Cotton management in a compacted subsurface microirrigated coastal plain soil of the southeastern US

A loamy sand Acrisol (Aquic Hapludult) that had been microirrigated for 6 years became so severely compacted that it had root limiting values of soil cone index in the Ap horizon and a genetic hardpan below it. Deep and surface tillage systems were evaluated for their ability to alleviate compaction. Deep tillage included subsoiling or none. Both deep tillage treatments were also surface tilled by disking, chiseling, or not tilling. Subsoiling was located in row or between rows to avoid microirrigation tubes (laterals) that were buried under every other mid row or every row. Cotton (Gossypium hirsutum) was planted in 0.96-m wide rows. Cotton yield was improved by irrigation from 485 to 1022 kg ha⁻¹ because both 2001 and 2002 were dry years. Tillage loosened the soil by an average of 0.5–1.3 MPa; but compacted zones remained outside tilled areas. Subsoiling improved yield by 131 kg ha⁻¹ when performed in row where laterals were placed in the mid rows; but subsoiling did not improve yield when it was performed in mid rows. For subsurface irrigation management in these soils, the treatment with laterals buried under every other mid row was able to accommodate in-row subsoiling which improved yield; and this treatment was just as productive as and had been shown to be less expensive to install than burying laterals under every row.     

铜对土壤中功夫菊酯和氯氰菊酯迁移和扩散的影响

Repeated applications of bordeaux mixture （a blend of copper sulfate and calcium hydroxide） and pyrethroid insecticides （Pys） have led to elevated copper （Cu） and Pys concentrations in vineyard surface soils. To understand the potential influence of Cu on the fate of Pys in the soil environment, we selected two Pys, cypermethrin （CPM） and lambda-cyhalothrin （λ-CHT）, and two typical Chinese vineyard soils, Haplic Acrisol and Luvic Phaeozem, as experimental samples. The dissipation experiment was conducted at room temperature in the dark, and the transport of both Pys through the soils was investigated using soil thin-layer chromatography. The results showed that the transport of Pys in both soils increased as the Cu²⁺ concentration increased from 0 to 100 mg L^-1 , and Pys were more transportable in Haplic Acrisol （HA） than in Luvic Phaeozem （LP） under the same experimental conditions. For CPM, only 100 mg L^-1 of Cu²⁺ significantly （P<0.05） increased Pys transport through both soils relative to water. Lambda-CHT was significantly （P<0.05） transported through HA by all the Cu²⁺ concentrations compared to water, and all but the 1 mg L^-1 of Cu²⁺ significantly （P<0.05） increased the transport of λ-CHT through LP relative to water. However, the dissipation rates of CPM and λ-CHT decreased with the addition of Cu to soils. Our findings suggest that the risk of groundwater contamination by Pys increases in the soils with elevated Cu concentrations.     

Nitrogen and phosphorus limitations of microbial respiration in a tropical phosphorus-fixing acrisol (ultisol) compared with organic compost

We studied the nutrient limitations of microbial respiration over time after the addition of glucose (G), glucose+nitrogen (G+N) or glucose+phosphorus (G+P) to a phosphorus-fixing tropical acrisol down to a depth of 80 cm, compared with those from compost. In the acrisol, the initial rate of respiration increase was higher when P was added together with glucose than when P was excluded. Without N, respiration reached a plateau faster and at a lower level than when N was added in excess. With glucose alone, the respiration kinetics followed the lower of the curves with G+N or G+P at any given time. Thus, nitrogen limited the maximum level of microbial respiration in the acrisol if ample carbon was available, but the initial respiration rate was limited by phosphorus. In contrast, for compost respiration was always lowest when N was not added. In conclusion, microbial respiration depended on the P-fixing properties of the soil, the time scale and the carbon availability.     

Vegetative and reproductive performance of maize to nitrogen and phosphorus fertilizers in Plinthic Acrisol and Gleyic Plinthic Acrisol

Soil specific maize response to N and P may provide guidelines for improving nutrient management. Three replicates of N and P fertilizer combinations (N₀P₀, N₀P₉₀, N₁₂₀P₀, and N₁₂₀P₉₀) were arranged in randomized complete block design on Plinthic Acrisol (PA) and Gleyic Plinthic Acrisol (GPA) in Ghana. Treatment effects on maize plant height and yield parameters were assessed. Plant height differed consistently with N₁₂₀P₉₀ > N₀P₉₀ > N₁₂₀P₀/N₀P₀ from 3 to 7?weeks after planting on the GPA. On the GPA, grain yield ranged from 1.20 to 2.40 t ha^?1 and increased by 10, 77 and 95% in the N₁₂₀P₀, N₀P₉₀ and N₁₂₀P₉₀, respectively. Residual effect of N₀P₉₀ and N₁₂₀P₉₀ increased maize yields on the GPA than on the PA. Rather than N, P was more critical to maize performance and should be externally supplied not exceeding the critical level of N₀P₆₀ (Plinthic Acrisol) and N₀P₉₀ (Gleyic Plinthic Acrisol) for optimum maize yield.     

Characterizing farming systems around Kakamega Forest,Western Kenya,for targeting soil fertility–enhancing technologies

Kakamega district in Western Kenya represents the smallholder farming systems typical for much of the densely populated humid highlands in East Africa. A specific feature, however, is the presence of a protected forest reserve (Kakamega Forest National Park), covering some 20% of the district area. Year‐round crop production with little use of external inputs is resulting in declining soil fertility and crop yields. Technologies to counteract fertility constraints are rarely implemented, as they do not consider system diversity or farm‐specific characteristics. We surmised that farm type–specific targeting of technology options to address soil fertility–related production constraints would reduce the anthropogenic pressure on the resources of the adjacent Kakamega rainforest reserve. Based on Kenyan national census data, we selected 168 farms in physical proximity of the Kakamega forest and characterized them regarding production system and soil attributes. Cluster and principal component analyses identified five distinct farm categories. Three representative farms from each cluster group were subsequently selected to establish labor‐use patterns, draw resource‐flow maps, and determine NPK balances. Small subsistence‐oriented farms were most common (> 50%), with maize yields of 0.9 t ha^–1 (Cluster 1). Most farmers relied on the forest to provide fire wood, animal feed, and medicinal plants. Mixed farms, combining subsistence maize with industrial crops, were differentiated by soil type, with tea being grown on Ferralsol (Cluster 3), and sugar cane being grown on Acrisol (cluster 4). The dependence on forest resources was limited to animal grazing and the collection of feed stuff (Cluster 3), or the extraction of medicinal plants (Cluster 4). Only few farms showed a high degree of market orientation of the food‐crop production. These comprised either small farms with high investments in fertilizer and maize yields close to 2 t ha^–1 (Cluster 2), or larger farms (1.6–3.9 ha) with low fertilizer but high hired‐labor use (Cluster 5). Their reliance on forest resources was generally low. Resource flows showed mainly patterns of nutrient export in subsistence farms, and more complex flow patterns, involving several farm compartments, in the diversified farms. Partial nutrient balances were strongly negative for N and K, irrespective of soil or farm type. Soil‐fertility characteristics reflected the nutrient balances with generally low C and N in all farms on Acrisol, and low P in farms not applying mineral fertilizers or farmyard manure. The proposed typology is expected to improve the targeting of technologies addressing soil fertility–related production constraints, and to reduce the pressure on forest resources. This is of particular importance in the case of small‐scale subsistence and mixed farms close to the forest margin.     

Changes in soil chemical and microbial properties after a wildfire in a tropical rainforest in Sabah, Malaysia

Changes in soil caused by drought and wildfire in a Dipterocarp rainforest in Sabah, Malaysia were assessed by phosphorus fractionation, extractable nitrogen and nutrient limited respiration kinetics (after addition of glucose+N or P). Fire increased the concentration of total phosphorus (P) in the litter layer (per ha and per dry soil) by raising the 0.2 M NaOH extractable-P. In the soil organic layer, membrane exchangeable P was reduced by fire while 1.0 M HCl extractable-P, and 0.5 M NaHCO₃ extractable-P increased. Microbially available P increased after the fire and was most closely related to NaOH extractable-P that has been considered available to plants only over long time-scales. Total nitrogen (N) increased in the litter layer (per ha and per dry soil) due to post-fire litter fall, while the NO₃⁻ increased up to 10-fold down to the 10 cm mineral soil. In contrast, the microbially available N decreased by 50%. Basal respiration and substrate-induced respiration increased in the litter layer and decreased in the organic horizon (per dry soil and per organic matter). P limited microbial growth resulted in a slow and non-exponential increase in respiration, presumably reflecting the P-fixing nature of the soils, while N limitation resulted in a fast exponential increase. However, higher respiration rates were eventually achieved under P limitation than under N limitation.     

Soybean expansion impacts on soil organic matter in the eastern region of the Maranhão State (Northeastern Brazil)

Recently, the eastern region of the Maranhão state (Northeastern Brazil) became a hotspot of land-use change (LUC) directly from native vegetation to soybean cultivation, but due to the soil characteristics, LUC has caused substantial soil organic carbon (SOC) and nitrogen depletion. Therefore, we quantified these impacts arising from two factors: (i) different timeframes after LUC and (ii) contrasting soil management practices. For the first study, soil samples (0–30 cm; six replicates) were taken on soybean fields year one, year eight and 15 years after LUC. It the second study, another area was sampled, of which part was managed under no-tillage (NT) and the other using a mouldboard plough (MP). For both studies, native vegetation (NV) was sampled as the control. NV stored about 50 Mg of carbon (C) ha⁻¹; but LUC reduced C stocks by 35% (after 8 and 15 years); moreover, labile-C decreased between 20% and 45%, while, microbial-C decreased between 20% and 60%, considering the interval between year one and 15 years. Regarding soil management, the MP did not cause differences on C stock (24 Mg C ha⁻¹) in comparison to NT; however, both labile-C and microbial-C decreased by 15% to NT, while, decreased by 40% to MP. These results lead us to believe that, since LUC is inevitable, we suggested the adoption of the best agricultural management practices, in order to preserve/increase the SOC, reducing the impacts on GHG emissions and, thus, achieving sustainability and profitability.