , cultivated for two years. In all variants, the negative BNF balance was identified. Meanwhile application of biomass of these legume for the green manure (mixed or mulching method), led to the positive BNF balance (29.5–148.9 kg ha^-1). Application of the whole biomass for manure led to the higher positive nitrogen balance if compared to its mixed application. Application aboveground biomass of sole legumes led to averagely 46.8 kg ha^-1 higher BNF balance than in case of their mixture with festulolium.

The highest increase of total nitrogen in soil, if compared to data prior the experiment establishment, was identified in the crop-rotation part when lucerne or their mixture with festulolium were cultivated (Table 2).

Table 2

The variation of total nitrogen content in the soil 2008–2010

Data in literature indicate, that lucerne have the greater roots mass than clovers. Moreover, the wider C:N ratio lead to the less nitrogen release from lucerne roots if compared to the aboveground part. Researchers indicate the positive importance of lignified roots in supplementing the soil organic matters’ and total nitrogen resources. Correlation regression analysis indicate that the total soil nitrogen (y) correlate with the nitrogen balance of crop-rotation part (x) and is directly proportioned. This link is described by the equation: y = 1.295 + 0.0002x; r = 0.538, P<0.05.

Conclusions. Application of aboveground mass of legumes or their mixtures with festulolium for the manure determined the positive nitrogen balance and higher total nitrogen accumulation in soil in crop rotation part: legumes (or legumes / festulolium) – winter wheat – winter triticale.

References:

1.  hatch, D.J. et al. 2007. The effect of cutting, mulching and applications of farmyard manure on nitrogen fixation in ared clover/grass sward. Bioresource technology, vol. 98, No. 17, p. 3243–3248.

2.  kustermann, B.; Cristen, O.; Hulsbergen, K.J., 2010. Modelling nitrogen cycles of farming systems as basis of site- and farm-specific nitrogen management. agriculture. Ecosystems and environment, No. 135, p. 70–80.

3.  schmidtke, K., 2005. How to calculate nitrogen rhizodeposition: a case study in estimating n rhizodeposition in the pea (pisum sativum l.) and grasspea (lathyrus sativus l.) using a continuous n  labeling split-root technique. Soil biology & biochemistry, No. 37, p. 1893–1897.

4.  watson, C.A.; Atkinson, Gosling P.; Jackson, L.R.; Rayns, F.W., 2002. Managing soil fertility in organic farming systems. Soil use and management, No. 18, p. 239–247.

5.  wivstad, M., 1998. Nitrogen mineralization and crop uptake of n from decomposing 15 N labeled red clover and yellow sweetclover plant fractions of different age. Plant and soil, No. 208, p. 21–31.