Search

Potash resources in China are very scarce. It is especially important to correctly evaluate the potential potassium-supplying power of soils in northern China in order to use soil potassium sufficiently and potash fertilizer properly. Regional differences in crop yield responses to long-term potassium application in northern China were determined in this study. Twenty-five representative soil samples from 13 provinces, municipalities, and autonomous regions of major agricultural regions in northern China were collected from the surface layer (0-20 cm) before crop seeding in 1993. A soil potassium-depletion study was carried out in a pot experiment with successive planting of corn seedlings for 10 harvests in the 25 soils. Since 1993, field trials on wheat and corn response to long-term potassium application were conducted at the fixed sites of HLJ-SC (Shuangcheng of Heilongjiang), JL-LFZ (Liufangzi of Jilin), HB-XJ (Xinji of Hebei), SX-LF (Linfen of Shanxi), QH-NKY (Nongkeyuan of Qinghai), and XJ-CJ (Changji of Xinjiang). Soil-available potassium, slowly available potassium, total potassium, main clay minerals, cation exchange capacity, particle size, other available nutrients, and potassium concentration in plants were measured. The results showed that potential potassium-supplying powers of the 25 tested soils, which were respectively evaluated by the contents of slowly available potassium in soils and the amount of total net potassium uptake in the pot experiment, generally tended to increase from eastern to western regions in northern China. Significant wheat yield responses to long-term potassium application in the field trials were found since 2000 in the north-central region but not observed until 2004 in the northwestern region. Significant corn yield responses to long-term potassium application in the field trials were found starting in soils of the northeastern region, following in soils of the north-central region, and then in soils of the northwestern region. These were consistent with potential potassium-supplying power of the soils, which tended to increase from east to west regions. [ABSTRACT FROM AUTHOR]

Scientific evaluation of nutrient balance in soil-crop systems is very helpful for improving soil fertility management. Nutrient balance in a soil-vegetable system in a vegetable production area of 55 ha was evaluated using nutrient permissible surplus or deficit rate. The study area consisted of 182 farmer plots belonging to six production groups. A total of 217 soil samples from the 0- to 20-cm depth were collected on a 50×50-m grid in the study area before the first crop seeding. Prior to the first crop harvest and the next crop harvest, respectively, vegetable yields were determined and vegetable samples were collected at sites corresponding to the soil sampling locations. The information on fertilizer use such as varieties, rotations, chemical fertilizer and organic manure use, and vegetable yield was surveyed for all farmer plots. The results indicated that significant surpluses of nitrogen (N), phosphorus (P2O5), and potassium (K2O) in the soil-vegetable system were observed, with an average of 314.5, 236.1, and 103.4 kg/ha.a, respectively. Nitrogen practical surplus rates was 46.3%, 35.2 percentage points higher than N permissible surplus rates of 11.1%, indicating that excessive N fertilizer was applied in the vegetable production area. Phosphorus practical surplus rates (255.8%) were 256.7 percentage points higher than P2O5 permissible deficit rates (-0.9%). Phosphorus surpluses in the vegetable production area greatly exceeded its rational range. Potassium practical surplus rates (44.6%) were 87.1 percentage points higher than its permissible deficit rates (-42.5%). Application of K fertilizer in the study area should be improved by balanced fertilization to rationalize soil K status. [ABSTRACT FROM AUTHOR]