Objective We studied the effects of tillage methods combined with straw mulching on soil carbon, nitrogen and water storage to provide technical and theoretical support for water-saving potato production in southern Ningxia.
Methods A field experiment was conducted from 2014 to 2016 in Guyuan City, Ningxia. There were six treatments, including no-tillage with and without straw mulching (NS, NN), sub-soiling tillage with and without straw mulching (SS, SN), and traditional tillage with and without straw mulching (CS, CN). The organic carbon and total nitrogen (TN) in 0–20 cm and 20–40 cm soil layer were determined at maturing stage of potato in 2016. Soil samples were collected at 0–200 cm deep every 20 cm to determine the water storage before sowing and the key growth stages of potato. The potato plants were sampled at whole growing stages to investigate aboveground biomass (AB), while potato yield was investigated at harvest.
Results Compared with no straw mulching in the three tillage methods, straw mulching (P<0.05) increased soil total C and N content and water storage. SS treatment had higher soil C and N than CN (29.9% and 24.7%) in the 0–20 cm layer; NS recorded the highest soil C and N in the 20–40 cm layer. Before sowing potatoes, the highest soil water storage in 2014 and 2015 was recorded in NS and SS, respectively. SS (P<0.05) increased the potato's mean soil water storage at key growth stages by 21.6% and 26.0% in 2014 and 2016, respectively. Similarly, NS increased mean soil water storage by 17.2% in 2015. According to the logistic growth equation simulation, the potato's rapid growth stage was the earliest in SS treatment. The maximum accumulation rate of potato biomass was higher in NS in 2014 and SS in 2015 and 2016. NS treatment recorded the highest potato yield in 2014, with an increase of 51.8% over CN. Similarly, SS had the highest yield in 2015 and 2016, increased by 36.7% and 87.5% over CN. Annual precipitation, tillage method, and straw mulching were highly significant on soil water storage, potato aboveground biomass and yield. Straw mulching (P<0.05) affected soil C and N contents. Potato yield was (P<0.05) positively correlated with soil C, and potato yield had a significantly positive relationship with soil N, water storage and potato biomass. We found a (P<0.05) correlation among soil C, N, and water storage.
Conclusions Combining the three tillage methods with straw mulching increases the soil carbon and nitrogen contents in the 0–40 cm layer and water storage in the 0–200 cm layer throughout the potato growing period, promoting the accumulation of aboveground biomass and potato yield. Applying straw mulching to the subsoiling increases soil C and N in the 0–20 cm layer, rapidly enhances the growth stages and fosters optimum biomass accumulation in dry years. No-tillage with straw mulching treatment had the highest yield in the first year but was lower than the range recorded under subsoiling with straw mulching and conventional tillage with straw mulching. Therefore, comprehensively considering the synergistic effect of soil carbon, nitrogen, water storage and crop yield, the application of straw mulching to no-tillage and sub-soiling are recommended for the potato production in southern Ningxia.
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