Soil N‐related properties under soybean (Glycine max L. Merrill) cultivation as affected by different soil tillage systems and seasonal changes

Abstract

The reduction of soil tillage with the application of catch crop green mass in the form of a mulch is a conservation practice that is being used more and more frequently in agriculture to improve the functioning of the soil ecosystem by enhancing soil organic matter content and quality through improving soil biological activity and nutrient availability, and simultaneously reducing soil disturbance. Globally, conflicting results have been obtained with regards to the influence of various tillage methods on the soil environment under soybean cultivation. To date, only limited Polish studies have been conducted concerning the effect of reduced tillage on plant and soil properties under soybean cultivation, while as yet there are no national surveys concerning the strip‐till cultivation of soybean. Because of the growing interest in soybean cultivation in Poland, and also because of the limited and contradictory data concerning the influence of the various tillage systems (especially strip‐till) applied for soybean cultivation on plant yield and also on soil properties under the climatic condition of Poland, a study was undertaken to evaluate the effect of three tillage methods (TMs) (conventional, CT; reduced, RT and strip‐tillage, ST) on the seed yield of soybean (Glycine max. (L.) Merrill), some plant characteristics, N‐associated soil properties (mineral N content, the activity of urease, proteases and nitrate reductase) and some basic soil properties in a three‐year field experiment in the years 2017–2019. The study was conducted in a field, it was a one‐factor experiment and soil samples were collected five times a year: in April (before the sowing of soybean) and also in May, June, August and September (before soybean harvesting). In 2017, the average soybean seed yield was twice as high (2.42 t ha−1) as in the other 2 years (mean 0.87 t ha−1) and was significantly higher in CT than in RT or ST. Neither the TMs nor the sampling dates differentiated between the content of organic carbon and total nitrogen. Most of the N‐related properties (mineral N content and enzymatic activity) were highest in May and/or June. The RT increased the activity of proteases and nitrate reductase as well as mineral and microbial biomass N content when compared with CT and ST. In turn, the urease activity behaved differently and in 2017 and 2019 was significantly higher in CT, than in RT and ST tillage methods. In general terms, reduced tillage combined with plant residues return may be recommended for increasing inorganic N content as well as improving soil quality by enhancing microbial biomass nitrogen content and soil enzymatic activity.