Swine wastewater can be used as a biofertilizer and promote significant improvements in soil physical-chemical attributes and yield. The objective of this study was to evaluate the effects of swine wastewater application on soil and maize yield. The experiment was conducted at the Agricultural Sciences Center of the Federal University of Piauí, in Teresina, Piauí, Brazil, from August to November 2015. The experimental design used completely randomized blocks in split-plot scheme, with five doses of swine wastewater (0, 25, 50, 75 and 100 m3 ha-1) in the plots and two soil depths (0.20 and 0.40 m) in the subplots, with four replications. Exchangeable contents of calcium, magnesium, phosphorus, potassium and sodium, electrical conductivity, pH, sum of bases, base saturation, potential acidity and cation exchange capacity, and crop yield were evaluated. Results showed calcium, magnesium, sum of bases and cation exchange capacity increased with elevated levels of swine wastewater. Potassium and sodium contents however decreased with doses of 51.58 and 52.28 m3 ha-1, respectively. Except for potassium and potential acidity, variables showed higher values at the 0-0.20 m depth.

Water and nitrogen availability are fundamental for obtaining a high yield of the watermelon plant. However, the appropriate levels of irrigation and nitrogen to be applied according to specific cultivation conditions should be previously determined. The objective of the present study was to evaluate the effects of irrigation and nitrogen levels in fertigation on the phytotechnical parameters and yield of the Top Gun hybrid watermelon plant. The experiment was conducted at São Luiz Ranch, in Bom Jesus (PI), from August 4 to October 15, 2015. The blocks in strips experimental design was used with four repetitions, and the treatments consisted of five irrigation depths (114.17, 156.86, 221.16, 268.87, and 317.09 mm) and five doses of nitrogen in fertigation (0, 50, 100, 150, and 200 kg ha-1). The growth rate of the main and primary branches, leaf area, specific leaf area, stem diameter, dry mass of the aerial part, number of fruits, and commercial production per plant were evaluated. Both hydric and nutritional stress caused decreased growth rates, leaf areas, and specific leaf areas, and the highest growth expressions were found with the combination of a 317.09 mm irrigation depth and 200 kg ha-1 nitrogen. The irrigation depths did not influence the diameter of the stem nor the accumulation of dry mass. Nitrogen doses did not influence the number of fruits and production. The 247.95 mm irrigation depth promoted the highest commercial fruit production of the watermelon plant.

Phytotechnical parameters, yield and fertilizer use efficiency are relevant to the rational management of fertigation, especially in cultivation of high technological level. Thus, the objective was to evaluate the influence and efficiency of nitrogen (N) and potassium (K) application on the phytotechnical parameters, yield and nutritional efficiency of yellow melon in a fertigation system. The experiment was conducted in the city of Bom Jesus-PI, Brazil, from January to April 2016, in a strip-block design with four replicates, and the treatments consisted of five N levels (0, 45, 90, 135 and 180 kg ha-1 in the form of urea) and five K levels (0, 60, 120, 180 and 240 kg ha-1 in the form of potassium chloride), applied through fertigation. Collar diameter, main branch length, leaf chlorophyll content, number of leaves, leaf area index, biomass accumulation, fruit yield, and N and K use efficiencies were evaluated. Applications of 180 kg ha-1 of N and 240 kg ha-1 of K, respectively, led to the highest growth of the melon, while maximum production was obtained with the use of 112.50 and 165 kg ha-1 of N and K, respectively. The efficiency of N and K use decreased with increasing levels.

Organic waste from agricultural activities has the potential for reuse when treated and applied to the soil as organic fertilizers. This study investigated the effects of composted bovine ruminal content (CBR) and composted chicken litter (CCL) on the soil attributes, growth, and nutrition of Capsicum chinense Jacq. plants. The experiment was conducted at the Federal University of Piauí, Teresina, using a randomized block design with four replications in a 3⨯2 + 2 factorial scheme. Treatments included doses of 30, 60, and 90 Mg ha-1 of CBR and CCL and two additional treatments (mineral fertilization, NPK; unfertilized soil, CK). The monitored variables included soil biological and chemical attributes, plant nutritional status, biometry, and dry matter. Results indicate that organic compost has the potential to improve soil attributes, such as pH, organic carbon, nitrogen, phosphorus, potassium, calcium, sodium, microbial biomass carbon, and soil respiration. Moreover, plant variables were positively affected by CBR and CCL, with a linear increase in response to CBR and a quadratic increase due to CCL. Nutrient concentrations in the leaves increased with compost application, except for iron. Therefore, CBR and CCL have the potential to improve soil chemical and microbiological attributes as well as support the development and nutritional status of Capsicum chinense Jacq. plants, suggesting that the use of organic waste as a fertilizer is a sustainable cultivation strategy.