Seasonal Variation Of The Mollisols Physical And Chemical Properties In Different Tillage Systems

Northeast China, one of the most important bases for commercial grain production in China. In recent years, this area has a decline of soil productivity potential, as a result of the excess reclamation land and the irrational exploitation. No tillage and reduced tillage, important component of conservation tillage, were applied as the effective practices to improve soil quality in the past decade. The previous investigations on conservation tillage systems were mostly focused on annual differences in soil properties, and few studies were conducted to investigate the seasonal changes of soil properties under different tillage systems in this region. In this study, we mainly determined the seasonal variation of soil physical and chemical properties in different tillage systems in two separate fields, i.e. flat farmland and sloping farmland(5°)., based on the long-term trial in Mollisols region of Northeast China. The results were as follows:A similar result of bulk density(BD) was observed in the flat and sloping farmland. In the 0-5 and 10-15 cm depth, little seasonal variation of BD and no difference of BD between ridge and furrow were in no tillage(NT).The lowest BD under reduced tillage(RT) in furrow was in June. The BD under conventional tillage(CT) in ridge increased with time, but no seasonal difference in furrow. The results also showed NT had a higher BD than CT in the ridge and in June, RT had a significant lower on BD than NT and CT in the furrow but no differences in other months. BD increased with increasing depth, and BD under all the tillage systems in the sloping farmland was higher than in the flat farmland.In the 0-20 cm layer, soil water content was determined by rainfall. When compared with RT and CT, NT could keep greater water content in both flat and sloping farmland, especially in low rainfall, significant(P<0.05) difference was observed between NT and other tillage systems.The 2-10 mm and 0.5-1 mm size water stable aggregate(WSA) varied with time and little seasonal variation was in 1-2 mm and 0.25-0.5 mm size WSA. In the 0-40 cm layer, for NT, 2-10 mm size WSA and mean weight diameter(MWD) in August was greater than other months. However, the 2-10 mm size WSA and MWD under RT and CT decreased with time. The result also found >0.25 mm water stable aggregate content(WR0.25) under all the tillage systems had a decline trend with time. NT had a greater WR0.25 and MWD than RT and CT in 0-20 cm depth, which proved that NT had a more stable soil structure when compared with RT and CT.NT had the greatest initial infiltration rate(IIR) in August in the ridge and furrow, but the steady infiltration rate(SIR) decreased with time. Soil infiltration rate for RT in the ridge decreased with time, but the highest IIR and SIR in the furrow was found in June. The IIR and SIR under CT had a decline trend during the growth season. In June, RT had a higher IIR and SIR in the furrow than NT and CT, while the greater IIR and SIR under NT in the ridge were observed in August when copared with other tillage systems. NT had greater IIR than CT in October.Soil organic carbon(SOC) and total nitrogen(TON) had similar seasonal variation. In 0-20 cm depth, NT had a highest SOC and TON in August, and decline in SOC and TON under RT and CT were found in the flat and sloping farmlands. No seasonal differences were in all the tillage systems in 0-100 cm depths. CT had a lower SOC and TON than NT and RT in 0-20 cm depth. In 20-40 cm layer, higher SOC in the sloping farmland was observed under NT than under CT, while a contrast result was found in the flat farmland. No significant differences on SOC among all the tillage systems were in 40-100 cm layer and little differences on TON were found among all the treatments in 20-100 cm layer. The SOC and TON contents decreased with increasing depth, and the higher SOC and TON under NT were found in the flat farmland than in the sloping farmland in the 0-20 cm depth.In 0-20 cm layer, the greatest of ammonium nitrogen(NH+4-N) and total phosphorus(TOP) contents under all the tillage systems were in June. In the flat farmland, NT and RT had a greater NH+4-N and TOP than CT in 0-15 cm layer. In the sloping farmland, lower NH+4-N was found under NT than under CT in 0-5 cm layer, CT had a greater TOP than NT in 0-10 cm layer. The study also found that the greater of NH+4-N under NT and RT was in the flat farmland than in the sloping farmland, while the contrast result was found under CT in 0-10 cm layer. In 10-20 cm depth, the lower in NH+4-N under RT and CT was observed in the flat farmland than in the sloping farmland. The TOP in the flat farmland was higher than in the sloping farmland.Little soil and water loss for NT was observed during all the growing season, while RT and CT had the highest numbers of runoff and sediment transport、erosion modulus in the highest rainfall in July. During all the growing season, NT had the least numbers of runoff and sediment transport、erosion modulus when compared with RT and CT, which proved that NT was a tillage practice significant in soil-water conserving effect. However, no better in soil-water conserving effect was found in RT.In a word, the seasonal variation of soil physical and chemical properties under different tillage systems focused on the 0-20 cm layer. In all the growing season, NT could keep a stable soil structure, improve aggregate stability and increase SOC、TON and soil nutrients, reduce soil and water loss. In RT, deep tillage of the furrows in summer significantly increased total porosity and infiltration rate. RT had a lower runoff and sediment content than CT, but significant higher than NT. Hence, NT should be applied widely in the Black soil area of Northeast China, especially in the sloping farmland.