Residual Nitrogen Effects in Organically Cultivated Beetroot Following a Harvested/Green Manured Grass-Clover Ley

ABSTRACT

The residual nitrogen (N) effect on beetroot following harvested grass-clover (H-ley) or corresponding twice-cut green manure (GM-ley) was compared with a barley control. The residual N at beetroot harvest, calculated as N in beetroot crop and mineral N in the 0–90 cm soil layer, was 83 kg ha⁻¹ for the GM-ley when barley was set to zero. The effect of GM-ley exceeded that of 3H-ley (3 harvests) by 74 kg N ha⁻¹ and 2H-ley (2 harvests) by 42 kg N ha⁻¹. Prediction of residual effects was studied using a model with a humification coefficient (hc) of 0.35 and another with different hc values for different plant materials. The former gave the best fit to observed data in regression analysis. The latter gave the best fit to observed data in absolute values. The residual N effect of GM biomass from summer cuttings corresponded to 40–70% of the potential effect.

Keywords:

• N dynamics
• mixed ley
• barley
• previous crop
• grass-clover ratio
• Manova
• humification coefficient
• sandy soil

ACKNOWLEDGMENTS

We thank the staff at Lilla Böslid Experimental Station for skilful technical assistance. This investigation was supported with grants from the special funds for research on organic agriculture of the Swedish Research Council Formas.

Notes

¹KaliVinass is a residue from yeast production, containing 33% K, 1% organic N, 0% NH₄-N, 0.002% P, 0.7% Ca, 0.6% Mg and 20% S. Besal consists of crushed rock salt containing 38% Na as NaCl.

²1/3 of DM as beet leaves, 2/3 as grass-clover ley biomass. The effluent had 6% dry matter and the nutrient concentrations (kg ton⁻¹) were: 1.3 NH₄-N, 3.2 total N (ratio NH₄-N/total N = 0.43), 0.4 P, 4.2 K, 1.0 Na, 0.4 Mg and 0.2 S, 0.141 Fe, 0.006 Mn, 0.005 Zn, 0.004 B and 0.001 Cu. C/N_org ratio was 10. The effluent was spread with a band spreader and incorporated into the soil within one hour after spreading.

¹C and N determined according to Dumas; P, K, Mg and Ca: AL-method according to Egnér et al. (1960); Boron: water extractable.

¹Irrigation was only applied to beetroots, not in the year with pre-crops. For beetroots in 2003 the irrigation corresponded to 14 mm in late July and 35 mm in the first half of August. In 2004, 10 mm were applied in May and 20 mm in August.

²Mean values 1961–1990 (Alexandersson et al., 1991).

³Mean values for the full months.

¹Mean for leys harvested twice and three times (2H-ley and 3H-ley).

²Calculated with Manova.

¹See equation 2.

²Without reducing effect of cut GM-ley in June + July.

³Tendency for interaction (p = 0.07) between pre-crop and fertilization regime when comparing 3H-ley and barley in a pairwise test with Manova but not for total Manova including all treatments.

¹For regression coefficient.

²Fraction suggested by Granstedt (1995).

¹33 % stubble, 12 % white clover and 55% perennial ryegrass and non leguminous weeds.

¹Two-sided test.

²One-sided test.

¹b.s. = Before seeding. Average dates: N_min: 16 May, effluent b.s: 20 May, seeding: 26 May.

²No interaction therefore mean for the main factors. Thus results for pre-crop refer to the means for No N-t and Low N-t and results for fertilization regimes are means of the pre-crops.

³Two-sided test.

⁴Interaction between fertilization regime and pre-crop (p = 0.025).

⁵One-sided test.