Differences of basic soil productivity between yellow-mud and grey-mud paddy fields in southern China

Objectives Yellow-mud paddy field (YPF) is low in basic productivity, and is widely distributed in the red-yellow soil region of southern China. In order to provide a basis for the amelioration of YPF fertility and rice fertilization, we quantificationally evaluated the basic soil productivity and revealed differences in absorption and utilization of nitrogen, phosphorus and potassium of rice between YPF and high-producing grey-mud paddy field (GPF).

Methods A pot culture experiment was conducted using rice cultivar ‘zhongzheyou 1’ as tested materials. The tested soils were collected in the typical YPFs and GPFs nearby having the same micro-geomorphy in twenty counties, Fujian Province, China. Two treatments of applying N 0.60 g/pot, P₂O₅ 0.24 g/pot, K₂O 0.42 g/pot and no fertilization control (CK) were designed for all the fields. Urea with 10% abundance of ¹⁵N was used for nitrogen fertilizer, calcium dihydrogen phosphate for phosphate fertilizer and potassium chloride for potassium fertilizer. Fertilizers were firstly dissolved and applied. Two column seedlings were transplanted in each pot. After harvest, the grain yield and biomass were investigated, the plants were divided into above ground part and root part, and the NPK contents of plant were analyzed. The basic soil fertility and the NPK contents after harvest were determined.

Results Compared with the GPF in the CK, the economic yield and above-ground rice biomass in YPF were decreased by 26.9% and 23.5%, respectively, and the corresponding contribution rate of basic soil productivities (BSP) were decreased by 14.1 and 9.7 percent points, respectively. The contribution rate of BSP to economic yield had a significant positive correlation with soil organic matter content, but a significant negative correlation with soil bulk density. In both treatment and CK, the effective panicles in YPF were significantly lower than those in GPF. The effective panicles had a significant positive correlation with organic matter content but a significant negative correlation with bulk density in CK. Under fertilization, the N, P and K contents in grains, stems and leaves, roots in YPF were all lower than those in GPF at the ripening stage, of which, the P contents in the three parts were significantly decreased by 9.6%, 38.4% and 46.3% in turn, and K contents in grains, stems and leaves were significantly decreased by 10.8% and 18.5%, respectively. Under fertilization at the ripening stage, the N uptakes of rice grains and stem & leaf in YPF were 10.8% and 17.3% lower than those in GPF, the P uptakes were 12.5% and 46.2% lower and K uptakes were 16.6% and 28.5% lower (P < 0.05). Under fertilization, N use efficiency (NUE) in YPF was 4.6 percentage points lower than in GPF, but N residual rate in soil was 3.0 percentage points higher.

Conclusions The soil organic matter and bulk density are the two most important poverty obstacles in yellow-mud fertility, which affect the contribution of basic soil productivity and the effective panicle number of yield components. Comparing with high-productivity field, the nitrogen use efficiency in yellow-mud field is lower while the nitrogen residual rate in soil is higher. By improving organic matter content and decreasing bulk density, yellow-mud paddy fields have a yield increasing potential of over 20%.