Improving soil respiration while maintaining soil C stocks in sunken plastic greenhouse vegetable production systems – Advantages of straw application and drip fertigation

Abstract

The absence of fertile surface soil combined with high temperature and moisture in sunken plastic greenhouse vegetable production (SGVP) leads to low soil organic carbon (SOC) storage. This limits the rapid growth of vegetable crops in SGVP as low SOC goes along with a low capacity of soils for water and nutrient retention. It also results in low soil respiration, which leads to indoor CO2 limitations during the winter crop growing season. In our experiments we explored if drip fertigation might lead to an improvement of soil respiratory activity, specifically when maize straw is incorporated additionally into the soil. To address these questions, a two-factor field experiment with four treatments was conducted across four growing seasons. The treatments are (1) Conventional flood irrigation with over fertilization (CIF), (2) CIF + maize straw (CIF + S), (3) Drip irrigation with reduced fertilization (DIF), (4) DIF + maize straw (DIF + S). Compared to CIF, DIF significantly increased water and nitrogen use efficiency by 93% and 296%, respectively. Moreover, cumulated CO2 emission was significantly lower than assimilated carbon in plant for both CIF and DIF without straw incorporation, but the opposite result was obtained when straw was added (CIF + S and DIF + S). DIF results in reduced rates of soil respiration, mainly due to significantly reduced mineralization of autochthonous SOC stocks as compared CIF. Tracing the δ13C signature of added straw into the SOC indicated that DIF leads to a larger incorporation of straw-derived C into soil than CIF. Our results show that adding straw is a suitable measure for both to meet the CO2 demand of vegetable photosynthesis and to maintain SOC stocks associated soil functions. However, the tested and widely recommended straw application rate of 3.5 t C ha−1 appears to be still too low to reverse the trend of a net mineralization of SOC stocks. Thus, our results call for targeted experiments to optimize the amount of straw addition and to explore in field experiments if the application of mixed straw and biochar produced from vegetable residues, are a suitable way forward to increase soil health of SGVP systems.