ABSTRACT Garlic (Allium sativum) is normally grown under conventional tillage (CT) with soil being excessively mixed by plowing and harrowing operations that degrade soil structure, increase production costs, and increase environmental contamination. Alternatively, cover crops can be grown and their residues placed on soil surface, enabling garlic to be grown under no-tillage (NT) system. However, for subtropical climate there is little information on the impacts of tillage systems and cover crop species, particularly of their decomposition process and nutrients release, on garlic nutritional status and yield. This study aimed to evaluate garlic yield, and the decomposition rate and nutrient release from aboveground residues of cover crops cultivated in CT and NT methods, in a subtropical climate. Pearl millet (Pennisetum glaucum), bean (Phaseolus vulgaris) and sunn hemp (Crotalaria ochroleuca) were cultivated as cover crops previous to garlic, under CT or NT, for two consecutive years in the same area. The highest dry matter yield and nutrient release by cover crops were observed for millet and sunn hemp. The highest accumulations of P and K were observed in millet residue. Total garlic yield averaged 16.2 Mg ha-1 yr-1 and was affected neither by tillage method nor by cover crop species. The yield of marketable garlic was higher when soil was covered with bean residue in NT. Yield of non-marketable garlic was higher under CT in the first year, when high precipitation occurred shortly before harvest. The highest residue decomposition and nutrient release rates were observed under CT, in the three cover crop species. No-tillage increases marketable yield of garlic and the residence time of cover crop residues. We recommend cultivation in NT systems using cover crops, thus increasing marketable garlic yield and nutrient cycling. Allium sativum (CT structure costs contamination Alternatively surface notillage no (NT system However species methods Pennisetum glaucum, glaucum , glaucum) Phaseolus vulgaris Crotalaria ochroleuca area 162 16 2 16. ha1 ha 1 ha- yr1 yr yr- nonmarketable non year harvest Notillage No cycling

ABSTRACT The study aimed to propose critical levels (CL) and sufficiency ranges of phosphorus (P) in leaves and soil, and rates of maximum technical (MTE) and economic (MEE) efficiency, to maximize marketable bulb yield in garlic (Allium sativum) cultivars grown in a subtropical climate. Field experiments were conducted for two seasons on clay soils in southern Brazil. The cultivars ‘Chonan’, ‘Ito’, and ‘Roxo Caxiense’ were subjected to the application of P rates (0, 50, 100, 250, and 500 kg P2O5·ha-1·yr-1). Garlic yield, soil P concentrations (Mehlich-1), and total P in leaves were determined. The CL in relation to total yield garlic yield were 3.5, 4.5, and 3.4 g P·kg-1 in leaves and 18, 28, and 14 mg P·dm-3 in soil, for ‘Chonan’, ‘Ito’, and ‘Roxo Caxiense’, respectively. The CL in relation to marketable garlic yield were 4.0, 3.5, and 3.6 g P·kg-1 in leaves and 22, 26, and 13 mg P·dm-3 in soil, for the respective cultivars. The MTE rates were 397 and 336 kg P2O5·ha-1, and the MEE rates were 353 and 297 kg P2O5·ha-1, for total and marketable garlic bulb yield. Based on our results, we recommend that garlic growers use when possible the individual nutritional reference values for specific garlic cultivars. (CL (P (MTE (MEE efficiency Allium sativum climate Brazil ‘Chonan, Chonan ‘Chonan , ‘Chonan’ ‘Ito, Ito ‘Ito ‘Ito’ Roxo Caxiense 0, 0 (0 50 100 250 P2O5·ha1·yr1. P2O5ha1yr1 POhayr P2O5·ha 1·yr 1 . P2O5 ha yr O P2O5·ha-1·yr-1) Mehlich1, Mehlich1 Mehlich (Mehlich-1) determined 35 3 5 3.5 45 4 4.5 34 3. P·kg1 Pkg1 Pkg P·kg P·kg- 18 28 P·dm3 Pdm3 Pdm P·dm dm P·dm- Caxiense, respectively 40 4.0 36 6 22 26 39 33 P2O5·ha1, P2O5ha1 POha 1, P2O5·ha-1 29 results ( 10 25 ha1 yr1 P2O5·ha1·yr1 P2O5ha1yr P2O5ha 1yr PO P2O P2O5·ha-1·yr-1 (Mehlich-1 4. kg1 2 dm3 P2O5·ha1 P2O5·ha- P2O5·ha1·yr P2O5·ha-1·yr- (Mehlich- P2O5·ha-1·yr (Mehlich

ABSTRACT Excessive phosphorus (P) applications can increase nutrient levels in the soil, facilitating its transference to aquatic environments and causing contamination. Thus, the environmental P threshold (P-threshold) is a tool to establish a sound level of P in the soil, in which P values below the threshold are harmless to the environment. This study aimed to establish a P-threshold equation for the soils of Mato Grosso State, Brazil. Twenty samples of representative soils from the main swine production regions of the State were collected. These samples were characterized chemically and in terms of P adsorption capacity, then incubated with P rates for 30 days. After incubation, the water-soluble P content (P-water) and the available P content were determined by Mehlich-1 method (P-Mehlich-1). The relationship between P-water and P-Mehlich-1 allowed the determination of the P-Mehlich-1 content from which the amount of nutrient in water increases abruptly, establishing this point as the limit P (P-limit). Subsequently, the P-limit values were plotted against the clay content of the soils, and the resulting equation was used to calculate the P-threshold by adding a safety margin of 20 % to the P-limit versus clay equation. The model was tested on 120 soil samples from Mato Grosso State, and it was able to separate them into two groups with low and high P-water, classified as below or above P-threshold, respectively. Based on that, the simplified equation “P-threshold (mg dm-3) = 13 + 0.5 * % clay” was proposed. (P contamination Thus Pthreshold (P-threshold environment Brazil collected capacity 3 days incubation watersoluble soluble Pwater (P-water Mehlich1 Mehlich 1 Mehlich- PMehlich1. PMehlich1 PMehlich . (P-Mehlich-1) P-Mehlich- abruptly Plimit. Plimit (P-limit) Subsequently 2 12 Pwater, water, Pthreshold, threshold, respectively that mg dm3 dm dm-3 05 0 5 0. proposed (P-Mehlich-1 P-Mehlich (P-limit dm- (P-Mehlich- (P-Mehlich

ABSTRACT Soils with low potassium (K) availability require corrective fertilization for grain crops. The recommended rate to increase K availability up to the critical level depends on the soil K buffering capacity (KBC). This study aimed to quantify the KBC and recalculate the rates necessary to reach the K critical level in 23 soils from Southern Brazil. Soil samples were incubated with six K rates, that were thus grouped according to CECpH7.0: below 7.5 cmolc dm-3 (0, 30, 60, 90, 120 and 180 kg K2O ha-1); from 7.6 to 15 cmolc dm-3 (0, 30, 60, 120, 180 and 240 kg K2O ha-1) and from 15.1 to 30 cmolc dm-3 (0, 30, 60, 120, 240 and 360 kg K2O ha-1). The soil test K (STK) was extracted by Mehlich-1 and the fertilizer rates necessary to increase the STK by 1 mg dm-3 were quantified. The KBC values were correlated with a suite of soil testing metrics. The relationship between the cation exchange capacity (CECpH7.0) and KBC was modeled, and a linear-plateau equation presented the best fit. The K rates were calculated using the following equation: K rate = ( Critical Level − S T K ) × K B C and were compared with the current rate indicated by the Local Soil Fertility Committee. The K fertilizer rates by KBC were about 2.5 times higher than the values currently indicated, and the largest differences were observed in soils with low STK and high CECpH7.0.

ABSTRACT The phosphorus (P) rates recommended for corrective fertilization-P of soils from southern Brazil may be insufficient to reach the critical level for optimal plant growth. This study aimed to quantify the fertilizer-P rates for total correction fertilization with varying soil buffering capacity in the states of Rio Grande do Sul (RS) and Santa Catarina (SC). Soil samples from 0.00-0.10 and 0.10-0.20 m layers were collected from 41 locations distributed in both states. Twelve P rates were applied to each soil, varying between 0 and 100 % of the maximum adsorption capacity (P-max), and incubated for 20 days. After incubation, the extractable P was determined by Mehlich-1. Based on the relationship between applied rates and extracted P, the P buffer capacity (trP_M1) of the soils was quantified, relating it to soil properties. The trP_M1 values, that is, amounts of P2O5 required to increase 1 mg dm-3 of P extracted by Mehlich-1, varied between 2.4 and 34.5 kg ha-1 of P2O5. A multiple explanatory equation for the variable P was generated, in which only P-max, clay content, and initial P availability have a significant effect. The P buffer capacity was significantly higher in the soils with the highest clay content, and there was a reduction in trP_M1 for soils with higher initial P availability. Considering 270 soil samples with low P, the P rate to reach the sufficient levels may be 2-folds higher than the values currently indicated for the RS and SC states, especially for soils with more than 40 % of clay. Phosphorus rates for corrective fertilization must be based on the soil clay content and in P initial availability. The fertilizer-P in clayey soils must be increased.