[Effects of conservation tillage measures on soil water and NO3--N leaching in dryland maize cropland]. / 保护性耕作措施对旱地春玉米土壤水分和硝态氮淋溶累积的影响.

Based on a field experiment on conservation tillage over 15 years in Weibei Highland maize cropland, six conservation tillage patterns, i.e., conventional tillage (CT), no-tillage (NT), no-tillage plus biochar (NB), no-tillage and straw mulching (NS), no-tillage and plastic film mulching (NF), and no-tillage and straw-plastic film mulching (NSF), were investigated for their effects on soil water and nitrate nitrogen(NO3--N) leaching, to seek sustainable agricultural cultivation measures suitable for the region. Results showed that, compared with NT treatment in the first water recharge period, CT had no effect on water recharge in 0-100 cm soil layer, and NS, NB, NSF and NF significantly reduced soil water recharge. In 100-300 cm soil layer, NS, NB, NF and NSF significantly increased soil water recharge, but CT significantly reduced soil water recharge. During the second water recharge period, water recharge depth was mainly concentrated in 0-100 cm soil layer, and there was no significant difference between each treatment and NT. During the water depletion period, compared with NT treatment, other treatments had no significant effect on water depletion in 0-100 cm soil layer, but NF and NSF increased soil water depletion by 33.9% and 59.9% in 100-300 cm soil layer, respectively. In 0-200 cm soil layer, compared to NT, CT significantly increased the accumulation of NO3--N by 2.2 fold, NS, NB, NF and NSF reduced soil NO3--N accumulation by 44.6%, 61.5%, 69.2% and 69.8%, respectively. In 200-300 cm soil layer, NS significantly reduced the accumulation amount of NO3--N, but CT had no significant effect on the accumulation amount of NO3--N, and NS, NB, and NSF all had negative effects on NO3--N accumulation. Soil water movement had significant effect on the distribution of NO3--N in soil profile. Soil NO3--N was mainly distributed in 0-40 cm soil layer for NB, NF and NSF treatments, in 0-100 cm and 200-300 cm soil layers for NS treatment, and over the entire profile for NT and CT, and NS, NT and CT treatments had two NO3--N accumulation peaks in soil profile. Different agricultural cultivation measures could reduce soil NO3--N leaching by regulating soil water content, and subsequently improve nitrogen utilization efficiency. Among those measures, NSF could effectively control soil water movement to reduce the NO3--N leaching and accumulation, and thus is a feasible measure to improve soil water and fertility conditions and increase dryland maize yields.

Effect of long-term fertilization on wheat yield under different precipitation patterns.

Rational application of nitrogen and phosphorus is one of the main pathways to enhance wheat yield. The optimum dosage of nitrogen and phosphorus used in different precipitation patterns was studied using the binary quadratic regression equation, which could provide a basis for fertilization of wheat in Loess Plateau. The results showed that the amount of nitrogen and phosphorus ferti-lizer required for the maximum yield was dependent on precipitation patterns. The maximum wheat yield in normal years was 4229 kg·hm-2, with the dosage of nitrogen and phosphorus applied being 172 and 164 kg·hm-2, respectively. The maximum wheat yield in wet years was 4896 kg·hm-2, with the dosage of nitrogen fertilizer being 2% more than that in normal years, 175 kg·hm-2, and the dosage of phosphorus was about 1% less than that in normal years, 162 kg·hm-2. The application of nitrogen and phosphorus in dry years was about 16% and 5% less than that in normal years. When the dosage was more than that, wheat yield began to decline. The economic optimum fertilization differed in different precipitation patterns. The economic optimum nitrogen and phosphorus fertilization in normal years was 161 and 151 kg·hm-2, while in dry years it was 135, 143 kg·hm-2, respectively. The economic optimum fertilization in wet years was about 3% and 1% more than that in normal years, 167 and 153 kg·hm-2. The economic optimum fertilization was 6%-8% lower than optimum amount of fertilization. In actual production, it was recommended to reduce the amount of nitrogen and phosphorus by 10% in order to improve the utilization rate of fertilizer and get the maximum benefit.

[Effect of long-term fertilization on winter wheat yield from the dry land under different precipitation patterns]. / 不同降水年型下长期施肥旱地小麦产量效应.

Based on 30 years long-term fertilization experiment on the semiarid Loess Plateau in China, we studied the effect of different fertilizer treatments on the winter wheat yield, fertilizer contribution rate (FCR) and precipitation use efficiency (PUE) in different precipitation years (drought, normal and wet years). The result showed that the wheat yield, FCR and PUE were significantly higher in nitrogen + phosphorus (NP) and nitrogen + phosphorus +potassium (NPK) treatments than in control (CK) and phosphorus (P) treatments when winter wheat was planted for 30 consecutive years. The wheat yield, FCR and PUE in NPK treatment were highest, with values of 3480 kg·hm-2, 61.45 kg·kg-1 and 6.13 kg·mm-1·hm-2, respectively, and those in the wet years were higher than in drought and normal years. The stepwise regression analysis showed that wheat yield was mainly influenced by the amount of nitrogen, phosphorus input and precipitation during fallow period and wintering period. Accordingly, increasing nitrogen and phosphorus input accompanying with potassium and water conservation practices during the fallow period could improve the wheat yield on the semiarid Loess Plateau in China.

[Effects of different re-vegetation patterns on soil organic carbon and total nitrogen in the wind-water erosion crisscross region, China].

This study was conducted to analyze the responses of soil organic carbon (SOC) and total nitrogen (TN) to three typical re-vegetation patterns, i.e., grassland, alfalfa land and peashrub land on the Loess Plateau of China, and also to assess the dynamics of SOC and TN with re-vegetation age. The results showed that all the three re-vegetation practices increased the concentrations of SOC and TN in the 0-10 cm soil layer, but their effects differed with re-vegetation age. Compared with adjacent croplands, the concentrations of SOC and TN in the 0-10 cm soil layer in grassland did not change within 10 years of succession, but increased after 20 years of succession. In alfalfa land, the concentrations of SOC and TN increased by 51.6%-82.9% and 43.4%-67.0% in the 0-10 cm soil layer, with the increasing rates of stocks of SOC and TN being 0.17-0.46 and 0.015-0.043 t · hm⁻² · a⁻¹, respectively. However, SOC and TN were not affected by re-vegetation age in alfalfa land. The increases of concentrations of SOC and TN remained high in the first 20 years after conversion of cropland to peashrub land, but decreased after 40 years of conversion. In conclusion, the conversion of croplands to peashrub or alfalfa land could be better in contributing to high stocks of SOC and TN than natural succession of grassland. However, their positive effects on the enrichment of SOC and TN may not be sustainable due to the scarcity of soil moisture and high water consumption of these two re-vegetation plants.

[Effects of continuous cropping of wheat and alfalfa on soil enzyme activities and nutrients].

Based on a long-term rotation and fertilization experiment in Changwu, Shaanxi, China, we determined the enzymatic activities and nutrients in soils after 27 years continuous cropping of alfalfa and wheat, respectively. The activities of invertase, urease and phosphatase were not affected by fertilization treatment within each cropping system, but they were significantly higher in the alfalfa continuous cropping system than in the wheat continuous cropping system under each fertilization treatment. The activity of hydrogen peroxidase was not affected by the type of cropping system or fertilization treatment. Across the cropping systems, the activities of soil urease, phosphatase and hydrogen peroxidase were higher while soil invertase activity was lower in N, P and manure (NPM) combined treatment compared with the other fertilization treatments. The accumulations of soil organic matter, total nitrogen and available nitrogen were greater in the alfalfa cropping system than in the wheat continuous cropping system, and the NPM treatment could improve the soil fertility.

[Effects of long-term rotation on the nutritional quality of wheat grain protein on dryland of Loess Plateau, Northwest China].

A long-term experiment was conducted on the dryland of Loess Plateau to study the effects of three typical rotation systems, including wheat-sainfoin rotation, wheat-pea rotation, and wheat-maize rotation, on the nutritional quality of wheat grain protein. Rotation system and the cropping years of rotated plants affected the nutritional quality of wheat grain protein in varying degrees. As compared with continuous wheat cropping, wheat-sainfoin rotation made the nutritional quality of wheat grain protein relatively stable, and the essential amino acid content, amino acid score, amino acid ratio coefficient, chemical score, and amino acid index of the protein all relatively high, being able to be adopted as a cropping system to product high quality protein wheat in Loess Plateau. Under wheat-pea rotation, the nutritional quality of wheat grain protein after 1-year pea cropping was relatively high, but the essential amino acid content of wheat grain protein after 2-year pea cropping was relatively low, and several essential amino acid scores and chemical score of the grain protein were lower than those under continuous wheat cropping. Furthermore, the essential amino acid index was 12.2% lower than that under continuous wheat cropping. Therefore, wheat-pea rotation showed a relatively low nutritional quality of wheat grain protein. Under wheat-maize rotation, the nutritional quality of wheat grain protein was also relatively stable, but the crude protein and essential amino acid contents and amino acid balance level were lower than those under continuous wheat cropping.

[Coupling analysis of agro-ecolomic system in gully area of Loess Plateau in 1949-2008: a case study in Changwu County of Shaanxi Province].

Based on the analysis of the coercing and dynamic evolution relationships between agro-economic system and agro-ecological system, and by using modified entropy method, the weight of each evaluation index for the agro-ecolomic system in Changwu County of Shaanxi Province was determined, and, by employing coupling degree model, the coupling processes of agro-ecolomic system in the gullyarea of Loess Plateau were investigated. From 1949 to 2008, the agro-ecolomic system in the County experienced three stages of "traditional extensive agriculture", "agricultural mechanization", and "agricultural pre-modernization". In corresponding to the implement of national macro policies, the coupling degree of the agro-ecolomic system reached two peaks standing for utmost increasing phase and three valleys standing for coordinate development phase. Periods 1955-1961 and 1984-1992 were the utmost increasing phases of the coupling degree; periods 1962-1965 and 1981-1983 were the rapid transition periods responding to the national-wide policies controlling; while periods 1949-1954 and 1966-1980 were the low-level coordinated development phases. Since 1993, the system had been in the harmonious phase by a spiral development. At present, the system had a potential risk of changing from the harmonious phase to the utmost development phase. Appropriate agricultural policies and better external environment could promote the stable development of the agro-ecolomic system on a harmonious level; otherwise, a retrogressive system might be expected.

[Effects of different patterns surface mulching on soil properties and fruit trees growth and yield in an apple orchard].

Taking a nine-year-old Fuji apple orchard in Loess Plateau as test object, this paper studied the effects of different patterns surface mulching (clean tillage, grass cover, plastic film mulch, straw mulch, and gravel mulch) on the soil properties and fruit trees growth and yield in this orchard. Grass cover induced the lowest differentiation of soil moisture profile, while gravel mulch induced the highest one. In treatment gravel mulch, the soil moisture content in apple trees root zone was the highest, which meant that there was more water available to apple trees. Surface mulching had significant effects on soil temperature, and generally resulted in a decrease in the maximum soil temperature. The exception was treatment plastic film mulch, in which, the soil temperature in summer exceeded the maximum allowable temperature for continuous root growth and physiological function. With the exception of treatment plastic film mulch, surface mulching increased the soil CO2 flux, which was the highest in treatment grass cover. Surface mulching also affected the proportion of various branch types and fruit yield. The proportion of medium-sized branches and fruit yield were the highest in treatment gravel mulch, while the fruit yield was the lowest in treatment grass cover. Factor analysis indicated that among the test surface mulching patterns, gravel mulch was most suitable for the apple orchards in gully region of Loess Plateau.

[Seasonal characteristics of soil respiration and affecting factors under typical vegetations in the water-wind erosion crisscross region of the Loess Plateau].

By the soil respiration system, the characteristics of soil respiration were investigated to explore the correlations between soil respiration and soil temperature, soil water and soil nutrient under different land use patterns in the water-wind erosion crisscross region of the Loess Plateau. The results indicated that the seasonal changing characteristics of soil respiration were distinguished significantly among different vegetations, and soil water content and temperature were the main influencing factors. Soil respiration seasonal changing ranges, such as bare land, crop land, Medicago sativa land, Caragana korshinskii land, abandoned wild grass land, Stipa bungeana land, wild grass land, degraded Medicago sativa land, sloping Medicago sativa land, sloping abandoned wild grass land, sloping crop land and terraced crop land, were 0.32-0.82, 0.41-2.83, 0.74-2.81, 0.76-3.07, 0.67-2.79, 0.51-2.12, 0.56-2.05, 0.59-1.66, 0.42-2.09, 0.31-1.86, 0.32-1.93 and 0.41-3.17 micromol x (m2 x s)(-1). Comparing seasonal changing magnitudes of soil respiration, crop land was the biggest (167% - 203%), abandoned wild grass land (117% -154%), Caragana korshinskii land (134%), Stipa bungeana land (129%), Medicago sativa land (119%-120%) and bare land (94%) followed crop land. The smallest was degraded Medicago sativa land (92%). Bare land and degraded Medicago sativa land had small seasonal variation during the study period. Monthly average values of soil carbon flux (soil respiration) of Medicago sativa land and Caragana korshinskii land were maximal, but the maximum values under crop land were observed in July and August. Besides Q10 of crop land was also maximal, which reached 1.86. There were significant correlations between soil respiration and soil organic matter and available K. Moreover, soil respiration was affected by soil organic matter and total nitrogen in July and August when the water and heat condition were plentiful, but soil ammonium nitrogen had negative impact on soil respiration in the seasons when water and heat were not optimal.