Long-term straw returning improve soil K balance and potassium supplying ability under rice and wheat cultivation.

The aims of the present study were to provide scientific bases for rational use of crop straw to substitute chemical potassium (K) input. The effects of potassium fertilization and straw incorporation on soil K balance and K supplying in a long-term (14 years) field experiment. Five treatments were examined: (1) no fertilization (CK); (2) mineral fertilizing (NPK); (3) straw 6000 kg h m-2 (S); (4) NPK with straw 3000 kg h m-2 (NPK1/2S); and (5) NPK with straw 6000 kg h m-2 (NPKS). K composition, K balance and quantity-intensity (Q/I) relationship were studied. Under no fertilization or low straw returned conditions, soil K was unbalanced and deficienct seriously. Straw return at 6000 kg h m-2 per season with fertilization improved the soil potassium supply and K balance. Long-term K surplus (4 or 5 years), compared with NPK, the NPKS significantly increased non-special K adsorption (Knsa) and non-exchangeable K (Kne) by 5.7-11.2 mg kg-1 and 65.7-128.1 mg kg-1, respectively. Q/I relationship showed cropping without straw K or without fertilizer K resulted in lower quantity (nonspecifically and specifically held K i.e. - ∆K0 and Kx) and intensity (equilibrium activity ratio i.e. CR0K) of K in tested soils. K-fertilization with straw maintain higher exchangeable K (EK0) and a higher difference between EK0 and minimum exchangeable K(EKmin), and would help to prevent depletion in non-exchangeable pool of soil K under intensive cropping. Additionally, The straw return mainly decreased potential buffering capacity for exchangeable pool (PBCKn), 43.92-48.22% of added K in soil might be converted to exchangeable pool while it was 25.67-29.19% be converted to non-exchangeable pool. The contribution of exchangeable K towards plant K uptake would be higher in the soil with straw than the soil without straw and the non-exchangeable K would be the long-term fixed K as a supplement to the potassium pool. K fertilizer with 6000 kg h m-2 straw return in each crop season increased soil available K and slowly available K. The findings underlined importance of the straw return and contribution for sustain K supplying ability of soils.

Joint analytical hierarchy and metaheuristic optimization as a framework to mitigate fertilizer-based pollution.

The emission of nitrogenous pollution from agricultural lands in form of ammonia volatilization, leaching, runoff, N2O emissions, etc. is still a serious challenge to which agricultural sector faces. In this context, a vast number of decision support systems have been developed and tested to find the best nitrogen application rate. These models are highly dependent on crop simulation models, mathematical and regression models, evolutionary algorithms and artificial intelligent, GIS-based models, etc., while in most cases have ignored to be interfered with regional and national regulations established by experts in the field. In this study, a new framework combining analytical hierarchy (AHP)/modified AHP methods (MAHP) plus metaheuristic optimization techniques has been suggested to find the best nitrogen application rate considering regional capacities and requirements. To reach the objectives of the present study a three yield field experiment was conducted upon which crop yield, nitrogen use efficiency, nitrogen uptake, soil nitrate, ammonia volatilization, N2O emissions, and N leaching were monitored or measured. Using the results from the field experiments and a survey from local experts, the models were developed. AHP-assisted optimization model could cause some biases in the final results due to its intrinsic nature which avoids direct pairwise comparison among indicators (so called sub-criteria) under two different main-criteria. On the contrary, MAHP-assisted model could well reflect the concerns of experts and notably decrease hotspot pollution. Such decision support system can satisfy both farmers and environmentalists' need because of the created high profit and low environmental pollution, while saving resources and ensuring a sustainable production system.

Effects of long-term straw retention on soil microorganisms under a rice-wheat cropping system.

The objective of this study was to investigate how straw-incorporating practices affect bacterial communities and carbon source utilization capacity under a rice-wheat rotational farming practice in central China. To clarify the effect of long-term straw incorporation in microbial abundance and carbon metabolism, a long-term field experiment was initiated in May 2005 (rice-planting season). Soil bacterial communities were revealed by high-throughput sequencing technology. After ten cycles of annual rice-wheat rotation (2005-2015), 2 M (straw incorporation) and 2 M + NPK (high straw incorporation + chemical fertilizer) treatments had significantly more bacterial phyla compared with CK (non-fertilization) and NPK (chemical fertilizer) treatments. Taxonomic analysis revealed that 2 M and NPK + 2 M treatments had a significantly greater abundance of microbial communities, especially the Gemmatimonadetes, Acidobacteria, Firmicutes, and Actinobacteria. In the NPK versus 2 M, 2 M treatment had a significantly greater abundance of Rozellomycota (P < 0.05). In the NPK + 2 M versus NPK, NPK + 2 M treatment also had significantly greater abundance of Ascomycota (P < 0.05). Principal component analysis (PCA) analysis showed that 2 M treatment was separate from other treatments. Using biolog-ECO method, the metabolic diversity and functional characteristics of microbial communities were used to indicate the ability of microorganisms to utilize carbon source. The carbon utilization ability of soil microorganisms in 2 M + NPK treatment was significantly higher than that of CK treatment (P < 0.05). The utilization ability of carboxylic acids, polymers, and other mixtures of carbon sources in 2 M treatment was higher than those of other treatments. These findings suggest that long-term straw incorporation affects the abundance and carbon utilization ability of soil microorganisms within 0-20 cm soil depths, among which, Gemmatimonadetes, Firmicutes, and Actinobacteria may play crucial roles in bacterial communities and carbon source utilization capacity.

Cadmium accumulation, availability, and rice uptake in soils receiving long-term applications of chemical fertilizers and crop straw return.

Fertilization and straw return have been widely adopted to maintain soil fertility and increase crop yields, but their long-term impacts on the accumulation and availability of cadmium (Cd) in paddy soils are still unconfirmed. Therefore, this study was undertaken in central China to investigate the accumulation, availability, and subsequent uptake of Cd by rice (Oryza sativa L.) in two adjacent field trials (P1 and P2, lasting for 10 and 12 years, respectively) under long-term straw return or in combination with chemical fertilizers. Obvious Cd accumulation, probably due to the notable Cd input from irrigation and traffic exhaust in the bulk soil (0-20 cm) of P1, was observed. The bulk soil of P2 received homogeneous straw return and chemical fertilizers, as did that of P1; however, the P2 soil almost showed Cd balance. Long-term straw return increased the portion of soil DTPA-extractable Cd to the total pool for both sites, but only P1 showed significant differences when compared to the controls. However, the highest Cd concentrations and the maximum bioconcentration factors in rice straw and grain were obtained using solo application of chemical fertilizers at both sites. Continuous additional applications of crop straw, in contrast, resulted in slightly decreased Cd uptake in rice straw, but not in grain. These findings demonstrate that neither long-term straw return nor fertilization leads directly to notable Cd accumulation, but that the promotion effects of long-term chemical fertilizer applications on Cd uptake in rice need more attention.

[Nutrient spatial variability of tobacco soil restoration area and fertility suitability level evaluation].

By using geographic information system technology (GIS) and geostatistics methods, this paper studied the spatial variability of soil properties and available nutrients in the new regulation area units located in Qingjiangyuan modern tobacco agriculture science and technology park (Enshi, Hubei), suburb of Enshi City and the Baiyang base of Lichuan City, and further evaluation of the soil fertility suitability index (SFI) was carried out by use fuzzy mathematics. The results indicated that the effects of land restoration on the soil available phosphorus content variability and spatial distribution were very obvious, possibly due to the landform characteristics and restoration extent. The effect of land restoration on soil pH was small, however, serious soil acidification was detected in the soil sampled from Baiyang (pH < 5.5). Low SFI was found in 77.6%, 17.1% and 31.4% of the soils taken from the suburb, Baiyang and Qingjiangyuan, respectively. In conclusion, attentions should be paid on soil acidification in Baiyang, soil fertility and equalization in the suburb, and soil fertility in the region of Qingjiangyuan with low SFI.

Straw mulching reduces the harmful effects of extreme hydrological and temperature conditions in citrus orchards.

Extreme weather conditions with negative impacts can strongly affect agricultural production. In the Danjiangkou reservoir area, citrus yields were greatly influenced by cold weather conditions and drought stress in 2011. Soil straw mulching (SM) practices have a major effect on soil water and thermal regimes. A two-year field experiment was conducted to evaluate whether the SM practices can help achieve favorable citrus fruit yields. Results showed that the annual total runoff was significantly (P<0.05) reduced with SM as compared to the control (CK). Correspondingly, mean soil water storage in the top 100 cm of the soil profile was increased in the SM as compared to the CK treatment. However, this result was significant only in the dry season (Jan to Mar), and not in the wet season (Jul to Sep) for both years. Interestingly, the SM treatment did not significantly increase citrus fruit yield in 2010 but did so in 2011, when the citrus crop was completely destroyed (zero fruit yield) in the CK treatment plot due to extremely low temperatures during the citrus overwintering stage. The mulch probably acted as an insulator, resulting in smaller fluctuations in soil temperature in the SM than in the CK treatment. The results suggested that the small effects on soil water and temperature changes created by surface mulch had limited impact on citrus fruit yield in a normal year (e.g., in 2010). However, SM practices can positively impact citrus fruit yield in extreme weather conditions.