Strategies to optimise biological nitrogen fixation in legume/grass pastures in the southern region of Chile

Abstract

Pastures in southern Chile are composed of forage grasses and associated legumes. Apart from native grass species, in many areas perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) have been introduced. It is thought that most of the N in these pastures is derived from the symbiosis between rhizobium bacteria and the clover. However, various factors can limit the biological nitrogen fixation (BNF) potential. Soils of Chiloe´(southern Chile) are derived from volcanic ash (Andisols), and show high acidity and phosphorus (P) retention capacity and there is often a low availability of exchangeable cations and, sometimes, micronutrients, which together with high aluminium (Al) concentrations can inhibit BNF potential by nodulated legumes. An experiment was carried out on an Andisol of Chiloe´, on a permanent pasture, to evaluate the influence of these fertility factors grass and legume productivity and on the BNF contribution to white clover. Treatments included two rates of lime (0 and 4 Mg ha )1 ) and eight fertilisation treatments: 1. Complete (macronutrients in kg ha )1 : N-50, P 2 O 5 -180, K 2 O-100, MgO-70, S-50, and micronutrients); six other treatments with complete fertilisation but, respectively, without N, P, K, Mg, S and micronutrients, and a control without fertiliser application. The experiment was conducted over 2 years and soil fertility parameters, grass and clover biomass production were evaluated and the BNF contribution to the clover was estimated using 15 N isotope dilution technique. Potassium was found to be the most limiting element for dry matter production, especially for the clover. Liming increased soil pH values and Ca and Mg contents, strongly reduced Al saturation and increased dry matter production. The proportional contribution of BNF to the white clover was high, reaching 80% of total N accumulated by the plants and not significantly affected by addition of lime or fertiliser. However, the accumulation of dry matter and total N, and the total N derived from BNF by the clover were over three times higher in the complete fertilisation treatments than in the control in both years and in the limed and unlimed treatments. The results of this study indicate that pasture productivity can be improved by liming and fertilisation which favour growth of the legume and ryegrass to the detriment of the native grasses. The increase in the proportion of ryegrass and clover should result in improved quality of the available forage, and in the case of the clover, stimulates an increase in the N contribution from BNF thus dispensing with the need for N fertiliser.

Integrated effects of abiotic stresses on inoculant performance, legume growth and symbiotic dependence estimated by 15N dilution

“…Chile (Campillo et al 2005), with only a single report concerning a grain legume (common bean) in Cuba (Garcia et al 2007). Addition of lime at 7.5 t ha −1 (Edmeades et al 1986) to a white clover-ryegrass pasture or 5-10 t ha −1 to a sub-clover-ryegrass pasture (Wheeler et al 1997) had no effect on DM, symbiotic dependence or N fixed by the clover (Table 10).…”

“…The surface pH of a moderately acid soil in Chile (pH 5.3-5.4) increased to 5.7-5.9 and exchangeable Al decreased from~1.0 to~0.1 cmol c kg −1 soil following surface application of lime at 4 t ha −1 (Campillo et al 2005; Table 11). The response of DM, symbiotic dependence and fixed N of white clover foliage to addition of lime and basal nutrients was measured over two growing seasons.…”

“…However, for the full potential of the clover to produce DM and to fix N 2 , both lime and basal fertilizer applications were required (Table 11). Potassium was the most deficient nutrient in the acid soil that was derived from volcanic ash, but deficiencies of P, S and micronutrients were also present in the unfertilized soil (Campillo et al 2005). Presumably, the beneficial effect of lime was due to the significant reduction in exchangeable Al.…”

“…When lime was applied to the loam (higher dose) there was little response in the N content of the clover but a large Table 11 Response of DM, symbiotic dependence and fixed N of white clover foliage to addition of lime and basal nutrients over two growing seasons a in Chile. After Campillo et al (2005) Season Lime (t ha −1 ) Basal nutrients b Soil pH c Al 3+ (cmol c kg −1 ) DM d (t ha −1 ) Clover ( response in the N content of the grass, while the very opposite response occurred in the sand despite the smaller dose of lime. With the addition of lime, a very small response of both P atm and N fixed occurred in the loam (Table 13), but when lime was applied to the sand there was a dramatic response in both P atm and N fixed (Table 13).…”

Human-Induced Soil Degradation in Chile

“…These soils present a high risk of acidification and usually show a high Al saturation of the ECEC (effective cation exchange capacity) where ISRID (Incentives System to Recovery Degraded Soils) has subsidised farmers to apply lime. Several studies have confirmed that addition of lime to neutralise the acidity and reduce the toxic effect of Al 3+ increases yield, forage quality, botanical composition and nitrogen symbiosis by legumes in pastures (Campillo et al 2005;Bernier and Alfaro 2006 (Sadzawka 2006). For example, a study by Bernier and Alfaro (2006) in a strongly acidic soil (pH 5.3) compared the effects of nitrate sodium and urea, where the maximum doses of N (250 kg ha -1 ) as urea clearly generated a significant acidification effect on soil (Fig.…”