Read on:

• Plants Use Alternative Strategies to Utilize Nonexchangeable Potassium in Minerals. Wang, H.Y., Q.H. Shen, J.M. Zhou, J. Wang, C.W. Du, and X.Q. Chen. 2011.
  Plant Soil 343:209-220
• Potassium Assessment of Grain Producing Soils in North China. Deshui Tan et al. 15 February 2012.
  Agriculture, Ecosystems & Environment 148:65-71
• Rate of Global Plant Carbon Uptake and Release Revised. Macaulay, C. 10 October 2011.
  ECOS magazine, CSIRO
• Phosphorus Cycle: A Broken Biogeochemical Cycle. Elser, J., and E. Bennett. 6 October 2011.
  Nature 478:29-31
• Persistence of Soil Organic Matter as an Ecosystem Property. Schmidt et al. 6 October 2011.
  Nature 478:49-56
• Solutions for a Cultivated Planet. Foley et al. 20 October 2011.
  Nature 478:337-342
• Carbon Footprints: Relative Drop for Farming Emissions. Seip, H.M. 15 December 2011.
  Nature 480:321
• Sugar-cane Biofuel Fouls Air. 15 December 2011.
  Nature 480:295
• Food Security: Overcome India’s GM Crops Prejudice. Govindarajan Padmanaban. 15 December 2011.
  Nature 480:321
• Five Innovations that are Boosting Soil Fertility. Zaleski, J. 22 November 2011.
  Nourishing the Planet
• Nutritional and Physiological Significance of Potassium Application in Maize Hybrid Crop Production. M. Ahmad Alias Haji A. Bukhsh et al. 2012.
  Pak. J. Nutr. 11(2):187-202
• Microbial Activity, Community Structure and Potassium Dynamics in Rhizosphere Soil of Soybean Plants Treated with Glyphosate. Lane et al. 26 December 2011.
  Pedobiologia

Potassium Management during the Rotation from Alfalfa to Corn

High K fertilizer prices in recent years have made it imperative for growers to apply optimum K rates to alfalfa (Medicago sativa L.). Current university fertilizer guidelines in the Corn Belt do not change for the last production year, when alfalfa stand persistence is not a major concern. Furthermore, little is known about carryover of K applied to alfalfa on first-year corn (Zea mays L.) grain and silage yields. In 2008 to 2010, on-farm research was conducted on 10 fields with medium soil test potassium (STK) to determine response to K for alfalfa yield and quality in the last production year, and to estimate K carryover to first-year corn. Alfalfa yield and relative feed value (RFV) and quality (RFQ) did not improve with K fertilization. Herbage K concentration and K uptake increased with K fertilization across sites, indicating that applied K was available during the season of application. When corn relied on carryover K alone, each 100 kg ha^-1 increase in the index of available K increased corn grain yield by 0.5 Mg ha⁻¹, decreased stover yield by 0.4 Mg ha⁻¹, and did not affect silage yields. Regardless of K rate applied to alfalfa, additional K applied to corn increased corn stover and silage yields by 10 and 8%, respectively. This suggests that carryover K was less available than K applied to corn. On medium STK soils going into the last year of alfalfa, applying fertilizer K to first-year corn rather than alfalfa may enhance economic return.

No-Till and Strip-Till Soybean Production with Surface and Subsurface Phosphorus and Potassium Fertilization

Compared to no-till, strip-till can offer improved seedbed conditions and deep banding of fertilizer. The objective of this study was to quantify the effect of rate and placement of P and K in no-till and strip-till systems on soybean [Glycine max (L.) Merr.] seed yield. A 3-yr field experiment was conducted near Urbana, IL, on Flanagan silt loam (fine, smectitic, mesic Aquic Argiudolls) and Drummer silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquolls) soils, with soybean planted following corn (Zea mays L.). Tillage/fertilizer placement was the main plot with no-till/broadcast (NTBC); no-till/deep band (NTDB); and strip-till/deep band (STDB); deep band placement was 15 cm beneath the planted row. Phosphorus–fertilizer rate (0, 12, 24, and 36 kg P ha⁻¹ yr⁻¹) was the subplot, and K-fertilizer rate (0, 42, 84, and 168 kg K ha⁻¹ yr⁻¹) was the sub-subplot. Soil water, soil and trifoliate P and K, and seed yield were measured. Overall, STDB produced 3.1 Mg seed ha⁻¹, 10, and 7% more yield than NTBC and NTDB, respectively. Seed yield, number of pods plant⁻¹, and trifoliate P concentration and accumulation increased with P fertilization uniformly across tillage/fertilizer placement indicating that fertilization cannot be reduced with deep band applications relative to broadcast applications without a reduction in seed yield, but deep banding increased subsurface soil test levels. Potassium fertilization decreased seed yield in both no-till systems but not in the STDB system. While P and K placement produced no differences, improved soybean yield and nutrient accumulation resulted from a tillage effect with STDB relative to the no-till systems.

Responses of Fruit Yield and Quality of Processing Tomato to Drip-Irrigation and Fertilizers Phosphorus and Potassium

Water and nutrient management are essential to achieve high yield and desirable quality attributes in processing tomato (Lycopersicon esculentum Mill.). A 4-yr field study (2006–2009) was conducted to assess effects of contrasting water management (drip-irrigation vs. nonirrigation), fertilizer P (0, 30, 60, and 90 kg P ha⁻¹), and K (0, 200, 400, and 600 kg K ha⁻¹) on yields and quality of processing tomato when the optimum N rate of 270 kg N ha⁻¹ was applied. Compared with nonirrigation, drip irrigation increased marketable fruit yield by 127%, total fruit yield by 66%, and fruit size by 32%, while it decreased soluble solids content (SSC) by 19% and lycopene content by 8%, with no effects on dry biomass of stems and leaves (DBSL). Phosphorus addition had no effects on marketable yield and SSC, but increased the DBSL and lycopene content to maximum values at 60 kg P ha⁻¹. Fertilize K rate affected all examined variables but the lycopene content. Increasing K rates from 0 to 200 kg K ha⁻¹ increased marketable fruit yield by 10% and total fruit yield by 9%, but fruit size declined by 3%. Increasing K rates from 200 to 600 kg K ha⁻¹, however, had no effects on yield and fruit size. Fertilizer K rate had no effects on SSC with nonirrigation, but resulted in a linear increase in SSC with drip-irrigation. The results suggested that, with optimum N supply, K application is required to increase fruit yield and quality of drip irrigated processing tomato.

Addition of Cover Crops Enhances No-Till Potential for Improving Soil Physical Properties

Inclusion of cover crops (CCs) may be a potential strategy to boost no-till performance by improving soil physical properties. To assess this potential, we utilized a winter wheat (Triticum aestivum L.)–grain sorghum [Sorghum bicolor (L.) Moench] rotation, four N rates, and a hairy vetch (HV; Vicia villosa Roth) CC after wheat during the first rotation cycles, which was replaced in subsequent cycles with sunn hemp (SH; Crotalaria juncea L.) and late-maturing soybean [LMS; Glycine max (L.) Merr.] CCs in no-till on a silt loam. At the end of 15 yr, we studied the cumulative impacts of CCs on soil physical properties and assessed relationships between soil properties and soil organic C (SOC) concentration. Across N rates, SH reduced near-surface bulk density (ρ_b) by 4% and increased cumulative infiltration by three times relative to no-CC plots. Without N application, SH and LMS reduced Proctor maximum ρ_b, a parameter of soil compactibility, by 5%, indicating that soils under CCs may be less susceptible to compaction. Cover crops also increased mean weight diameter of aggregates (MWDA) by 80% in the 0- to 7.5-cm depth. The SOC concentration was 30% greater for SH and 20% greater for LMS than for no-CC plots in the 0- to 7.5-cm depth. The CC-induced increase in SOC concentration was negatively correlated with Proctor maximum ρ_b and positively with MWDA and cumulative infiltration. Overall, addition of CCs to no-till systems improved soil physical properties, and the CC-induced change in SOC concentration was correlated with soil physical properties.

Influences of Long-Term Fertilizer and Tillage Management on Soil Fertility of the North China Plain

In the North China Plain, fertilizer management and tillage practices have been changing rapidly during the last three decades; however, the influences of long-term fertilizer applications and tillage systems on fertility of salt-affected soils have not been well understood under winter wheat (Triticum aestivum L.)-maize (Zea mays L.) annual double cropping system. A field study was established in 1985 on a Cambosol at the Quzhou Experimental Station, China Agricultural University, to investigate the responses of soil fertility to fertilizer and tillage practices. The experiment was established as an orthogonal design with nine treatments of different tillage methods and/or fertilizer applications. In October 2001, composite soil samples were collected from the 0–20 and 20–40 cm layers and analyzed for soil fertility indices. The results showed that after 17 years of nitrogen (N) and phosphorous (P) fertilizer and straw applications, soil organic matter (SOM) in the top layer was increased significantly from 7.00 to 9.3–13.14 g kg^-1 in the 0–20 cm layer, and from 4.00 to 5.48–7.75 g kg^-1 in the 20–40 cm layer. Soil total N (TN) was increased significantly from 0.37 and 0.22 to 0.79–1.11 and 0.61–0.73 g N kg^-1 in the 0–20 cm and 20–40 cm layers, respectively, with N fertilizer application; however, there was no apparent effect of straw application on TN content. The amounts of soil total P (TP) and rapidly available P (RP) were increased significantly from 0.60 to 0.67–1.31 g kg^-1 in the 0–20 cm layer, and from 0.52 to 0.60–0.73 g kg^-1 in the 20–40 cm layer with P fertilizer application, but were decreased with combined N and P fertilizer applications. The applications of N and P fertilizers significantly increased the crop yields, but decreased the rapidly available potassium (RK) in the soil. Straw return could only meet part of the crop potassium requirements. Our results also suggested that though some soil fertility parameters were maintained or enhanced under the long-term fertilizer and straw applications, careful soil quality monitoring was necessary as other nutrients could be depleted. Spreading straw on soil surface before tillage and leaving straw at soil surface without tillage were two advantageous practices to increase SOM accumulation in the surface layer. Plowing the soil broke aggregates and increased aeration of the soil, which led to enhanced organic matter mineralization.

Impact of Long-Term Alfalfa Cropping on Soil Potassium Content and Clay Minerals in a Semi-Arid Loess Soil in China

Alfalfa cropping has been considered an efficient method of increasing soil fertility. Usually nitrogen increase in root nodules is considered to be the major beneficial effect. A 21-year time series (five sampling periods) of alfalfa cultivation plots on a loess soil, initially containing illite and chlorite, in Lanzhou of northwestern China was selected to investigate the relationships among alfalfa cropping, soil potassium (K) content and soil clay minerals. The results indicated that soil K significantly accumulated after cropping, with a peak value at about 15 years, and decreased afterwards. The accumulated K was associated with the K increase in the well-crystallized illite mineral, which was not extracted by the traditional laboratory K extraction methods in assessing bioavailability. The steep decline in soil K content after 15-year cropping was in accord with the observed fertility loss in alfalfa soils. Plant biomass productivity peaked at near 9 years of culture, whereas soil K and clay minerals continued to increase until copping for 15 years. This suggested that K increased in the topsoil came from the deep root zone. Thus alfalfa continued to store K in clays even after peak production occurred. Nitrogen did not follow these trends, showing a general decline compared with the native prairie soils that had not been cropped. Therefore, the traditional alfalfa cropping can increase K content in the topsoil.

Interactive Effect of Potassium and Phosphorus on Grain Quality and Profitability of Sunflower in Northwest Pakistan

A field experiment was conducted using a split plot randomized complete block design with three replications to study the effects of potassium (K) and phosphorus (P) application on sunflower (Helianthus annuus L.) growth at the New Developmental Research Farm of Khyber Pakhtunkhwa Agricultural University in Peshawar, Pakistan. Six levels of K (0, 25, 50, 75, 100 and 125 kg K ha^-1) were main plots while four levels of P (0, 45, 90 and 135 kg P ha^-1) were subplots. Increase in both K and P levels enhanced grain oil concentration of sunflower. Increase in P level increased grain protein concentration, while increase in K level decreased grain protein concentration. Both oil and protein yields increased significantly with increase in K and P levels. The increase in oil and protein yields of sunflower was mainly attributed to the improvement in yield components (grains per head, grain weight and head size) and the significant increase in grain yield. The highest net returns of 297 and 368 US$ ha^-1 based on grain and oil yields, respectively, were obtained from a combination of 100 kg K ha^-1 + 45 kg P ha^-1.

Long-Term-Fertilization Effects on Soil Organic Carbon, Physical Properties, and Wheat Yield of a Loess Soil

The large dryland area of the Loess Plateau (China) is subject of developing strategies for a sustainable crop production, e.g., by modifications of nutrient management affecting soil quality and crop productivity. A 19 y long-term experiment was employed to evaluate the effects of fertilization regimes on soil organic C (SOC) dynamics, soil physical properties, and wheat yield. The SOC content in the top 20 cm soil layer remained unchanged over time under the unfertilized plot (CK), whereas it significantly increased under both inorganic N, P, and K fertilizers (NPK) and combined manure (M) with NPK (MNPK) treatments. After 18 y, the SOC in the MNPK and NPK treatments remained significantly higher than in the control in the top 20 cm and top 10 cm soil layers, respectively. The MNPK-treated soil retained significant more water than CK at tension ranges from 0 to 0.25 kPa and from 8 to 33 kPa for the 0–5 cm layer. The MNPK-treated soil also retained markedly more water than the NPK-treated and CK soils at tensions from 0 to 0.75 kPa and more water than CK from 100 to 300 kPa for the 10–15 cm layer. There were no significant differences of saturated hydraulic conductivity between three treatments both at 0–5 and 10–15 cm depths. In contrast, the unsaturated hydraulic conductivity in the MNPK plot was lower than in the CK plot at depths of 0–5 cm and 10–15 cm. On average, wheat yields were similar under MNPK and NPK treatments and significantly higher than under the CK treatment. Thus, considering soil-quality conservation and sustainable crop productivity, reasonably combined application of NPK and organic manure is a better nutrient-management option in this rainfed wheat–fallow cropping system.

Influence of Organic and Mineral Fertilizerson Nutrient Leaching

Between 2002 and 2009 the influence of fertilizer type on drainage water formation and nutrient leaching was investigated in one crop rotation at the Bern-Liebefeld lysimeter station. Slightly higher crop yields were obtained with purely organic fertilizer than with pure mineral or organic-mineral fertilizers. One of the reasons for this may be that optimum manure management is possible in a lysimeter trial. However the three fertilizer methods differed only slightly in amounts of drainage water, drainage water nitrate concentrations and leached nutrient loads. These were much more strongly influenced by climatic conditions and the crop cultivated. A greater differentiation between the treatments could presumably have been achieved with a longer trial period because of the long-term after-effects of organic nitrogen. On the one hand these after-effects produce slight yield increases over the years, but on the other hand an increase in leaching losses can be expected owing to greater humus mineralization.