Effect of composted organic matter on boron uptake by plants

Boron uptake by plants is controlled by the B level in soil solution rather than the total B content in soil. The affinity of organic matter for B can affect B uptake by plants because of changing B concentration in soil solution. The role of soil organic matter content on B soil solution concentration and uptake by bell pepper (Capsicum frutescens L.) were studied. The organic matter used was mature compost (COM), produced from the solid fraction of separated straw-containing cattle manure. Plants were grown in five soil-sand-COM mixtures containing 0, 1, 3, 6, or 10% COM by weight. Four levels of B were applied. The soil was analyzed for B content at the beginning of the experiment and at harvest. Boron concentration in the leaves was determined 45 d from planting. Boron concentration in the soil solution at the beginning of the experiment decreased with increasing levels of COM. This decrease was most prominent at high levels of B application. The effect of the COM level on leaf B concentration was also prominent at high B application rates, with increasing levels of COM resulting in less B in the leaf tissues. Boron concentration in the leaves was highly significantly correlated (r² = 0.88) with the B concentration adjusted in the soil solution. This correlation coefficient was further improved (r² = 0.98) when B concentration in the soil solution was calculated using a B adsorption model. The results presented herein indicate that organic matter plays an important role in controlling B concentration in the soil solution, and that it has a prominent effect on reducing B uptake by plants.