Significant soil degradation is associated with intensive vegetable cropping in a subtropical area: a case study in southwestern China

<p>Within the context of sustainable development, soil degradation driven by land use change is considered a serious global problem, but the conversion from growing cereals to vegetables is a change that has received limited attention, especially in subtropical regions. Here, we studied the effects of the conversion from paddy rice to an oilseed rape rotation to vegetable production in southwestern China on soil organic carbon (SOC), total nitrogen (TN), the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">C</mi><mo>/</mo><mi mathvariant="normal">N</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f135772273124e8de131c1d3d27c70de"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-7-333-2021-ie00001.svg" width="24pt" height="14pt" src="soil-7-333-2021-ie00001.png"/></svg:svg></span></span> ratio, pH, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) based on face-to-face farmer surveys and soil analysis. In the vegetable cropping system, fertilizer application often exceeds the crop demand or levels recommended by the local extension service several times over. Thus, the crop use efficiency of N, P, K, Ca, and Mg was only 26 %, 8 %, 56 %, 23 %, and 28 %, respectively. In the vegetable cropping system studied, SOC, C stock, TN, and N stock were decreased significantly due to low organic inputs from crop residues and high tillage frequency. Furthermore, the soil <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">C</mi><mo>/</mo><mi mathvariant="normal">N</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="de4c857a5316d0d8e75c5f4965b9bc96"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="soil-7-333-2021-ie00002.svg" width="24pt" height="14pt" src="soil-7-333-2021-ie00002.png"/></svg:svg></span></span> ratio decreased slightly; available P (AP) in the topsoil increased by 1.92 mg kg<span class="inline-formula">⁻¹</span> for every 100 kg ha<span class="inline-formula">⁻¹</span> of P surplus, and the critical levels of AP and CaCl<span class="inline-formula">₂</span>-soluble P in P leaching were 104 and 0.80 mg P kg<span class="inline-formula">⁻¹</span>. Besides, compared to the current paddy–rape rotation system, a clear trend of soil acidification was observed in the vegetable fields. However, increasing the contents of soil Ca and Mg significantly alleviated topsoil acidification, with the effect increasing over time. Given our findings, the potential benefits of conservation agricultural practices, integrated soil–crop system management strategies, and agricultural technology services for recovering the degraded soil and improving the vegetable productivity are discussed here.</p>