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Abstract: Soil structural degradation is widespread in cropping lands and efforts to restore deteriorated soil structure very often fail, largely as a result of unchanged tillage and traffic practises. Significant reductions in biological activity in the soil environment occur where random traffic is practiced, limiting the regenerative capacity of soils. This study assessed the changes in soil structure after random field wheeling was replaced with controlled traffic through four cropping seasons. The rate and depth of soil amelioration by natural processes was assessed by changes in, soil water retention characteristics, macroporosity and bulk density. Soil moisture characteristics indicated that the available water capacity (AWC) was 10.2mm per 100mm depth of soil before restoration. Amelioration of the soil matrix increased AWC to 15.4mm per 100mm depth of soil. Macropore density improved from very marginal conditions by 50% at 100mm and 27% at 300mm depths. Bulk density prior to restoration was ∼1.40gcm−3, which was typical for a degraded vertosol, however values improved significantly to 1.25gcm−3 at 100mm depths, with deeper zones improving to 1.30gcm−3. Zero till, controlled traffic, permanent bed farming offers opportunities for restoration of physically degraded vertosols and therefore, for improving the productivity and sustainability of mechanised farming. [Copyright &y& Elsevier]

Subsurface drip irrigation can reduce off-farm movements of fertilizers and pollutants and improve the water use efficiency of irrigated agriculture. Here we compared the effects of furrow and subsurface drip at different irrigation rates, based on a percentage of daily crop-evapotranspiration rates (ETc), on run-off and off-site movement of suspended sediment, nutrients and pesticides from cotton crops grown on a vertisol. Our results show that furrow irrigation significantly increased suspended soil loss, of 5.26 t ha-1, compared to that of subsurface drip irrigation at 120% of ETc, of 2.53 t ha-1, whereas no erosion was recorded with deficit subsurface drip irrigation. Off-site movement of nitrogen in furrow, of 18.63 kg ha-1, was five times greater than subsurface drip irrigation at 120% ETc. It was much less with 105% ETc (0.37 kg ha-1) and 90% ETc (0.15 kg ha-1), and absent for 75% and 50% of ETc. Phosphorus loss from furrow, of 778 g ha-1, was greater than for the wetter subsurface drip treatments that gave 23 g ha-1 for 90% ETc and 19 g ha-1 for 120% ETc. No P loss was recorded from drier subsurface drip irrigation rates. Herbicides such as atrazine and diuron were applied in the year prior to the experiment, but considerable amounts were recorded in furrow run-off in both years, but only at 90 and 120% ETc subsurface drip irrigation in the first year. Concentrations of applied herbicide residues in the runoff exceeded the minimum threshold level for 99% species protection and, although the total amount of herbicide movement was higher in furrow, at times the concentration was greater for wetter subsurface drip irrigation run-off. Residues of insecticides, such as endosulphan applied in a previous year and dimethoate applied in the current years, were recorded in runoff from subsurface drip at 120% and furrow irrigation. Their concentrations in each year exceeded minimum threshold level. Subsurface drip irrigation at 75% ETc offered the best trade-off between off-site run-off, erosion and pesticide movement and yield and water use efficiency. [ABSTRACT FROM AUTHOR]

The combined effects of soil waterlogging and compaction are important concerns in crop production. Two field experiments were performed over two seasons to examine the effects of soil waterlogging and high bulk density (BD) on the performance of winter wheat in terms of its agronomic and physiological traits. Trial 1 applied soil waterlogging at different stages (started at tillering, jointing, booting and anthesis). Trial 2 was conducted with soil waterlogging and compaction that created BD of the topsoil (1.6 g cm −3 ). Results from trial 1 showed that the tillering stage was the most waterlogging-sensitive period. A 12% lower grain yield caused by waterlogging was primarily reflected in reductions in spike numbers. Waterlogging at jointing and booting stages reduced grain weight through decreased dry matter translocation. Results from the field trial 2 showed that soil compaction decreased grain yield by 4.8%, and waterlogging aggravated this reduction by 20.7% and 22.4% when fields were waterlogged for 2 weeks (WL 2w ) and 4 weeks (WL 4w ), respectively. A reduction in spike number from fewer tillers at stem elongation stage was the main reason for grain yield loss. Soil compaction combined with waterlogging duration did not affect root weight, but soil compaction reduced above ground biomass and root weight after the jointing stage. Furthermore, waterlogging accelerated leaf senescence, especially under compacted conditions, which significantly decreased photosynthetic capacity, resulting in a lower maximal PSII photochemical efficiency (F v /F m ), apparent electron transport rate (ETR), effective quantum yield of photosystem II (ΦPSII) and photochemical quenching (qP). Root weight was positively related to the total above ground biomass; whereas the final grain yield was not linearly related to the shoot weight. SPAD value correlated positively with yield and PSII parameters (F v /F m , F v /F 0 ). The study concluded that the tillering stage was most susceptible to waterlogging, and soil compaction combined with waterlogging at tillering stage had a larger harmful effect on root and shoot growth during or after waterlogging. SPAD readings may be a good surrogate for photosynthetic activity under waterlogging and compaction conditions. [ABSTRACT FROM AUTHOR]

Abstract: On the semi-arid Loess Plateau of northern China, water is typically the biggest constraint to rainfed wheat production. Controlled traffic, combined with zero tillage and residue cover has been proposed to improve soil water, crop yield and water use efficiency. From 1998 to 2005, we conducted a field experiment comparing the water storage and wheat productivity of controlled traffic farming and conventional tillage farming. Three treatments were studied: controlled traffic with no tillage and full residue cover (NTCN), controlled traffic with shallow tillage and full residue cover (STCN) and random traffic with traditional tillage and partial residue cover (CT). Compared to CT, the controlled traffic treatments significantly reduced soil bulk density in 10–20cm soil layer, significantly increased soil water content in the 0–150cm soil profile at sowing, 9.3% for NTCN, 9.6% for STCN. These effects were greater in dry seasons, thus reducing the yearly variation in water conservation. Consequently, mean wheat yield of NTCN, STCN and CT were 3.25, 3.27 and 3.05tha−1, respectively, in which controlled traffic treatments increased by 6.9% with less yearly variation, compared to traditional tillage. Furthermore, controlled traffic had greater economic benefits than conventional tillage. Within controlled traffic treatments, NTCN showed better overall performance. In conclusion, controlled traffic farming has a better performance with respect to conserving water, improves yields and increases economic benefits. No tillage controlled traffic farming appears to be a solution to the water problem facing farmers on the Loess Plateau of China. [Copyright &y& Elsevier]

Abstract: Soil compaction caused by random traffic or repetitive tillage has been shown to reduce water use efficiency, and thus crop yield due to reduced porosity, decreased water infiltration and availability of nutrients. Conservation tillage coupled with subsoiling in northern China is widely believed to reduce soil compaction, which was created after many years of no-till. However, limited research has been conducted on the most effective time interval for subsoiling, under conservation tillage. Data from conservation tillage demonstration sites operating for 10 years in northern China were used to conduct a comparative study of subsoiling interval under conservation tillage. Three modes of traditional tillage, subsoiling with soil cover and no-till with soil cover were compared using 10 years of soil bulk density, water content, yield and water use efficiency data. Cost benefit analysis was conducted on subsoiling time interval under conservation tillage. Yield and power consumption were assessed by based on the use of a single pass combine subsoiler and planter. Annual subsoiling was effective in reducing bulk density by only 4.9% compared with no-till treatments on the silty loam soils of the Loess plateau, but provided no extra benefit in terms of soil water loss, yield increase or water utilization. With the exception of bulk density, no-till and subsoiling with cover were vastly superior in increasing water use (+10.5%) efficiency and yield (+12.9%) compared to traditional tillage methods. Four years of no-till followed by one subsoiling reduced mechanical inputs by 62%, providing an economic benefit of 49% for maize and 209% for wheat production compared to traditional tillage. Annual subsoiling reduced inputs by 25% with an increased economic benefit of 23% for maize and 135% for wheat production. Yield and power consumption was improved by 5% and 20%, respectively, by combining subsoiling with the planting operation in one pass compared with multipass operations of subsoiling and planting. A key conclusion from this is that annual subsoiling in dryland areas of northern China is uneconomical and unwarranted. Four years of no-till operations followed by 1 year subsoiling provided some relief from accumulated soil compaction. However, minimum soil disturbance and maximum soil cover are key elements of no-till for saving water and improving yields. Improved yields and reduced farm power consumption could provide a significant base on which to promote combined planter and subsoiling operations throughout northern China. Further research is required to develop a better understanding of the linkages between conservation tillage, soil quality and yield, aimed at designing most appropriate conservation tillage schemes. [Copyright &y& Elsevier]