Field Crop 2025, Vol.8, No.5, 231-237 http://cropscipublisher.com/index.php/fc 232 2 Principles and Application Techniques of Formula Fertilization 2.1 Overview of soil nutrient diagnostic methods The first step in formulating fertilizer for cowpea is to find out what is missing in the soil. The common practice is to take soil samples first, test the nitrogen (N), phosphorus (P), potassium (K) content, and also measure the pH value and organic matter. After the test, using methods such as the STCR model, you can calculate how much nutrients are needed to achieve a certain yield, and you can also estimate how much soil, fertilizer and organic fertilizer can contribute (Long et al., 2011). Many studies have found that cowpea lacks nitrogen the most, followed by potassium and phosphorus, so special attention should be paid to the amount of nitrogen fertilizer. 2.2 Matching mechanism between supply and demand Formulated fertilization, to put it simply, is: soil, fertilizer, and farmyard manure, which must match the actual needs of crops at each stage. The usual approach is to first calculate "how much nutrients are needed to produce one ton of cowpea", then deduct the part that can be provided by the soil and organic fertilizer according to the soil inspection results, and then use chemical fertilizers to make up the rest. Now there are many "formula calculators" that can directly input soil inspection data to give specific fertilizer amounts (Pandey et al., 2019). This can not only ensure production, but also reduce waste, be environmentally friendly and save money. 2.3 Intelligent recommendation systems for fertilizer formulations In recent years, many intelligent fertilizer distribution systems have emerged. They put soil testing, crop fertilizer requirements and local planting habits into a database and automatically calculate the most appropriate fertilizer plan (Beena et al., 2018). Farmers can get accurate suggestions immediately by simply entering the soil inspection results on their mobile phones or computers. Relying on these digital tools, fertilization formulas are more accurate and easier to promote, which can help cowpea cultivation achieve a win-win situation of "high yield, fertilizer saving, and environmental protection". 3 Impacts on Growth Performance of Yard-Long Bean 3.1 Seedling uniformity and early growth Test the soil first, then match the fertilizer, especially the combination of phosphorus and nitrogen, phosphorus and potassium, so that the cowpea seedlings can grow uniformly and quickly. When the soil lacks phosphorus, add a little phosphorus fertilizer, and the aboveground part of the seedlings will grow more vigorously, which is more obvious for those "fast-responding" varieties (Sukyankij et al., 2022). If you add some organic materials such as earthworm compost, the soil will be looser and have more nutrients, and the vitality of the seedlings can be taken to a higher level (Islam et al., 2016). 3.2 Plant height and leaf area index dynamics Supplement nitrogen, phosphorus and potassium according to the soil test results, and add a little growth regulator, the plant will grow taller, have more leaves, and have a larger leaf area index. If the nutrition keeps up, the photosynthetic capacity will be strong, and the growth of the whole plant will naturally be good (Sihotang et al., 2022; Nahid et al., 2024). 3.3 Root development and stress resistance Soil testing and formula fertilization, especially phosphorus supplementation and organic fertilizer, can make the root system thicker and longer. The deeper the roots are, the faster they absorb water and fertilizer, and the more they can withstand drought or nutrient deficiency (Purnama et al., 2025). If root-promoting bacteria (PGPR) and a small amount of lime are added, the root system will be healthier, with fewer diseases and the whole plant will be more vigorous (Yadav et al., 2017). In short, this method can not only make the roots grow longer, but also help cowpeas better resist various stresses. 4 Regulatory Effects on Yield and Quality 4.1 Number of pods and average yield per plant Test the soil first, then accurately match fertilizers, especially phosphorus, nitrogen, and potassium, and add a little biochar or lime, which can make each plant produce more pods, longer pods, and more and heavier grains
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