Impact of loosening and straw addition to the subsoil on crop performance and nitrogen leaching: A lysimeter study

Poor subsoil properties are difficult to ameliorate and detrimental to soil fertility and crop yield. The effects of loosening (L) and loosening + straw (LS) ∼60 Mg ha^-1 into the subsoil (25-40 cm depth) on crop yield, water flow, and the nitrogen (N) balance components under bare soil conditions and a barley (Hordeum vulgare L.) crop were investigated in an about 21-mo lysimeter study and compared with a control treatment. Undisturbed soil columns (n = 12) were excavated from an agricultural field in May 2016, installed at a lysimeter station, and exposed to outdoor climatic conditions in Uppsala, Sweden, in August 2016. Spring barley ('Makof') was grown between June and September 2017. Total N leaching loads over the 21 mo were high (74-193 kg ha^-1 ). The LS treatment reduced the N load by 49% (P = .01) and 62% (P = .001) compared with the L and control treatments, respectively. Loosening reduced N load by 25% (P < .07) compared with the control. Emissions of N₂ O were low (0.04-0.07 kg N ha^-1 ), and no differences were observed between treatments. Leaf relative chlorophyll content was lower in the LS treatment than in the L and control treatments (P < .05). Yield was also lowest in the LS treatment (5.8 Mg ha^-1 ) and was 7 and 8.5% lower than in the control and L treatments (P > .05), respectively. These results suggest that LS can reduce N leaching. The overall effects of LS on crop performance and N removal and leaching should be further scrutinized in long-term field studies.