Understanding the characteristics and influences of various factors on phosphorus (P) fractions is of significance for promoting the efficiency of soil P.  Based on long-term experiments on black soil, fluvo-aquic soil, and loess soil, which belong to Phaeozems, Cambisols, and Anthrosols in the World Reference Base for Soil Resources (WRB), respectively, five fertilization practices were selected and divided into three groups: no P fertilizer (CK/NK), balanced fertilizer (NPK/NPKS), and manure plus mineral fertilizer (NPKM).  Soil inorganic P (Pi) fractions and soil properties were analyzed to investigate the characteristics of the Pi fractions and the relationships between Pi fractions and various soil properties.  The results showed that the proportion of Ca₁₀-P in the sum of total Pi fractions was the highest in the three soils, accounting for 33.5% in black soil, 48.8% in fluvo-aquic soil, and 44.8% in loess soil.  Long-term fertilization practices resulted in periodic changes in soil Pi accumulation or depletion.  For black soil and fluvo-aquic soil, the Pi accumulation was higher in the late period (10–20 years) of fertilization than in the early period (0–10 years) under NPK/NPKS and NPKM, whereas the opposite result was found in loess soil.  The Pi accumulation occurred in all Pi fractions in black soil; mainly in Ca₈-P, Fe-P, and Ca₁₀-P in fluvo-aquic soil; and in Ca₂-P, Ca₈-P, and O-P in loess soil.  Under CK/NK, the soil Pi was depleted mainly in the early period in each of the three soils.  In addition to the labile Pi (Ca₂-P) and moderately labile Pi (Ca₈-P, Fe-P, Al-P), the Ca₁₀-P in black soil and fluvo-aquic soil and O-P in loess soil could also be used by crops.  Redundancy analysis showed that soil properties explained more than 90% of the variation in the Pi fractions in each soil, and the explanatory percentages of soil organic matter (SOM) were 43.6% in black soil, 74.6% in fluvo-aquic, and 38.2% in loess soil.  Consequently, decisions regarding the application of P fertilizer should consider the accumulation rate and the variations in Pi fractions driven by soil properties in non-acidic soils.

Soil productivity (SP) without external fertilization influence is an important indicator for the capacity of a soil to support crop yield. However, there have been difficulties in estimating values of SPs for soils after various long-term field treatments because the treatment without external fertilization is used but is depleted in soil nutrients, leading to erroneous estimation. The objectives of this study were to estimate the change of SP across different cropping seasons using pot experiments, and to evaluate the steady SP value (which is defined by the basal contribution of soil itself to crop yield) after various longterm fertilization treatments in soils at different geographical locations. The pot experiments were conducted in Jinxian of Jiangxi Province with paddy soil, Zhengzhou of Henan Province with fluvo-aquic soil, and Gongzhuling of Jilin Province with black soils, China. Soils were collected after long-term field fertilization treatments of no fertilizer (control; CK-F), chemical fertilizer (NPK-F), and combined chemical fertilizer with manure (NPKM-F). The soils received either no fertilizer (F0) or chemical fertilizer (F1) for 3–6 cropping seasons in pots, which include CK-P (control; no fertilizer from long-term field experiments for pot experiments), NPK-P (chemical fertilizer from long-term field experiments for pot experiments), and NPKM-P (combined chemical and organic fertilizers from long-term field experiments for pot experiments). The yield data were used to calculate SP values. The initial SP values were high, but decreased rapidly until a relatively steady SP was achieved at or after about three cropping seasons for paddy and fluvo-aquic soils. The steady SP values in the third cropping season from CK-P, NPK-P, and NPKM-P treatments were 37.7, 44.1, and 50.0% in the paddy soil, 34.2, 38.1, and 50.0% in the fluvo-aquic soil, with the highest value observed in the NPKM-P treatment for all soils. However, further research is required in the black soils to incorporate more than three cropping seasons. The partial least squares path mode (PLS-PM) showed that total N (nitrogen) and C/N ratio (the ratio of soil organic carbon and total N) had positive effects on the steady SP for all three soils. These findings confirm the significance of the incorporation of manure for attaining high soil productivity. Regulation of the soil C/N ratio was the other main factor for steady SP through fertilization management.

In order to reveal the impact of various fertilization strategies on carbon (C) and nitrogen (N) accumulation and allocation in corn (Zea mays L.), corn was grown in the fields where continuous fertilization management had been lasted about 18 years at two sites located in Central and Northeast China (Zhengzhou and Gongzhuling), and biomass C and N contents in different organs of corn at harvest were analyzed. The fertilization treatments included non-fertilizer (control), chemical fertilizers of either nitrogen (N), or nitrogen and phosphorus (NP), or phosphorus and potassium (PK), or nitrogen, phosphorus and potassium (NPK), NPK plus manure (NPKM), 150% of the NPKM (1.5NPKM), and NPK plus straw (NPKS). The results showed that accumulated C in aboveground ranged from 2 550–5 630 kg ha–1 in the control treatment to 9 300–9 610 kg ha–1 in the NPKM treatment, of which 57–67% and 43–50% were allocated in the non-grain organs, respectively. Accumulated N in aboveground ranged from 44.8–55.2 kg ha–1 in the control treatment to 211–222 kg ha–1 in the NPKM treatment, of which 35–48% and 33–44% were allocated in the non-grain parts, respectively. C allocated to stem and leaf for the PK treatment was 65 and 49% higher than that for the NPKM treatment at the both sites, respectively, while N allocated to the organs for the PK treatment was 18 and 6% higher than that for the NPKM treatment, respectively. This study demonstrated that responses of C and N allocation in corn to fertilization strategies were different, and C allocation was more sensitive to fertilization treatments than N allocation in the area.

The improvement of soil productivity depends on a rational input of water and nutrients, optimal field management, and the increase of basic soil productivity (BSP). In this study, BSP is defined as the productive capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local field management. Based on 19-yr data of the long-term agronomic experiments (1989–2008) on a fluvo-aquic soil in Zhengzhou, Henan Province, China, the decision support system for agrotechnology transfer (DSSAT ver. 4.0) crop growth model was used to simulate yields by BSP of winter wheat (Triticum aestivium L.) and summer maize (Zea mays L.) to examine the relationship between BSP and soil organic carbon (SOC) under long-term fertilization. Five treatments were included: (1) no fertilization (control), (2) nitrogen, phosphorus and potassium fertilizers (NPK), (3) NPK plus manure (NPKM), (4) 1.5 times of NPKM (1.5NPKM), and (5) NPK plus straw (NPKS). After 19 yr of treatments, the SOC stock increased 16.7, 44.2, 69.9, and 25.2% under the NPK, NPKM, 1.5NPKM, and NPKS, respectively, compared to the initial value. Among various nutrient factors affecting contribution percentage of BSP to winter wheat and summer maize, SOC was a major affecting factor for BSP in the fluvo-aquic soil. There were significant positive correlations between SOC stock and yields by BSP of winter wheat and summer maize (P<0.01), and yields by BSP of winter wheat and summer maize increased 154 and 132 kg ha–1 when SOC stock increased 1 t C ha–1. Thus, increased SOC accumulation is a crucial way for increasing BSP in fluvo-aquic soil. The manure or straw combined application with chemical fertilizers significantly enhanced BSP compared to the application of chemical fertilizers alone.

A 2-yr field experiment was conducted on a calcareous alluvial soil with four summer maize intercropping systems at Shangzhuang Experiment Station (116.3°E, 39.9°N) in the North China Plain. The objective was to determine nitrate leaching from intercropping systems involving maize (Zea mays L.): sole maize (CK), maize + soybean (CST), maize + groundnut (CGT), maize+ ryegrass (CHM), and maize + alfalfa (CMX). Intercropping greatly reduced nitrate accumulation in the 100-200 cm soil layers compared with maize monoculture. Nitrate accumulation under intercropping systems decreased significantly at the 140-200 cm soil depth; the accumulation varied in the order CK>CST>CMX>CHM>CGT. However, compared to the CK treatment, nitrate leaching losses during the maize growing period were reduced by 20.9- 174.8 (CGT), 35.2-130.8 (CHM), 60.4-122.0 (CMX), and 30.6-82.4 kg ha-1 (CST). The results also suggested that intercropping is an effective way to reduce nitrogen leaching in fields with N fertilizer over-dose.