Effects of loosening combined with straw incorporation into the upper subsoil on soil properties and crop yield in a three-year field experiment

Subsoil management needs to be integrated into the current tillage regimes in order to access additional resources of water and nutrients and sustain crop production. However, arable subsoil is often deficient in nutrients and carbon, and it is compacted, affecting root growth and yield. In this study, crop yield and soil responses to loosening of the upper subsoil, without and with straw injection below the plough layer (25-34 cm), were studied during three crop cycles (2016-2018) in a field experiment near Uppsala, Sweden. Responses to straw injection after loosening were studied after single and triple consecutive applications of 24-30 Mg ha-1 during 2015-2017 to spring-sown barley and oats. Subsoil loosening combined with one-time or repeated straw addition (LS treatments) significantly reduced soil bulk density (BD) and increased porosity, soil organic carbon (SOC) and total nitrogen (N) compared with loosening (L) alone (one-time or repeated annually) and the control. In treatment L, the soil re-compacted over time to a similar level as in the control. Field inspections indicated higher abundance of earthworms and biopores in and close to straw incorporation strips. Aggregates readily crumbled/fragmented by hand and casts (fine crumbs) were frequently observed in earthworm burrows. The treatment LS improved soil properties (SOC and porosity) and water holding capacity, but had no significant influence on crop yield compared with the control. Crop yield in all treatments was 6.5-6.8 Mg ha-1 in 2017 and 3.8-4.0 Mg ha-1 in 2018, and differences were non-significant. Absence of yield effect due to treatments could be possibly due to other confounding factors buffering expression of treatment effects on yield. Lower relative chlorophyll content in leaves in the loosening with straw treatment during early growth stages, did not affect final crop yield. Subsoil loosening performed three times gave no further improvement in soil properties and grain yield compared with one-time loosening. There was no difference in yield between repeated subsoil loosening + straw and one-time treatment. It will be interesting to study the long-term effects of deep straw injection and evaluate its impact under other soil and weather conditions

Lysimeter deep N fertilizer placement reduced leaching and improved N use efficiency

Deep fertilization has been tested widely for nitrogen (N) use efficiency but there is little evidence of its impact on N leaching and the interplay between climate factors and crop N use. In this study, we tested the effect of three fertilizer N placements on leaching, crop growth, and greenhouse gas (GHG) emissions in a lysimeter experiment over three consecutive years with spring-sown cereals (S1, S2, and S3). Leaching was additionally monitored in an 11-month fallow period (F1) preceding S1 and a 15-month fallow period (F2) following S3. In addition to a control with no N fertilizer (Control), 100 kg N ha(-1) year(-1) of ammonium nitrate was placed at 0.2 m (Deep), 0.07 m (Shallow), or halved between 0.07 m and 0.2 m (Mixed). Deep reduced leachate amount in each cropping period, with significant reductions (p < 0.05) in the drought year (S2) and cumulatively for S1-S3. Overall, Deep reduced leaching by 22, 25 and 34% compared to Shallow, Mixed and Control, respectively. Deep and Mixed reduced N leaching across S1-S3 compared with Shallow, but Deep further reduced N loads by 15% compared to Mixed and was significantly lowest (p < 0.05) among the fertilized treatments in S1 and S2. In S3, Deep increased grain yields by 28 and 22% compared to Shallow and Mixed, respectively, while nearly doubling the agronomic efficiency of N (AE(N)) and the recovery efficiency of N (REN). Deep N placement is a promising mitigation practice that should be further investigated

Fertilizer placement for improved nitrogen use efficiency and mitigation of N2O emissions

Deep fertilizer placement is a promising strategy to increase crop yield and nitrogen (N) use efficiency while decreasing leached N and fertilizer-induced nitrous oxide (N2O) emissions from soil to atmosphere. The objective was to test three fertilization depth treatments to compare greenhouse gas emissions of N2O, methane (CH4) and carbon dioxide (CO2), as well as leaching and crop response. A deep fertilizer placement (Deep) at 0.20 m, a shallow placement (Shallow) at 0.07 m and a mixeddepth placement (Mixed) where the same amount of fertilizer was split between the depths of 0.07 and 0.20 m, and a non-fertilized control (Control) were evaluated. These fertilizer treatments were tested in a two-year field experiment, a five-year lysimeter experiment consisting of three years with crops, in addition to a 12-day lab incubation using labeled fertilizer. Deep placement significantly increased grain N uptake and yield and decreased N2O and CH4 emissions. CO2 emissions from bare soil were not significantly affected by fertilizer placement. Further, Deep reduced N leaching and increased crop water utilization. The tracer incubation indicated that indigenous soil N was the primary contributor to total N2O emissions in Deep, and CH4 emissions were correlated to N2O fluxes originating from fertilizer N. X-ray tomography of the incubated soil cores revealed that fluxes of N2O from fertilizer were affected by compaction level. Overall N use efficiency (NUE) was evaluated in the soil-crop system via an N balance, % NUE, agronomic efficiency of N (AEN) and the recovery efficiency of N (REN). Over the five years with crops, all indices indicated a higher N use efficiency with greater fertilizer placement depth

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) similar to 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 .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